Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: AbruptSLR on February 28, 2013, 03:56:45 AM

Title: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 28, 2013, 03:56:45 AM
The PIG/Thwaites Glacial drainage basin system is the soft underbelly to the potential collapse of the WAIS this century, and the destabilization mechanisms for initial time period from 2012 to the 2040 to 2060 time frame are the most critical aspects of the entire WAIS collapse hazard analysis scenario.  This tread thus focuses on this topic, while later threads will focus on the 2050/2060 to 2100 time period, for the Amundsen Sea Embayment, ASE, the Ross Sea Embayment, RSE, the Weddell Sea Embayment, WSE and the Bellingshausen Sea areas.  I will call the timeframe from 2012 to 2040/2060 the collapse initation period and the timeframe from 2050/2060 to 2100 the collapse main period.  For this collapse initiation period scenario for the PIG/Thwaites system, the Thwaites Glacial drainage system is particularly unique and critical and will be the focus of this hazard analysis; however the PIG collapse initiation period started earlier (and has been more extensively modeled) than for the Thwaites Glacier, therefore the PIG response will serve as a base case that will be adjusted to project the expected response for Thwaites.
The PIG grounding line reached the crest of a submerged ridge leading to a negative slope by about 1994 and that grounding line retreated about 25km from 1994 to 2010 (a 16-yr period) and the width of the PIG gateway is about 40 km.  I believe that by 2012 a subglacial cavity (and intercepted lake) for the Thwaites Glacier, TG, has extended about 55 km (from the 1994 grounding line) to a submerged ridge leading to a negative slope (leading to BSB) with about the same gradient as for the PIG negative slope (see the first figure).  Now the collapse initiation of the TG is highly dependent on the vertical advective process (which will be shown in the second post) in order to extend this pre-existing 55-km long by 25-km wide by 0.8-km tall cavity into a cavity that is approximately 155-km long by 50-km wide by 1 km tall by about 2040 (as shown in the second figure), where it is expected to intercept another subglacial lake behind a damming ridge identified by Scheoder et al 2013 (see the "surge' thread).  As the Thwaites Gateway is about 50-km wide it is assumed that advection will widen it naturally by 2040.  In regard to lengthening the TG cavity by 100-km in 2040-2012 = 28 year, we make the following three adjustments to the 25 km that the PIG cavity extended over 16-years (see the third figure): (a) the factor for time 28/16 = 1.75; (b) for an expected increase in the average CDW temperature from 1.2 C to 1.8 C (a figure for a sensitivity analysis for ice volume loss with a cavity like that for TG with temperatue from Goldberg et al will be included in the next post) give a factor of: 1.5; and (c) the factor due to both the influence of the significant basal melt water system at Thwaites and the influence of the steeper ice surface slope: 1.5.  This gives 25 x 1.75 x1.5 x1.5 + 55 = 155-km long cavity.  Inaddition to presenting the Goldberg sensitivity information the next post will look at the PIG extension.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 28, 2013, 03:24:28 PM
Continuing from the last post, below I re-post a figure from Gladstone et al 2012 from the "surge" thread because it is such a key figure in that Gladstone et al ran over 1,000 computer runs with different assumptions for such key parameters as: basal friction, bathymetry, CDW temperature (note that the figure shows the SRES A1B case which the post in the "forcing" thread shows that we are currently following, & which has slightly more forcing than RCP 8.5 until about 2032), etc (and they bounded the reasonable runs between the heavy black lines) and they found the histogram of blue rectangles indicating the frequency count of the location of the end of the cavity for the runs made.  Gladstone et al also identified an area of local bottom bathymetry indicated by the green histogram showing that an area of possible local stability/pinning that  could temporarily stall the extension of the subglacial cavity after it extends another 40km from the 2010 location of the grounding line by about 2040, which is verified by Goldberg et al 2012 analysis (plan view instead of profile) shown in the second figure in this post (again reposted from the "surge" thread).  This matches the extent assumed for PIG by 2040 in the second figure of the previous post, while the activation of the side spur to the main PIG trough shown in the previous post assumes that the front of the PIG ice shelf  retreats past this side spur location by about 2020 to 2025 so as to active this side trough.
While in the previous post I used the historical (1996-2010) grounding line retreat for PIG as the basis for the future (2012-2040) groundling line retreat for Thwaites  adjust for time by 1.75, by temperature by 1.5, and by basal melt water interaction by 1.5, factors.  The 1.5 temperature factor is justified by the ratio of the model projected ice mass loss within a cavity similar to that for Thwaites for the 1.2 C to the 1.8 C curves shown in the third accompanyin figure (which I believe is related to the geometry of the Thwaites cavity immediately before 2012 after which the cavity intercepted the lake infront of submerged sea mount thus extending part grounding line at the tip of the cavity around to the eastern ice flow stream (see Tinto and Bell 2011 plan view) on the east side of the mount and allowing the grounding line on the west side of the mount [where most of the basal water channel flows] to begin to descend down into the BSB, this mount is assumed to be the primary pinning point holding back the acceleration of the two Thwaites ice streams [see Tinto & Bell 2011 in the "surge" thread] and is why Goldberg et al 2012 show in the third figure posted here that the ice mass loss in their assumed cavity (the first 55 km of the cavity) slows down after year 20 (which I assume to by 2012) when the cavity runs into the mount.  As the PIG case does not have a submerge mount temporarily pinning its ice stream flow, it might seem that my assumption of using the PIG groundling line retreat response (1996 - 2010) as unfair or biased (ie not accounted for by an adjustment factor less than one in my hazard analysis); however, I have assumed the following (a) advection (see the fourth figure) melts the ice around the base perimeter of the mount while ice thinning and periodic ice stream surges (see the "surge" thread) rapidly degrades the pinning action of the mount by 2015 thus allowing the two Thwaites ice streams to converge into one stream by that data which may allow the ice velocities in the assumed 50-km TG gateway to accelerate up to about 4.5 km/yr by about 2020 (note that the top of the mount is at about El -500m while the top of the assumed cavity by 2012 is also assumed to be near El-500m (see Rignot's figure as the beginning of this thread); therefore, the ice stream near the mount likely does not need to thin too much before the postulated new Thwaites ice shelf floats over the top of the mount thus eliminating this pinning (the same can be said about the two pinning points for the Thwaites Ice Tongue pointed out by Tinto & Bell 2011).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 28, 2013, 03:47:48 PM
Regarding the 1.5 factor that I applied to adjust for both the steep ice slope for Thwaites (than for PIG) and for the stronger basal ice melt stream (particularly for the west Thwaites ice stream), I (a)  first provide the accompanying figure from Gladstone et al 2012 showing how once the temporary pinning point between 100km and 150km (using the coordinates in the figure) that the velocity of the ice at the calving front accelerates rapidly once the grounding line retreats back to the area with a steeper ice surface slope (around 170km) (see the second figure to compare the steepness of the ice surfaces both along the PIG trough and along the TG gateway); thus as the ice surface slope is already as steep as PIG will be after 2040 we need an adjustment factor; and (b) the figure in the immediate previous post regard the advective process indicates that it is driven by the siphon action of the fresh melt water floating up thus suction in more warm CDW to melt more ice (and note that the CDW indicated in this 2D case has the thermal potential to melt more ice if it could access a sufficiently large ice contact area as in this 2D case most of the warm CDW flows back to the sea); however, the presence of the strong basal melt water stream coming from the melt water network beneath Thwaites would provide an induction jetting action to supplement the siphon mechanism this increasing the activity of the advection process with in the Thwaites cavity as compared to the PIG cavity (also note that if methane gas is released by methane hydrate decomposition at the retreating grounding line within a cavity then this would further accelerate the advective process (note the Thwaites gateway has plenty of sediment that could accommodate buried methane hydrates beneath the grounding line for Thwaites).  As with regard to the expected rate of thinning of the newly forming ice shelf for Thwaites please see third accompanying figure showing a current thinning rate of over 3 m per year for the Thwaites (and the PIG) ice shelfs/tongues.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 28, 2013, 04:33:15 PM
I do not have time to explain the following two figures (for the 2040-2060 timeframe for Thwaites) in detail.  But I will say that in the first figure it is assume that the subglacial cavity previously indicated for Thwaites by the end of 2040 show immediately thereafter intercept the damming ridge and the assumed associated subglacial lake identified by Schroeder, D.M., Blankenship, D.D., Young, D.A. 2013, which it is assumed would have the effect of both: (a) releasing a lot of water from the assumed subglacial lake which accelerate ice flow and ice shelf thinning (possibly in a concentrated surge) and (b) it is assumed would laterally extend the cavity in the east-west directions the full length of the assumed lake behind the damming ridge, which would allow the cavity to then extend in three directions at once (east, west and south), following the bathymetry indicated in the second posted figure.  In follow-up posts I expect to talk about: (a) the possible accelerated calving from this new ice shelf circa 2060; (b) the influence of more frequent surface ice melting around this time frame possibly leading to a melt pond mechanism similar to what has happened in 2002 for Larsen B ice shelf and is soon expected to happen to Larsen C ice shelf as indicated in the third accompanying figure; and (c) El Nino effects, and others effects
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 03:49:08 PM
The first two images of the previous post is a gross over simplification of the sequence of events that I have in mind for the area indicated in transparent orange and labeled Thwaites Ice Shelf (& its indicated extent needs refinement).  This orange area is not intended to represent a continuous ice shelf and is best thought of here as the area from which the grounding line has retreated as indicated in images in the "collapse" thread.  Over the next several days of posts I hope to clarify the various factors, mechanisms, sequences and timing that could possibly lead to such an extensive grounding line retreat in such a relatively short period of time, and with the grounding line retreat following particular pattern of the deep troughs carved into the seafloor during previous interglacial events (such as the Eemian).  I would like to start the series of posts on this matter by postulating that between 2020 and 2040 the calving front of new Thwaites Ice Shelf will undergo a sequences of large calving events similar to that exhibited by the recent PIG Ice Shelf calving event (illustrated by the accompanying image).  I expect that within the next year the portion of the PIG Ice Shelf infront of the large crevasse will have broken free resulting in the rapid retreat of the ice shelf face to a location many km upstream of the face location previously expected by many researchers by this time.  As the postulated new Thwaites Ice Shelf in 2020 is expected to be roughly 50-km wide I expect that such major calving events will happen regularly between 2020 and 2040, which would relieve the buttressing support of the lost portions of Thwaites Ice Shelf to the grounded ice on the sides of the threshold, and thus I expect that by 2040 the Thwaites gateway will have widened from about 50-km to about 80-km (roughly a retreat of 15-km for the face of each gateway sidewall over a 20-year period).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 04:09:18 PM
By 2040 when the postulated threshold Thwaites subglacial cavity is proposed by me to intercept the subglacial lake (indicated by the dashed yellow line in the transparent orange area), I expect that the temporary outburst of high pressure subglacial lake water will cause a surge of ice outflow (into the gateway with a receding ice shelf) which will rapidly thin the grounded ice along the longitudinal axis of the subglacial lake in the east-west direction so that before 2045 the ice streams in the two deep east-wast troughs will be subjected to the "Jakobshavn Effect" instability.  For those unfamiliar with the Jakobshavn Effect", I provide the accompanying two figures and the following Wiki quote discussing this effect and the rapid retreat of the Jakobshavn Glacier from 2000 to 2005:
"Jakobshavn is one of the fastest moving glaciers, flowing at its terminus at speeds of around 20 metres per day. The speed of Jakobshavn Glacier varied between 5700 and 12600 metres per year between 1992 and 2003. The ice stream's speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about 0.06 millimeters (about 0.002 inches) per year, or roughly 4 percent of the 20th century rate of sea level rise. Jakobshavn Isbrae, retreated 30 km from 1850–1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining the Greenland Ice Sheet. The glacier terminus region also had a consistent velocity of 20 meters/day (maximum of 26 m/day in glacier center), from season to season and year to year, the glacier seemed to be in balance from 1955-1985. After 1997 the glacier began to accelerate and thin rapidly, reaching an average velocity of 34 m/day in the terminus region. It also thinned at a rate of up to 15 m/year and retreated 5 km in six years. Jakobshavn has since slowed to near its pre-1997 speed, the terminus retreat is still occurring. On Jakobshavn the acceleration began at the calving front and spread up-glacier 20 km in 1997 and up to 55 km inland by 2003. The position of this calving front, or terminus, fluctuated by 2.5 km around its annual mean position between 1950 and 1996. The first mechanism for explaining the change in velocity is the "Zwally effect" and is not the main mechanism, this relies on meltwater reaching the glacier base and reducing the friction through a higher basal water pressure. A moulin is the conduit for the additional meltwater to reach the glacier base. This idea, proposed by Jay Zwally, was observed to be the cause of a brief seasonal acceleration of up to 20% on the Jakobshavns Glacier in 1998 and 1999 at Swiss Camp. The acceleration lasted 2–3 months and was less than 10% in 1996 and 1997 for example. They offered a conclusion that the "coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming". The acceleration of the three glaciers had not occurred at the time of this study and they were not concluding or implying that the meltwater increase was the cause of the aforementioned acceleration. Examination of recent rapid supra-glacial lake drainage documented short term velocity changes due to such events, but they had little significance to the annual flow of the large outlet glaciers.
The second mechanism is a "Jakobshavn effect", coined by Terry Hughes, where a small imbalance of forces caused by some perturbation can cause a substantial non-linear response. In this case an imbalance of forces at the calving front propagates up-glacier. Thinning causes the glacier to be more buoyant, even becoming afloat at the calving front, and is responsive to tidal changes. The reduced friction due to greater buoyancy allows for an increase in velocity. The reduced resistive force at the calving front is then propagated up glacier via longitudinal extension in what R. Thomas calls a backforce reduction.
This mechanism is supported by the data indicating no significant seasonal velocity changes at the calving front and the acceleration propagating upglacier from the calving front. The cause of the thinning could be a combination of increased surface ablation and basal ablation as one report presents data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, and suggests that the changes in Jakobshavn Glacier are due to the arrival of relatively warm water originating from the Irminger Sea near Iceland.
Recent large calving events where the glacier produces icebergs have also been found to trigger earthquakes due to the icebergs scraping the bottom of the fjord."

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 05:17:42 PM
The transparent orange area indicates that I expect the groundling line to retreat in two main branches (one arcing east [along the PNE-TG yellow arc line] and the other a mirror image arcing to thw west) for a distance of about 200 km (along each arc) over an appoximately 20-year period from 2040 to 2060, which is along three times the rate of grounding line retreat that I justified for the 2012 to 2040 period earlier in this thread.  It is noted here that unlike the Jakobshavn Glacier retreat where the calving front retreated 10 km from 2001 to 2004 and then stablized as the Jakobshavn Glacier grounding line retreated up a positive slope (and stabilized for other reasons), for reasons that I will cite in the next post I believe that the Thwaites Glacial ice along the two nominally 200-km arcs is particularly unstable and is likely to retreat this full distance by 2060 as the "Jakobshavn Effect" will be amplified by a series of factors that when multiplied together will account for the expected 300% increase in grounding line retreat rate as postulated to be the case for the postulated 2040 Thwaites situation.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 08:23:22 PM
While the "Jakobshavn Effect" approximately doubled the rate of calving face retreat for the Jakobshaven Glacier from 2001 to 2004, I believe that some of the parameters related the the "Jakobshavn Effect" are already considered in my calculation supporting the postulated 100-km retreat of the Thwaites grounding line from 2012 to 2040; therefore, I will assume an additional factor of 1.7 for the "Jakobshavn Effect" for the next postulate 200-km grounding line retreat from 2040 to 2060 (note that I believe that the geometry of the ice streams along these two 200-km arcs are particularly susceptible to the "Jakobshavn Effect" due to the probable steep ice surface gradients from the dropping elevation of the ice surface near the calving from relative to the adjoining ice).  Furthermore, I postulate another 1.1 factor for the increase in CDW temperature by 2050 (assuming RCP 8.5 50%CL radiative forcing). As the rate of basal ice melt due to geothermal heat in the very thin crust in these two 200-km arced trough, I will assume another 1.1 factor.  Furthermore, I assume that by at least 2050 warming of the surface temperature in WAIS will increase the frequency of austral summer ice surface melting (particularly in strong El Nino years), which may introduce the "Zwally Effect" to the Thwaites Basin, for which I apply another 1.1 factor.  To account for the influence of the projected increase in cyclonic activity in this area (including waves, barometric pressure fluctuations and storm surge) I take another 1.1 factor.  Also, by 2050 I believe that the sea ice around Antarctica will begin to melt earlier and will expose more sea water for which I take another 1.1 albedo effect.  Finally, as I believe that methane generated by hydrate decomposition in the exposed seafloor in the transparent orange area, will accelerate advection, I take another 1.1 factor.
Also of these factors taken together: 1.7x1.1x1.1x1.1x1.1x 1.1 x 1.1 = 3.0, which supports the rate of grounding line retreat postulated for these two 200-km arcs by 2060.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 08:42:54 PM
To provide sum support for my 1.1 factor for the "Zwally Effect", I: (a) provide the attached figure of ice surface melt days for the 2004-2005 season, and I postulate that between 2040 to 2060 the surface melt days near the calving fronts for PIG and TG will be similar to that for the Antarctic Peninsula indicated in the figure; and (b) if the ice velocities are as high along these two 200-km long arcs as I postulate for this period then the amount of internal ice melt from internal friction should contribute to the "Zwally Effect".
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2013, 10:49:44 PM
The attached figure from Levermann et al 2012 indicates that the 50% CL RCP 8.5 projected CDW temperature for 2060 is about 0.15 C above the 2040 temperature thus supporting my 1.1 acceleration factor on grounding line retreat over this time period.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 01:57:45 AM
The first figure shows that cyclones in the seas offshore WAIS are becoming more intense (lower central pressure) and more frequent (higher density); while the second figure indicates that both strong La Nina and strong El Nino events drive rossby wavetrains directly towards the ASE which is significant as strong ENSO events have been projected as global warming progresses.  Thus both of these figures support my 1.1 factor for storm and wave effects on grounding line retreat for TG.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 02:05:50 AM
The WAIS-Divide Ice-Core was taken near to the transparent orange area and the following public statement about the measured basal ice melting rate at the WAIS Divide ice-core location supports the 1.1 factor that I used for grounding line retreat in this area:

"High Basal Melt at the WAIS-Divide ice-core site
T.J. Fudge, Gary Clow, Howard Conway, Kurt Cuffey, Michelle Koutnik, Tom Neumann,
Kendrick Taylor, and Ed Waddington
We use the depth-age relationship and borehole temperature profile from the WAIS-Divide ice
core site to determine the basal melt rate and corresponding geothermal flux. The drilling of the
WAIS-Divide ice core has been completed to 3400 m depth, about 60 m above the bed. The age
of the deepest ice is 62 ka, younger than anticipated, with relatively thick annual layers of ~1 cm.
The borehole temperature profile shows a large temperature gradient in the deep ice. We infer a
basal melt rate of 1.5 (±0.5) cm yr-1 using a 1-D ice flow model constrained by these data sets.
The melt rate implies a geothermal flux of ~230 mW m-2, three times the measured value of 70
mW m-2 at Siple Dome.
We compile radio-echo sounding data sets to assess the spatial extent of high melt. Deep internal layers are the most useful for inferring spatial patterns of basal melt. Unfortunately, the
IceBridge WAIS-core flight and two site-selection surveys did not image consistent reflectors
deeper than Old Faithful (2420 m and 17.8 ka). A ground-based survey by CReSIS (Laird et al.,
2010) was able to image consistent layers as deep as 3000 m, but the survey is not oriented along the ice-flow direction making interpretation more difficult. There is no obvious draw down of
deep internal layers that would indicate an area of localized melt. While this suggests a uniform
melt rate within the survey, it might also indicate that other factors (e.g. accumulation gradients,
rough bed topography) obscure the influence of basal melt on the internal layer depths."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 03:05:02 PM
It would appear that the heart of my arguement against Pfeffer et al 2008's supposed limit on ice export out of their assumed 120 sq km gateway at an assumed "upper bound" average ice export velocity just under 15 km/yr boils down to the following hazard analysis sequence (already presented) and ice flow activation mechanisms (see all previously discussed multipliers to the base PIG grounding line retreat rate from 1996 to 2010, including most significantly: advection, CDW temperature, basal meltwater network, and the Jakobshavn Effect) not previously considered by Pfeffer et al 2008 (or the NRC 2012 or the IPCC WG1 AR5 SOD, see the "Critique" thread):
(1) First the following sequence discussion is intended to clarify how the hazard scenario for the period from 2012 to 2040 sets-up the case for the "Jakobshavn Effect" for the period from 2040 to 2060: (1a) First I will note that Pfeffer et al 2008's ice velocity limit of about 15 km/yr by 2100 assumes a linear acceleration from about 2 to 2.5 km/yr for a beginning year of about 2005 and that basal friction is involved/contolling during this whole period, while I assume that for the period from 2012 to 2040 that the combination of advective subglacial cavity formation and periodic (quasi-annual) surges thin the new Thwaites ice shelf thins sufficiently (in the about 100km distance from the submerge mount to the ridge dammed lake) so that this ice shelf is not "pinned" on any seafloor features and so that the side shear on the ice shelf is progressively being degraded to offer buttressing support from the new ice shelf so that by 2040 the average floating ice export velocity through the Thwaites gateway is about 4 to 5 km/yr; and (1b) By 2040 when the subglacial cavity intercepts the subglacial lake behind the damming ridge that the associated major surge event further thins the new Thwaites Ice Shelf and degrades the side shear resistance on the shelf (by ice fracturing) that the Jakoshavn Effect instability can rapidly propagate upstream along the two 200-km long arcs previously discussed along the deep two east-west troughs.  I will continue my second point as to why the Jakoshavn Effect is so unique for the Thwaites case that I propose (that if confirmed) it should be called the "Thwaites Effect"
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 03:51:06 PM
This discussion continues directly from my previous post, elaborating on both the Jakobshavn Effect and why the Thwaites geometry/condition is so unique that along the indicated ice streams/troughs (east-west 200-km long arcs) that the ice velocities will accelerate into a "Thwaites Effect":
(2)  First the readers may want to review the attached pdf elaborating on the theory of the Jakobshavn Effect, where it is possible that a warm ocean water advection sufficiently thinned the Jakobshavn Ice Tongue rapidly that this created a dynamic out of balance force equilibrium instability that was rapidly propogated upstream resulting in a relatively rapid grounding line retreat and rapid doubling of the average ice export velocity.  For the "Thwaites Effect" I assume that the major surge from the lake water outburst circa 2040 leads to a reduction of lateral support from the ice shelf that would be propogated rapidly upstream along the two east-west arcs due to a combination of: continued undermining of the glacial ice at the tip of the subglacial cavities, rapid basal ice melting due to high geothermal effects shown by the WAIS-Divide ice-core, steep ice surface slopes resulting in high driving forces, and decreasing ice viscosity parameter primarily due to the increase in internal ice friction as the glacier ice stream velocities along the east-west troughs have been steadily increasing from 2012 through 2060; and with regard to the numerical relationships of the ice viscosity parameter, basal friction and driving stress upstream from the grounding line see the accompanying Figure 8 from Van der Veen et al 2011 [see attached pdf].  Figure 8 shows that depending on the details of the dynamics it is theorically possible for the ice stream velocities (of the ice immediately upstream of the grounding line) to accelerate from 4km/yr upto (in extreme cases) 50 km/yr within the limits of the ice stream trough, while down steam of the grounding line the continued thinning of the new Thwaites ice shelf (for parallel cases see how the Filchner-Ronne Ice Shelf and the Ross Ice Shelf thin in the third attachment) not only keeps this exporting ice from interacting (which might otherwise slow down the ice export velocity and allow the ice shelf to buttress the glacial ice velocity and impede the "Jakobshavn Effect" at the grounding line) with bottom features and further accelerating the thinning ice shelf ice velocity (in the fourth attachment see how the ice shelf velocities for both the Filchner-Ronne Ice Shelf and the Ross Ice Shelf accelerate as the ice shelf thins due to continued subice shelf drag/melting from the existing advective water transferring momentum from the existing water into the ice shelf) as it exists out of the assumed gateway width of about 80km by 2040 (note that (i) the two east-west ice stream flows are assumed to be about 40km wide until they converge to flow north through the 80-km wide Thwaites gateway, and (ii) the retreat of the grounding line from the subglacial lake location to the south is assume to proceed relatively slowly from 2040 to 2060 due to a combination of blocking of ice export from the two major eas-west ice streams, rougher bottom features towards the south, and reduced negtive bottom gradient towards the south).  I expect to elaborate on the likelihood of this hazard scenario and "Thwaites Effect" in my next post later today.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 07:02:58 PM
The two points made in this post provide some supporting evidence as to why the hazard analysis presented so far in this thread (on the proposed PIG/Thwaites system collapse initiation scenario from 2012 to 2060) may be supported by selected historical evidence and by the bathymetric pattern left on the seafloor from the last Eemian peak :
-   The Byournoy-renn Ice Stream (see the first attachment), and the Hudson Strait Ice Stream (see the second attachment, and note that the indicated 50-year peak ice velocity pulse of about 4.5 km/yr flowed through a much wider gateway than is the case for Thwaites but that the water depths of the two gateways are similar), exhibited periods of 50 to 100-years where their ice velocities rapidly accelerated and then rapidly slower-down (see the third attachment) when their grounding lines retreated down a reverse/negative marine seafloor slope.  My collapse initiation scenario postulates that the Thwaites Glacier (which has comparable geometries to both the Byournoy-renn, see the first attachment to this post), rather than rapidly slowing-down as occurred in the Byournoy-renn, and the Hudson Strait, Ice Stream cases (see third attachment), when their (Byournoy-renn & Hudson Strait) grounding line retreat beyond the reverse/negative slope area back into ascending/positive slope regions.  Due to the extreme depth of the BSM troughs the length of reverse/negative slopes for the Thwaites east-west 200-km long ice stream arcs, the ice stream velocities get high enough to decrease primarily the ice viscosity parameter sufficiently (and also for geothermal basal ice melting to decrease basal friction sufficiently) so that the Thwaites ice stream continues to accelerate by means of the "Thwaites Effect(Jakobshavn Effect) to at least 2060 (and beyond for the eastern ice stream branch as will be discussed in the next thread).  It is also noted here that as in the case of the Byournoy-renn record, the lateral force required to turn the two ice stream arcs toward the gateway (in the case of Thwaites the lateral force required to turn the two east-west ice streams toward the north) serves as a buttress to the ice streams seeking to flow directly (without turning) out of the gateways, until the ice flow from the arcing ice streams slows sufficiently to allow the direct flow paths to gradually take over.
-   While the precision of historical record is subjected to meaningful degree of uncertainty, taken cumulatively I believe that is provide considerable evidence of abrupt sea level rise for periods of at least 50 to 100 years associated with the collapse of past marine ice sheets (see the discussion in the "collapse" thread) including during the Eemian peak (MIS 5e, or LGM) where the fourth figure indicates possible surges in sea-level during the Eemian peak that could only be associated with the rapid collapse of the WAIS.  Also note that the ice scour and associated sediment deposits associated with the Byournoy-renn Ice Stream indicate very high ice flow velocities. Furthermore, I  believed that a more detailed examination of historical Dansgaard-Oeschger Events, and Bond Events (during the Holocene including the sustained 4m/century SLR rate sustained during Melt-Pulse 1A for five centuries) may help to characterize the sensitivity of marine ice sheets such as the WAIS to sudden collapse due to various triggering parameters.  Such an investigation may further help to identify the role played by bottom topography/bathymetry on the dynamics of marine ice sheet collapse.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 07:23:38 PM
Also briefly in regard to related (but indirect) historical evidence I would like to point out that:
- The Larsen B ice shelf survived during the Eemian peak, and it's collapse in 2002 raises the prospect that the current anthropogenic forcing conditions may degrade the Antarctic ice even more quickly than occurred during the Eemian peak.
- The fact that the WAIS-Divide ice-core contained at most 62k old ice (taken with 60 m of the BSB seafloor) demonstrates conclusively that the Thwaites glacial ice was not there during the Eemian peak (however, this does not necessarily mean that the WAIS ice mass loss all occurred within one hundred years as I am contending is physically possible), as previously indicated by Strugnell et al. 2012 observation that the modern distribution of the Antarctic adult Turquet's octopuses provides biological evidence that the Weddell, the Bellingshausen, the Amundsen and the Ross Seas were all interconnected at the peak of the Eemian.
- Muhs et al. 2012 (and other studies) present physical evidence from several sites around demonstrate that during Eemian peak/MIS 5.5 RSLR (including a RSLR of over 6 m offshore of California) was sufficiently high that the WAIS clearly melted-out during the Eemian peak.
- Recent (2012) ice cores from the GIS indicate that during the Eemian peak that the Antarctic must have contributed from 3.4 to 3.8 m to eustatic SLR (most of which must have come from the WAIS).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 02, 2013, 11:46:33 PM
Before opening a new thread on the "Collapse Main Period from 2060 to 2100" I would like to make couple of more comments about the transparent orange area labelled ice shelf previously: (a) the reverse/negative slope along one of the arced ice stream flows needs to rise from El-2000m to El -500 within a distance of approximately 300km, or 5m/km, which as indicated by the PIG case is not difficult for advective sub-ice shelf melting to achieve (without the ice shelf re-grounding) for a rate of grounding line retreat such as that for PIG (retreating 25 km in 16 years or about 1.6km/yr ); however, for the period from 2040 to 2060 I have stated that for the Thwaites case the grounding line will be retreating at a rate of approximately 200km in 20years of 10 km/yr, which might be difficult for advective sub-ice shelf melting to achieve; however, (b) after 2040 I have postulated that the "Jakobshavn Effect" will take hold, which should result in more of an "Ice Melange" rather than an "Ice Shelf" (see the attached image for the distinction) in the transparent orange area; which may cause some entrained icebergs within the Ice Melange to bump along the seafloor (causing mini-ice earthquakes of magnitude 2 or so) but given the expected driving force of the ice melange flow such seafloor bumping events are not expected to pin such icebergs entrained with the ice melange flow.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 08, 2013, 12:16:16 AM
I don't believe that I have shown the attached figure before, but it helps to clarify how the Belgica Trough focuses warm CDW towards the Ferrigno Glacier, which inturn should lead to the formation of a subglacial cavity below the Ferrigno Glacier, which should result in the rapid retreat of the groundling line for the Ferrigno Glacier down to the floor of the rift valley that it rests in by 2060.  Also, note that this rift valley leads directly to the upstream end of the PIG drainage basin, and thus the degradation of the Ferrigno Glacier will contribute to ice mass loss from the PIG drainage basin.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 08, 2013, 07:24:25 PM
If it is not clear to some readers what type of major calving events that could occur within the Thwaites ice drainage basin during the period from 2040 to 2090, that could result in an ice melange in the transparent orange shaded areas, then I recommend that they watch the much viewed youtube clip from "CHASING ICE" showing the largest glacier calving event (in Greenland) ever filmed.

http://www.youtube.com/embed/hC3VTgIPoGU?rel=0 (http://www.youtube.com/embed/hC3VTgIPoGU?rel=0)


Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Laurent on March 08, 2013, 08:50:58 PM
I add the ted talk of James Balog for those who don't know about it !

http://www.ted.com/talks/lang/en/james_balog_time_lapse_proof_of_extreme_ice_loss.html (http://www.ted.com/talks/lang/en/james_balog_time_lapse_proof_of_extreme_ice_loss.html)

Laurent
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 17, 2013, 06:34:27 PM
I make this post in this thread as a continuation of the discussion (as of yesterday) in the "Surge" thread, but I plan to focus here on possible event from 2013 moving forward (to 2060).

First, I would like to note that for the past many years it is likely that the Thwaites Ice Tongue does not provide any significant pinning/buttressing action as indicated by the following quote from MacGregor et al 2012:

"Thwaites Glacier Tongue is not believed to buttress Thwaites Glacier significantly (Rignot, 2001), which is consistent with the muted recent acceleration of the grounded ice directly upstream of the ice tongue (up to 16% between 1992 and 2007; Rignot, 2006, 2008) compared with other glaciers in the ASE (63–108% over the same period), despite similar observations of marginal rifting and terminus retreat.  The terminus advance rate did not change significantly after the 2010 calving event, which removed most of the remaining ice tongue; this observation supports the earlier calculations of its limited buttressing effect."

To me this implies that for the past several years the increasing velocities of the Thwaites Glacier ice streams have not been due to a reduction of the buttressing action from the degrading Thwaites Ice Tongue, but instead possibly due to an activiation of a subglacial lake about 100km south of the current grounding line; resulting in an increase in basal lubrication.  The activiation of the subglacial lake is supported by the location of maximum ice mass loss identified by the GRACE satellite {however, note that if meltwater is flowing out of this subglacial lake, then the GRACE data needs to be corrected for: (a) local glacial isostatic adjustment due to magma backfilling under this very thin crust at this location; and (b) local snow fall in this location [replacing dense meltwater with less dense snow] that might partially mask (both from GRACE and altimeters) the acceleration of glacial ice mass loss}.

Thus if it is the case that a significant portion of the ice mass loss of the Thwaites Glacier is due to the outflow of basal meltwater from a subglacial lake, then this would mean that some relatively large subglacial cavity already exists over the length of the 100km long Thwaites Gateway, with freshwater currently flowing out of this 100km long conduit/cavity.  However, the advection of CDW through a large cavity in the Thwaites trough, could be accelerated by a jet of fresh meltwater (from the drainage of the subglacial lake at the south end of the 100km long gateway); and if so this could facilitate the acceleration of the retreat of the grounding line from the south end of the trough down into the BSB.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on April 17, 2013, 09:45:16 PM
Article on PIG in cryosphere discuss, kilometer scale resolution. 87Km^3 /yr over 2008-2011. Nice pics

http://www.the-cryosphere-discuss.net/7/1591/2013/tcd-7-1591-2013.html (http://www.the-cryosphere-discuss.net/7/1591/2013/tcd-7-1591-2013.html)

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 22, 2013, 01:47:19 AM
The attached figure showing the average snowfall accumulation across Antarctica from 1955 to 2005.  This data clearly indicates that the area at the south end of the Thwaites gateway is one of areas that receives the most snowfall anywhere in Antarctica; however, as discussed in the "Surge" thread the GRACE satellite indicates that this same area has the highest rate of ice mass loss of anywhere in Antarctica.  This clearly indicates that if one were to subtract out the mass of snowfall in this area one would then calculate a higher rate of acceleration of glacial/meltwater ice mass loss from this area than would would calculate from the uncorrected GRACE reading; which implies that future ice mass loss from this area are likely to be higher than current projections based on the uncorrected GRACE data.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 23, 2013, 01:02:49 AM
In the following AGU abstract from 2012, DeSanto et al postulate that geothermal energy from the active volcano Mount Takahe may be accelerating ice flow along on of the seven tributary ice streams feeding into the Thwaites Glacier.  The attached figure from MacGregor et al 2009 showing lateral shear strain clearly indicates moderate ice flow from the tributary ice stream passing by the base of Mt Takahe.

C31A-0576: Evaluating transience of a potential geothermal heat flux anomaly beneath a tributary ice stream of Thwaites Glacier, West Antarctica
Authors: John B DeSanto, Donald D Blankenship, Duncan A Young, Luc L Lavier, Eunseo Choi
Author Institutions: Institute for Geophysics, University of Texas, Austin, TX, USA
The Amundsen Sea Embayment of the West Antarctic ice sheet (WAIS) is currently one of the most rapidly changing sectors of a continental ice sheet. As a marine ice sheet, the WAIS is in a potentially unstable configuration. In addition to known active volcanoes such as Mt. Takahe and Mt. Murphy, subglacial volcanic activity has been identified using ice layer drawdown anomalies. Drawdown anomalies are features identifiable by a characteristic radar signature and represent significant loss of basal ice. We identify several features with the geometry of drawdown anomalies in the Thwaites Glacier along an ice stream tributary near Mt. Takahe. By modeling the flow of ice along the ice stream, we assess the hypothesis that these drawdown anomalies are a coherent feature caused by basal melt that is consistent with subglacial volcanic activity. The melt rate is then used to determine the spatial and temporal variations of geothermal heat flux in the region. We discuss these variations in the context of their geologic, morphologic and glaciologic setting and their implications for local volcanism and its impact on ice flow.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 23, 2013, 03:25:38 PM
This following summary regarding the current version of the PISM glacial model (and the two attached figures) indicate that: (a) older glacial models project less ice mass loss than does the PISM model that considers enthalpy; and (b) the liquid fraction with ice streams (including in the Pine Island Glacier and the Thwaites Glacier, Antarctica) play an important role with regard to both ice viscosity and basal melt water:
An enthalpy formulation for glaciers and ice sheets
By Andy ASCHWANDEN et al, Journal of Glaciology, Vol. 58, No. 209, 2012 doi: 10.3189/2012JoG11J088 441
"Polythermal glaciers contain both cold ice (temperature below the pressure-melting point) and temperate ice (temperature at the pressure-melting point). This poses a thermal problem similar to that in metals near the melting point and to geophysical phase-transition processes in mantle convection and permafrost thawing. In such problems the part of the domain below the melting point is solid while the remainder is at the melting point and is a solid/liquid mixture.  Generally, the liquid fraction of that mixture may flow through the solid phase. For ice specifically, viscosity depends both on temperature and liquid water fraction, leading to a thermomechanically coupled and polythermal flow problem."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 01, 2013, 03:03:55 PM
The attached figure is from: SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products
Reference : CLS-DOS-NT-06-034
Nomenclature : SALP-MU-P-EA-21065-CLS
Issue : 3rev 4
Date : 2013/01/29

This Handbook contains the following statements that are relevant to the figure:
"Since February 6th, 2012, Cryosat-2 mission has been integrated in the sytem. This mission is dedicated to the observation of the floating sea-ice as well as the continental ice sheets, but all data acquired over ocean are valuable for the observation of oceanic circulation and mesoscale variations. This major change is the result of the long-standing and fruitful partnership between ESA and CNES and a response to the request from scientific and operational oceanography users. The integration of Cryosat-2 impacts the delivering of Near real time and Delayed time Sea Level Anomalies (SLA) and maps of SLA (MSLA)."
"A Cryosat-2 Processing Prototype (C2P) (described in Boy et al, 2011) has been developed on CNES side to lay the ground for various SAR processing studies. The processing chains ingest Level-0 telemetry files distributed by ESA, and perform the following steps to generate Sea Level Anomalies (SLA) values for each altimeter measurements:
- Level-1: Decommutation, time-tagging and localization of measurements
- Level-1b: Calculation of instrumental corrections and geophysical/meteorological corrections
-  Level-2: MLE4 waveforms Retracking and calculation of SLA
The prototype processes data almost continuously over ocean, either in Low Resolution Mode (LRM) or in the Doppler/SAR mode processed as pseudo-LRM mode allowing to increase the coverage (figure 2)."

This figure clear shows the very high (up to positive 0.3 meters in the ASE) SLA, from 2011 to 2012, all along the coastline of West Antarctica; very possibly due to upwelling of warm CDW along these coastlines.  This very high SLA in the Amundsen Sea Embayment (ASE) can directly contribute to destabilizing the PIG and Thwaites glaciers.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 01, 2013, 03:04:41 PM
The attached figure is from: SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products
Reference : CLS-DOS-NT-06-034
Nomenclature : SALP-MU-P-EA-21065-CLS
Issue : 3rev 4
Date : 2013/01/29

This Handbook contains the following statements that are relevant to the figure:
"Since February 6th, 2012, Cryosat-2 mission has been integrated in the sytem. This mission is dedicated to the observation of the floating sea-ice as well as the continental ice sheets, but all data acquired over ocean are valuable for the observation of oceanic circulation and mesoscale variations. This major change is the result of the long-standing and fruitful partnership between ESA and CNES and a response to the request from scientific and operational oceanography users. The integration of Cryosat-2 impacts the delivering of Near real time and Delayed time Sea Level Anomalies (SLA) and maps of SLA (MSLA)."
"A Cryosat-2 Processing Prototype (C2P) (described in Boy et al, 2011) has been developed on CNES side to lay the ground for various SAR processing studies. The processing chains ingest Level-0 telemetry files distributed by ESA, and perform the following steps to generate Sea Level Anomalies (SLA) values for each altimeter measurements:
- Level-1: Decommutation, time-tagging and localization of measurements
- Level-1b: Calculation of instrumental corrections and geophysical/meteorological corrections
-  Level-2: MLE4 waveforms Retracking and calculation of SLA
The prototype processes data almost continuously over ocean, either in Low Resolution Mode (LRM) or in the Doppler/SAR mode processed as pseudo-LRM mode allowing to increase the coverage (figure 2)."

This figure clear shows the very high (up to positive 0.3 meters in the ASE) SLA, from 2011 to 2012, all along the coastline of West Antarctica; very possibly due to upwelling of warm CDW along these coastlines.  This very high SLA in the ASE can directly contribute to destabilizing PIG and Thwaites Glacier.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 05, 2013, 08:35:28 PM
I thought that I would post this image from NASA's QuikScat satellite detected extensive areas of snowmelt, shown in yellow and red, in west Antarctica in January 2005.  The 2005 melt was intense enough to create an extensive ice layer when water refroze after the melt. However, the melt was not prolonged enough for the melt water to flow into the sea.

A NASA scientist said "Water from melted snow can penetrate into ice sheets through cracks and narrow, tubular glacial shafts called moulins. If sufficient melt water is available, it may reach the bottom of the ice sheet. This water can lubricate the underside of the ice sheet at the bedrock, causing the ice mass to move toward the ocean faster, increasing sea level."

While such melting periods are episodic, such melting events should become more frequent with global warming (particularly during significant El Nino events) and are likely to have a major impact on the Thwaites drainage basin.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 10, 2013, 12:03:48 AM
I thought that I would post the attached figure that shows the change in ocean bottom pressure (in cm of water head) as an indication of water mass distribution in the ocean.  This image from the GRACE satellite for December 2012 would area to indicate a relatively high water mass loss from around Greenland and a relatively high addition of water mass around the Bellingshausen and ASE for last December.  While this ocean bottom pressure distribution is transient (with time); still this transient ocean water pressure off the coast from the PIG and the Thwaites Glacier could have helped to accelerate (at least temporarily) ice mass loss from these key ice features.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 10, 2013, 10:51:28 PM
To me the attached figure (from the University of Southern Florida) indicates: (a) a substantial amount of heat has entered the ocean during the El Nino hiatus period; and (b) the past trend of ice mass contribution to SLR has been roughly linear for the past 10-years, unless the El Nino hiatus effect is depositing more ocean water on land than is running back into the ocean (thus potentially masking any acceleration in SLR due to ice mass loss).  Again I would like to point out that much of the heat content going into the ocean eventually makes it into the Southern Ocean where an end of the El Nino hiatus would mean an increase in upwelling, which would deliver the extra heat in the CDW to the grounding lines of ice features around much of Antarctica.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Laurent on May 10, 2013, 11:08:59 PM
Am I seeing an increase of 1cm between 2011 and 2012 and probably the same amount in 2013 !?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 10, 2013, 11:31:01 PM
Laurent,

As confirmed by the attached image (to April 2013) from the Aviso website (http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/ (http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/)), yes roughly what you are seeing from the USF image is correct.  However, Aviso currently only cites a long term SLR slope of 3.18 mm/yr (rather than 20 to 25 mm/yr); because during the El Nino hiatus period the pothole in sea level from roughly 2010 to 2012 occurred to more preciptation falling on land than was returning to the sea.  Thus we will need to watch to see if a high SLR trend line slope continues into the future, or reverts to lower levels again.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 12, 2013, 02:33:23 AM
From an article at:
http://www.realclimate.org/index.php/archives/2013/04/ice-hockey/ (http://www.realclimate.org/index.php/archives/2013/04/ice-hockey/)
Eric Steig states:
"Looking at the very long term record from the WAIS Divide ice core, it appears that similar conditions could have occurred about once per century over the last 2000 years. Hence our answer to the question, “are the observations of the last few decades a harbinger of continued ice sheet collapse in West Antarctica?”, is tentative: “Probably”."

Eric Steig also provides the accompanying figure and the related statements:
"Figure 1. (a) Comparison of averaged δ18O (blue) across West Antarctica with the recent temperature record of Bromwich et al. (2013) from central West Antarctica (yellow). The light blue background is the decadal smoothed values +/- 1 standard error assuming Gaussian statistics. (b) Number of records used, and probability that the decadal average is as elevated as the 1990s (green).
Data sources: Most of the data for this figure have been available at http://nsidc.org/data/NSIDC-0425.html (http://nsidc.org/data/NSIDC-0425.html) for some time. There’s a new location (which will link to the old one) where more recent data sets will be placed, but it’s not all up yet: http://nsidc.org/data/nsidc-0536.html. (http://nsidc.org/data/nsidc-0536.html.)
Our results show that the strong trend in δ18O in West Antarctica in the last 50 years is largely driven by anomalously high δ18O in the most recent two decades, particularly in the 1990s (less so the 2000s). This is evident in the temperature data as well (top panel of the figure). The 1990s were also very anomalous in the tropics — there were several large long-lived El Niño events with a strong central tropical Pacific expression, as well as only very weak La Niña events. As in the tropics, so in West Antarctica: the 1990s were likely the most anomalous decade of the last 200 years."
Here I note that the longer the current El Nino hiatus period lasts, the more likely the next El Nino cycle will exceed that from the 1990's period; with potentially serious consequences for the WAIS ice mass loss.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 13, 2013, 04:28:05 AM
The attached image from a NASA/Goddard model simulation of the change in ice elevation from 2002 to 2011 shows upward of 60m of elevation for a portion of the ASE glaciers (not the PIG is on the east (left) side of this image.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 26, 2013, 07:48:36 PM
I provide the following relevant abstracts from the Nineteenth Annual WAIS Workshop, 2012 (note that the first abstract is particularly relevant to the potential widening of the Thwaites Gateway towards the eastside as noted by MacGregor et al 2013):

1. "Thermal migration of ice stream shear margins
C. Schoof and M. Haseloff

Ice stream shear margins can be viewed as boundary layers connecting a Poiseuille-like shear flow in ice ridges with a membrane-like, lateral-shear dominated flow in the ice stream itself.  The discharge of the ice stream is then highly sensitive to its width: with a Glen's law rheology, ice velocity scales as the fourth power of ice stream width. A crucial question therefore is how the width of the ice stream evolves over time.  Existing, depth-integrated models of ice stream dynamics typically predict that the bed underlying an ice ridge should freeze over time, while the ice stream bed remains unfrozen, and the transition between the two should occur in the shear margin. Depth-integrated models however cannot describe the details of that transition, which would allow the rate of margin migration to be computed.  We consider this boundary layer problem in detail, focusing on an abrupt transition from free slip to no slip at the point where the bed temperature changes from temperate (i.e., at the melting point) to subtemperate (i.e., below the melting point). This engenders multiple singularities in both, stress field and hence volumetric heating rate, and in heat flux. We show that the strength of these singularities is controlled by the far field, and that one of the singularities in the heat flux must be alleviated in order to allow the ice stream to widen. In the process, we show that at least a small zone of temperate ice must also form above the transition between frozen and unfrozen ice.  We show that the alleviation of the heat flux singularity is possible only for specific combinations of the following quantities: i) the strength of shear heating in the margin dictated by lateral shear stress acting on the ice stream margin ii) the background temperature gradient dictated by surface temperatures and advection in the ice ridge and iii) the margin migration rate.  More specifically, in the absence of significant advection from the ice ridge, we are able to show (by using the Wiener-Hopf technique) that margin migration rate is determined uniquely by lateral shear stresses and background temperature gradient."

2. "The Losers Next Door: Mass loss from Thwaites, Pope and Smith glaciers
Ben Smith, Ian Joughin, and David Shean

Headlines about mass loss from the Amundsen Sea sector are often dominated by the antics of Pine Island glacier. But just next door, three large glaciers have each made their own contributions to sea level. A synthesis of laser-altimetry and photogrammetry from ICESat, IceBridge, and Worldview, shows that Thwaites, Pope and Smith have together lost more mass since 2009 than PIG, and while the near-grounding-line thinning on PIG appears to be thinning, it has held steady over the last year on Smith Glacier. The cause of the large ice losses in these glaciers is probably ongoing changes near the grounding line. Visible-light and radar imagery reveals changes in crevassing patterns and in the configuration of ice rises near the fronts of all of these glaciers, suggesting that thinning ice shelves have lost some support from submarine peaks that once helped buttress them against ice flowing form upstream, while combined altimetry and ice-sounding measurement reveal changes in the extent of grounded ice.  At the same time, melt near the grounding lines has eroded contact between ice and rock. In some cases, the changes have been subtle, as in the Thwaites Ice Shelf, where the freeboard of nearly-floating ice has decreased, leading to patchy flotation; in the case of Pope Glacier, the change is not subtle at all: beneath the fastest-flowing part of the glacier, the ice has thinned by nearly 30 m/yr since early measurements in 2002, creating a dramatic new embayed area upstream of the grounding line. The extent to which these changes can continue will depend greatly on the future rate and pattern of marine melt, the specifics of which will be discussed in a companion presentation by Ian Joughin."

3. "Model--‐Based Analysis of Ice Sheet Thinning in the Amundsen Sea Embayment
Ian Joughin and Ben E. Smith

Strong thinning as ice streams have sped up along the Amundsen Coast produces ice loss well in excess of that from other regions of Antarctica. Much of the increases in speed appear to be caused by the loss of buttressing as ice shelves have thinned in response to warmer ocean water and subsequent loss of basal traction as the grounding line has retreated. We examine this response for Pine Island and Thwaites glaciers using models constrained by satellite data. Our earlier work reproduced the transient response on Pine
Island Glacier and predicted that strong near thinning near the grounding line should abate, but that overall losses should remain high as thinning diffuses inland. Here we find that this conclusion is supported by new IceBridge data, which show recent reduction of near grounding line thinning as speeds have leveled off. On Thwaites Glacier, we conducted a series of numerical experiments to investigate sensitivity of ice flow to ice-shelf loss and grounding-line retreat. The model suggests that recent changes in speed are the result of enhanced rifting that weakened the ice shelf followed by retreat of the grounding line. In response, surface slopes have thinned causing the speedup to migrate inland. We also use a prognostic model to investigate whether such thinning will continue over the next century."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 27, 2013, 03:22:19 AM
From the INSTAAR University of Colorado, Boulder, website, regarding the WAIS Divide Core:

"The project as been ongoing since the WAIS field site was established in 2005, and during 5 subsequent (short) austral summer field seasons of drilling, over 4,405 meters of ice have been recovered. The cores are allowing scientists from many different universities and research groups to apply their individual measurement expertise to extract the highest resolution climate record ever created for a polar ice core. The WAIS Divide climate records have an absolute, annual-layer-counted chronology for the most recent ~40,000 years. It was expected that the lower temporal resolution records would extend beyond ~100,000 years before present, but it was a big surprise to many that the oldest ice at the bottom of this core was less than 70,000 years old. Basal melting has played a role in removing ice from the bottom of the ice core."

This quote implies that over the last approximately 100,000 years, basal melting has removed over 1,300 meters of ice from the bottom of the WAIS Divide location (assuming that the scientist's expectation to find approximately 100,000 year old ice at the bottom of the core is correct).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 27, 2013, 03:28:07 AM
The attached figure from Nature Geoscience 2012, DOI: 10.1038/NGEO1671, show in good detail the areas of the Antarctic subject to the indicated number of days of surface ice melting in January 2005.  This figure indicates that both the PIG/Thwaite drainage basins and the Ross Sea Embayment areas are subject to a substantial risk of surface ice melting in the future.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on June 22, 2013, 07:36:48 PM
From the Center for Remote Sensing of Ice Sheets (CReSIS):

https://www.cresis.ku.edu/ (https://www.cresis.ku.edu/)

A seismic investigation of the subglacial environment along Thwaites Glacier, West Antarctica
By: Leo E. Peters, Sridhar Anandakrishnan, Richard B. Alley, Huw J. Horgan, Joseph A. MacGregor, Anthony, M. Hoch, Donald E. Voigt

The first image shows the area of the seismic investigation of TG (circa 2009).

The second image shows on overview of the observed basal shear stress in the study area of TG.  I would like to note that in the areas of high basal shear stress, where the ice velocities are also relative high (such as in the Thwaites Glacier, TG, gateway near the submerged mount that is helping to pin TG; that the frictional heat associated with this basal shear stress can be sufficient to melt a portion of the basal ice; which inturn can contribute to the accumulation of basal meltwater in associated subglacial lakes and/or drainage systems.

The third image shows a close-up of the portion of the study area shown in the second image, indicating the lines and selected parameters of the seismic investigation (circa 2008-2009).

The fourth image shows the investigators interpretation of the bed conditions along one of the lines of investigation shown in the third image.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on June 29, 2013, 04:50:27 PM
The following paper points out that when the Amundsen Sea sector ice mass change measurements are corrected for the condition of the firn then the corrected measurements indicate more ice mass loss than previously reported:

Continuously accelerating ice loss over Amundsen Sea catchment, West Antarctica, revealed by integrating altimetry and GRACE data
By: Hyongki Lee; C.K. Shum; Ian M. Howat; Andrew Monaghan; Yushin Ahn; Jianbin Duan; Jun-Yi Guo; Chung-Yen Kuo; Lei Wang

Earth and Planetary Science Letters; Volumes 321–322, 1 March 2012, Pages 74–80

"Abstract
Satellite altimetry and Gravity Recovery and Climate Experiment (GRACE) measurements have provided contemporary, but substantially different Antarctic ice sheet mass balance estimates. Altimetry provides no information about firn density while GRACE data is significantly impacted by poorly constrained glacial isostatic adjustment signals. Here, we combine Envisat radar altimetry and GRACE data over the Amundsen Sea (AS) sector, West Antarctica, to estimate the basin-wide averaged snow and firn column density over a seasonal time scale. Removing the firn variability signal from Envisat-observed ice-sheet elevation changes reveals more rapid dynamic thinning of underlying ice. We report that the net AS sector mass change rates are estimated to be − 47 ± 8 Gt yr− 1 between 2002 and 2006, and − 80 ± 4 Gt yr− 1 between2007 and 2009, equivalent to a sea level rise of 0.13 and 0.22 mm yr− 1, respectively. The acceleration is due to a combination of decreased snowfall accumulation (+ 13 Gt yr− 1 in 2002–2006, and − 6 Gt yr− 1 in 2007–2009) and enhanced ice dynamic thinning (− 60 ± 10 Gt yr− 1 in 2002–2006, and − 74 ± 11 Gt yr− 1 in 2007–2009) after 2007. Because there is no significant snowfall trend over the past 21 yr (1989–2009) and an increase in ice flow speed (2003–2010), the accelerated mass loss is likely to continue."

The caption for the attached image is:
"Spatial distributions of the standard deviations of the Envisat time series from September 2002 to December 2009 for all 1° × 1° regions (a) before and (b) after the surface gradient correction using the Antarctic DEM. The AS sector is shown with dashed lines. Spatial plots of elevation change rates (c) and their formal uncertainties (d) are also shown"


For a more current discussion of the GIA for the Amundsen Sea sector please go to:

http://www.sciencedirect.com/science/article/pii/S0921818112001567 (http://www.sciencedirect.com/science/article/pii/S0921818112001567)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 08, 2013, 05:21:46 PM
I thought that I would post the two attached images from a AGU presentation by Alley June 2013.  The first image shows how the current ice flow lines passing through the Thwaites Gateway crowd together to restrict ice mass loss through the limited with of the current gateway; while if the grounding line retreats by about 100km upstream (Southward) then the crowding effect would become much less, so the ice mass loss is expected to accelerate due to geometrical considerations alone.  The second attached image reinforces the same geometrical message as the first image except in terms of horizontal ice velocities through the Thwaites Gateway.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: JMP on July 10, 2013, 07:16:29 AM
This linked article seems to be new (to me anyway!) information about Thwaites Glacier and information on how the water underneath Glaciers affects their movement.
Quote
The University of Texas at Austin’s Institute for Geophysics have used an innovation in radar analysis to accurately image the vast subglacial water system under West Antarctica’s Thwaites Glacier. They have detected a swamp-like canal system beneath the ice that is several times as large as Florida’s Everglades.
Quote
Distinguishing subglacial swamps from streams is important because of their contrasting effect on the movement of glacial ice. Swamp-like formations tend to lubricate the ice above them whereas streams, which conduct water more efficiently, are likely to cause the base of the ice to stick between the streams.
  http://www.utexas.edu/news/2013/07/09/scientists-image-vast-subglacial-water-system-underpinning-west-antarctica (http://www.utexas.edu/news/2013/07/09/scientists-image-vast-subglacial-water-system-underpinning-west-antarctica)’s-thwaites-glacier/
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 10, 2013, 03:07:57 PM
JMP,

Thanks, the linked information provides expanded (new) information on the work presented by Dustin Schroeder et al that I discuss in the Surge thread, replies #1, 72, and 73 at:

http://forum.arctic-sea-ice.net/index.php/topic,21.0.html (http://forum.arctic-sea-ice.net/index.php/topic,21.0.html)

And of course the information in the Subglacial Lakes & Meltwater Drainage Systems thread is also relevant at:

http://forum.arctic-sea-ice.net/index.php/topic,404.0.html (http://forum.arctic-sea-ice.net/index.php/topic,404.0.html)

The concept of a swamp (rather than a subglacial lake as I had previous assumed) upstream from the Thwaites Gateway is an important refinement on earlier work.

Thank you,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 10, 2013, 07:35:53 PM
For those who are interested in the topic that JMP posted on, the paper entitled: Evidence for a water system transition beneath Thwaites Glacier, West Antarctica; by: Dustin M. Schroeder, Donald D. Blankenship, and Duncan A. Young; July 2013; can be downloaded at the following link:

http://www.pnas.org/content/early/2013/07/03/1302828110.full.pdf+html (http://www.pnas.org/content/early/2013/07/03/1302828110.full.pdf+html)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 11, 2013, 12:42:09 AM
I realize that I have posted about the Pine Island and Thwaites Glaciers in many different threads, and recently on to significant papers in replies #78 and 88 of the "Collapse" thread here:

http://forum.arctic-sea-ice.net/index.php?topic=31.50 (http://forum.arctic-sea-ice.net/index.php?topic=31.50)

Nevertheless, this is the most appropriate thread for posting the attached images that come from the following PowerPoint:

Recent Changes in Greenland & Antarctica
April 23, 2013 @ Ice and Climate, ATM S 514; by: Kristin Poinar and Ian Joughin, from the Polar Science Center

The first image (after Jacobs 2011) shows the increase in ice melting potential temperature difference (as a future of depth and year) for the warm CDW entering the Pine Island Ice Shelf from 1994 until 2009.  As I have shown evidence that this sam CDW continues on to the Thwaites Trough; where it represents a very serious threat to activate the Thwaites Glacier from now until 2060.

The second image (after Alley 2012) discusses how high tides flex up ice shelves and ice tongues such as the Thwaites Ice tongue, thus forming a basal gap allowing seawater to flow some distance (on the order of a kilometer) up the gateway of the glacier; while low tides flex down the ice shelves and ice tongues, thus squeezing out the seawater that was introduced during the previous high tide.  This action degrades the gateway ice.

The third image (from Joughin) shows how the outer face ice velocity for the Jakobshavn Glacier accelerated from about 4,000 m/yr in 1995 to about 8,000 m/yr in 2003 to about 16,000 m/yr in 2012 primarily due a combination of warming local ocean water temperatures and a loss of buttress support.  I have repeatedly stated that I foresee such a trend beginning for the Thwaites Glacier possibly within about 10 years.

The fourth image shows a floating ice melange infront of the Jakobshavn Glacier in 2004 following the 2003 acceleration event.  I have repeatedly that a acceleration of the Thwaites Glacier could lead to such a melange in the Thwaites Gateway before 2060.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 11, 2013, 05:38:41 PM
I believe that my comments about the second attached image in my immediately proceeding post (reply #43) contained errors; as I now believe that Richard Alley was most probably talking about the tidal influence on basal gaps (and intruding seawater) beneath the Siple Coast Ice Streams and most likely not the Thwaites Ice Tongue.  This is important to correct for reasons including the following:

- The offshore end of the Thwaites Ice Tongue is pinned by a submerged ridge; which stops the outer end of the tongue from flexing up and down with the tides.  I believe that this submerged ridge keeps the outer end of the tongue generally flexed up (in cantilever action), thus contributing to the existence of a basal gap (at the downstream portion) beneath the ice stream in the Thwaites Trough; which tidal water can then flow into, and out of (together with the fresh upstream meltwater flowing out through the trough); which in my opinion accelerates the formation of a new subglacial cavity in the Thwaites Trough.
- I have noted elsewhere (see the "Surge" thread) that the Thwaites Ice Tongue not only surged in the Fall of 2012 but also in 2002; leading me to speculate that in the ten year period the subglacial cavity in the Thwaites Trough grew to be long enough that stresses associated with tidally induce simple beam flexural stresses (with a beam span length from the offshore submerged ridge to the grounding line of the subglacial cavity in the Thwaites Trough by September 2012), caused the old ice tongue to crack vertically near mid-span, causing the old tongue to be rotated out of the way as the new tongue surged outward in the Fall of 2012 (see the "Surge" thread).
- I also believe that as the volume and temperature of the warm CDW currently forming a new subglacial cavity (note that the old cavity appears to have infilled when the tongue surged in 2012) in the Thwaites Trough; the time duration until the next tongue surge event will be less than ten years (particularly considering that the end of the current El Nino hiatus period will soon episodically drive more warm CDW into the ASE); which, will sufficient cycles could thin the overlaying ice sufficiently to lead to the formation of a permanently floating ice shelf in the Thwaites Trough, resulting in a direct channel for warm CDW to spread out laterally near the lip leading down into the Byrd Subglacial Basin, BSB (see the maps attached to the first post in this thread).
- The lateral spreading of warm CDW along the lip leading down into the BSB, could within several decades float much of the ice in the current Thwaites Gateway; which could inturn lead to a collapse mechanism for the Thwaites Glacier (see the low basal friction area in the "swampy" area, upstream of the Thwaites Gateway, shown in the attached image from Schroeder et al 2013) which could trigger a Jakobshavn (or Thwaites) Effect, as I have previously discussed in this (and other) threads.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 20, 2013, 03:53:07 PM
I have previously talked at length about the risks that the end of the current El Nino hiatus period presents particularly with accelerating ice mass loss from the Thwaites Glacier without adequately discussing some aspects of my assumptions in the 2012 to 2040 timeframe:

I have assumed that the hiatus period will end between 2014 and 2017, and that the associated influx of warm surface seawater will cause the Thwaites Ice Tongue and Ice Shelf to largely collapse by 2025; which will both: (a) contribute to rapid thinning of the ice stream in the Thwaites Trough, with an associated acceleration of the subglacial cavity formation in the trough so that by about 2040 the grounding line, GL, in the trough has retreated back to about the location of the submerged mount in the Thwaites Gateway; and (b) eastward of the Thwaites Trough the GL will retreat in an accelerated fashion partially due to the turbulent convection process illustrated in the attached image that shows that the combination of warm ocean water and fresh basal meltwater emerging from beneath the glacier can cause accelerated mixing due to bouyancy effects.

I assume that the positive PDO (Pacific Decadal Oscillation) period (signalling the end of the hiatus period) after about 2014 to 2017 will last for about 20 to 30 years; by which time I assume that the GL will have retreated back to the subglacial lake infront of the submerged mount in the Thwaites Gateway; and thereafter the retreat of the GL down the negative slope into the BSB will accelerate without the assistance of periodic El Nino events (associated with the positive PDO); shortly thereafter leading to the "Thwaites Effect" that I have previously postulated.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 24, 2013, 08:17:45 PM
While I made a less complete post on this topic in the "Collapse" thread; the information contained in the following University of Michigan website and in the following referenced paper, abstract, and attached figure; is of such fundamental importance to the "Thwaites Effect" discussed in this thread, that I am making this additional post on this topic:

http://www.ns.umich.edu/new/multimedia/videos/21600-sea-level-rise-new-iceberg-theory-points-to-areas-at-risk-of-rapid-disintegration (http://www.ns.umich.edu/new/multimedia/videos/21600-sea-level-rise-new-iceberg-theory-points-to-areas-at-risk-of-rapid-disintegration)

Diverse calving patterns linked to glacier geometry
by:J. N. Bassis & S. Jacobs; Nature Geoscience; (2013); doi:10.1038/ngeo1887

Abstract: "Iceberg calving has been implicated in the retreat and acceleration of glaciers and ice shelves along the margins of the Greenland and Antarctic ice sheets. Accurate projections of sea-level rise therefore require an understanding of how and why calving occurs. Unfortunately, calving is a complex process and previous models of the phenomenon have not reproduced the diverse patterns of iceberg calving observed in nature. Here we present a numerical model that simulates the disparate calving regimes observed, including the detachment of large tabular bergs from floating ice tongues, the disintegration of ice shelves and the capsizing of smaller bergs from grounded glaciers that terminate in deep water. Our model treats glacier ice as a granular material made of interacting boulders of ice that are bonded together. Simulations suggest that different calving regimes are controlled by glacier geometry, which controls the stress state within the glacier. We also find that calving is a two-stage process that requires both ice fracture and transport of detached icebergs away from the calving front. We suggest that, as a result, rapid iceberg discharge is possible in regions where highly crevassed glaciers are grounded deep beneath sea level, indicating portions of Greenland and Antarctica that may be vulnerable to rapid ice loss through catastrophic disintegration."

This paper (and accompanying find) indicate that the actions of the submerged seamount in Thwaites Gateway to buttress the thicker upstream ice; and of the high snowfall rates in this area to thicken the upstream ice; actual contribute to the instability of the Thwaites Glacier once the: (a) calving; and (b) advective basal ice melting; have cleared the ice downstream and around the submerged seamount in the Thwaites Gateway.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on July 25, 2013, 06:45:16 PM
I seem to have commented on the Bassis paper on a different thread. Sorry!

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 18, 2013, 05:09:36 PM
The following reference (the link provides a free pdf) and associated Conclusions (which I like more than the abstract), emphasizes the importance of kilometer scale variations in ice shelf melting.  This work indicates that averaging these kilometer scale variations results in non-conservative (w.r.t. public safety) results regarding the risk of accelerating SLR:

http://www.the-cryosphere-discuss.net/7/1591/2013/tcd-7-1591-2013.pdf (http://www.the-cryosphere-discuss.net/7/1591/2013/tcd-7-1591-2013.pdf)

Pine Island Glacier ice shelf melt distributed at kilometre scales
by: P. Dutrieux, D. G. Vaughan, H. F. J. Corr, A. Jenkins, P. R. Holland, I. Joughin, and A. Fleming; The Cryosphere Discuss., 7, 1591–1620, 2013; www.the-cryosphere-discuss.net/7/1591/2013/; (http://www.the-cryosphere-discuss.net/7/1591/2013/;) doi:10.5194/tcd-7-1591-2013

Conclusions:
"Previous work has indicated high melt-rates near the grounding line of PIG (Payne et al., 2007; Rignot and Jacobs, 2002) and the presence of basal channels in the ice (Bindschadler et al., 2011; Mankoff et al., 2012; Vaughan et al., 2012). Our observations show that the pattern of melting on PIG ice shelf is highly complex. Within 10km of the grounding line, the melt rate is at least 100myr−1. Only 20 km downstream this reduces to 30myr−1. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr−1, in close agreement with 2009 oceanographically-constrained estimates.  Close to the grounding line, melting is concentrated in the basal channels and carves out those channels at 80myr−1. Further downstream, melting on the keels is 30myr−1 faster than in the channels, which explains the gradual loss of channels in the downstream part of the ice shelf and the inversion of the surface elevation anomalies relative to free floatation. The gradual regime shift in channel melt could be explained by the initial formation, near the grounding line, of buoyant meltwater plumes rising up the ice base and most efficiently entraining heat to the channel crests, and a decrease in the heat entrainment efficiency downstream as the slope weakens, the ice base shallows and the warm water source gets further away. At some stage, the plumes within the channels deliver less heat to the ice shelf than the warmer deeper waters bathing the channel keels.  With the advent of ice surface DEMs of even higher resolution (few meters) taken at regular time intervals, we can expect that the methodology developed here will reveal unforeseen details about the distribution of surface elevation changes and by inference of basal melt where the underlying assumptions are valid, thereby increasing our understanding of atmosphere-ice-ocean interaction dynamics and their temporal and spatial variability.

Our observations of the area close to the grounding line therefore indicate melt rates that are 80% higher in channels than on neighbouring keels, and point to high spatial variability in the melt-rates across the ice shelf, indicating strong modulation of ice-ocean interactions at kilometre scales. This implies that in-situ observations need to be interpreted within their contextual position relative to the channels. Possibly the most important implication of this work concerns the modelling of sub-ice shelf cavities. Accurately representing sub-kilometre scales using conventional ocean models is challenging even for dedicated regional studies, and will remain impossible for global coupled climate models for some time to come. One approach to solving this problem is to use unstructured computational meshes to focus the model resolution on features of interest, such as these channels (Kimura et al., 2013; Timmermann et al., 2012).  A more conventional alternative would be to parameterise their effect on the larger scales that models are able to resolve. For either of these approaches to be successful, an essential prerequisite is a detailed observational understanding of the channels, for which the present study provides a significant advance."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 23, 2013, 02:30:23 AM
I posted this ENSO figure (and associated weblink) in the "Antarctic Weather and Meteorology" thread; but as I am concerned that some people may miss it over there, I am re-posting this image here as the possible return of an El Nino event in the mid-2014 could have serious consequences on ice mass loss from the Thwaites Glacier.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 01, 2013, 06:05:50 PM
Considering the conceptual correlation that I have made between the "Jakobshavn Effect" and the "Thwaites Effect"; the linked reference that indicates that the outflow of surface meltwater accumulated within crevasses along the margins of the Jakobshavn Glacier; could very well have significant parallel importance to the Thwaites Glacier by 2060 should a strong El Nino effect induced (superimposed on top of the strong warming trend in this area) surface melting in the Thwaites Basin by (or after) 2060.  Such an occurrence in the Thwaites Basin could serve as a trigger to destabilize the Thwaites Glacier before the end of this century"

http://onlinelibrary.wiley.com/doi/10.1002/jgrf.20039/abstract (http://onlinelibrary.wiley.com/doi/10.1002/jgrf.20039/abstract)


Lampkin, D. J., N. Amador, B. R. Parizek, K. Farness, and K. Jezek (2013), Drainage from water-filled crevasses along the margins of Jakobshavn Isbræ: A potential catalyst for catchment expansion, J. Geophys. Res. Earth Surf., 118, 795–813, doi:10.1002/jgrf.20039.



Abstract:
"Saturated crevasses occur in local depressions within the shear margins of Jakobshavn Isbræ at inflections in the ice stream's flow direction. Spatio-temporal variability of seven distinctive saturated crevasse groups was examined during the 2007 melt season. The area of saturated crevasses reached its maximum extent, ~1.8 km2, in early July, and remained largely constant until early August. Filling rates are correlated with regional melt production, while drainage rates are highly correlated with areal extent. Estimates on potential drainage volume from the largest crevasse system are ~9.23 × 10−3 km3 ± 2.15 × 10−8 km3 and ~ 4.92 × 10−2 km3 ± 3.58 × 10−8 km3, respectively, over a 16 day interval and are more than required for a distributed basal hydrologic system across this area to temporarily flood bedrock obstacles believed to control basal sliding. Future drainage events, likely extending farther inland with warming, could result in enhanced lateral mass discharge into the ice stream, with implications for the dynamic evolution of the entire basin."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 02, 2013, 01:16:06 AM
The following link leads to a free access pdf of the reference cited below; which not only indicates that Synthetic Aperture Radar is a good tool for correlation surface winds with deep water velocities (in this case for the Amundsen Sea); but also their findings indicate that the sea ice in the Amundsen Sea dissipates with increasing local warming, that the CDW velocity will increase; which in-turn should accelerate ice mass loss from glaciers, ice streams and ice shelves around the Amundsen Sea coastal areas:


http://www.mdpi.com/2072-4292/5/8/4088 (http://www.mdpi.com/2072-4292/5/8/4088)


Carvajal, G.K.; Wåhlin, A.K.; Eriksson, L.E.; Ulander, L.M. Correlation between Synthetic Aperture Radar Surface Winds and Deep Water Velocity in the Amundsen Sea, Antarctica. Remote Sens. 2013, 5, 4088-4106.


"Abstract: The recent observed thinning of the glacier ice shelves in the Amundsen Sea (Antarctica) has been attributed to warm deep currents, possibly induced by along-coast winds in the vicinity of the glacial ice sheet. Here, high resolution maps of wind fields derived from Synthetic Aperture Radar (SAR) data have been studied and correlated with subsurface measurements of the deep water velocities in the Amundsen Sea area. Focus is on periods with low ice coverage in 2010 and 2011. In 2010, which had comparatively low ice coverage, the results indicate a more rapid response to wind forcing in the deep currents than in 2011. The SAR wind speed maps have better spatial resolution than available reanalysis data, and higher maximum correlation was obtained with SAR data than with reanalysis data despite the lower temporal resolution. The maximum correlation was R = 0.71, in a direction that is consistent with wind-driven Ekman theory. This is significantly larger than in previous studies. The larger correlation could be due to the better spatial resolution or the restriction to months with minimum ice coverage. The results indicate that SAR is a useful complement to infer the subsurface variability of the ocean circulation in remote areas in polar oceans."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 02, 2013, 08:10:30 PM

The following reference indicates that short ice shelves / ice tongues such as those for PIG and/or Thwaites are particularly subjected to calving induced by long period waves:

Normal modes of a coupled ice-shelf/sub-ice-shelf cavity system; by Sergienko, Olga V.; Journal of Glaciology, Volume 59, Number 213, March 2013, pp. 76-80(5); DOI: http://dx.doi.org/10.3189/2013JoG12J096 (http://dx.doi.org/10.3189/2013JoG12J096)


"Abstract:
Ice shelves and ice tongues are dynamically coupled to their cavities. Here we compute normal modes (eigenfrequencies and eigenfunctions) of this coupled system using a thin-plate approximation for the ice shelf and potential water flow in the ice-shelf cavity. Our results show that normal modes depend not only on the ice-shelf parameters (length, thickness, Young's modulus, etc.) but also on the cavity depth. The dominant eigenmodes are higher for ice shelves floating over deeper cavities; they are also higher for shorter ice shelves and ice tongues (< 50 km long). The high-eigenfrequency eigenmodes are primarily controlled by the ice flexure and have similar periods to sea swell. These results suggest that both long ocean waves with periods of 100-400 s and shorter sea swell with periods of 10-20 s can have strong impacts on relatively short ice shelves and ice tongues by exciting oscillations with their eigenfrequencies, which can lead to iceberg calving and, in some circumstances, ice-shelf disintegration."

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 03, 2013, 04:44:47 PM
The following linked reference (with a free pdf) presents information on the sediment layer beneath the PIG, needed for more accurate modeling of ice mass loss from this critical glacier:


http://www.igsoc.org/annals/54/64/a64A110.pdf (http://www.igsoc.org/annals/54/64/a64A110.pdf)


Subglacial bathymetry and sediment layer distribution beneath the Pine Island Glacier ice shelf, West Antarctica, modeled using aerogravity and autonomous underwater vehicle data; Atsuhiro MUTO, Sridhar ANANDAKRISHNAN, Richard B. ALLEY, 2013; Annals of Glaciology 54(64) 2013 doi: 10.3189/2013AoG64A110


"ABSTRACT. Pine Island Glacier (PIG), West Antarctica, has been experiencing acceleration in its flow speed and mass loss for nearly two decades, driven in part by an increase in the delivery of relatively warm Circumpolar DeepWater (CDW). However, at present, the configuration of the sub-ice-shelf cavity and bed conditions beneath the PIG ice shelf that dictate such oceanic influences remain poorly understood. Here, we use aerogravity data and ocean bottom depths measured by an autonomous underwater vehicle (AUV) to model the bathymetry and sediment layer thickness beneath the PIG ice shelf. Results reveal that the deep basins, previously found by AUV on both landward and seaward sides of a submarine ridge, extend substantially to the north and south. The water column thickness of the basins reaches 400–550m on the landward side of the ridge and 500–600m on the seaward side. The sediment layer covers the whole expanse of the seabed beneath the ice shelf, and the thickness is in the range ~ 200–1000 m. The thinnest sediments (<200 m) are found on the seaward slope of the submarine ridge, suggesting that erosion by advancing ice may have been concentrated in the lee of the topographic high."

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 06, 2013, 02:17:45 AM
The linked reference (with a free pdf and see the attached reference figure) presents a very interesting discussion of the potential migration of the eastern shear margin of the Thwaites Glacier, that could someday contribute to the accelerated ice mass loss from this critical basin:

http://www.igsoc.org/journal/59/217/j13J050.pdf (http://www.igsoc.org/journal/59/217/j13J050.pdf)


Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica; Joseph A. MacGREGOR, Ginny A. CATANIA, Howard CONWAY, Dustin M. SCHROEDER, Ian JOUGHIN, Duncan A. YOUNG, Scott D. KEMPF, & Donald D. BLANKENSHIP; Journal of Glaciology, Vol. 59, No. 217, 2013 doi: 10.3189/2013JoG13J050


"ABSTRACT. Recent acceleration and thinning of Thwaites Glacier, West Antarctica, motivates investigation of the controls upon, and stability of, its present ice-flow pattern. Its eastern shear margin separates Thwaites Glacier from slower-flowing ice and the southern tributaries of Pine Island Glacier. Troughs in Thwaites Glacier’s bed topography bound nearly all of its tributaries, except along this eastern shear margin, which has no clear relationship with regional bed topography along most of its length. Here we use airborne ice-penetrating radar data from the Airborne Geophysical Survey of the Amundsen Sea Embayment, Antarctica (AGASEA) to investigate the nature of the bed across this margin.  Radar data reveal slightly higher and rougher bed topography on the slower-flowing side of the margin, along with lower bed reflectivity. However, the change in bed reflectivity across the margin is partially explained by a change in bed roughness. From these observations, we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties. Given the potential for future increases in ice flux farther downstream, the eastern shear margin may be vulnerable to migration. However, there is no evidence that this margin is migrating presently, despite ongoing changes farther downstream."

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 06, 2013, 07:50:30 PM
The MacGregor et al 2013 paper that I cite in the immediately preceding post is more significant than my brief comments from yesterday (and also in this post) indicate for reasons including:

(1) The first attached figure from MacGregor et al 2013 indicates: (a) In panel "b" the red jiggly line shows the crack location for the large iceberg that just calved from the Pine Island Ice Shelf, PIIS, this austal winter; which indicates that the next major calving event from PIIS will likely relieve the buttressing action on the glacier labeled "SW tributary", which will most likely accelerate the ice velocity, and will likely extend the upstream flow stream, for this "SW tributary" glacier; and  (b) Panel "a" shows that if the flow stream for the "SW tributary" glacier extends about 50km upstream then it will link with the eastern shear margin of the Thwaites Glacier (see also the figure in the preceding post that shows the shear strain from 2009).

(2) The back ground image of the second attached figure from NASA-JPL shows the changes in ice mass loss through 2012 as measured by the GRACE satellite (note that no scale is provided as the amounts may need to be increase by up to 40% to correct for GIA interpretation according to: An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica; A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich; http://dx.doi.org/10.1016/j.gloplacha.2012.08.001 (http://dx.doi.org/10.1016/j.gloplacha.2012.08.001)).  Nevertheless this background image clearly shows that along the deep eastern portions of the Byrd Subglacial Basin and just west of the "Thwaites Glacier eastern shear margin" that the amount of ice mass loss has increased significantly between 2009 and 2012, indicating that either: (a) the ice flow in this critical area is slowly accelerating [and if the link between the flow stream for the "SW tributary" and the "Thwaites Glacier eastern shear margin" link as discussed in point (1) this may accelerate even faster]; and/or (b) a large amount of basal melt water is flowing out of the deep eastern portion of the Byrd Subglacial Basin.

(3) The third attached image shows the altimeter measured ice surface elevation change along the Amundsen Sea coastline by 2011 (see the "Surge" thread for details), indicating that the coastal zone of the Thwaites Glacier Gateway area is thinning rapidly and if the acceleration of ice flow along the "Thwaites Gacier eastern shear margin" discussed in points (1) and (2) occur then this thinning would both accelerate and would extend toward (and would link with) the thinning area upstream of the "SW tributary" glacier. 

(4) Given sufficient time, and/or sufficient ice flow acceleration, the ice thinning along the extended Thwaites Glacier Gateway discussed in point (3) could convert the ice in this area into an ice shelf that floats over the top of the somewhat rough bottom topology in this area shown in the fourth attached image.

If the scenario develops as discussed above over the next three decades then this would match the WAIS collapse scenario that I have presented both in this thread and elsewhere in the Antarctica folder.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 06, 2013, 08:45:55 PM
The following link leads to a copyrighted Bachelor's thesis entitled:  Evaluating Transience of a Potential Geothermal Flux Anomaly Beneath a Tributary Ice Stream of Thwaites Glacier, West Antarctica, by John Boone DeSanto, 2013, the University of Texas at Austin:


http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=10&ved=0CGIQFjAJ&url=http%3A%2F%2Frepositories.lib.utexas.edu%2Fbitstream%2Fhandle%2F2152%2F20103%2FDeSantoThesis_physics.pdf%3Fsequence%3D2&ei=o-EpUp7rDMWY4wSohYC4Aw&usg=AFQjCNFRPM5uuUOFDknpwow-haI6e_tnbQ&bvm=bv.51773540,d.bGE (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=10&ved=0CGIQFjAJ&url=http%3A%2F%2Frepositories.lib.utexas.edu%2Fbitstream%2Fhandle%2F2152%2F20103%2FDeSantoThesis_physics.pdf%3Fsequence%3D2&ei=o-EpUp7rDMWY4wSohYC4Aw&usg=AFQjCNFRPM5uuUOFDknpwow-haI6e_tnbQ&bvm=bv.51773540,d.bGE)

Abstract:
"The Amundsen Sea Embayment of the West Antarctic ice sheet (WAIS) is currently one of the most rapidly changing sectors of a continental ice sheet.  As a marine ice sheet, the WAIS is in a potentially unstable configuration.  A model is proposed to evaluate the effect of geothermal flux on flow in ice streams using ice layer drawdown anomalies, features identifiable by a thick layer package resting on top of deformed ice. Drawdown anomalies represent either significant loss or mechanical deformation of basal ice.

Several features with the geometry of drawdown anomalies are identified in Thwaites Glacier along an ice stream tributary near Mt. Takahe. These anomalies correlate with the surface ice velocity and have thick layer packages that age at a constant rate, implying deformation at a single origin corresponding to an upstream edifice. The abnormal amplitude of upstream drawdown anomalies implies a thermal event at the same edifice 1000-2000 years ago.

This provides another example of high heterogeneous geothermal flux in the WAIS."

This thesis indicates that high geothermal basal heat fluxes may have occurred on the perimeter of Mt Takahe (a volcano) 1,000 to 2,000 years ago; which supports the concept that if sufficient ice mass loss occurs from the Thwaites Glacier (say by the end of this century), then significant heat fluxes may occur again around Mt Takehe, which could serve to accelerate ice mass loss from Thwaites Glacier.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 07, 2013, 08:04:39 PM
The following abstract is taken from the proceedings of the following IGSOC sponsored symposia.  The finding that the rate of retreat of the PIG grounding line is very sensitive to increasing ice shelf basal melting rate; implies that PIG will continue to contribute ice mass loss to SLR if we stay on the current BAU pathway that we are currently following, which would also serve to accelerate ice mass loss from the Thwaites Glacier as indicated in the MacGregor et al 2013 discussed a in a couple of prior posts:

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)



Sensitivity of Pine Island Glacier, West Antarctica, to ocean melting
G. Hilmar GUDMUNDSSON
Corresponding author: G. Hilmar Gudmundsson
Corresponding author e-mail: ghg@bas.ac.uk
The sensitivity of Pine Island Glacier (PIG) to different ocean melting scenarios is investigated through numerical modelling. Melt rates are derived using an ocean circulation model (MIT/GCM), and an ice-flow model is used to calculate rates of grounding-line migration and ice drawdown over the next two centuries. The ice-flow model uses unstructured grids and allows for robust and accurate calculation of grounding-line positions and ice-shelf buttressing effects. It is found that changing a baseline reference ice-shelf melt-rate distribution by a factor of two can either lead to a stable grounding line at approximately the currently observed location, or to an irrevocable retreat of PIG. Calculated near-future ice loss is, hence, strongly dependent on applied basal melt rates. This high sensitivity illustrates the importance of using realistic ocean forcing when assessing the future contribution of PIG to global sea levels."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 08, 2013, 03:46:21 AM
The linked reference indicates that over the last 30-yrs of measurements that is no observable trend for increased snow fall in the Thwaites Basin:

http://onlinelibrary.wiley.com/doi/10.1002/grl.50706/abstract (http://onlinelibrary.wiley.com/doi/10.1002/grl.50706/abstract)

Medley, B. et al. (2013), Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models, Geophys. Res. Lett., 40, 3649–3654, doi:10.1002/grl.50706.

"Abstract
We use an airborne-radar method, verified with ice-core accumulation records, to determine the spatiotemporal variations of snow accumulation over Thwaites Glacier, West Antarctica between 1980 and 2009. We also present a regional evaluation of modeled accumulation in Antarctica. Comparisons between radar-derived measurements and model outputs show that three global models capture the interannual variability well (r > 0.9), but a high-resolution regional model (RACMO2) has better absolute accuracy and captures the observed spatial variability (r = 0.86). Neither the measured nor modeled accumulation records over Thwaites Glacier show any trend since 1980. Although an increase in accumulation may potentially accompany the observed warming in the region, the projected trend is too small to detect over the 30 year record."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 08, 2013, 07:26:48 PM
The following abstracts come from the linked sources and are relevant to the Thwaites Glacier:

www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm (http://www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm)
Contact: Secretary General, International Glaciological Society

67A030
Sensitivity of Thwaites Glacier to ice-shelf melting
Ian JOUGHIN, Ben SMITH
Corresponding author: Ian Joughin
Corresponding author e-mail: ian@apl.washington.edu
Strong thinning as ice streams have sped up along the Amundsen coast produces ice loss well in excess of that from other regions of Antarctica. Much of the increases in speed appear to be caused by the loss of buttressing as ice shelves have thinned in response to warmer ocean water and subsequent loss of basal traction as the grounding line has retreated. We have developed a finite-element implementation of a prognostic shallow-shelf ice-stream/shelf model, which we have applied to Thwaites Glacier, Antarctica. The model uses an improved bed map from data recently acquired as part of operation IceBridge. We have conducted a number of numerical tests to examine the sensitivity of the glacier to increased melting and surface accumulation. For melt rates comparable with present, the glacier continues to lose mass at roughly its present rate. Strong sub-shelf melt produces stepped retreat of the grounding line by >40 km over 250 years. Examination of the annual thinning rates shows rapid evolution of the spatial distribution of loss over periods of several years (i.e. comparable in length to a typical satellite altimetry mission). In particular, with each episode of grounding-line retreat, a pattern of strong thinning initially develops near the grounding line that then diffuses inland over periods of several years. Only with increased surface accumulation and reduced melting does the glacier stabilize. Thus, it is likely that Thwaites Glacier will continue to lose mass over the next several centuries at a rate largely determined by the amount of warm circumpolar deep water that makes its way to near the grounding line.


67A005
The implications of reflector geometry on radar data acquisition
Nicholas HOLSCHUH, Sridhar ANANDAKRISHNAN, Knut CHRISTIANSON
Corresponding author: Nicholas Holschuh
Corresponding author e-mail: ndh147@psu.edu
The structure of internal layers in ice sheets is used to interpret ice-sheet flow dynamics. The goal of radio-echo sounding is to accurately reproduce that layer geometry. Radar data from Thwaites Glacier and the northeast Greenland ice stream (NEGIS) show that layers whose dip angle exceeds a threshold do not produce a coherent signal in the data. This is likely due to destructive interference in trace stacking and off-nadir backscatter. Reduction of signal amplitude due to destructive interference in stacking is a function of radar center frequency, reflector dip angle and stacked trace spacing. As the stacked trace spacing increases over a dipping horizon, the phase difference between component pre-stack traces increases, resulting in a less coherent stack. Airborne data are more prone to this signal loss given the higher velocity acquisition platform. In addition to destructive interference in stacking, dipping reflectors sample off-nadir portions of the antenna radiation pattern, reducing the signal recorded by the receiver. Imaging reflectors from wide angles also results in longer englacial travel times and thus additional englacial attenuation relative to horizontal reflectors at comparable depths. Both of these effects lead to further reduction in reflection amplitude. Here we use signal amplitudes to interpolate the slope field of the internal layers and reconstruct layer geometries in radar data from Thwaites Glacier and NEGIS. Our results show that it is possible to infer layer angle with reasonable uncertainty for most dip angles and thereby also provide useful data on current/past stress state and the basal properties responsible for internal layer folding even when layers are not directly imaged."


67A033
Flow history of Thwaites Glacier inferred from radar-detected flowlines and flowbands
T.J. FUDGE, H. CONWAY, G. CATANIA, D. BLANKENSHIP, K. CHRISTIANSON, I. JOUGHIN, S. KEMPF, D. YOUNG
Corresponding author: T.J. Fudge
Corresponding author e-mail: tjfudge@uw.edu
Patterns in radar-detected internal layers in glaciers and ice streams can often be tracked several hundred kilometers downstream from their origin. Here we use distinctive patterns detected in the onset region of Thwaites Glacier in the Amundsen Sea sector of West Antarctica to delineate flowlines and flowbands. Flowbands in the onset region contain information about flow over the past 700 years, which is the approximate time for ice to flow along the flowband. Our analysis of flow conditions over century scales gives perspective on recent changes observed on Thwaites Glacier. Along the eastern margin, flow measured with GPS between 2009 and 2010 is rotated outward by about 1° compared with the long-term flow direction. However, such small rotation is within the directional uncertainty of the long-term flow (about 3°); it is not clear that this apparent outward rotation is a response to changes at the grounding line. We use two radar-detected flowlines to define a 110 km flowband in the middle tributary. The ratio of fluxes through gates at the downstream and upstream ends of the flowband is calculated from continuity for a range of values for past thinning and accumulation rate along the flowband. For comparison, we use InSAR-derived surface velocities (from 1996) and estimates of accumulation rate, to define the geometry of the present-day flowband and to calculate the present-day thinning rate and flux ratio. The geometry of the modern flowband is closely similar to the long-term average, but the flux ratio is higher than the long-term average. The simplest explanation for the change is that the modern rate of thinning along the flowband (about 0.52 m a–1) is larger than the long-term average. The method does not allow us to determine when in the past 700 years the rate of thinning increased.

67A036
Buried information: constraining bed geometry and material from the Doppler-dependent radar-scattering function
Dustin M. SCHROEDER, Donald D. BLANKENSHIP, R. Keith RANEY, Duncan A. YOUNG
Corresponding author: Dustin M. Schroeder
Corresponding author e-mail: dustin.m.schroeder@utexas.edu
The morphological, lithological and hydrological basal boundary conditions of ice sheets and glaciers can exert strong, even dominating, control on their behavior, evolution and stability. However, the scales at which the physical processes and observable signatures of this control occur are typically smaller than the spatial resolutions achievable using ice-penetrating radar. Further, the strength of calibrated radar bed echo returns is a combination of both the material (i.e. relative permittivity, conductivity) and geometric (i.e. rms height, rms slope, auto-correlation length) properties of the ice–bed interface. This ambiguity in the relative contribution of material and geometric bed properties, along with uncertainty in englacial attenuation from underconstrained ice temperature and chemistry, also makes definitive assessment of basal conditions from echo strengths extremely difficult. To address these challenges in interpreting geometric and material bed properties at glaciologically relevant scales, we present a new algorithmic approach to measuring the radar-scattering function of the ice–bed interface with varying Doppler frequency by performing range-migrated SAR focusing using multiple reference functions spanning different ranges of Doppler frequencies from the bed. We parameterize this scattering function in terms of the relative contribution of angularly narrow specular energy and isotropically scattered diffuse energy. This specularity content of the bed echo is insensitive to englacial attenuation and is a measure of both the angular distribution of returned echo energy and the geometry of the ice–bed interface at the sub-azimuth-resolution scale. We present an application of this technique to a gridded airborne radar survey over the entire catchment of Thwaites Glacier, West Antarctica. We show how the information in the along-track scattering function of the bed can be used to assess the extent and configuration of distributed water across the catchment and detect the transition of the water system from distributed canals to concentrated channels. We also show how this information can be used to constrain the morphology of basal bedforms and infer the distribution of deformable sediments and exposed bedrocks across the catchment. These applications demonstrate the potential to extract rich information from focusable radar-sounding data to constrain the radar-scattering function as well as the material and geometric properties of the bed.


67A040
Firn variability derived from a statistical analysis of airborne ice-penetrating radar over the Thwaites Glacier catchment, West Antarctica
Cyril GRIMA, Dustin M. SCHROEDER, Don D. BLANKENSHIP, Duncan A. YOUNG
Corresponding author: Cyril Grima
Corresponding author e-mail: cyril.grima@gmail.com
A dry firn layer covers most of the Antarctic ice sheet. Firn characteristics are a function of accumulation rate, air temperature and surface winds. As such, they are indicators of ice-sheet accumulation history and mass balance. To date, most of the observational techniques for firn characterization at depths of a meter or more achieve limited geographical coverage (i.e. ice/firn cores, ground-based GPR). During the aerogeophysical campaign of the 2004/05 austral summer the Airborne Geophysical Survey of the Amundsen Sea Embayment, Antarctica (AGASEA) project surveyed a 15 km grid over a 600 km &mult; 400 km area covering the Thwaites Glacier catchment, West Antarctica, with the High-Capability Radar Sounder (HiCARS) system operated by the University of Texas Institute for Geophysics (UTIG) onboard a de Havilland DHC-6 Twin Otter aircraft. The HiCARS system transmits pulses with a 60 MHz (λ = 5 m) central frequency that are chirped over a 15 MHz bandwidth and 8000 W peak power. One resulting data product is a calibrated radar dataset sampled every ~10 m along the survey tracks that have been coherently integrated and range compressed. In this study, we applied a statistical method to the surface echo in order to separate the coherent (specular) and incoherent (scattered) parts of the signal. We use these estimated components with a backscattering model to derive and map the roughness and real part of the surface permittivity. The resulting permittivity values reflect the physical properties of the first 5 m of the firn. We analyze these results in the context of firn density and/or possibly wetness spatial variability. We observe a ~30 km wide vein of high surface permittivities ~100 km inward from the coastline with a northern boundary that matches a prominent slope break for the surface. We discuss the implications of our results for formation climatological context of catchment-wide firn properties in general and the high-permittivity vein in particular.

67A041
Constraining the recent sea-level contributions of Pine Island and Thwaites Glaciers, West Antarctica, using CReSIS ultra-wideband airborne radar systems
Brooke MEDLEY, Ian JOUGHIN, Sarah B. DAS, Eric J. STEIG, Howard CONWAY, Sivaprasad GOGINENI, Alison S. CRISCITIELLO, Joseph R. McCONNELL, Ben E. SMITH, M. R. VAN DEN BROEKE, J.T.M. LENAERTS, D.H. BROMWICH, J. P. NICOLAS
Corresponding author: Brooke Medley
Corresponding author e-mail: bmed@u.washington.edu
One of the largest sources of uncertainty in quantifying the glacial contribution to sea-level rise originates from our lack of understanding of spatio-temporal snow accumulation rates. Traditional in situ measurements of the accumulation rate (i.e. using firn cores, snow pits and stake farms) are time-consuming and inadequately capture the complex spatial variations in regional accumulation. We use ultra-wideband airborne radar data to track near-surface internal horizons to calculate spatio-temporal accumulation rates over Pine Island and Thwaites Glaciers along the Amundsen coast of West Antarctica. Here, we combine data from both CReSIS snow and accumulation radar systems to generate a spatially complete high-resolution gridded map of mean accumulation rate, thereby constraining the total mass input into these dynamic glaciers over the past 25 years. We furthermore find the snow radar is capable of imaging annual horizons, an improvement over the multi-year resolution available using the accumulation radar system. Based on the annual accumulation rates generated from the snow-radar echograms, we find no significant trend in the accumulation rate over much of Thwaites Glacier. These data indicate that the recent substantial increase in Thwaites ice discharge to the ocean has not been balanced inland by additional snow accumulation. This suggests the Thwaites contribution to sea-level rise has increased over the past few decades as regional accumulation rates have not increased to offset the accelerating discharge of this glacier.


67A074
How well can we determine ice thickness? Examples from Thwaites Glacier
Duncan A. YOUNG, Donald D. BLANKENSHIP, Scott D. KEMPF, Chad A. GREENE
Corresponding author: Duncan A. Young
Corresponding author e-mail: duncan@ig.utexas.edu
Ice-sheet models increasingly require high-resolution ice thickness and topographic data to resolve basal hydrology and internal stress fields. Additionally, new technologies for sampling the bed (e.g. RAID) will require good understanding of bedrock topography. Our primary tool for ice thickness determination has been airborne ice-penetrating radar. A variety of different systems have been fielded over ice sheets, with variations in center frequency, power, range, cross track and azimuth resolutions. Given the expense of fielding airborne campaigns, we need to be able to assess the resolutions and uncertainties that can be retrieved with through both legacy datasets and new systems, to target campaigns appropriately. Bed uncertainty quantification for ice-sheet models requires an evaluation of the spatial distribution of uncertainty in the ice thickness data upon which they rely. Ice thickness uncertainties are dominated by errors caused by cross-track reflectors, which bias thickness measurements low. Cross-track uncertainty is anisotropic, meaning that determinations of cross-over uncertainty do not capture our full knowledge of the bed. The grounding zone of Thwaites Glacier in West Antarctica is an area of fast and changing ice; ice flow is fast and the bed is rough. It has been a target of data acquisition both by the AGASEA program of 2004–05 and Operation IceBridge (OIB) between 2008 and 2012. AGASEA fielded a 60 MHz, 15 MHz bandwidth coherent system on a Twin Otter flying at 60 m s–1. OIB fielded a 195 MHz, 10 MHz system on a DC-8 flying at 130 m s–1. Both systems had broad cross-track beam patterns. The surveys were designed to interleave over the grounding-zone region, with one line reflown for intercomparison purposes. Over deeper ice we also have incoherent data from the 1990s with much less along-track resolution, but tighter line spacing. We evaluate the along-track repeatability and orthogonal cross-overs of these three surveys and construct a model for sensor-based uncertainty as a function of basal roughness and sensor configuration.


67A075
Joint seismic- and radar-sounding analysis of the subglacial environment of upper Thwaites Glacier, West Antarctica
Leo E. PETERS, Joseph A. MacGREGOR, Sridhar ANANDAKRISHNAN, Anthony HOCH, Huw J. HORGAN
Corresponding author: Leo E. Peters
Corresponding author e-mail: lep144@psu.edu
Thwaites Glacier is one of the fastest and largest glaciers draining the West Antarctic ice sheet. While much attention has been given to recent retreat, thinning and acceleration near its grounding line, little is known of the subglacial environment of Thwaites Glacier farther inland and how ice dynamics there might respond to coastal changes. Here we present both ground-based seismic- and radar-sounding surveys from upper Thwaites Glacier, characterizing the subglacial environment and its influence upon ice dynamics. During the 2008–2009 Antarctic field season, we collected 60 km of seismic data and 440 km of radar data ~200 km inland of Thwaites Glacier grounding line. These coincident surveys extend 40 km along flow and 10 km across flow. We find large variability in the subglacial environment, even in this slow-flowing region of the glacier (<200 m a–1), with distinct regions of wet unconsolidated sediments and potentially lithified dewatered sediments at the bed. Some of the brightest bed reflections in the radar data are observed across seismically inferred lithified beds, suggesting that in regions where bed roughness varies significantly, bright radar reflections are not indicative exclusively of wet ice-sheet beds. Modeled basal shear stress, seismically inferred basal conditions and radar-inferred small-scale bed roughness are all correlated. Our observations will allow modelers to better conceptualize the subglacial environment and to predict how Thwaites Glacier will respond to ongoing perturbations in ice flow originating near the grounding line.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 08, 2013, 07:28:38 PM
The following abstracts come from the linked sources and are relevant to the PIG:

www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm (http://www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm)
Contact: Secretary General, International Glaciological Society

67A038
Tomographic observation and bedmapping of polar glaciers and ice sheets with IceBridge sounding radar
Xiaoqing WU, John PADEN, Ken JEZEK, Eric RIGNOT, Younggyu GIM
Corresponding author: Xiaoqing Wu
Corresponding author e-mail: xiaoqing.wu@jpl.nasa.gov
We produced high-resolution bedmaps of several glaciers in western Greenland and Antarctica from IceBridge mission sounding radar data using the tomographic sounding technique. The bedmaps cover three western Greenland regions (Russell, Umanaq and Jakobshavn Glaciers) and one Antarctic region (Pine Island Glacier). The ground resolution is 50 m and the average ice thickness accuracy is 10–20 m. There are some void areas within the swath of the tracks in the bedmaps where the ice thickness is not known. Tomographic observations of these void areas indicate that the surface and shallow sub-surface pockets, likely filled with water, are highly reflective and greatly weaken the radar signal and reduce the energy reaching, and reflected from, the ice-sheet bottom. We present these interesting observations and the bedmaps, which can soon be accessed by the public through the National Snow and Ice Data Center website.


67A060
Ice thickness and density of the Pine Island Glacier floating ice shelf
Kiya RIVERMAN, Sridhar ANANDAKRISHNAN, Knut CHRISTIANSON, Leo PETERS
Corresponding author: Kiya Riverman
Corresponding author e-mail: klw367@psu.edu
Pine Island Glacier (PIG) in West Antarctica flows into an ice shelf that has been thinning since at least 1990. This has resulted in a 34% increase in the flow speed of Pine Island Glacier from 1996 to 2006 due to reduced buttressing forces on grounded ice. With the potential for this glacier to contribute dramatically to future sea-level rise, there is strong interest in modeling the current and future melt dynamics of the PIG floating ice shelf using coupled ocean–ice models. These models require ice thickness and density data. We present high-resolution gridded ice density and thickness data for use in future modeling work. We have used a digital elevation model (DEM) generated from stereographic pairs of images from high-resolution (WorldView) imagery. We determine variations in ice density and degree of flotation from precise ice thickness (from seismic and radar data) and elevation measurements. In January 2013, ice thickness measurements were collected from ground-based reflection seismology, ice-penetrating radar and hot-water drilling. By inverting for ice density and degree of flotation and interpolating across the shelf, we have used these data to generate an ice thickness map from the WorldView DEM.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 09, 2013, 02:08:41 AM
Unfortunately, I did not (and will not) have time to comment about all of the IGSOC Beijing and Kansas Symposia abstracts that I posted.  But I would like to say that the number of references being published about the Thwaites & PIG Basins indicate that this is a rapidly changing area of study and readers should take the various references as sign-posts on a long journey and not as welcome signs of your final destination.

For example I will make a few brief comments about the following sentence by Joughin & Smith 2013, reference 67A030 of the IGSOC Kansas Symposia (entitled: "Sensitivity of Thwaites Glacier to ice-shelf melting"):


"Strong sub-shelf melt produces stepped retreat of the grounding line by >40 km over 250 years."

Joughin & Smith are excellent researchers but when they say that their model says strong sub-shelf melting produces a stepped retreat of the grounding line by over 40km over 250 years, this is not a prediction of what is going to happen (but it is a sound guide post for further research).  Their shallow-shelf ice stream/shelf finite element model certainly does not fully model such issues as (also see the "Risks and Challenges for RCMs of the Southern Ocean" thread): (a) the increasing occurrence and influence of crevasses as the ice stream thins more than the boundaries of the ice stream; (b) the influence of the "SW tributary" glacier accelerating once the PIIS retreats sufficiently so that the increased SW tributary velocities destabilizes the eastern shear margin of the Thwaites Glacier; thus causing the Thwaites Glacier velocites to accelerate; (c) increased CDW flow when the current El Nino hiatus period comes to an end; (d) the influence of probable future surface water melt on both the ice shelf and of calving of the ice streams; (e) the observed subglacial hydrological system beneath TG; and all of the other issues such as: geometric/basal friction (Thwaites Effect) and the rate of regional warming, that I have discussed in this and other threads.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 10, 2013, 05:53:26 PM
For my one thousandth post, I would like to just note that the interaction between the PIG and the Thwaites Glacier drainage basins may well represent the largest risk to the stability of the WAIS this century.  Unfortunately, very few reseachers consider multiple synergistic feedback factors at the same time in their analysis, thus giving a false sense of security.  In this regard, I have the following points about such multiple synergistic feedback factors for the PIG/Thwaites system in the 2012 to 2060 timeframe:

- MacGregor et al 2013 clearly cite: (a) the possibility that the Thwaites Glacier may have retreated back at least to the eastern shear margin during the Eemian, as the radar signal might indicate the occurrence of marine sediment beneath the glacier; and (b) the SW tributary glacier could be activated by one more major calving event for the PIIS; which in turn could active the eastern shear margin for the Thwaites Glacier, that should accelerate ice velocities out of the Thwaites Gateway, with associated ice thinning and grounding line retreat.

- The continued retreat of PIG combined with the recurring major El Nino events (though 2060) could synergistically increase what I called "horizontal advection" of warm CDW from the trough leading to the PIG to the trough in the Thwaites Gateway leading to the BSB; where the ice is current thinner and has more crevasses since the local ice tongue surge event during the late austral winter and spring of 2012; and thus the ice is this trough area is much more susceptible to calving acceleration from the warm CDW.

- The possibility that GIA corrections will increase estimate ice mass loss estimate from PIG/Thwaites by up to 40%, raises the possibility that the basal meltwater subglacial hydrological system is more active under both the PIG and especially under the Thwaites Glacier than previously expected; and if so this active subglacial drainage system would promote ice mass loss.
- The austral winter of 2013 was the warmest on record, thus raising the probability that in the near future there will be more days of surface melt during the austral summer, which would likely flow into the increasing number of surface crevasses in the ice in the Thwaites Gateway (especially as it thins); which should promote accelerated calving of the ice in this area (which is not constrained laterally as is the PIIS).
- The observed trend of increasing concentration of methane in the atmosphere over Antarctica will likely lead to increased coastal wind velocities which will likely increase the flow of warm CDW into the ASE; which will promote ice mass loss for both the PIG and the Thwaites Glacier.
- Based on the observed snowfall trend it is unlikely that snowfall will increase before the grounding line for the Thwaites Glacier retreats to upstream of the gateway; at which point an increase in snowfall will actually accelerate the "Thwaites Effect" by providing more driving force to promote rapid calving and groundling line retreat after the 2040 to 2060 timeframe.
- It should be remembered that any significant acceleration of ice mass loss from the GIS in the 2013 to 2060 timeframe will help to de-stabilize the PIG/Thwaites system by raising sea level in the ASE due to the fingerprint effect.

There are other feedback factors discussed in this and other threads, but it is impossible at this time to predict the rate and amount of their synergistic interaction; and thus we will need to keep a close watch on this critical area in the coming years in order better assess the timing of any possible tipping point in the PIG/Thwaites system.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on September 11, 2013, 05:27:40 AM
Agree on Thwaites. Alley admits that after the next pinning point under Thwaites comes loose, next stop is the Transantarctic mountains. I do not know what the effect of CDW will be once it pours into the Byrd Subpolar Basin, but I think it will be beyond anything that even Mercer imagined.

To paraphrase Hadane, "WAIS is not only more dangerous than we suppose, it is more dangerous than we can suppose."

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 11, 2013, 06:43:21 AM
Sidd,

You certainly know how to put this matter into prospective!

I am traveling, so I will not be posting much.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 23, 2013, 10:34:10 AM
The following NASA website offers the accompanying description of gravimeter measurements and the accompanying image of one of the highest resolution figures of the Thwaites Gateway that I have yet seen:

http://www.nasa.gov/mission_pages/icebridge/instruments/gravimeter.html (http://www.nasa.gov/mission_pages/icebridge/instruments/gravimeter.html)
July 2013

"The gravimeter measures the shape of seawater-filled cavities at the edge of some major fast-moving glaciers. Data about the amount of water under ice fills in a crucial gap in knowledge related to calving and melting of glaciers. Water has less mass than rock and thus exhibits a lower gravitational pull, meaning that the gravimeter can show what lies under the ice. The AIRGrav gravimeter, developed by Sander Geophysics (www.sgl.com (http://www.sgl.com)), uses several sensitive gyroscopes to keep the instrument orientation stable. Accelerometers measure the force of gravity from the Earth below while GPS is used to record, and then remove, the motion of the aircraft.
More details on the AIRGrav system can be found here: http://www.sgl.com/Gravity.html (http://www.sgl.com/Gravity.html)
The University of Texas Institute for Geophysics' (UTIG) obtains gravimeters for its surveys through leases or partnerships with other agencies."

The caption for the accompanying figure is:
"Gravimeter data showing bedrock and sub-ice water near the Thwaites Glacier, Antarctica"

This 2013 image indicates the presences of large body of water beneath the location of 1996 grounding line at the entrance to the Thwaites Trough (see earlier posts in this thread); and if this body of water remains after the 2012 surge of the Thwaites Tongue then this large body of water should decrease the stability of the ice in the Thwaites Gateway.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 25, 2013, 10:23:59 AM
I thought that I would magnify the image of the gravimeter corrected Thwaites Gateway bathymetry (from the University of Texas) in order to make it clearer that the top elevation of the submerged seamount in the middle of the gateway (between the ice shelf and the ice tongue) is almost 100m deeper than previously estimated.  This is a critical finding as this submerged seamount is one of the key pinning points for the ice in the gateway, and when the ice stream in this area thins sufficiently (due to such factors as CDW advection and also if the PIIS has one more major calving event that removes the ice shelf buttressing of the SW Tributary glacier, this will re-direct ice flow away from the eastern side of the Thwaites Gateway towards the PIG, which will lead to more rapid ice thinning in the Thwaites Gateway), then the ice in the Thwaites Gateway will float over the top of this one-time pinning point; which will lead to an acceleration of ice flow through the gateway.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 25, 2013, 10:41:56 AM
My previous post on this reference on the PIG did not provide a link to a free pdf (which indicates areas of grounding line retreat of up to 0.06 m per day), so I am providing that here:

Channelized Ice Melting in the Ocean Boundary Layer Beneath Pine Island Glacier, Antarctica
By: T. P. Stanton, W. J. Shaw, M. Truffer, H. F. J. Corr, L. E. Peters, K. L. Riverman, R. Bindschadler, D. M. Holland, S. Anandakrishnan (2013), Science.


http://www.sciencemag.org/content/341/6151/1236.full.pdf (http://www.sciencemag.org/content/341/6151/1236.full.pdf)

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: JimD on October 07, 2013, 07:17:54 PM
ASLR

I am sure you would find this interesting.

Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1977.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1977.html)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 08, 2013, 02:04:22 PM
JimD,

Thank you.  I have reposted this linked reference in the FRIS/RIS thread.  These types of very large channels are more common for ice shelves with the advection of warm ocean water; however, this is not the case for these channels in the FRIS, and their discovery indicates that the FRIS is less stable than previously thought.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 01, 2013, 06:17:05 PM
The linked thesis work by Docquier (2013) represents some of the most recently available modeling work on the Thwaites Glacier:

http://theses.ulb.ac.be/ETD-db/collection/available/ULBetd-08222013-150617/unrestricted/Thesis_Docquier2.pdf (http://theses.ulb.ac.be/ETD-db/collection/available/ULBetd-08222013-150617/unrestricted/Thesis_Docquier2.pdf)

However, the author acknowledges the limitations of his model and of his findings and suggests that the following improvements could be made to his model:
"• Compare the results obtained for TG (Chaps. 5 and 6) with other models, e.g. Elmer/Ice (finite-element full-Stokes model) [Favier and others, 2012] or BISICLES (finite-volume higher-order model) [Cornford and others, 2013], as already carried out for Pine Island Glacier [Favier and others, submitted].
• For the 3D simulations (Chap. 6), take into account the whole drainage basin of TG (see Section 6.5) and use lateral boundary conditions that involve a prescribed amount of lateral drag obtained from observed velocity gradients at the sides.
• For the 3D simulations (Chap. 6), test the sensitivity of grounding-line migration on both Glen’s flow and basal friction coefficients.
• Include iceberg calving [Nick and others, 2009; Bassis, 2011; Nick and others, 2013], atmospheric and oceanic coupling, sedimentation effect [Alley and others, 2007], subglacial processes [Schroeder and others, 2013], thermomechanical coupling [Pattyn, 2003], etc. in the models. For example, oceanic coupling would permit us to better
understand how the ocean interacts with the ice shelf base and what is the effect of basal melting on grounding-line migration [Goldberg and others, 2012].
• Acquire higher bedrock spatial resolution close to the grounding line of TG and use Bedmap2 data with the Tinto and Bell [2011] bathymetry.
• Test other methods to interpolate data onto our model grid (e.g. nearest neighbor, spline, cubic)."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 28, 2013, 09:31:38 AM
The following link leads to an article indicating that in January 2014 the British will begin their six-year iStar program to survey PIG and PIIS.  I believe that this will be a critical time for the PIIS and I look forward to monitoring their results (particularly during January 2014):

http://www.deccanherald.com/content/376323/uk-scientists-probe-pine-island.html (http://www.deccanherald.com/content/376323/uk-scientists-probe-pine-island.html)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on December 30, 2013, 07:43:01 AM
Thanks for the link to the Docquier thesis. I have not yet had the time to do more than scan it, although I did read Ch. 6 more carefully, and I agree with the caveats in the last chapter, especially the lack of basal hydrology.

That led me to reread Gladstone(2013). Earth and Planetary Science

http://dx.doi.org/10.1016/j.epsl.2012.04.022 (http://dx.doi.org/10.1016/j.epsl.2012.04.022)

and they are much darker than i remember, with 7.6-18.9 cm. SLR from PIG alone by end century.
This is from a reduced dimensionality ice sheet model (integrated vertical shear, if I recall correctly this approximation increases the effective viscocity of the ice. Other approximations are an isothermal ice sheet, and no basal hydrology) coupled to a two box model for ocean iceshelf interaction and basal shelf melt, with BRIOS for ocean forcing. Nice. Can be improved, and I am sure it will be, but nice nonetheless.

They state, and I agree:

"If the real PIG system is as susceptible to collapse as indicated by the more rapidly retreating members of the confidence set, it may be that other WAIS outlet glaciers are similarly vulnerable"

and some in EAIS also.

Thwaites is the current gorilla, but i harbour fears about others.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 30, 2013, 06:32:47 PM
Sidd,

Hopefully in the next ten to twenty years the Antarctic glacial models will be able to more fully account for such factors as: (a) retreating grounding lines; (b) ocean-ice interaction (including changing currents and winds); (c) calving risks (both for ice shelves and at the grounding line; (d) subglacial hydrological systems; (e) surface melting risks; etc.

However, at the moment I am particularly concerned about the interactions between the PIG and Thwaites Glacier with regard to: (a) the growing risk that the PIIS will retreat sufficiently in the next few years to activate the SW Tributary which MacGregor et al 2013 (see reference below) indicated could more strongly activate the Thwaites Eastern shear margin; and (b) the synergy between the advection of warm CDW from PIG toward the Thwaites Ice Shelf and Ice Tongue (note that when the current El Nino hiatus ends, this local circulation pattern could amplify).

MacGregor, J.A., Catania, G.A., Conway, H., Schroeder, D.M., Joughin, I., Young, D.A., Kempf, S.D., and Blankenship, D.D., (2013), "Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica",  Journal of Glaciology, Vol. 59, No. 217, doi:10.3189/2013JoG13J050,
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 01, 2014, 01:52:53 AM
The following link (posted by Hans in the ASIB), indicates that a large El Nino event may be likely to occur around January 2015.  If so the austral summer of 2014-2015 could sign a significant increase in ice mass loss from the WAIS:

http://news.imau.nl/?p=1056 (http://news.imau.nl/?p=1056)

Quote from link:
"Based on anomalously low sea surface temperatures in the southwestern Indian Ocean north of Madagascar (see http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml (http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml)), I predict the evolution of a big El Niño in the Pacific that will peak around January 2015. We have an ongoing fight to get our analysis published."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 03, 2014, 12:49:59 AM
The following linked article supports the point that in a big El Nino year both PIIS and PIG will lose ice more rapidly than normal:

http://www.science20.com/news_articles/antarcticas_pine_island_glacier_melt_blame_el_nino-127129 (http://www.science20.com/news_articles/antarcticas_pine_island_glacier_melt_blame_el_nino-127129)

Pine Island Glacier is one of the biggest routes for ice to flow from Antarctica into the sea and the floating ice shelf at the glacier's tip has been melting and thinning for the past four decades, causing the glacier to speed up and discharge more ice.

It's been a key factor in estimates for sea level rise in a warming world but it turns out that the ice shelf melting depends on the local wind direction, which is tied to tropical changes associated with El Nino.

The Pine Island ice shelf seems to have thinned nearly continuously, though observations only began in the 1970s. Earlier studies have said that warm deep-ocean water is melting the ice shelf from below, suggesting that warming global oceans are gradually targeting the underside of the ice sheet, but the picture turns out to more complex than simple cause and effect. The deep ocean has been getting warmer but, more importantly, more warm water has been reaching the ice shelf. 
The study, led by author Pierre Dutrieux at the British Antarctic Survey, uses new data to show how winds and topography control how much warm water reaches the ice shelf. University of Washington co-authors provided atmospheric modeling expertise to help interpret the observations and show how they are related to climate conditions in the tropical Pacific Ocean.
"These new results show that how much melt the Antarctic ice sheet experiences can be highly dependent on climatic conditions occurring elsewhere on the planet," said co-author Eric Steig, a University of Washington professor of Earth and space sciences. 
Under the right conditions, the warm deep water that surrounds Antarctic can flood the continental shelf and make its way to the glacier margin. Measurements during the last two decades have shown the persistent presence of a thick layer of warm water on the continental shelf, in contact with the Pine Island ice shelf.
In January 2012, British Antarctic Survey researchers and colleagues from Germany and Korea revisited the area to gather more data. They found the layer of warm water was much thinner than before and was topped by a thicker-than-usual layer of cold water that surrounded, and thus protected, the ice shelf. They estimated half as much meltwater was being produced from the glacier compared to 2010, making 2012 the year with the lowest summer melting of the Pine Island Glacier on record.
Detailed measurements of water temperature, combined with a computer model of ocean circulation, shows that the reduced melting in 2012 was because less warm, deep water was able to make it across an underwater ridge that separates Pine Island Glacier from the Southern Ocean. Reduced flow across the ridge can be explained by a change in winds, which were persistently easterly for most of the preceding year, researchers noted. Winds in this region are normally westerly.
This raises the question of why the winds were different in 2011 and early 2012 than in previous years. Steig was co-author of a 2011 study in Nature Geoscience, led by UW postdoctoral research Qinghua Ding, that showed that winds in the Pine Island Glacier area are related to changes in the tropical Pacific tied to El Nino events. In 2012 Steig and Ding published a paper with UW atmospheric scientist David Battisti and co-author Adrian Jenkins of the British Antarctic Survey that linked the Pine Island Glacier melting to the tropical Pacific.
The new study provides the observations to back up the UW authors' theoretical work.
"We had thought that the wind variability played an interesting, but relatively small role, but the new data supports our idea and shows that it has a strong effect," Steig said. "The wind field in late 2011 and early 2012 had changed dramatically compared to previous years – the dominant westerly winds in the surrounding area were easterly almost all through late 2011 and early 2012, and those changes were related to the very large 2011 La Nina event."
In 2012, the El Nino tropical system switched to a La Nina, reversing the local winds in this region of Antarctica and causing less warm water to flow into the area.
If the conditions observed in 2012 were to continue, the authors write, it would have profound implications for the Pine Island ice shelf. Continuation of this thick layer of cold surface water would reverse the current thinning trend, potentially allowing the glacier edge to rebuild. It is not likely, however, that such conditions will persist.
"2012 was probably just a rare event," said Steig, "and I expect that a return visit to Pine Island area would find conditions much more similar to those observed in earlier years."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 03, 2014, 11:42:50 AM
To those who would like access to the source material for the information cited in my immediate past post, please see the following links, abstract, and related references:

http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract (http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract)

http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf (http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf)

Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, and Michael Schröder, 2014, "Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability", Science; Published online 2 January 2014 [DOI:10.1126/science.1244341]

Abstract:
"Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate."

Supplemental references:

1. S. S. Jacobs, A. Jenkins, H. Hellmer, C. Giulivi, F. Nitsche, B. Huber, R. Guerrero, The
Amundsen Sea and the Antarctic Ice Sheet. Oceanography 25, 154–163 (2012).
doi:10.5670/oceanog.2012.90
2. S. S. Jacobs, A. Jenkins, C. F. Giulivi, P. Dutrieux, Stronger ocean circulation and increased
melting under Pine Island Glacier ice shelf. Nat. Geosci. 4, 519–523 (2011).
doi:10.1038/ngeo1188
3. S. S. Jacobs, H. H. Hellmer, A. Jenkins, Antarctic Ice Sheet melting in the southeast Pacific.
Geophys. Res. Lett. 23, 957–960 (1996). doi:10.1029/96GL00723
4. A. Jenkins, P. Dutrieux, S. S. Jacobs, S. D. McPhail, J. R. Perrett, A. T. Webb, D. White,
Observations beneath Pine Island Glacier in West Antarctica and implications for its
retreat. Nat. Geosci. 3, 468–472 (2010). doi:10.1038/ngeo890
5. D. J. Wingham, D. W. Wallis, A. Shepherd, Spatial and temporal evolution of Pine Island
Glacier thinning, 1995–2006. Geophys. Res. Lett. 36, L17501 (2009).
doi:10.1029/2009GL039126
6. A. Shepherd, E. R. Ivins, G. A, V. R. Barletta, M. J. Bentley, S. Bettadpur, K. H. Briggs, D. H.
Bromwich, R. Forsberg, N. Galin, M. Horwath, S. Jacobs, I. Joughin, M. A. King, J. T.
Lenaerts, J. Li, S. R. Ligtenberg, A. Luckman, S. B. Luthcke, M. McMillan, R. Meister,
G. Milne, J. Mouginot, A. Muir, J. P. Nicolas, J. Paden, A. J. Payne, H. Pritchard, E.
Rignot, H. Rott, L. S. Sørensen, T. A. Scambos, B. Scheuchl, E. J. Schrama, B. Smith, A.
V. Sundal, J. H. van Angelen, W. J. van de Berg, M. R. van den Broeke, D. G. Vaughan,
I. Velicogna, J. Wahr, P. L. Whitehouse, D. J. Wingham, D. Yi, D. Young, H. J. Zwally,
A reconciled estimate of ice-sheet mass balance. Science 338, 1183–1189 (2012).
Medline doi:10.1126/science.1228102
7. E. Rignot, Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR
data. Geophys. Res. Lett. 35, L12505 (2008). doi:10.1029/2008GL033365
8. I. Joughin, E. Rignot, C. E. Rosanova, B. K. Lucchitta, J. Bolhander, Timing of Recent
Accelerations of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 30, 1706 (2003).
doi:10.1029/2003GL017609
9. I. Joughin, B. E. Smith, D. M. Holland, Sensitivity of 21st century sea level to ocean-induced
thinning of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 37, L20502 (2010).
doi:10.1029/2010GL044819
10. H. D. Pritchard, S. R. Ligtenberg, H. A. Fricker, D. G. Vaughan, M. R. van den Broeke, L.
Padman, Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502–
505 (2012). Medline doi:10.1038/nature10968
11. A. Shepherd, D. Wingham, D. Wallis, K. Giles, S. Laxon, A. V. Sundal, Recent loss of
floating ice and the consequent sea level contribution. Geophys. Res. Lett. 37, L13503
(2010). doi:10.1029/2010GL042496
12. A. Shepherd, D. Wingham, E. Rignot, Warm ocean is eroding West Antarctic Ice Sheet.; Geophys. Res. Lett. 31, L23402 (2004). doi:10.1029/2004GL021106
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 13, 2014, 01:34:51 AM
The linked reference indicates that the PIG is now entering a period where its contribution to SLR will increase by a factor of 5 over the next 20-years.  While this article indicates that the rate of ice mass loss from PIG will roughly stabilize after that; however, I would like to point out that it the retreat of the PIG triggers accelerated ice mass loss from the Thwaites Glacier then it is probable that ice mass loss from the PIG will continue to accelerate well after 2030:
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html)

L. Favier, G. Durand, S. L. Cornford, G. H. Gudmundsson, O. Gagliardini, F. Gillet-Chaulet, T. Zwinger, A. J. Payne & A. M. Le Brocq, (2014) "Retreat of Pine Island Glacier controlled by marine ice-sheet instability", Nature Climate Change,  (2014); doi:10.1038/nclimate2094; 12 January 2014

Abstract:
"Over the past 40 years Pine Island Glacier in West Antarctica has thinned at an accelerating rate, so that at present it is the largest single contributor to sea-level rise in Antarctica. In recent years, the grounding line, which separates the grounded ice sheet from the floating ice shelf, has retreated by tens of kilometres. At present, the grounding line is crossing a retrograde bedrock slope that lies well below sea level, raising the possibility that the glacier is susceptible to the marine ice-sheet instability mechanism. Here, using three state-of-the-art ice-flow models, we show that Pine Island Glacier’s grounding line is probably engaged in an unstable 40 km retreat. The associated mass loss increases substantially over the course of our simulations from the average value of 20 Gt yr−1 observed for the 1992–2011 period, up to and above 100 Gt yr−1, equivalent to 3.5–10 mm eustatic sea-level rise over the following 20 years. Mass loss remains elevated from then on, ranging from 60 to 120 Gt yr−1."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 13, 2014, 06:35:24 AM
Due to the importance of the information in my immediate past post in this thread, I provide both the attached image, and the following links to articles about the research:

http://www.abc.net.au/science/articles/2014/01/13/3924653.htm (http://www.abc.net.au/science/articles/2014/01/13/3924653.htm)

http://phys.org/news/2014-01-giant-antarctic-glacier.html (http://phys.org/news/2014-01-giant-antarctic-glacier.html)

http://elmerice.elmerfem.org/37-an-antarctic-outlet-glacier-engaged-in-an-irreversible-retreat (http://elmerice.elmerfem.org/37-an-antarctic-outlet-glacier-engaged-in-an-irreversible-retreat)

The attached image is from the paper and shows: "Relaxed surface velocities plotted on the Elmer/Ice computational domain, the solid black line represents the relaxed grounding line. b, Domain zoom-in with the bedrock elevation (in m). The 2011 grounding line from is shown "
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on January 13, 2014, 07:26:18 AM
agreed. PIG is gone. I posted a comment at realclimate on this paper, which  i reproduce below. The Livingstone paper is really nice, check it out.

Realclimate comment:

Here’s to you John Mercer ! Wish we had listened.

doi:10.1038/NCLIMATE2094

Last para: (MISI is marine ice sheet instability)

“Here we show that for the next decade the PIG grounding line is probably engaged in an irreversible retreat over tens of kilometres and that the dynamic contribution to SLR will remain at a significantly higher level compared with preretreat conditions. All three models, despite their differing physics, numerics and parameters, support the notion of MISI in PIG, and two out of three cast doubt on any possible recovery. Starting from the first years of significant imbalance increase, the variation of the mass loss between experiments after 20 years is relatively narrow with a cumulative contribution to SLR of 3.5–10 mm over this period (Fig. 4). Afterwards, estimates diverge dependent on further retreat of the grounding line across a region of gentler slopes and stronger basal traction behind the instability zone. Once the grounding line has crossed the steep retrograde slope, imbalance decreases but remains between three and six times higher than the mean estimates obtained for the past 20 years (20 Gt yr−1 ; ref. 4).”

Now consider that these models are not coupled to the ocean, except thru a prescribed melt rate. No basal hydrology as far as I can tell (In this context see Livingstone et al. (doi:10.5194/tc-7-1721-2013 which I find fascinating.) And Thwaites is next door, and order of mag wider. And every prediction has underestimated so far.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 14, 2014, 02:15:09 PM
I agree with sidd, and I note that the PIIS is loosing its grip on the adjoining shoreline due to increasing cracking.

Also,
The following link provides some new WAIS information by the BAS (mixed together with information previously cited here):

http://www.reportingclimatescience.com/news-stories/article/researchers-focus-on-pine-island-glacier-says-bas.html (http://www.reportingclimatescience.com/news-stories/article/researchers-focus-on-pine-island-glacier-says-bas.html)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 20, 2014, 10:45:53 PM
The following link and abstract are for a poster presentation at the 2014 Ocean Science meeting in Hawaii Feb 23 to 28.  This research indicates that ice mass loss from the ASE is expected to increase significantly over the next 20-years:
http://www.sgmeet.com/osm2014/viewabstract.asp?AbstractID=18136 (http://www.sgmeet.com/osm2014/viewabstract.asp?AbstractID=18136)

by: Eric Larour, Y. (NASA/Jet Propulsion Laboratory, USA, eric.larour@jpl.nasa.gov); Dimitris Menemenlis, Michael Schodlok, & Helene Seroussi

"Abstract

TOWARDS BETTER SIMULATIONS OF ICE/OCEAN COUPLING IN THE AMUNDSEN SEA SECTOR, WEST ANTARCTICA, USING A COUPLED OCEAN, SEA-ICE, AND ICE-SHEET MODEL.
Currently, observations of polar ice sheets (Antarctica and Greenland) show a contribution to Sea Level Rise (SLR) of approximately 1 mm/yr, out of 3.4 mm/yr globally. This contribution is expected to increase significantly in the future, to a point where steric expansion will be overtaken by the contribution of melt-water runoff as well as calving and melting of ice shelves. It is therefore paramount to better understand the interaction between the ocean and ice-sheets, in order to better quantify the feedbacks between melting under ice shelves, ocean circulation, and ice-sheet dynamics. Here, we show recent results of coupled ice/ocean simulations in the Amundsen Sea Embayment region of Antarctica, using the Massachusetts Institute of Technology general circulation model (MITgcm) and the Ice Sheet System Model (ISSM), over a period of 20 years, coinciding with the acceleration of the Pine Island and Thwaites Glaciers. Our simulations take into account the shape of the cavities (generated by the ice-sheet model), as well as melting rates (generated by the ocean circulation model) under ice shelves in a fully two-way coupled mode. We show results on the sensitivity of ice-sheet dynamics and ocean circulation to the shape of the cavity, as well as the underlying circulation. Our approach demonstrates the influence of a fully coupled approach on the evolution of the Ocean/Ice System, and presents an efficient way of implementing such two-way coupling."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 31, 2014, 10:15:42 PM
The linked (free access) pdf summarizes recent mass balance observations for both the Pine Island and Thwaites glaciers.  While this article is an excellent summary, it does not provide sufficient discussion about the influence of changes in ENSO and the PDO on the response of these two important glaciers:

Medley, B., I. Joughin, B. E. Smith, S. B. Das, E. J. Steig, H. Conway, S. Gogineni, C. Lewis, A. S. Criscitiello, J. R. McConnell, M. R. van den Broeke, J. T. M. Lenaerts, D. H. Bromwich, J. P. Nicolas, and C. Leuschen, 2014: Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica with airborne observations of snow accumulation. The Cryosphere, in review.

http://polarmet.osu.edu/PMG_publications/medley_joughin_cryo_2014.pdf (http://polarmet.osu.edu/PMG_publications/medley_joughin_cryo_2014.pdf)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 02, 2014, 08:34:53 PM
According to the linked blog post science begins today on the ocean component (Ocean2ice) of the iSTAR - NERC Ice Sheet Stability Programme to Investigating the stability of the West Antarctic Ice Sheet.  On Feb 2nd 2014, the RRS James Clark Ross has crossed into the Amundsen Sea and they will take metocean data, during a 30-day mission, all the way to PIIS:

http://www.istar.ac.uk/2014/02/02/below-the-antarctic-circle/ (http://www.istar.ac.uk/2014/02/02/below-the-antarctic-circle/)

The Ocean2ice goals are stated at the following link:

http://www.istar.ac.uk/projects/ocean2ice-istar-a/ (http://www.istar.ac.uk/projects/ocean2ice-istar-a/)

Other iSTAR missions are described at the following links:

http://www.istar.ac.uk/projects/ocean-under-ice-istar-b/ (http://www.istar.ac.uk/projects/ocean-under-ice-istar-b/)
http://www.istar.ac.uk/projects/dynamic-ice-istar-c/ (http://www.istar.ac.uk/projects/dynamic-ice-istar-c/)
http://www.istar.ac.uk/projects/ice-loss-istar-d/ (http://www.istar.ac.uk/projects/ice-loss-istar-d/)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 08, 2014, 01:33:33 AM
The linked reference (with a free access pdf) indicates that airborne measures of the snow accumulations for both the PIG and the Thwaites Glacier, indicate that there is less snow accumulation near the coastal/low-elevation areas and more snow accumulation in the interior/higher-elevations, than previously expected.  This means that the gravitational driving force exerted on these glaciers is increasing faster than previously expected (which means that ice flow velocities for these glaciers will be accelerating faster than previously expected):

Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., van den Broeke, M. R., Lenaerts, J. T. M., Bromwich, D. H., Nicolas, J. P., and Leuschen, C.: Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica with airborne observations of snow accumulation, The Cryosphere Discuss., 8, 953-998, doi:10.5194/tcd-8-953-2014, 2014.

http://www.the-cryosphere-discuss.net/8/953/2014/tcd-8-953-2014.html (http://www.the-cryosphere-discuss.net/8/953/2014/tcd-8-953-2014.html)

"Abstract. In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea Coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (> 25 km) over the Pine Island-Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18 yr mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 21, 2014, 09:36:34 PM
The attached image from the British Antarctic Survey, showing differences in Antarctic sea ice from 1979 to 2012; confirm that the Antarctic sea ice around the ASE is declining, which will expose the ice shelves in the ASE to more degradation from storm action:
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 25, 2014, 07:18:46 AM
Many people are concerned about an abrupt collapse of WAIS ice shelves due to melt pond mechanism similar to what happened for the Larsen B ice shelf; however, it may be many decades before such a mechanism could cause a rapid collapse of the PIIS.  Nevertheless, the rate of retreat of the PIG grounding is expected to accelerate markedly over the next 15 to 20-years due to both gravitational (becoming unpinned from the ridge shown in the first attached image) and ocean-ice interaction reasons (possible El Nino events and continued warming of the CDW), and this in-turn should accelerate the rate of the PIIS ice velocities at least five times resulting in accelerated thinning of the PIIS.  Thus both the enlargement (elongation) of the sub-ice shelf cavity and the thinning of the over-lying ice, will markedly increase the susceptibility of the PIIS to abrupt collapse in the next two decades due to events that might increase the hydrodynamic, and hydrostatic, pressure within the sub-ice-shelf cavity.  Sources of hydrodynamic & hydrostatic pressure that could destabilize the Pine Island Ice Shelf, PIIS (or other marine glaciers with rapidly retreating grounding lines), include:

(a) Large El Nino events, could temporarily raise eustatic sea level by 6 to 8mm (due to increased rainfall over the ocean and concurrent increased drought over land) over a one or two year period, and could also induce the ABSL to direct more wind and ocean currents into the ASE,
(b) Accelerated land water mining due to increasing anthropogenic water demand;
(c) The fingerprint effect associate with ice mass loss from Greenland.  Note that several Greenland marine terminating glaciers appear to be primed for rapid grounding line retreat over the next approximately twenty years;
(d) Storm surge & storm tide could increase due to increased storm activity in the Amundsen Sea.
(e) King tide (high astronomical tides) amplitudes can increase with increasing regional sea level;
(f) Local steric sources: The Southern Ocean is freshening rapidly, resulting in regional steric SLR.
(g) Winds (such as that associate with the ABSL) and ocean currents (such as the CDW) re-directed into the ASE, which would increase ocean elevation in the embayment, and stagnation pressure beneath the PIIS;
(h) Tsunamis have been proven to induce cracking in Antarctic ice shelves (see Walker et al. 2013, DOI: 10.1002/2013JF002742), and a large Pacific seismic event could readily direct a large tsunami into the ASE and from there into the PIIS cavity.
(i) Hydraulic connections (jokulhlaup or glacial outburst flood) of the sub-ice-shelf cavity to the pressurized basal meltwater subglacial hydrological system underneath the PIG.  The second attached image shows red dots where satellites have measured rapid changes in the ice surface elevation, which indicate a rapid movement of pressurized basal meltwater (ie. subglacial drainage events).  This image indicates that there is a significant amount of subglacial basal meltwater periodically being released from beneath the PIG into the sub-ice-shelf cavity.  Note that the build-up of hydrostatic pressure from say storm surge, or a tsunami, could serve to trigger a jokulhlaup event; so the simultaneous increase of hydrostatic, and increase of hydrodynamic, pressure is not improbable.
(j) Passing high pressure atmospheric systems, could temporarily increase the hydrostatic pressure in the PIIS cavity.
(k) Continuing eustatic SLR contributions from mountain glaciers.
(l) Local seismic activity could temporarily increase hydraulic pressure within the confined PIIS cavity.
(m) Tidal amplification due to funnel effect within a sub-ice-shelf cavity that narrows upstream.

The third attached image shows how far upstream the PIG grounding line has already retreated, and the longer the bending moment arm, and the thinner the ice shelf thickness, and the higher the sub-ice-shelf hydrostatic/hydrodynamic pressure within the cavity; the more likely the PIIS might fracture in a brittle manner, at the upstream end of the moment arm.  Note that the build-up of hydrostatic and hydrodynamic pressures beneath PIIS would also likely degrade the lateral shear restraint provided by the sidewalls of the PIG/PIIS trough.  Lastly, as I have noted before, a major upstream retreat of the calving face of PIIS (as could happen for the postulated hydraulically pressurized induced upstream flexural fracturing of the PIIS), would decrease buttressing of the SW Tributary Glacier; which in turn could activate the eastern shear margin of the Thwaites Glacier. 
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 01, 2014, 10:16:09 PM
The linked article about how the BAS has installed ice penetrating radar systems with millimeter accuracy and 3D image capability on to the PIIS this summer and will retrieve data from the units during the next austral summer, in an effort to determine how quickly the ice shelf is deteriorating (primarily from ocean-ice interaction).  However, on disturbing finding from this effort is that the researchers found a much higher concentration of crevasses extending to the surface of the PIIS than was expected; indicating that the ice is accelerating (which increases stress in the ice) and/or basal melt water channels may be causing stress concentrations in the bottom of the shelf.  The following are selected quotes from the article:

"The radars, developed with funding by the Engineering and Physical Sciences Research Council (EPSRC), have been placed on the ice shelf surrounding Pine Island by University College London (UCL) and British Antarctic Survey (BAS) scientists to record changes of the Antarctic ice in unprecedented detail."

"Although we've previously taken snapshots of the ice with radar, this is the first time year-round monitoring has been possible," said Dr Keith Nicholls of the British Antarctic Survey. "Where changing ocean currents interact with the underside of the ice shelf, the rate of melting can change season by season, month by month, even over days or hours. The advantages of this new system cannot be overstated."

"The units also boast antenna arrays – Multiple Input Multiple Output (MIMO – different from the WiFi router philosophy) – that allow the researchers to construct 3D images of the ice.
"This will be very useful because of the uneven shape of the ice-sheet's underside," Dr Nicholls commented. "We will be able to see how the shape of the surface influences the melt rate."
Pine Island Glacier is thought to be highly sensitive to climate variability and has thinned rapidly over recent decades.
"The main culprit is warm water in the circumpolar current, which is eating away at the underside of the ice shelf floating at the edge of Pine Island Glacier," said Dr Keith Nicholls of the British Antarctic Survey. "A continuous record of seasonal changes, which is what the new array should give us, will give us a far better understanding of how that's happening."
The deteriorating state of the ice shelf was revealed in another way by the recent mission: the plan had been to emplace eight of the small radar stations, but new crevassing of the ice prevented the team landing by plane at many planned locations
"The increased crevassing may be a result of accelerated movement of the ice shelf, or stresses from channels melted into the underside of the ice – they were certainly unexpected from our planning survey," said Dr Nicholls.
Daily bulletins remotely posted by the installed radars reveal they are working well. The data though will remain a mystery until the researchers return to download them in person next year."

http://phys.org/news/2014-02-custom-designed-radar-antarctic-ice-millimetre.html (http://phys.org/news/2014-02-custom-designed-radar-antarctic-ice-millimetre.html)


Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 27, 2014, 01:24:52 AM
With a nod to Colorado Bob in the ASIB, the following links lead to articles indicating that six studied marine glaciers in the ASE are losing ice mass at a rate that could result in an instability mechanism and that these marine glaciers can "feel" events (such as the major PIIS calving in November 2013) happening at their calving face, several hundred kilometers upstream, very quickly after the ice face event:

Mouginot, J., E. Rignot, and B. Scheuchl (2014), Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013, Geophys. Res. Lett., 41, doi:10.1002/2013GL059069.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL059069/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013GL059069/abstract)

Abstract: "We combine measurements of ice velocity from Landsat feature tracking and satellite radar interferometry, and ice thickness from existing compilations to document 41 years of mass flux from the Amundsen Sea Embayment (ASE) of West Antarctica. The total ice discharge has increased by 77% since 1973. Half of the increase occurred between 2003 and 2009. Grounding-line ice speeds of Pine Island Glacier stabilized between 2009 and 2013, following a decade of rapid acceleration, but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes. Flow speeds across Thwaites Glacier increased rapidly after 2006, following a decade of near-stability, leading to a 33% increase in flux between 2006 and 2013. Haynes, Smith, Pope, and Kohler Glaciers all accelerated during the entire study period. The sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of Antarctica."

http://phys.org/news/2014-03-major-west-antarctic-glacial-loss.html#jCp (http://phys.org/news/2014-03-major-west-antarctic-glacial-loss.html#jCp)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on April 08, 2014, 05:19:32 AM
I posted a short comment about Seroussi(2014) on realclimate which i expand here:

http://www.the-cryosphere-discuss.net/8/1873/2014/ (http://www.the-cryosphere-discuss.net/8/1873/2014/)

doi:10.5194/tcd-8-1873-2014

PIG may keep melting even if melting from warm ocean is reduced. The model is a 3D treatment, but alas, is not coupled to ocean, rather drivers such as rates of basal melt are imposed by hand. They find grounding line is not so sensitive, in contrast to Favier(2014) DOI: 10.1038/NCLIMATE2094 which they attribute to smaller rates of basal melt in their model.

" This is probably caused by the different patterns of melting rates: basal melting rates in Favier et al. (2014) are as high as 100 m/yr over large areas, while only a few points have melting rates above 50 m/yr in our study. "

I should also refer to Gladstone(2012) doi:10.1016/j.epsl.2012.04.022  with a simple (ish) coupled ocean ice model that sees PIG retreating for a couple centuries. I am looking forward to other coupled ocean ice models such as Goldberg(2012) doi:10.1029/2011JF002247 for detailed cases with PIG and Thwaites bathymetry and in situ validation.

but i fear that nature outruns our calculations

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 08, 2014, 03:17:30 PM
sidd,

Thanks for the great reference.  Regarding your comment: "but i fear that nature outruns our calculations"; I couldn't agree more, particularly as I believe that a major El Nino event will be coming in 2014-15; which should significantly accelerate sub-ice-shelf basal melting for the PIIS; particularly after September 2014 when a large El Nino should help position the ABSL so that it directs wind/current towards the PIG at least from the end of Sept. 2014 to February 2015.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: nukefix on April 21, 2014, 03:35:23 PM
The attached figure showing the average snowfall accumulation across Antarctica from 1955 to 2005.  This data clearly indicates..
What data is that? RACMO2 or similar?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 21, 2014, 04:22:50 PM
nukefix,

Could you provide the reply # as I cannot readily remember when I made this post.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 25, 2014, 05:05:01 PM
The linked Discover Magazine article about the Pine Island Bay glaciers includes a nice video of the use of ESA's SAR satellite radar interferometry use to estimate the retreat of the PIG grounding line (see attached image and the YouTube link below).  I note that 2010-11 was a strong La Nina event, so we will need to wait & see whether the rate of grounding line retreats accelerates during the current possible 2014-15 El Nino event:

http://blogs.discovermagazine.com/imageo/2014/04/24/antarctic-glaciers-flow-faster-iceberg-drifts-toward-sea/ (http://blogs.discovermagazine.com/imageo/2014/04/24/antarctic-glaciers-flow-faster-iceberg-drifts-toward-sea/)

Quote related to the following video: "In the visualization, based on data from radar instruments on European Space Agency satellites, the Pine Island Glacier is seen where it empties into Pine Island Bay. Past what’s known as the “grounding line,” where the glacier rests on bedrock, the ice floats and is part of a giant, permanent ice shelf that fringes the coast and tends to hold back the flow of the glaciers.
In the visualization, the ice shelf can be seen flexing up and down from tidal action. And as sea water, which has become warmer at least in part from human-caused global warming, circulates under the ice, it causes the shelf to thin. With less of a buttress to hold things back, the glacier speeds up. This, in turn, causes the grounding line to retreat."

http://www.esa.int/spaceinvideos/Videos/2014/03/Pine_Island_retreat (http://www.esa.int/spaceinvideos/Videos/2014/03/Pine_Island_retreat)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on April 25, 2014, 09:10:02 PM
The ESA page links to Park(2014) doi:10.1002/grl.50379
I attach figs 3a and 3b below. Note the bedrock peak at 25Km upstream of the 2011 grounding line which :" ... does not straddle the entire glacier width [Vaughan et al., 2006], and relief to the south side of the glacier, in particular, slopes gently."

The south side is toward Thwaites. Upstream of the peak the bed is again retrograde for a hundred or two hundred klicks, almost all the way to the Transantarctic mountains.

They state that although
" ... further retreat is at odds with simulations of the glacier evolution under conditions of increased ocean melting [Joughin et al., 2010]."

but then go on:

"However, the PIG geometry has impeded retreat at other times during our survey, and yet the retreat has progressed over time. Moreover, recent simulations of the PIG evolution that utilizes an adaptive-resolution domain [Gladstone et al., 2012; Cornford et al., 2013] have suggested that the grounding line may be able to retreat much farther inland should ocean melting persist. It is also possible that ocean melting has exceeded that imposed during existing simulations."

Gladstone(2012) is a good paper. That last sentence in the quote above is borne out by the ocean simulation papers you linked by Bromwich and Dinniman in 2014, which indicate the models have difficulty advecting enough CDW into the sub-iceshelf  cavity.

In short, retrograde bed to the next peak 25Km up, and then next stop the Transantarctic mountains. Meanwhile Thwaites at 55 Km width (10 times Jacobshawn) wants to play too.

We desperately need good fine scale coupled atmosphere-ocean-iceshelf-icesheet models. Bromwich and Dinniman both have static ice, hopefully will include ice dynamics in the next iteration, and succeed in getting up to the "right" CDW borne heat influx.

One phrase that shocked me in the Park paper:

" ... relatively warm (~4 C above freezing) seawater to access the glacier grounding line."

4C above freezing is HOT.

Another thought that occurred to me was that recent paper demostrating that a kilometer is about the maximum stable thickness of an iceshelf, but unfortunately i cannot now recall the reference.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 26, 2014, 12:00:05 AM
sidd,

Thanks for the great post.  I think that the reference that you are thinking of regarding 1km thick ice is:

Bassis, J.N., and Jacobs,S., (2013), "Diverse calving patterns linked to glacier geometry", Nature Geoscience, 6, 833–836, doi:10.1038/ngeo1887.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on April 26, 2014, 04:32:27 AM
yes, Bassis was the one. thanx

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 23, 2014, 05:28:43 AM
While I posted the reference for the attached image in the Forcing thread Reply #197, it is from a paper about GCM projections for the Pliocene.  I posted the reference in the Forcing thread as the paper clearly shows the importance of polar amplification on global warming in a world with GHG close where we are headed in the next few decades.  However, I am re-posting this image because polar amplification is only part of the significance the study; while this image makes it particularly clear that with Pliocene levels of GHG the ambient temperatures in the ASE during the austral summer will be well above freezing, lead to extensive surface melting.  Furthermore, if the ESS is above 4.5 degrees C (say due to Arctic Sea Ice extent loss by 2020), then it may be possible that extensive surface melting will occur in the ASE during the austral summer, beginning around the 2040-2060 time-frame.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 29, 2014, 11:27:11 PM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

The following extract from Nias et al 2014 confirms that the Thwaites Glacier, TG, will degrade in a different manner than the PIG currently is exhibiting:

70A0919
Contrasting dynamics and sensitivity of the Amundsen Sea ice streams
Isabel NIAS, Stephen CORNFORD, Tamsin EDWARDS, Tony PAYNE
Corresponding author: Isabel Nias
Corresponding author e-mail: isabel.nias@bristol.ac.uk

Abstract: "Ice loss from Antarctica is centred on an area of West Antarctica known as the Amundsen Sea Embayment (ASE). The stability of this area is a key control on future global sea level. Within the ASE, loss appears to be primarily associated with ice streams draining the area, including Pine Island and Thwaites Glaciers. The majority of research that attempts to understand the mechanisms responsible for this ice loss is based on modelling and satellite studies of Pine Island Glacier (PIG). From these studies a mechanism for accelerated flow and dynamic thinning of PIG has been identified whereby relatively warm Circumpolar Deep Water upwells onto the continental shelf and migrates under the ice shelves, causing increased melt and retreat of the grounding line. By comparison, there has been relatively little model-based research carried out on Thwaites Glacier (TG) and the cause of the thinning observed in the glacier interior is less clear. We seek to understand the differences in sensitivity to various parameters between PIG and TG using an advanced numerical model. BISICLES is a vertically integrated high-order ice flow model with adaptive mesh refinement (AMR). AMR provides a means of accurately modelling grounding-line migration with sub-km resolution, while avoiding the computational demands of a uniformly fine resolution. The position of the grounding line is important to ice-stream dynamics and stability, particularly on upward-sloping bedrock, typical of the ASE. Using BISICLES, we ran a perturbed model ensemble for PIG and TG. Latin hypercube sampling was used to generate sets of parameter values for a range of physical conditions, including ice rheology, basal sliding and bed topography. We present probability density functions of the likelihood of sea-level contributions from PIG and TG under the same oceanic forcing. Initial results suggest that these probability density functions are very different."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 30, 2014, 01:46:39 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

The Mouginot et al 2014 reference provides a nice summary of recent ice mass loss from the ASE:

70A1041
Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013
Jeremie MOUGINOT, Eric RIGNOT, Bernd SCHEUCHL
Corresponding author: Jeremie Mouginot
Corresponding author e-mail: jmougino@uci.edu

Abstract: "The glaciers draining into the Amundsen Sea Embayment (ASE) are known to be major contributors to sea-level rise from Antarctica, with a total mass flux comparable to the entire Greenland ice sheet. Since first revealed with satellite radar interferometry in the 1990s, this sector has been significantly out of balance due to glacier speed-up. Here, we combine measurements of ice velocity, and ice thickness from existing compilations to document 41 years of change in mass flux from the ASE. We derive ice-surface velocity from Landsat satellites between 1973 and 1989, ERS-1 for the winters of 1992 and 1994, ERS-1/2 for the winter of 1995, RADARSAT for the six winters between 2000 and 2005, ALOS PALSAR for the five consecutive winters between 2006 and 2010, RADARSAT-2 during fall 2011 and spring 2013, and TANDEM-X for winter 2012 and summer 2013. We also present the evolution of the grounding lines of the ASE glaciers between 1992 and 2011 using differential synthetic aperture radar interferometry (dinsar) data from the ERS-1/2 satellites. We estimate here that the total ice discharge has increased by 77% since 1973, with half of the increase occurring between 2003 and 2009. Grounding-line flow speeds at Pine Island Glacier stabilized between 2009 and 2013, following a decade of rapid acceleration and ungrounding of its ice plain, but acceleration reached far inland and occurred at a rate faster than predicted by advective processes. Ice flow speeds across Thwaites Glacier increased rapidly beginning in 2006, following a decade of near stability, leading to a 33% increase in ice flux between 2006 and 2013. Haynes, Smith, Pope and Kohler glaciers all accelerated during the entire study period, undergoing rapid ungrounding of ice plains or losing floating ice extensions. These results and satellite measurements give a good overview of the ice dynamic of the ASE during the last four decades , which is of great importance for understanding the evolution of a major part of West Antarctica."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 30, 2014, 02:08:43 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

Candy et al 2014 discuss progress made towards an adaptive resolution multiscale model of the PIIS ocean cavity:

70A1106
Towards an adaptive resolution multiscale model of Pine Island Glacier ice-shelf ocean cavity
Adam CANDY, Paul HOLLAND, Adrian JENKINS, Matthew PIGGOTT
Corresponding author: Adam Candy
Corresponding author e-mail: adam.candy@imperial.ac.uk

Abstract: "Recent observational studies have helped to constrain estimates of the melt behaviour underneath Pine Island Glacier (PIG). Generally, however, observations are limited due to the relatively inaccessible and inhospitable environment. A solid ice cover, up to many kilometres thick, bars access to the water column, so that observational data can only be obtained by inference from above, drilling holes through, or launching autonomous vehicles beneath, the ice. This is further exacerbated by the fact that results of these recent studies have implied a significant proportion of the melting (~80%) occurs in networks of sub-kilometre-scale basal channels close to the grounding line, some of the most inaccessible parts of sub-ice-shelf ocean cavities. Accurately representing these small-scale processes in conventional ocean models is a huge challenge even in focused regional studies, and will not be possible in global coupled climate simulations in the near future. We present the development of a new model of PIG that is capable of resolving the range of scales necessary to evaluate the melt distribution and forming processes that dominate. This is built on the fluidity model that simulates non-hydrostatic dynamics on meshes that, like the model of Timmermann and others (2012), can be unstructured. In this case, the grid can be unstructured in all three dimensions and use an anisotropic adaptive-in-time resolution to optimize the mesh and calculation in response to evolving solution dynamics. The parameterization of melting in this model has been validated in idealized cavity domains and a validation is underway for the dynamic treatment of the ice–ocean interface. The model is not limited to a vertical coordinate system, which enables it to accurately represent ice fronts, and small shallow features. We will discuss the development of this model of PIG; including the cavity domain, conforming to appropriately filtered boundaries generated from data collected during the BAS Autosub 2009 expedition, and the simulation of non-hydrostatic dynamics to date. This model has the potential to capture the high spatial variation seen in melt rates in the small-scale channels, and as a result provide valuable insights into the physical processes driving the observed large melting and modulation of ice–ocean interactions at kilometre scales."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 13, 2014, 05:48:05 PM
The linked reference discusses icequake seismicity associated with a propagating ice shelf rift, which typically occurs during a major calving event from an ice shelf (in this case the Amery Ice Shelf).  Such research should contribute to a better understanding of the risks of major ice shelf calving events, which if their frequency were to accelerate could contribute to the collapse of the ice shelf itself (note the Jakobshavn Glacier's Ice Shelf has already collapsed, and similar collapses could occur for the Thwaites Eastern Ice Shelf and the Pine Island Ice Shelf, within the next few of decades; which would greatly accelerate ice mass loss from the ASE basin):

Heeszel, D. S., H. A. Fricker, J. N. Bassis, S. O'Neel, and F. Walter (2014), Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure, J. Geophys. Res. Earth Surf., 119, 731–744, doi:10.1002/2013JF002849.

http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract)

Abstract: "Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important process involved in calving is the initiation and propagation of through-penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the austral summers of 2004–2007. We apply a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h. Even during periods of quiescence, we find significant deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes (Mw > −2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift-transverse crevasses. Small-scale variations in the mechanical structure of the ice shelf, especially rift-transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 13, 2014, 01:03:30 AM
The linked reference has an open access pdf, and provides guidance on the recent mass balance for the Pine Island, and Thwaites; glaciers:

Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., van den Broeke, M. R., Lenaerts, J. T. M., Bromwich, D. H., Nicolas, J. P., and Leuschen, C., (2014), "Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation", The Cryosphere, 8, 1375-1392, doi:10.5194/tc-8-1375-2014.

http://www.the-cryosphere.net/8/1375/2014/tc-8-1375-2014.html (http://www.the-cryosphere.net/8/1375/2014/tc-8-1375-2014.html)

Abstract: "In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on September 20, 2014, 08:19:52 PM
Since I have previously whined about the paucity of full Stokes analyses, i should point out Wilkens(2014)

www.the-cryosphere-discuss.net/8/4913/2014/tcd-8-4913-2014.pdf (http://www.the-cryosphere-discuss.net/8/4913/2014/tcd-8-4913-2014.pdf)

In particular Fig.6 and 7

Temperate beds under PIG, as suspected, but detail is nice.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 20, 2014, 10:02:47 PM
sidd,

Thanks for the reference and the pointers to Fig. 6 & 7; however, the points that I find most interesting are about what the authors call Tributary 13 (& MacGregor et al call the SW Tributary) in that: : (a) the first attached image shows clearly that Tributary 13 is located directly on the basin divide with the Thwaites Basin; and (b) the second attached image shows that the ice velocities in the Tributary 13 are as fast as any ice in PIG, and as soon as the PIIS calving face retreats upstream sufficiently then these velocities will accelerate serving to destabilize Thwaites.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 24, 2014, 11:40:05 PM
The linked reference (with an open access pdf) makes conservative estimates of the sensitivity of PIG dynamics (groundling line retreat, ice velocities etc.) to climate forcing for the next fifty years.  Significantly, the attached image shows the results of one such conservative projection indicating that the grounding line for the SW Tributary is primed for early retreat; which could serve to trigger an early destabilization of the Thwaites Glacier.

Seroussi, H., Morlighem, M., Rignot, E., Mouginot, J., Larour, E., Schodlok, M., and Khazendar, A., (2014), "Sensitivity of the dynamics of Pine Island Glacier, West Antarctica, to climate forcing for the next 50 years", The Cryosphere, 8, 1699-1710, doi:10.5194/tc-8-1699-2014.

http://www.the-cryosphere.net/8/1699/2014/tc-8-1699-2014.pdf (http://www.the-cryosphere.net/8/1699/2014/tc-8-1699-2014.pdf)

Abstract: "Pine Island Glacier, a major contributor to sea level rise in West Antarctica, has been undergoing significant changes over the last few decades. Here, we employ a three-dimensional, higher-order model to simulate its evolution over the next 50 yr in response to changes in its surface mass balance, the position of its calving front and ocean-induced ice shelf melting. Simulations show that the largest climatic impact on ice dynamics is the rate of ice shelf melting, which rapidly affects the glacier speed over several hundreds of kilometers upstream of the grounding line. Our simulations show that the speedup observed in the 1990s and 2000s is consistent with an increase in sub-ice-shelf melting. According to our modeling results, even if the grounding line stabilizes for a few decades, we find that the glacier reaction can continue for several decades longer. Furthermore, Pine Island Glacier will continue to change rapidly over the coming decades and remain a major contributor to sea level rise, even if ocean-induced melting is reduced."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on September 30, 2014, 04:07:19 AM
They said it couldn't be done.

"GOCE was designed to determine the Earth’s mean gravity field [Visser et al., 2002], and it was not anticipated that it could observe temporal gravity field variations."

"While Moore and King [2010] predicted that GOCE cannot detect an Antarctic ice change, ... "

But it seems it can ... when combined with GRACE ...

Results: For the period Nov 2009-July 2012
PIG -55+/-9 GT/yr,
Thwaites/Haines/Smith/Kohler -63+/-12 GT/y,
Metz -67+/-7 GT/y

Pretty,pretty work. Bouman(2014) doi:10.1002/2014GL060637

Compare say with Helm(2014) Cryostat result for WAIS for Jan2012-2013 of -188+/11 GT/yr
doi:10.5194/tcd-8-1673-2014

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 30, 2014, 05:38:43 AM
sidd,

Thank you for a great post about GOCE's triumph.  The following two links have the same beautiful video showing the extreme precision of the measurement of the annual changing in ice mass in the ASE marine glaciers from 2009 to 2012:

http://grist.org/article/antarctic-ice-melt-causes-small-shift-in-gravity/ (http://grist.org/article/antarctic-ice-melt-causes-small-shift-in-gravity/)

http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_reveals_gravity_dip_from_ice_loss (http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_reveals_gravity_dip_from_ice_loss)

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on September 30, 2014, 06:56:38 AM
A surprise is Getz, mass loss was estimated to be around a third of the result from this paper.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 30, 2014, 04:38:39 PM
sidd,

Yes Getz is the surprise as every article before this that I had since implied that the ice mass loss from Getz was from the floating ice shelf; however, the high precision of the GOCE (as indicated by the attached image taken from the ESA video) confirms that Getz has also made a serious contribution to SLR from Nov 2009 to June 2012.

However, I would like to say that during this time period we experienced a very strong La Nina event, which reduced the advection of warm CDW into the ASE; which in my opinion explains why the SLR contribution from the Thwaites Glacier was relatively low (it has twice the mass of the PIG).  Therefore, I am concerned that as we have ended a period of positive PDO/IPO it seems likely that the SLR contribution from all of the ASE marine glaciers will likely accelerate over the next 20 to 30 years (ie until the 2040-2060 Timeframe).

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 30, 2014, 06:05:53 PM
Given the importance of the Bouman et al (2014), I provide the following link and abstract:

Bouman, J., M. Fuchs, E. Ivins, W. van der Wal, E. Schrama, P. Visser, and M. Horwath (2014), Antarctic outlet glacier mass change resolved at basin scale from satellite gravity gradiometry, Geophys. Res. Lett., 41, 5919–5926, doi:10.1002/2014GL060637.

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060637/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060637/abstract)

Abstract: "The orbit and instrumental measurement of the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite mission offer the highest ever resolution capabilities for mapping Earth's gravity field from space. However, past analysis predicted that GOCE would not detect changes in ice sheet mass. Here we demonstrate that GOCE gravity gradiometry observations can be combined with Gravity Recovery and Climate Experiment (GRACE) gravity data to estimate mass changes in the Amundsen Sea Sector. This refined resolution allows land ice changes within the Pine Island Glacier (PIG), Thwaites Glacier, and Getz Ice Shelf drainage systems to be measured at respectively −67 ± 7, −63 ± 12, and −55 ± 9 Gt/yr over the GOCE observing period of November 2009 to June 2012. This is the most accurate pure satellite gravimetry measurement to date of current mass loss from PIG, known as the “weak underbelly” of West Antarctica because of its retrograde bed slope and high potential for raising future sea level."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on October 01, 2014, 09:57:25 PM
Just as I was admiring Bouman(2014)  here comes Velicogna(2014)
doi:10.1002/2014GL061052 which is at least as good.

Using GRACE data alone (!) it is possible to tease out regional variation.
I suspected this was possible, but they haveactually done it (!) using
a masscon approach. Very nice. They then couple with RACM02 for SMB.
I must say that RACM02 seems to be turning into the goto tool for this
sorta thing.

Now to the results:

1)"Overall, in Greenland, SMB has contributed 68% of the GRACE-derived
mass loss (-180±33 Gt/yr versus a total loss of -265±59 Gt/yr) and 79%
of the observed acceleration (23.3±4.7 Gt/yr2 versus a total acceleration of
29.7±1.3 Gt/yr2 ) during 2003-2012."

Agrees with Enderlin(2014) doi:10.1002/2013GL059010 in that SMB dominates
linear term, but they have shown it dominates quadrature (acceleration)
term as well. Interesting that they see little regional acceleration
in NEGIS, contrary to Khan(2014) doi:10.1038/nclimate2161

2)Amundsen sea sector they get -116+/-6GT/yr for the period 2003-2013 agrees
with Bouman(2014) within error for the time period in Bouman. Acceleration is

significant at 12.7+/- 1.6 GT/yr

3)those are  hefty accelerations. If the curves were really exponentials
instead of parabolae that would mean a doubling time of 7 yr. But i dont
think the data can differentiate between order 2 and exponential yet.
It will become clearer in a few decades.

What have i done to deserve _two_ such nice papers within a few days ?
I must have been very good lately.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Lennart van der Linde on October 01, 2014, 10:49:31 PM
Thank you, sidd, for keeping us up-to-date with these scary numbers. Are there any looming negative feedbacks in sight?

A 7-yr doubling time roughly resembles the doubling time of the Chinese economy over the past decade. But that would be a coincidence...
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 01, 2014, 10:57:35 PM
As a public service, I provide the following reference information for the Velicogna et al paper that sidd cited in Reply #111:

I. Velicogna, T. C. Sutterley and M. R. van den Broeke, (2014), "Regional acceleration in ice mass loss from Greenland and Antarctica using GRACE time-variable gravity data," Geophysical Research Letters, DOI: 10.1002/2014GL06105

http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/abstract)

Abstract: "We use GRACE monthly gravity fields to determine the regional acceleration in ice mass loss in Greenland and Antarctica for 2003–2013. We find that the total mass loss is controlled by only a few regions. In Greenland, the southeast and northwest generate 70% of the loss (280∓58 Gt/yr) mostly from ice dynamics, the southwest accounts for 54% of the total acceleration in loss (25.4∓1.2 Gt/yr2) from a decrease in surface mass balance (SMB), followed by the northwest (34%), and we find no significant acceleration in the northeast. In Antarctica, the Amundsen Sea (AS) sector and the Peninsula account for 64% and 17%, respectively, of the total loss (180∓10 Gt/yr) mainly from ice dynamics. The AS sector contributes most of the acceleration in loss (11∓4 Gt/yr2) and Queen Maud Land, East Antarctica is the only sector with a significant mass gain due to a local increase in SMB (63∓5 Gt/yr)."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 01, 2014, 11:03:17 PM
For those who would like to learn more about the Regional Atmospheric Climate MOdel (RACMO2), I provide the following link:

http://www.staff.science.uu.nl/~lenae101/pubs/Lenaerts2013aSOM.pdf (http://www.staff.science.uu.nl/~lenae101/pubs/Lenaerts2013aSOM.pdf)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Lennart van der Linde on October 01, 2014, 11:44:37 PM
Skeptical Science also gives a short update of some recent papers, including some mentioned above:
http://skepticalscience.com/Antarctica-Greenland-Losing-Ice.html (http://skepticalscience.com/Antarctica-Greenland-Losing-Ice.html)

Totten Glacier is also of concern.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on October 02, 2014, 01:21:16 AM
Re:feedbacks

Everything is deeply intertwingled.

1)I think we have activated the Weertmann instability in WAIS, and collapse is now inevitable. All we have left to discuss is the timeframe.
2)A feedback that was thought possible was a warming ocean dropping more snow on Antarctica. But as we see from Velicogna(2014) and others it seems  only to have operated very sporadically in Dronning Maud Land. And there is a a paper i believe that shows that increased snowfall can actually increase ice efflux but i do not immediately recall the reference.
3)The increase in Southern Ocean winter sea ice is another wicked synergy. Naively i thought that Antarctic ice flow ended at the coastline. Not so it seems. Consider: Ocean heat melts basal ice, fresh water efflux then exits, spreads north and refreezes where it is exposed to seasonally warmer water much more efficiently than when it was in the base of an ice shelf. In other words, the ocean is not only sucking ice outta the interior of WAIS by eroding the base and speeding flow, it is then transporting the ice as meltwater north, refreezing it in a region where it can melt it at leisure, reclaiming latent heat in the process. So the ocean is sucking ice much further north than the coastline. And observe the clever way it cycles the heat: it donates heat to the meltwater at the ice shelf base, and reclaims it further north as the meltwater freezes in winter.
4)In the case of Greenland, I fear that precipitation there will be increasingly rain as opposed to snow. I believe there is a paper by Tedesco or Fettweis or somebody that shows this happening over the next century. Again this is something that i did not understand, how could ocean heat get into Greenland except at the tongues of maritime glaciers.

In short, the ocean is very large, very clever, and wants in your basement.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 02, 2014, 01:55:37 AM
sidd & Lennart,

Don't forget that the Velicogna et al (2014) paper only considers ice mass loss during the El Nino hiatus period, during which time the advection of warm CDW into the ASE is reduced.  Now that we are entering a positive PDO/IPO phase advection of CDW into the ASE should accelerate for the next 20 to 35 years; which should further acceleration ice mass loss from the WAIS.

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 02, 2014, 07:28:43 PM
To provide some visual support for my position that advection of CDW into the ASE has (and is likely to continue) increased since the 2000-2013 timeframe, I attach the accompanying Terra image of the Pine Island Bay area showing extensive loss of sea ice in this area even though sea ice extent in Antarctica in general is near an all time high.  This local loss of sea ice in Pine Island Bay is clearly related to advection of CDW and is atypical of the 2000-2013 period.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 03, 2014, 01:03:50 AM
Further to my last post, the attached NSIDC image of Antarctic sea ice anomalies for Sept 2014 shows that not only is the sea ice in Pine Island Bay melting anomalously early, but also the outer perimeter of the sea ice offshore of the ASE is also anomalously low for this time of year.  This supports the idea that land-based ice mass loss in the ASE is likely anomalously high due to higher than normal ocean water advection.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 03, 2014, 11:45:18 PM
The attached image was taken from the Modis Oct 3 2014 mosaic for Antarctica and focuses on the Amundsen Sea area and shows how extensive the exceptionally early break-up of the sea ice throughout this region is occurring.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: johnm33 on October 05, 2014, 07:17:34 PM
Interesting vid of gravity changes. http://www.livescience.com/48083-antarctic-ice-loss-causes-dip-in-earth-s-gravity-video.html (http://www.livescience.com/48083-antarctic-ice-loss-causes-dip-in-earth-s-gravity-video.html)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 09, 2014, 08:14:06 PM
The first attached image if taken from the Modis Antarctic mosaic for Oct 9 2014, and shows how extremely fractured the sea ice is both the ASE and the Bellingshausen Sea.  The second attached image shows the earth surface wind map for Oct 9 2014, showing that the local winds in this area are currently blowing from land to offshore; and if this wind pattern continues from some days, a meaningful fraction of this local fractured sea ice could be blown out to more northerly latitudes where it would likely melt.  If this happens (now or soon), it would expose both the ASE, and the Bellingshausen Sea, coastlines to increase storm wave exposure that could promote glacial ice calving from the local ice shelves.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 14, 2014, 01:20:31 AM
The linked reference provides more evidence that the BSB is providing geothermal basal heat to accelerate the destabilization of the Thwaites Glacier:

Theresa M. Damiani, Tom A. Jordan, Fausto Ferraccioli, Duncan A. Young, and Donald D. Blankenship, (2014), "Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica", Earth and Planetary Science Letters Volume 407, 1, Pages 109–122, DOI: 10.1016/j.epsl.2014.09.023

http://www.sciencedirect.com/science/article/pii/S0012821X14005780 (http://www.sciencedirect.com/science/article/pii/S0012821X14005780)

Abstract: "Thwaites Glacier has one of the largest glacial catchments in West Antarctica. The future stability of Thwaites Glacier's catchment is of great concern, as this part of the West Antarctic Ice Sheet has recently been hypothesized to already be en route towards collapse. Although an oceanic trigger is thought to be responsible for current change at the grounding line of Thwaites Glacier, in order to determine the effects of this coastal change further in the interior of the West Antarctic Ice Sheet it is essential to also better constrain basal conditions that control the dynamics of fast glacial flow within the catchment itself. One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. The primary goal of our study is to investigate the crustal thickness beneath Thwaites Glacier, which is an important contributor to regional-scale geothermal heat flux patterns. Crustal structure is an indicator of past tectonic events and hence provides a geophysical proxy for the thermal status of the crust and mantle. Terrain-corrected Bouguer gravity disturbances are used here to estimate depths to the Moho and mid-crustal boundary. The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area's subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 14, 2014, 08:33:02 PM
The linked reference (with a free pdf) presents numerical model studies relating the oceanographic and geometric (of the cavity beneath the PIIS) controls on ice melting for the PIG (and PIIS).  They found that after an initial surge of ice melting after the 1970's with grounding line retreated past the well-known subglacial ridge; thereafter the melting rate was more dominated by the depth of the thermocline.  I remind readers that the depth of the thermocline has been related to the ENSO cycle (via the ASL) and that as we enter a period of increasingly positive PDO the depth of the thermocline should be increasingly conducive to accelerated rates of ice melting for at least the next 20 to 25 years.

J. De Rydt, P.R. Holland, P. Dutrieux, and A. Jenkins, (2014), "Geometric and oceanographic controls on melting beneath Pine Island Glacier", Journal of Geophysical Research-Oceans, 119:2420-2438. doi: 10.1002/2013JC009513

http://www.antarctica.ac.uk/met/ph/docs/2014_DeRydt&Al_JGRO.pdf (http://www.antarctica.ac.uk/met/ph/docs/2014_DeRydt&Al_JGRO.pdf)

Abstract: "Observations beneath the floating section of Pine Island Glacier have revealed the presence of a subglacial ridge which rises up to 300 m above the surrounding bathymetry. This topographic feature probably served as a steady grounding line position until sometime before the 1970s, when an ongoing phase of rapid grounding line retreat was initiated. As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause ice melting in the vicinity of the grounding line. In order to understand how melt rates have changed during the various phases of cavity formation, we use a high-resolution ocean model to simulate the cavity circulation for a series of synthetic geometries. We show that the height of the ridge and the gap between the ridge and ice shelf strongly control the inflow of warm bottom waters into the cavity, and hence the melt rates. Model results suggest a rapid geometrically controlled increase of meltwater production at the onset of ice thinning, but a weak sensitivity to geometry once the gap between the ridge and ice shelf has passed a threshold value of about 200 m. This provides evidence for a new, coupled, ice-ocean feedback acting to enhance the initial retreat of an ice stream from a bedrock high. The present gap is over 200 m, and our results suggest that observed variability in melt rates is now controlled by other factors, such as the depth of the thermocline."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 10, 2014, 03:05:30 AM
While I have cited the following Rignot et al 2014 reference previously; here I attached an image from this reference that shows that ice flux (from 1974 to 2013) across the 2011 Thwaites Glacier grounding line is currently accelerating faster than any other Amundsen Sea Embayment marine glacier (which is a very disturbing trend):

Rignot, E., Mouginot, J., Morlighem, M., Seroussi, H. and Scheuchl, B., (2014), "Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011", Geophysical Research Letter, DOI: 10.1002/2014GL060140.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 29, 2015, 01:57:29 AM
In order to give this important thread a bump, and to illustrate some of the consequences if the WAIS should start to collapse in this timeframe, I attach the two associated images from the linked pdf:

http://www.agci.org/dB/PPTs/05S1_RTol_0713.pdf (http://www.agci.org/dB/PPTs/05S1_RTol_0713.pdf)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on January 29, 2015, 05:48:41 AM
That paper from agci.org is by Tol, whom i distrust. He also says that SLR rates of greater than 1m/century breaks the model ...

I will wait for a more reliable source and a better model.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Lennart van der Linde on January 29, 2015, 07:55:40 AM
I think the presentation by Tol above was based on the Atlantis Project by Tol et al 2006:
http://dspace.ubvu.vu.nl/bitstream/handle/1871/31946/191890.pdf?sequence=1 (http://dspace.ubvu.vu.nl/bitstream/handle/1871/31946/191890.pdf?sequence=1)

Neo-Atlantis by Olsthoorn et al 2005 gave input for this:
http://www.fnu.zmaw.de/fileadmin/fnu-files/publication/working-papers/waishollandwp.pdf (http://www.fnu.zmaw.de/fileadmin/fnu-files/publication/working-papers/waishollandwp.pdf)

They published this as Olsthoorn et al 2008:
http://link.springer.com/article/10.1007%2Fs10584-008-9423-z (http://link.springer.com/article/10.1007%2Fs10584-008-9423-z)

And then nothing much happend with this work, probably because the risk of such WAIS-collapsed was judged to be too small to worry about. Which should really change now.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 29, 2015, 05:21:16 PM
And then nothing much happend with this work, probably because the risk of such WAIS-collapsed was judged to be too small to worry about. Which should really change now.

My purpose in posting the Tol information was not to give support to his work, but as Lennart points out the question of the consequence of a possible early start for abrupt SLR, ASLR, should be re-evaluated now (especially in light of the Bassis et al and Pollard et al findings about cliff failures and hydrofracturing [which I sometimes call meltpond mechanism and/or the Thwaites effect]).  We need to remember that scientists are happy to update their SLR projections whenever they have sufficient data, so the fact that even a few months ago that they discounted the rapid collapse of marine glaciers is no guarantee at all to protect society from the serious consequences of an early start to ASLR (here assumed to have a threshold of 1m of SLR in three decades and then probably accelerating).

The Olsthoorn et al 2008 just assumes a start date for ASLR of 2030, which seems plausible to me if we take the Greenland marine terminating glaciers as starting to collapse in 2030, and then the WAIS marine glaciers joining them in collapse by 2040.  As Lennart has pointed out previously, it will take some time before SLR guidance agencies recognize this risk (say by AR6 [if it is generated] by 2021), then it will take time for decision makers, financiers and designers/planners to decide where/how to fight ASLR and where/how to retreat from ASLR (say by 2030).  As ASLR will be happening everywhere in the world simultaneously we can assume at least the following consequence:

1. Where we fight or retreat the costs of new constructions will likely double or triple due to the simultaneous demand on contractors.
2. Those who cannot retreat in an organized fashion will become refugees which will put high demands on governments, who will lack sufficient revenues to meet their other challenges of degraded coastal road, rail and port/harbor transportation, degrades water supplies due to salinity contamination which will also corrode buried utilities, and blocked sewer systems.  Such effects will also collapse tax revenues.
3.  Food production will degrade rapidly in all of the deltas of the world & delivery of food from the upstream river systems will be blocked by sedimentation of the river mouth (eg the Mississippi, Mekong, Nile, etc).
4.  Compromise of the ability of all militaries worldwide to project power overseas to address local hotspots (both military & humanitarian), as all naval bases and many airports will be compromised.
5.  High-tides and storm surge will be made worse by ASLR.

I could go on but you get the idea.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 30, 2015, 08:56:30 PM
I thought that I would quickly note that I would not expect much of the cliff failure & hydrofracturing mechanisms postulated by Pollard et al 2015 in the PIG/Thwaites area prior to the 2040-2060 timeframe, and as Pfeffer et al 2008 does not include either of these two mechanisms, it is possible that the Pfeffer et al 2008 Beta PDF analysis by Lempert et al 2012, may provide some idea how likely ASLR is to begin by 2030.

Lempert, R., Sriver, R.L. and Keller, K., (2012); "Characterizing Uncertain Sea Level Rise Projections to Support Investment Decisions" Report to POLA.

The two attached associated images (that I have posted before) indicate that this probability may be on the order of about 15%
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 05, 2015, 09:47:06 PM
The linked reference (the second link has a free pdf) ties the warming of the Tropical Atlantic SST to a strengthening of both the Antarctic Circumpolar Winds and the Amundsen Bellingshausen Sea Low (ABSL/ASL) via atmospheric Rossby waves in all seasons except the austral summer.  The conclusions of this paper (see the extract below) recommends that efforts be made to inter-relate this Atlantic tropical-Antarctic teleconnection with other tropical teleconnections (such as those identified by Fogt et al 2011, see the first attached image relating El Nino events & negative Southern Annular Mode, SAM, conditions that promote teleconnection of Tropical Pacific energy towards the Amundsen Sea Embayment, via atmospheric Rossby wave-trains).  As we are now likely approaching very strong El Nino conditions by October 2015, it will be very interesting to see whether both the Tropical Atlantic and the Tropical Pacific soon teleconnect large amounts of atmospheric energy into Western Antarctica.

Additionally, the second attached image today from the Earth nullschool shows that the ABSL is relatively strong (i.e. has a relatively low central pressure) and is currently directing energy directly into the Amundsen Sea Embayment, ASE.

XICHEN LI, EDWIN P. GERBER, DAVID M. HOLLAND, AND CHANGHYUN YOO, (2015), "A Rossby Wave Bridge from the Tropical Atlantic to West Antarctica", J. Climate, 28, 2256–2273, doi: http://dx.doi.org/10.1175/JCLI-D-14-00450.1 (http://dx.doi.org/10.1175/JCLI-D-14-00450.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00450.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00450.1)

http://polarmet.osu.edu/ACCIMA/li_gerber_jc_2015.pdf (http://polarmet.osu.edu/ACCIMA/li_gerber_jc_2015.pdf)

Abstract: "Tropical Atlantic sea surface temperature changes have recently been linked to circulation anomalies around Antarctica during austral winter. Warming in the tropical Atlantic associated with the Atlantic multidecadal oscillation forces a positive response in the southern annular mode, strengthening the Amundsen–Bellingshausen Sea low in particular. In this study, observational and reanalysis datasets and a hierarchy of atmospheric models are used to assess the seasonality and dynamical mechanism of this teleconnection.  Both the reanalyses and models reveal a robust link between tropical Atlantic SSTs and the Amundsen–Bellingshausen Sea low in all seasons except austral summer. A Rossby wave mechanism is then shown to both explain the teleconnection and its seasonality. The mechanism involves both changes in the excitation of Rossby wave activity with season and the formation of a Rossby waveguide across the Pacific, which depends critically on the strength and extension of the subtropical jet over the west Pacific. Strong anticyclonic curvature on the poleward flank of the jet creates a reflecting surface, channeling quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen–Bellingshausen Sea region. In summer, however, the jet is weaker than in other seasons and no longer able to keep Rossby wave activity trapped in the Southern Hemisphere. The mechanism is supported by integrations with a comprehensive atmospheric model, initial-value calculations with a primitive equation model on the sphere, and Rossby wave ray tracing analysis."

Extract: "Antarctic climate is also influenced by other tropical–polar teleconnections (Fogt et al. 2011; Ding et al. 2012), and key questions remain concerning the relative importance of these effects. The time scales of tropical SST variability differs significantly from one region to another (e.g., ENSO and the east Pacific dominate on interannual time scales, while the AMO and Pacific decadal oscillation are more significant on longer time scales). Moreover, SSTs in different tropical ocean basins may interact with each other through tropical ocean interbasin teleconnections. It is thus important to further investigate the relative importance and the relationship between the teleconnections from different tropical ocean sectors as a function of time scale."

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 14, 2015, 07:39:20 PM
For what it is worth, the attached Earth MSLP surface Wind Map for April 14 2015 shows that the ABSL is currently positioned so that the associated winds are currently driving warm CDW into the ASE (below the sea ice).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 03, 2015, 05:52:37 PM
As I am particularly concerned about the probability that the grounded iceberg at the tip of the residual Thwaites Ice Tongue may become free floating either this austral summer (2015-16) or next (2016-17); which raises the risk that the trapped field of free floating approximately 1km by 2km icebergs that compose the residual Ice Tongue will then free to float away.  If/when the floating portion of the residual Ice Tongue floats away, I am then concerned that cliff failure (and possibly future hydrofracturing due to future surface ice melting) will then occur in the grounded fractured ice in the trough at the base of the Ice Tongue (see the first attached image from January 2013 that shows the boundary between floating and grounded ice above the trough and illustrates how the ice flowing into the trough developed through crevasses that pre-divided this grounded ice into approximately 1km by 2km chucks that are highly susceptible to calving and floating away).

In this regard I provide the second attached figure of the Thwaites residual Ice Tongue on August 1, 2015 per the Sentinel 1a satellite (from the linked Polarview site); which shows: (a) the iceberg at the tip of the residual Ice Tongue has moved beyond the tip of the Thwaites Eastern Ice Shelf; and (b) some approximately 1km by 2km icebergs have already begun to float away as compared to the third attached image from Landsat 8 for March 6 2015.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 04, 2015, 10:04:37 PM
The following paper finds that the disintegration of the Thwaites Ice Shelf (both the eastern ice shelf and the ice tongue) is accelerating due to basal melting and warm CDW intrusion beneath the eastern ice shelf since 2000), together with the shear stress between the eastern ice shelf and the residual ice tongue due to differential ice flow rates:

Kim et al (2015), "Disintegration and acceleration of Thwaites Ice Shelf on the Amundsen Sea revealed from remote sensing measurements", GIScience & Remote Sensing, Volume 52, Issue 4, DOI: 10.1080/15481603.2015.1041766

Abstract: "Thwaites Ice Shelf in the Amundsen Sea is one of the biggest ice shelves in West Antarctica and is well known for significant mass changes. In the shear zone between Thwaites Glacier Tongue and its eastern ice shelf, shear stress forced by different flow rates of the ice shelves is causing the ice to break apart. A time series analysis of remote sensing data obtained by Landsat 7 Enhanced Thematic Mapper Plus (ETM+), TerraSAR-X, and airborne synthetic aperture radar (SAR) revealed that the shear zone has extended since 2006 and eventually disintegrated in 2008. We quantified the acceleration of Thwaites Ice Shelf with time by using the feature tracking method. The buttressing loss induced by the extension of the shear zone and progressive disintegration accelerated the flow of Thwaites Glacier Tongue, which in turn increased the shear stress on its eastern ice shelf. We determine causes of disintegration in the newly formed shear zone to be oceanic basal melting and structural weakening induced by Circumpolar Deep Water intrusion beneath the eastern ice shelf since 2000. The structural weakening was examined by using the density distribution of rifts and crevasses on the ice shelf, which were well identified from high-resolution SAR and optical satellite images."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 04, 2015, 10:14:34 PM
The linked article discusses the October 2012 IceBridge Antarctica mission to survey the Thwaites Ice Shelf area.  The first attached image of the ice self is from before the 2012 Thwaites Ice Tongue breakage event, the section image is from Tinto & Bell 2011:

http://blogs.ei.columbia.edu/2012/10/18/launching-the-season-with-a-key-mission-icebridge-antarctica-2012/ (http://blogs.ei.columbia.edu/2012/10/18/launching-the-season-with-a-key-mission-icebridge-antarctica-2012/)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 07, 2015, 04:40:26 PM
The attached image of the Thwaites Eastern Ice Shelf, TEIS, is from Polarview (Sentinel 1a) for August 7 2015; and I want to draw attention to the somewhat recent calved iceberg from the southwest corner of the TEIS; which also be seen in the August 1 2015 image, but cannot be seen in the March 2015 images.  This provides support to the idea that not only is the Thwaites residual Ice Tongue degrading rapidly due to warm CDW advection, but so is the TEIS.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on August 12, 2015, 06:37:21 PM
Here is a view of the old Twaites shelf from 8/1 to 8/11.  I rotated it for maximum view.  It may not show up on this small scale, but all the cracks have expanded within the last 10 days.  It appears to me that disintegration will occur relatively soon.  2 second delay on gif.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 12, 2015, 10:13:46 PM
Here is a view of the old Twaites shelf from 8/1 to 8/11.  I rotated it for maximum view.  It may not show up on this small scale, but all the cracks have expanded within the last 10 days.  It appears to me that disintegration will occur relatively soon.  2 second delay on gif.

solartim27,

I think that what you are showing broke-off from the Thwaites Ice Tongue in 2002 and has been grounded ever since (see the attached image from MacGregor et al 2012).

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Gray-Wolf on August 14, 2015, 05:42:01 PM
Am I right in thinking we saw a  paper looking at how La Nina/ Nina like conditions slowed losses from PIG/Thwaites over the late noughties/early teens due to wind/current anoms?

If so are we about to see big losses over the coming Southern Summer?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 15, 2015, 01:23:23 AM
Am I right in thinking we saw a  paper looking at how La Nina/ Nina like conditions slowed losses from PIG/Thwaites over the late noughties/early teens due to wind/current anoms?

If so are we about to see big losses over the coming Southern Summer?

Gray-Wolf,

I believe that you are referring to the following article that I discussed (& provided images from) in Reply #245 in the "PIG has calved" thread.

Best,
ASLR

Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, and Michael Schröder, 2014, "Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability", Science; Published online 2 January 2014 DOI:10.1126/science.1244341

http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract (http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract)

http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf (http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf)

http://www.ccpo.odu.edu/~klinck/Reprints/PDF/dutrieuxScience14.pdf (http://www.ccpo.odu.edu/~klinck/Reprints/PDF/dutrieuxScience14.pdf)

Abstract:
"Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 15, 2015, 11:56:52 PM
The following link provides images and information about the March 2002 calving of Iceberg B-22 from the Thwaites Ice Tongue:

http://www.noaanews.noaa.gov/stories/s879.htm (http://www.noaanews.noaa.gov/stories/s879.htm)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on August 17, 2015, 02:23:11 AM
I had mentioned a calving on Thwaites on the PIG thread last week.  Here is a closeup of the area for 8/1, 8/11, and 8/16.  No big change for the 16th, but one of the bergs splits and rolls.  The Sentinal shot misses the last PIG remnant stuck on the pinnacle, so no idea what is going on there.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: steve s on August 17, 2015, 07:04:23 PM
ST, would you please estimate from the image pixels the distance the Thwaites calving face retreated during August? Since the retreat distance varies along the face, the maximum point of retreat would do.

I think of the maximum as a relatively easy qualitative measure of the release of stored strain, suitable for quick comparison with new nearby events. In the case of the Thwaites in the next few years, time series on retreat maximums and on the intervals between events may prove both interesting and useful.








Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on August 17, 2015, 07:50:26 PM
ST, would you please estimate from the image pixels the distance the Thwaites calving face retreated during August? Since the retreat distance varies along the face, the maximum point of retreat would do.

I think of the maximum as relatively easy qualitative measure of the release of stored strain suitable for quick comparison with new events nearby. In the case of the Thwaites in the next few years, time series on retreat maximums and intervals between events will probably prove interesting -- and useful for pedagogy.
Sorry, thats beyond my capabilities, I'm just eyeballing a screen shot to matchup as best I can.  I don't think the front has retreated, might have advanced some, except for the bit that cracked off. 
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: steve s on August 17, 2015, 10:54:59 PM
I was looking at a spot of obvious retreat. I don't know the scale of the image or the area covered by a pixel to approximate the distance, but I do wonder.

Given the rather obvious increase in floating ice chunks, if the calving face did not retreat, the glacier must have surged. Big icequake; near the grounding line as I have read the various posts.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on August 18, 2015, 11:07:49 PM
The article discussed in this link is previously posted under the Collapse Scenario thread by LvdL, but this link has a nice video of the glaciers retreating, though it covers 300 years.  I would not be surprised if it is faster than that.
http://www.climatecentral.org/news/west-antarctica-sea-level-estimates-19345 (http://www.climatecentral.org/news/west-antarctica-sea-level-estimates-19345)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 25, 2015, 01:45:15 AM
Here is a useful reference about changes in Amundsen sea ice from 1979 to 2014:

Stammerjohn SE, Maksym T, Massom RA, Lowry KE, Arrigo KR, et al. 2015. Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014. Elem. Sci. Anth. 3: 000055 doi: 10.12952/journal.elementa.000055

https://www.elementascience.org/articles/55 (https://www.elementascience.org/articles/55)

https://www.elementascience.org/articles/55/tabs/figures_and_data (https://www.elementascience.org/articles/55/tabs/figures_and_data)


Abstract: "Recent attention has focused on accelerated glacial losses along the Amundsen Sea coast that result from changes in atmosphere and ocean circulation, with sea ice playing a mediating but not well-understood role. Here, we investigated how sea ice has changed in the Amundsen Sea over the period of 1979 to 2014, focusing on spatio-temporal changes in ice edge advance/retreat and percent sea ice cover in relation to changes in winds. In contrast to the widespread sea ice decreases to the east and increases to the west of the Amundsen Sea, sea ice changes in the Amundsen Sea were confined to three areas: (i) offshore of the shelf break, (ii) the southern Pine Island Polynya, and (iii) the eastern Amundsen Sea Polynya. Offshore, a 2-month decrease in ice season duration coincided with seasonal shifts in wind speed and direction from March to May (relating to later ice advance) and from September to August (relating to earlier retreat), consistent with reported changes in the depth/location of the Amundsen Sea Low. In contrast, sea ice decreases in the polynya areas corresponded to episodic or step changes in spring ice retreat (earlier by 12 months) and were coincident with changes to Thwaites Iceberg Tongue (located between the two polynyas) and increased southeasterly winds. Temporal correlations among these three areas were weak, indicating different local forcing and/or differential response to large-scale forcing. Although our analysis has shown that part of the variability can be explained by changes in winds or to the coastal icescape, an additional but unknown factor is how sea ice has responded to changes in ocean heat and freshwater inputs. Unraveling cause and effect, critical for predicting changes to this rapidly evolving ocean-ice shelf-sea ice system, will require in situ observations, along with improved remote sensing capabilities and ocean modeling."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 15, 2015, 10:09:47 PM
Some people may feel that it is cherry picking to point at a daily NOAA surface temp anom plot such as the attached for Sept 15 2015; however, I believe that the exceptionally warmth indicated for the WAIS is characteristic of the strengthening El Nino that is underway.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Lennart van der Linde on September 29, 2015, 08:24:31 PM
Excellent article by Chris Mooney on the the risk of Thwaites collapse and the urgent need for more research on this key WAIS-glacier:
http://www.washingtonpost.com/news/energy-environment/wp/2015/09/29/scientists-declare-an-urgent-mission-study-west-antarctica-and-fast/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/09/29/scientists-declare-an-urgent-mission-study-west-antarctica-and-fast/)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 29, 2015, 09:08:57 PM
The linked article discusses a pay-walled report entitled: "A Strategic Vision for NSF Investments in Antarctic and Southern Ocean Research (2015)" that prioritizes science in Antarctica:

http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=21741 (http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=21741)


Extract: "Melting Ice Sheets, Genomic Studies, and Deep-Space Observations Are Top Priorities for Next Decade of Antarctic and Southern Ocean Research
 
WASHINGTON -- An initiative to better understand how melting ice sheets will contribute to sea-level rise, efforts to decode the genomes of organisms to understand evolutionary adaptations, and a next-generation cosmic microwave background experiment to address fundamental questions about the origin of the universe are the top research goals for Antarctic and Southern Ocean science recommended in a new report from the National Academies of Sciences, Engineering, and Medicine.
 
The report, which offers a strategic vision to guide the U.S. Antarctic Program at the National Science Foundation over the next 10 years, also recommends that NSF continue to support a core program of investigator-driven research across a broad range of disciplines and strengthen logistic and infrastructure support for the priority research areas.
 
“The discoveries emerging from the Antarctic and the Southern Ocean advance our understanding of how our planet works and how our universe formed,” said Robin Bell, professor of geology and geophysics at the Lamont-Doherty Earth Observatory of Columbia University in New York and co-chair of the committee that conducted the study.  “Continued Antarctic and Southern Ocean research will produce new insights that will be critical as society adapts to the global consequences of change in these remote regions.”
Informed by extensive input from the scientific community, the committee selected the three large-scale research goals based on the criteria of compelling science, potential for societal impact, time sensitivity, readiness and feasibility, and key areas for U.S. and NSF leadership.  Additional criteria included partnership opportunities, impacts on NSF program balance, and the potential to help bridge disciplinary divides.
 
The report proposes a major new effort called the Changing Antarctic Ice Sheets Initiative to investigate how much and how fast melting ice sheets will contribute to sea-level rise.  The initiative’s components include a multidisciplinary campaign to study the complex interactions among ice, ocean, atmosphere, and climate in key zones of the West Antarctic Ice Sheet, and a new generation of ice core and marine sediment core studies to better understand past episodes of rapid ice sheet collapse."
A second strategic research priority is to understand from a genetic standpoint how life adapts to the extreme Antarctic environment.  For more than 30 million years, isolated Antarctic ecosystems have evolved to adapt to freezing conditions and dramatic environmental changes, and now must adapt to contemporary pressures such as climate change, ocean acidification, invasive species, and commercial fishing.  Sequencing the genomes and transcriptomes of critical populations, ranging from microbes to marine mammals, would reveal the magnitude of their genetic diversity and capacity to adapt to change. 
 
In addition to being a vast natural laboratory, Antarctica has a dry, stable atmosphere that offers an ideal setting for astrophysical observations.  The report recommends a next-generation experimental program to observe cosmic microwave background radiation, the “fossil light” from the early universe.  This would include an installation of a new set of telescopes at the South Pole, as part of a larger global array, which will allow highly sensitive measurements that could detect signatures of gravitational waves.  Such observations might provide evidence that could confirm the theory of cosmic inflation and the quantum nature of gravity, as well as address other enduring questions about the nature of the universe.
 
“Although remote, the changes occurring in the Southern Ocean and Antarctica can directly influence the United States,” said committee co-chair Robert Weller, senior scientist at Woods Hole Oceanographic Institution in Massachusetts.  “But these are challenging areas to do research, so there is a pressing need to prioritize the allocation of resources in order to assure reliable, safe support for critical observations and research campaigns.”
 
The report recommends the following as key needs for supporting and implementing the priority research goals and other areas of Antarctic and Southern Ocean science:   
•         Expanded access to remote field sites, including a deep field camp and logistics hub, over-snow traverse capabilities, and improved all-weather access to research stations and field locations by air;
•         Design and acquisition of a new heavy icebreaker ship and an ice-capable polar research vessel;
•         Support for sustained observations through strategic augmentation and coordination of existing observational networks;
•         Improved communications and information technology for data transmission; and
•         Efforts to facilitate more open and coordinated data collection, sharing, and integration.
 
The report notes that the priority research initiatives all require some degree of collaboration among NSF divisions, with other U.S. agencies, and with other nations.  In addition, NSF can play an important role in developing Antarctic-themed educational resources for K-12, undergraduate and graduate programs, and informal education institutions."


http://www.nap.edu/catalog/21741/a-strategic-vision-for-nsf-investments-in-antarctic-and-southern-ocean-research (http://www.nap.edu/catalog/21741/a-strategic-vision-for-nsf-investments-in-antarctic-and-southern-ocean-research)

Committee on the Development of a Strategic Vision for the U.S. Antarctic Program; Polar Research Board; Division on Earth and Life Studies; National Academies of Sciences, Engineering, and Medicine

A Strategic Vision for NSF Investments in Antarctic and Southern Ocean Research (2015)
Description
Antarctic and Southern Ocean scientific research has produced a wide array of important and exciting scientific advances. Spanning oceanography to tectonics, microbiology to astrophysics, the extreme Antarctic environment provides unique opportunities to expand our knowledge about how our planet works and even the very origins of the universe. Research on the Southern Ocean and the Antarctic ice sheets is becoming increasingly urgent not only for understanding the future of the region but also its interconnections with and impacts on many other parts of the globe.
Prepublication: 978-0-309-37784-3
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 02, 2015, 10:07:55 PM
I was having trouble getting a Sentinel shot to line up, so chose to take a look at Worldview.  It looks to me like the whole of Thwaits moved recently.  I looked at some nearby areas, and saw no similar shift, so I don't think it's some sort of data error.

Here is a Gif looking at 2013, 2014 and then 2 recent shots.  Don't pay as much attention to the calving front as to the surface elements on the right side.  I'd be happy to be shown that I am but a crude ignoramus in this case.  Click is required.

Edit:  I tried looking between Sep 22 and Oct 1 versus Sep 24 and Oct 1, and saw little if any motion, which leads me to believe there is some sort of matching error.  Or could it be a tidal influence?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 02, 2015, 11:40:46 PM
solartim27,

I provide that attached first image of Thwaites Terra Oct 2 2014 and the second image of a blue filter Thwaites Aqua Oct 3, 2015.

These images indicate to me that the grounded iceberg at the outboard end of the residual Thwaites Ice Tongue has likely fractured and moved outward.  If so this is a bad sign for the stability of the residual Thwaites Ice Tongue, the nearby iceberg mélange and for Thwaites itself, this coming austral summer.

Best,
ALSR

Edit: The third image of Thwaites Eastern Ice Shelf & Ice Residual Tongue is from Sentinel 1a on Sept 26 2015, showing that the grounded iceberg is starting to move outward by that date.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 03, 2015, 10:37:55 PM
Here is a Sentinel gif from Aug 24 to Oct 3.  Time to invest in companies that make water wings?  I estimate the verticle edge to cover about 80 miles.

I left it as a large size, so click to animate.

Correction, should be Aug 28
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 04, 2015, 12:58:40 AM
Here is another gif, zoomed in a bit, and shifted to include the large ice island.  Has anyone researched developing gills like in the movie waterworld yet?

Click to animate.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 04, 2015, 05:35:51 PM
Here is a Sentinel gif from Aug 24 to Oct 3.  Time to invest in companies that make water wings?  I estimate the verticle edge to cover about 80 miles.

I left it as a large size, so click to animate.

Correction, should be Aug 28

solartim27,

Thanks for the great animation, which to my eyes indicates not only that the grounded iceberg at the outer end of the residual Thwaites Ice Tongue has slide seaward & may have become ungrounded, but also that:
1. The ice stream feeding the Thwaites Ice Tongue has surged downstream.
2. The advection of warm CDW (possibly associated with our strong El Nino event) as created a polynyas at the seaward end of the Thwaites Ice Tongue, which is most likely contributing to high rates of basal ice melting for the glacial ice in this area.
3. The surge of the residual Thwaites Ice Tongue debris field is prying a large iceberg at the Southwest corner of the base of the Eastern Thwaites Ice Shelf, ETIS; which could accelerate a major calving event for the ETIS possibly as early as this coming austral summer.
4. During the August 28 to Oct 3 timeframe (which the illustrated surge apparently occurred) the local winds were directed offshore, which probably accounts for the widespread movement of the icebergs in the mélange to west of the residual Thwaites Ice Tongue (& also indicating how weak the sea ice is in this area, possibly due to basal melting).

Best,
ASLR
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 14, 2015, 06:19:26 PM
The attached Aqua image of Thwaites taken Oct 14 2015, indicates to me that the mélange of icebergs forming the residual Thwaites Ice Tongue, continues to move seaward, and that the polynyas at the seaward end of the Ice Shelf/residual Ice Tongue indicate to me that there is substantial advected warm CDW in this area (melting the local sea ice)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 17, 2015, 09:17:52 PM
I provide the attached Aqua image of Thwaites for Oct 16 2015, because it is clearer than the images on Oct 15 or 17, and as it indicates that the previously grounded iceberg at the seaward end of the residual Thwaites Ice Tongue is not only slowly moving seaward but also westward.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 18, 2015, 09:19:18 PM
No big change, still lots of motion.  Had a nice match between Oct 6 and 18 Sentinel shots.  I estimate the calving is 1km by 2 km.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 18, 2015, 11:49:49 PM
Here's the area zoomed in a bit, again Oct 6 to 18.  I believe the  top of this image would be around the lower right corner of the Aqua images above posted by ASLR.  Left it as a larger size, so will need a click to animate.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 22, 2015, 11:10:35 PM
There is too much cloud cover today for any clear satellite images of the ASE; so instead I provide the attached Earth Surface Wind & MSLP Map (from nullschool) for Oct 22 2015; showing how the ABSL is perfectly positioned so that surface winds are driving warm CDW directly into the ASE, thus promoting basal Ice Shelf melting and grounding line retreat for associated marine glaciers.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 27, 2015, 07:49:03 PM
Here is an overview of the Thwaites area from Oct 3 to 27.  Click to animate.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 30, 2015, 09:26:23 PM
Nice cloud free day at PIG.  here is a gif from Sep 22 to Oct 30. 

Doesn't animate for me, it should though, weird. ( Clicking doesn't work either ) It's still a nice clear shot though.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 01, 2015, 07:23:08 PM
If you compare the attached Terra image of Thwaites for Nov 1 2015 with the comparable Oct 16 2015 image shown in Reply #157, it is clear that the iceberg that was previously pinned at the seaward end of the residual Thwaites Ice Tongue in now moving westward, indicating that it is no longer pinned and may likely float away when the surrounding sea ice melts this coming austral summer.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 02, 2015, 04:39:15 PM
The attached nullschool image issued today shows the Earth Surface Wind & Temperature Map forecast for Nov 4 2015; illustrating how our current Super El Nino event can both telecommunicate tropic atmospheric energy, and the surface winds can direct warm CDW, directly into the ASE where it will accelerate ice mass loss from key marine glaciers there, including PIG & Thwaites
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 02, 2015, 05:34:35 PM
Today's Terra image of the Thwaites Ice Shelf and Residual Ice Tongue, show that the local sea ice is beginning to fracture:
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 04, 2015, 07:55:11 PM
What is the background on the big berg, and am I right thinking that it is about 20 miles by 60 miles?  I assume it is an older part of Thwaites.  The southern part moved alot, possibly still pinned on the bottom offscreen.

Toggling worldview between the 3rd and 4th makes it look like it's blowing back towards land, but there seems to be an alignment error zooming out to a larger area.  The current wind certainly makes that possible.

Gif dates are Oct 27 to Nov 3
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 04, 2015, 10:52:37 PM
What is the background on the big berg, and am I right thinking that it is about 20 miles by 60 miles?  I assume it is an older part of Thwaites.  The southern part moved alot, possibly still pinned on the bottom offscreen.

Toggling worldview between the 3rd and 4th makes it look like it's blowing back towards land, but there seems to be an alignment error zooming out to a larger area.  The current wind certainly makes that possible.

Gif dates are Oct 27 to Nov 3

I think that what you are showing broke-off from the Thwaites Ice Tongue in 2002, and think that it is about 30 miles by about 17 miles in plan dimensions.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 13, 2015, 08:36:12 AM
Thwaites has a new calving, and a big crack advance.  Dates are 11/11 and 10/30.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 14, 2015, 10:19:58 PM
Had a nice clear day for world view.  Here is a gif from 11/3 to 11/14.  I left it large so that you could see the changes, so click to animate
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 24, 2015, 09:51:56 PM
Cross posted from the PIG thread, because I noticed the tabular bergs to the northwest(?) (or on the right about 1/2 way down) breaking up like the recent Zachariae Isstrom thread.  Here is the small gif, for the full size one go to the PIG post.
The pinned berg is showing a good bit of rotation on todays world view.

Meanwhile, in case you've missed the Thwaites thread, there's going to be some more calving there soon, and the big berg off of there is moving out.  Here are two of the same gifs from Oct 24 to Nov 11, one should animate, and one is saved full size (2.7 Mb) if you want to zoom in closer.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 25, 2015, 11:28:10 PM
Pollard et al. (2015) looked to the Pliocene for an example of abrupt SLR associated with Marine Ice Sheet Instability, MISI; while Hansen et al. (2015) turned to the Eemian for another example abrupt SLR due to MISI.  Unfortunately, the further back in time that modelers look to calibrate their projections the more uncertainties creep into the MISI response issue (giving denialist wiggle room for doubt).  However, one underutilized opportunity to calibrate ice sheet models with cliff failure mechanisms is the Holocene Optimum when the Jakobshavn Glacier abruptly retreated down the sill of its fjord shown in the first attached image.  Ice sheet models (with cliff failure mechanisms) calibrated to match this relatively recent event could then be applied to both the PIG and the Thwaites Glacier cases beginning around 2040 (see Replies #406, 408, 418 and 449-453 in the "PIG has Calved" thread for recent discussions of the timing of cliff failure for the PIG and Replies #5 and 13 in this thread for discussion of the timing of cliff failures for the Thwaites Glacier).

With a hat-tip to Sleepy's Reply #115 in the "what's new in Greenland?" thread:
(1) The first linked reference [Ouellet-Bemier et al. (2014), see the second image for the study area], points out that following a few thousand year long period while Disko Bugt was cleared of ice from about 10,000 years ago to about 7,300 year ago, there came an abrupt ice mass loss event from as the Jakobshavn Glacier retreated down the sill shown in the first image circa 7,300 years ago (near the Holocene Optimum). 
(2) The second linked reference [Kelley et al. (2013), see the third image for the study area] provides more details of the moderately dynamic ice mass loss from Disko Bugt from 10,800 to about 9,200 years ago.
Again, modelers such as Gomez, DeConto, Pollard and Alley should take advantage of this relatively recent example of a cliff failure driven abrupt ice mass loss event down a sustained negative slope:

Marie-Michèle Ouellet-Bemier, Anne de Vernal, Claude Hillaire-Marcel and Matthias Moros (September 2014), "PALEOCEANOGRAPHIC CHANGES IN THE DISKO BUGT AREA, WEST GREENLAND, DURING THE HOLOCENE", University of Quebec at Montreal, Canada.

http://www.archipel.uqam.ca/6996/1/M13491.pdf (http://www.archipel.uqam.ca/6996/1/M13491.pdf)

Extract: "In surface waters of the Disko Bugt, the northward penetration of the WGC likely occurred at about 7300 cal. yr BP as shown by the dinocyst-based reconstruction of SSTs and sea ice cover.



Data indicate glaciomarine conditions until -10 000 cal. yr BP while the earliest evidence of some Atlantic influence through the WGC appeared in deep water, when the benthic foraminifer Islandiella norcrossi was first recorded in the core. The WGC influence was recorded much later in surface waters, which were characterized locally by cold conditions with a dense ice cover until -7300 cal. yr BP, likely because of important discharge of ice and meltwater from the GIS."


Also see:

Samuel E. Kelley, Jason P. Briner and Nicolás E. Young (2013), "Rapid ice retreat in Disko Bugt supported by 10Be dating of the last recession of the western Greenland Ice Sheet", Quaternary Science Reviews, 82, pp. 13 to 22

http://www.uib.no/sites/w3.uib.no/files/attachments/kelley_13.pdf (http://www.uib.no/sites/w3.uib.no/files/attachments/kelley_13.pdf)

Abstract: "Due to rising sea levels and warming ocean currents, marine-based sectors of the Greenland and Antarctic ice sheets are particularly vulnerable to warming climate. Reconstructions of the timing of marine based ice margin fluctuations in Greenland during the early Holocene can provide context for historical and modern observations of ice-sheet change. Here, we generate a 10Be chronology of ice-sheet retreat through Disko Bugt, western Greenland. Our new chronology, consisting of twelve 10Be ages from sites surrounding and within Disko Bugt, fills a gap in the history of the western margin of the Greenland Ice
Sheet and allows for a continuous composite record of ice-margin recession between the continental shelf break and the current margin. We constrain the onset of ice-margin retreat from outer Disko Bugt to 10.8 _ 0.5 ka. When combined with previous chronologies, these results place the final Greenland Ice
Sheet retreat out of Disko Bugt onto land at Jakobshavn Isfjord and Qasigiaanguit at 10.1 _ 0.3 ka, and later at 9.2 _ 0.1 ka in southeastern Disko Bugt. The rate of retreat during this time period is between ~ 50 to 450 m a_1 for central Disko Bugt and ~50 to 70 m a_1 along the southern coast of Disko Bugt.
Deglaciation of Disko Bugt occurred ~1000 years later than in neighboring Uummannaq Fjord to the north. This asynchrony in the timing of deglaciation suggests that local ice dynamics played an important role in the retreat of the Greenland Ice Sheet from large marine embayments in western Greenland."

Conclusions: "New 10Be ages from around Disko Bugt, western Greenland, place the deglaciation of western Disko Bugt at 10.8 _ 0.5 ka, with the ice margin reaching the eastern coast of Disko Bugt near Ilulissat at 10.1 _0.3 ka and in southeastern Disko Bugt at 9.2 _ 0.1 ka.
This chronology yields a retreat rate between ~50 and 450 m a_1 across central Disko Bugt. This rate indicates that ~ 25% of the overall retreat between the shelf edge and the current position occurred in as little as 700 years. We suggest this retreat was the result of internal ice dynamics acting upon an ice sheet driven out of equilibrium by climatic factors. These findings further emphasize the ability of marine sectors of ice sheets to change rapidly due to ice dynamics in warming climates (e.g. Kjær et al., 2012). Our chronology fills a gap in the current understanding of the early Holocene behavior of the GrIS in Disko Bugt, and provides a dataset that completes a history of a western GrIS margin spanning from the continental shelf to the present ice position, and from the latest Pleistocene through the Holocene."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on December 09, 2015, 07:36:28 PM
The cracks at Thwaites have calved off, and the large berg continues to float away.
Gif from Dec 2 to Dec 9.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on December 09, 2015, 09:34:27 PM
Here's a zoomed in gif from the previous post.  Looking at Worldview, I estimate the vertical scale to be around 10 miles.  Anyone have a better measurement?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 22, 2015, 11:18:49 PM
The two attached Sentinel images of Thwaites from Nov 19 and Dec 20 2015, respectively, indicate that the pinned iceberg at the outer end of the residual Thwaites Ice Tongue is moving westward and slightly northward, thus relieving compressive stresses from the smaller icebergs within the body of the residual Thwaites Ice Tongue.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 28, 2015, 05:54:03 PM
The attached mosaic shows that the ASE (Pine Island Bay) sea ice is starting to break-up; which might eventually allow some of the icebergs trapped in the fast sea ice to float away.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 05, 2016, 12:52:33 AM
As the Landsat8 image of the Thwaites Ice Shelf/Tongue for Jan 4, 2016 is now available, I provide the attached extract to show that the adjoining sea ice is rapidly melting and will likely start to release entrapped icebergs before too long.  For those who are interested a comparable image for the PIIS on Jan 4 2016 is also available for download (but I am not posting it as it indicates to me that another major calving event for the PIIS will not result in a major iceberg that can float away before the austral Spring of 2016)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 19, 2016, 05:07:11 PM
The first attached images shows a Sentinel image showing that the sea ice in the Thwaites/Haynes/Pope area is now breaking up sufficient to release many previously trapped icebergs.  With continued melting of more fast sea ice, I expect more and more currently trapped icebergs to float away, which will reduce the associated buttressing action from this ice mélange in front of these key marine glaciers.  The second attached image is from Google Earth showing a rotated view of this area from several years ago (provided for comparison):
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 20, 2016, 11:52:22 PM
The first attached Terra image for Jan 20 2016 has a lot of clouds, but I think that it clearly shows a major loss of sea ice to the west of Thwaites (since the 18th).

The second image shows the Earth 1000-hPa Wind & Temperature Map for Jan 20 2016, showing anomalously high temperatures along the coastline in the ASE.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on February 15, 2016, 09:14:30 PM
Another 'small' calving at Thwaites.  I was surprised it took this long to develop.  It looks to me like it might just be the start of a larger event?  Dates are Feb 8 to Feb 15.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on February 17, 2016, 07:39:36 PM
Worldview had a nice clear view of the last calving today, so I went back to Jan 29 for a comparision shot.  Added a frame of Jacobshavn Isbrae for comparision purposes.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 22, 2016, 07:59:20 PM
I am posting the attached Aqua image of the Thwaites area from Feb 22 2016, mainly because it has been cloudy there and this shows the current status of the adjoining sea ice.  We will see whether any of it floats away before the austral winter refreeze begins:
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on March 02, 2016, 08:41:56 PM
Here is a small calving from an area that had no visible cracks.  There also seems to be a some advance over the whole area, but part of that may be an imprecise overlay on my part.  Calved bit about 1 mile long?
Dates are Feb 24 and Mar 2.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 16, 2016, 04:03:46 PM
While sidd has previously discussed the linked reference in the "What's new in Antarctica?" thread, I repost it here due its particular importance to both the Pine Island and Thwaites ice shelves:

Karen E. Alley, Ted A. Scambos, Matthew R. Siegfried & Helen Amanda Fricker (2016), "Impacts of warm water on Antarctic ice shelf stability through basal channel formation", Nature Geoscience, doi:10.1038/ngeo2675

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2675.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2675.html)

Abstract: "Antarctica’s ice shelves provide resistance to the flow of grounded ice towards the ocean. If this resistance is decreased as a result of ice shelf thinning or disintegration, acceleration of grounded ice can occur, increasing rates of sea-level rise. Loss of ice shelf mass is accelerating, especially in West Antarctica, where warm seawater is reaching ocean cavities beneath ice shelves. Here we use satellite imagery, airborne ice-penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding Antarctica. The highest density of basal channels is found in West Antarctic ice shelves. Within the channels, warm water flows northwards, eroding the ice shelf base and driving channel evolution on annual to decadal timescales. Our observations show that basal channels are associated with the development of new zones of crevassing, suggesting that these channels may cause ice fracture. We conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas."

See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/03/14/antarcticas-ice-is-being-carved-up-from-below/ (https://www.washingtonpost.com/news/energy-environment/wp/2016/03/14/antarcticas-ice-is-being-carved-up-from-below/)
Extract: "In the new study, led by Karen Alley of the National Snow and Ice Data Center at the University of Colorado in Boulder, the researchers document that the warm ocean water that’s undermining West Antarctica from below may also be weakening its ice shelves. It appears to be slowly carving deep channels into their bases, cavities ranging from 50 to 250 meters in vertical extent.
These channels appear to be formed as the warm water that hits the grounding line then bursts upward in a plume, combined with meltwater, and cuts into the ice shelf from below, Alley said. “They’re kind of like upside down rivers, or streams. Instead of the water flowing downhill, it’s flowing uphill, because it’s buoyant,” she says."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: wili on March 17, 2016, 11:45:27 PM
(Sorry if this has already been posted)

Quote
When I asked Richard Alley, almost certainly the most respected glaciologist in the United States, whether he would be surprised to see Thwaites collapse in his lifetime, he drew a breath. Alley is 58.

‘‘Up until very recently, I would have said, ‘Yes, I’d be surprised,’ ’’ he told me. ‘‘Right now, I’m not sure. I’m still cautiously optimistic that in my life, Thwaites has got enough stability on the ridge where it now sits that I will die before it does. But I’m not confident about that for my kids. And if someday I have grandkids, I’m not at all confident for them.’’

http://mobile.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html?referer=&_r=1 (http://mobile.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html?referer=&_r=1)

So he's not sure that he would be surprised if Thwaites collapsed within the next 20-30 years!

I find that rather...surprising!
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 24, 2016, 05:20:40 PM
The accompanying images come from the linked World Meteorological Organization's Polar Space Task Group (PSTG) reports.  The second link provides the first two images.  The first image indicates that thru 2012 most of the ice mass loss in Antarctic Ice Shelves has been concentrated in West Antarctica; which means that the associated marine glaciers are losing buttressing faster than other Antarctic marine glaciers.  The second image indicates that from 2010 to 2013 the WAIS contributed 0.45mm/yr to SLR.  The last two images come from the third link.  The third image indicates that the ice velocities for the PIG accelerated during the period when the groundling was retreating down the negative slope of the seafloor and then stabilized thru August 2015.  The fourth image shows that while the grounding line for the Thwaites Glacier has not yet reached the negative slope of the seafloor; nevertheless, its ice velocities have accelerated since 2006 as it has progressively lost buttressing from the Thwaites Ice Tongue:

http://www.wmo.int/pages/prog/sat/pstg_en.php (http://www.wmo.int/pages/prog/sat/pstg_en.php)


http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_06_EC-PHORS-ppt.pdf (http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_06_EC-PHORS-ppt.pdf)


http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_13-01_BScheuchl-Ice-Sheets-Final.pdf (http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_13-01_BScheuchl-Ice-Sheets-Final.pdf)

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on March 28, 2016, 06:05:30 PM
The attached Sentinel 1a image of Thwaites for March 25 2016, shows that the grounded iceberg at the seaward end of the residual Thwaites Ice Tongue has recently sustained a major calving event.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Yuha on March 29, 2016, 02:20:12 AM
The attached Sentinel 1a image of Thwaites for March 25 2016, shows that the grounded iceberg at the seaward end of the residual Thwaites Ice Tongue has recently sustained a major calving event.

The calving event actually took place already in January as shown in this animation of MODIS Terra images from January 9-12. For some reason the big piece never completely separated until now.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on April 04, 2016, 05:45:39 AM
To me the most significant hazard is Thwaites. Any teams trying to send submersibles under there in the next couple years ? A thermal profile a la Dutreux for PIG would be very nice.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 04, 2016, 09:56:47 AM
To me the most significant hazard is Thwaites. Any teams trying to send submersibles under there in the next couple years ? A thermal profile a la Dutreux for PIG would be very nice.

Per the two attached images (that you are familiar with) DeConto & Pollard (2016) seem to believe that the Antarctic Peninsula (AP), the Amundsen Sea Embayment (ASE) outlet glaciers (including the PIG), the Totten (T), and the Siple Coast (SC) and Weddell Sea (WS) grounding zones, will reach peak discharge before peak discharge occurs for the deep Thwaites Glacier basin (TG).  But of course they could be mixed-up in their order, and/or discharge magnitudes (or maybe TG just discharges for a very long time, or not).
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on April 20, 2016, 08:27:19 PM
I think it would be safe to adjust the dates on this thread earlier by a decade or two.

Here is a nice lineup from Apr 7 to 19 showing lots of motion across most of the glacier, one file reduced in size, one original size (2.4 Mb).

Source:  http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160419T044345_3B62_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160419T044345_3B62_S_1.final.jpg)

and S1A_EW_GRDM_1SSH_20160407T044345_1C67_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 22, 2016, 05:06:15 PM
I think it would be safe to adjust the dates on this thread earlier by a decade or two.

solartim27,

Thanks for the animation showing that the pinned iceberg is beginning to move; however, while you might be right that cliff faces may occur at the base of the residual Thwaites Ice Tongue by 2020, that is a far different matter than: (a) having cliff faces across the entire 50km Thwaites Gateway and (b) having hydrofracturing occurring which requires GMST being 2 to 3C above pre-industrial.  As previously noted, the linked article discusses how NOAA notified the insurance industry  that sea level might possibly rise by 3m in the 2050-2060 timeframe due to instabilities in the WAIS; which reasonably matches my 2040-2060 timeframe for the end of the initial stage of PIG/Thwaites collapse.

http://www.insurancejournal.com/news/national/2016/04/12/405089.htm (http://www.insurancejournal.com/news/national/2016/04/12/405089.htm)

Extract: "Think sea level rise will be moderate and something we can all plan for? Think again.
Sea levels could rise by much more than originally anticipated, and much faster, according to new data being collected by scientists studying the melting West Antarctic ice sheet – a massive sheet the size of Mexico.
That revelation was made by an official with the National Oceanic and Atmospheric Administration on Tuesday at the annual RIMS conference for risk management and insurance professionals in San Diego, Calif.
The conference is being attended by more than 10,000 people, according to organizers. It was day No. 3 of the conference, which ends Wednesday.
Margaret Davidson, NOAA’s senior advisor for coastal inundation and resilience science and services, and Michael Angelina, executive director of the Academy of Risk Management and Insurance, offered their take on climate change data in a conference session titled “Environmental Intelligence: Quantifying the Risks of Climate Change.”
Davidson said recent data that has been collected but has yet to be made official indicates sea levels could rise by roughly 3 meters or 9 feet by 2050-2060, far higher and quicker than current projections. Until now most projections have warned of sea level rise of up to 4 feet by 2100.
These new findings will likely be released in the latest sets of reports on climate change due out in the next few years.
“The latest field data out of West Antarctic is kind of an OMG thing,” she said.
Davidson’s purpose was to talk about how NOAA is sharing information with the insurance community and the public, and to explain how data on climate change is being collected.
She explained that reports like those from the Intergovernmental Panel on Climate Change and the National Climate Assessment, which come out roughly every five years, are going on old data.
By the time the scientists compiling those reports get the data it’s roughly two years old, because it took those gathering the data that long to collect it. It takes authors of the reports a few years to compile them.
“By the time we get out the report, it’s actually synthesizing data from about a decade ago,” she said.
Angelina’s focus was also on the data. He spoke about the ongoing development of the Actuaries Climate Index and the Actuaries Climate Risk Index.
The goals of the projects are to create climate change indices that reflect an actuarial perspective, to create an index that measures changes in climate extremes, use indices to inform the insurance industry and the public, and promote the actuarial profession by contributing statistically to the climate change debate.
So far their findings show the climate is definitely changing – though neither Davidson nor Angelina addressed the cause of this change, which they said was not the purpose of their talk.
Angelina said a new way of looking at weather is required when dealing with climate change, and that just looking at averages isn’t enough to give an accurate picture of climate change and the risk it presents.
The projects he’s involved with have instead looked at weather extremes.
“By looking at extremes I can actually acknowledge that I have a problem,” he said.
He used the notorious Bell Curve grading system to illustrate his point.
The goal of the curve is to achieve a 70 percent average among students. But if a teacher got to that 70 percent figure by having half the students failing poorly and half doing excellently, there’s a problem: half of the students aren’t getting it.
Looking at extreme temperature indices from more than 40 years ago and now, “things are different,” he said.
So too are days of excessive rain, and excessive dry days, wind power and the sea level index.
“They’re all up,” he said.
He added: “We’re in a different climate. The climate has changed.”

The main phase of PIG/Thwaites collapse is discussed here (which includes cliff failures & hydrofractuing; which I called the Thwaites Effect & melt ponds):

http://forum.arctic-sea-ice.net/index.php/topic,85.0.html (http://forum.arctic-sea-ice.net/index.php/topic,85.0.html)

Edit: For what it is worth I re-attach my expectation from three years ago of what the grounding lines this area might look like by 2040.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on June 02, 2016, 07:14:46 AM
For years now I have been whining about the lack of full stokes analyses for ice flow (mostly because i am too lazy to attempt the effort.) Lo, and behold

http://www.the-cryosphere-discuss.net/tc-2016-101/ (http://www.the-cryosphere-discuss.net/tc-2016-101/)

Usual suspects. Open access. Full Stokes(2D flowband, but perhaps they will do 3D). Top and bottom crevasses (but no surface melt or hydrofrac yet). Experiments with basal melt changes. Disparaging remarks about comparison models. Read all about it.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on June 02, 2016, 05:11:15 PM
For years now I have been whining about the lack of full stokes analyses for ice flow (mostly because i am too lazy to attempt the effort.) Lo, and behold

sidd,
Thanks for the great catch.  I seems like every time that we improve our models the Thwaites looks less and less stable.  For those who do not like to click, I provide the following abstract:
Best,
ASLR

Yu, H., Rignot, E., Morlighem, M., and Seroussi, H.: Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-101, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-101/ (http://www.the-cryosphere-discuss.net/tc-2016-101/)

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and iceberg calving.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: LRC1962 on June 02, 2016, 06:13:46 PM
If posted elsewhere sorry. Abrupt Sea Level Rise Looms
As Increasingly Realistic Threat (http://e360.yale.edu/feature/abrupt_sea_level_rise_realistic_greenland_antarctica/2990/)
Quote
For the Pliocene era 3 million years ago, for example — when seas were dozens of feet higher than today — older models estimated that a partially melting Antarctic added about 23 feet to global sea level rise. The new model increased Antarctica’s contribution to sea level rise during the Pliocene to 56 feet.
Quote
Even DeConto admits that, under the model used in his paper, the timing and pace of Antarctica’s ice loss is “really uncertain” — it could be a decade or two, or three or four, before these dramatic processes start to kick in, he says. “The paper just shows the potentials, which are really big and really scary,” says DeConto. But Scambos and other observers call DeConto’s numbers “perfectly plausible.”
Two articles referred to:
Contribution of Antarctica to past and future sea-level rise (http://www.nature.com/nature/journal/v531/n7596/full/nature17145.html)
Quote
Abstract
Abstract• Change history• References• Author information• Extended data figures and tables• Supplementary information
Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6–9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics—including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs—that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.
Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming could be dangerous (http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf)
Quote
Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on June 12, 2016, 09:18:19 PM
General advance, with one 'small' calving towards the center of the image.
Dates are May 30 and Jun 11
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final
S1A_EW_GRDM_1SSH_20160530T045153_044B_S_1.final
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on June 30, 2016, 11:37:58 PM
More ice movement, more calving.  Jun 30 vs Jun 11
S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 10, 2016, 11:50:45 PM
The linked ESA website provides both Sentinel 1a photos and ice velocity data for Thwaites Glacier (see first two attached images from March 29 2016, of along flow and across flow ice speeds) and for PIG (see last two attached images from April 26 2016).  While all images show that these two marine glacier are fluctuating about average conditions, the across flow velocities for Thwaites appear to indicate some local acceleration near the base of the residual ice tongue.  The data is regularly updated and may soon including information from Sentinel 1b:

http://www.cpom.ucl.ac.uk/csopr/iv/index.html (http://www.cpom.ucl.ac.uk/csopr/iv/index.html)

For Thwaites
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4)

For PIG
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=3 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=3)


See also:
http://www.bbc.com/news/science-environment-36051112 (http://www.bbc.com/news/science-environment-36051112)

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on July 17, 2016, 09:26:36 PM
Another big calving with general advance.  One wide area gif, and one zoomed in.
6/30 to 7/17.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on July 26, 2016, 06:04:09 AM
Another week, another calving.  Jul 17 to Jul 24.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg)

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg)

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 28, 2016, 04:50:17 PM
For Thwaites, I concur with the conclusion (of the linked open access reference) that: "… basal hydrological system may not be the most important feature of the ice sheet for models to capture…"

Smith, B. E., Gourmelen, N., Huth, A., and Joughin, I.: Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-180, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-180/ (http://www.the-cryosphere-discuss.net/tc-2016-180/)
http://www.the-cryosphere-discuss.net/tc-2016-180/tc-2016-180.pdf (http://www.the-cryosphere-discuss.net/tc-2016-180/tc-2016-180.pdf)

Abstract: "We present conventional and swath altimetry data from Cryosat-2 revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica. Much of the drainage happened in less than six months, with an apparent connection between three lakes spanning more than 130 km. Hydropotential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed large-scale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events, suggesting that there are important limitations in the ability of hydropotential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."


Extract: "While our data suggest water is routed in ways not presently accounted for in most ice sheet models, it also indicates that the basal hydrological system may not matter much. The basal water system is able to sequester large volumes of water over years which it then releases rapidly with little or no apparent change in glacier speed. This insensitivity suggests that the details of the basal hydrological system may not be the most important feature of the ice sheet for models to capture, especially now that data assimilation techniques allow us to infer the dynamic properties of the bed (e.g., the coefficients in a sliding law) directly (Joughin et al., 2010; Morlighem et al., 2010)."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 19, 2016, 06:35:11 PM
The linked reference is entitled: "Grounding Line Variability and Subglacial Lake Drainage on Pine Island Glacier, Antarctica", & presents state-of-the art findings from the past 6 years on these topics:

Ian Joughin, David E. Shean, Ben E. Smith & P. Dutrieux (17 August 2016), "Grounding Line Variability and Subglacial Lake Drainage on Pine Island Glacier, Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL070259

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070259/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL070259/abstract)

Abstract: "We produced a 6-year time series of differential tidal displacement for Pine Island Ice Shelf, Antarctica, using speckle-tracking methods applied to fine-resolution TerraSAR-X data. These results reveal that the main grounding line has maintained a relatively steady position over the last 6 years, following the speedup that terminated in ~2009. In the middle of the shelf, there are grounded spots that migrate downstream over the 6-year record. Examination of high-resolution DEMs reveals that these grounded spots form where deep keels (thickness anomalies) advect over an approximately flow-parallel bathymetric high, maintaining intermittent contact with the bed. These datasets also reveal several subsidence and uplift events associated with subglacial lake drainages in the fast-flowing region above the grounding line. Although these drainages approximately double the rate of subglacial water flow over periods of a few weeks, they have no discernible effect on horizontal flow speed."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on August 26, 2016, 02:42:41 AM
Nice present from Schoof and others, extending his model of marine ice sheet instability  to deformable beds. Loved it.

doi:10.5194/tc-10-1883-2016

Coulomb plastic till, with basal melt and freeze. Competent thermo (as always.) Binge and purge oscillation cycles. Stability regimes. Grounding line persistence on retrograde slopes. Implications for Antarctica.  " ... we step away from the limiting confines of the classical marine ice-sheet instability."

open access. read all about it.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Lennart van der Linde on August 26, 2016, 08:59:20 AM
Thanks for the tip, sidd.
Here's the full paper:
http://www.the-cryosphere.net/10/1883/2016/tc-10-1883-2016.pdf (http://www.the-cryosphere.net/10/1883/2016/tc-10-1883-2016.pdf)

Would this imply that the MISI on a retrograde bed could be less severe, depending on the kind of bed, than thought based on the simpler model? Or rather that the behaviour of such a grounding line could be more variable, without really slowing down the overall collapse of the ice stream/sheet? Or too early to tell?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on August 26, 2016, 07:20:16 PM
"The grounding line of an ice stream retreating onto a section of retrograde slope may continue to retreat irreversibly or may pause for centuries during stagnation before re-advancing onto the prograde slope."

Plastic beds could slow down the retreat is my takeaway. That is what i suspected. But not something to count on.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on August 26, 2016, 10:48:30 PM
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 27, 2016, 06:26:13 PM
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?

I note that the Schoof paper also does not address the influence of hydrofracturing on the destruction of ice shelves in the Weddell, Ross, Bellingshausen and Amundsen Sea Sectors when the GMST anom gets into the 2 to 2.7C range.  Once the ice shelves are degraded (or lost) the adjoining marine glacial ice flow will accelerate 4 to 7 times, which will effect the stability of the relevant grounding line retreat.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 27, 2016, 08:11:28 PM
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?

sidd,
Rignot's comments in the linked Washington Post article towards the end of this post, addresses the issue that you raise about the systemic impact of warmer CDW on both accelerating the melting of key Antarctic marine glaciers and the associated impact on the positive ice-climate feedback mechanism projected by Hansen et al (2016); which indicates that this process has already started.
Best,
ASLR

The linked open access reference studies AABW production in the Cape Darnley Polyna, adjoining Prydz Bay in East Antarctica. The reference concludes that: "Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."  The reference implies that the AABW is the "canary in the coal mine" for Hansen et al (2016)'s slowing of the global thermohaline circulation, which should result in a positive ice-climate feedback that may increase the planetary energy imbalance as indicated by the attached Figure 7 from Hansen et al (2016):


G. D. Williams, L. Herraiz-Borreguero, F. Roquet, T. Tamura, K. I. Ohshima, Y. Fukamachi, A. D. Fraser, L. Gao, H. Chen, C. R. McMahon, R. Harcourt & M. Hindell (August 23 2016), "The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay", Nature Communications, Volume: 7, Article number: 12577, doi:10.1038/ncomms12577

http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html (http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html)

Abstract: "A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate."

Extract: "There has been a lot of attention recently on the decadal-scale impact of icescape changes to AABW, resulting from major ice front calving events in polynyas regions, such as along Adélie Land after the calving of the Mertz Glacier. This study suggests the more ubiquitous process of enhanced ocean/ice shelf interaction could be a far greater long-term threat to AABW production. Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."

See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/08/23/how-elephant-seals-in-antarctica-are-helping-to-reveal-another-threat-caused-by-melting-ice/?utm_term=.42f9a2381634 (https://www.washingtonpost.com/news/energy-environment/wp/2016/08/23/how-elephant-seals-in-antarctica-are-helping-to-reveal-another-threat-caused-by-melting-ice/?utm_term=.42f9a2381634)

Extract: "The new study “significantly improves our understanding of the details of bottom water production around Antarctica,” said Rahmstorf, who was not involved in the new research, by email. “Scientists have long feared that global warming will slow down this vital process of deep and bottom water production, both in the North Atlantic and in Antarctic waters. With too much global warming, a critical threshold could be crossed where this process grinds to a halt, with incalculable and potentially catastrophic consequences for marine life and climate.” 

Rahmstorf isn’t the only researcher concerned about this issue, either. It’s a key component of a recent paper led by former NASA scientist James Hansen, now at Columbia University’s Earth Institute. The paper outlines a dire scenario in which even 2 degrees Celsius of warming above pre-industrial levels could lead to “dangerous” global consequences.
One of the paper’s key points is that rapid melting of both the Antarctic and Greenland ice sheets may not only contribute to dramatic sea-level rise in the next century, but also affect the world’s oceans in profound ways — including freshening the water at the poles and contributing to a slowdown of the oceans’ overturning circulation.
The new paper “tends to confirm one of the principal phenomena that we were drawing attention to: the effect of freshwater from ice shelves reducing [Antarctic bottom water] formation,” Hansen told The Post by email. “We concluded that this process, slowing down on Antarctic bottom water formation, has already begun.”

“While this particular area may not be the hotspot for this kind of activity, the fact that we have all the main players makes it a very unique lab experiment to try to understand how it works,” Williams said. “It provides observational evidence which should renew efforts to look for this happening in more key areas of Antarctica where we do know there’s accelerating melt occurring and where bottom water production is important as well.”"
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on August 27, 2016, 11:45:29 PM
That Robel, Schoof, Tziperman paper does not put in iceshelves or surface melt, hence cannot simulate either ice shelf buttressing or hydrofracture. I do not think the regions explored include ice faces taller than the stability limit, judging from the parameters for ice divide height of 100m, retrograde sections of 80 km at slopes of 1e-4 to 1e-3

The surface temperature is prescribed, so in principle one could raise it above freezing to get surface melt. As for ice shelves, and warmer than freezing seawater at the face, that would be more complicated, since one  has to put in a realistic ocean, instead of  a deus ex oceana who makes the ice thru the grounding line magically go poof.

But I like everything with Schoof's name on it.

I think i posted something about the paper with seals in anoher thread perhaps. Apart from the nice oceanographic data, the movements of the seals are also fascinating.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on August 30, 2016, 10:43:55 PM
The linked reference uses satellite radar interferometry data for the Amundsen Sea Embayment, ASE, into 2016 to determine that: .. ice shelf and glacier retreat in this sector remain unabated."

B. Scheuchl, J. Mouginot, E. Rignot, M. Morlighem & A. Khazendar (29 August 2016), "Grounding line retreat of Pope, Smith, and Kohler Glaciers, West Antarctica, measured with Sentinel-1a radar interferometry data", Geophysical Research Letters, DOI: 10.1002/2016GL069287

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069287/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL069287/abstract)
&
http://onlinelibrary.wiley.com/store/10.1002/2016GL069287/asset/supinfo/grl54607-sup-0001-supplementary.pdf?v=1&s=b625b6d95964be55c06e73d53ca8aa72336c940c (http://onlinelibrary.wiley.com/store/10.1002/2016GL069287/asset/supinfo/grl54607-sup-0001-supplementary.pdf?v=1&s=b625b6d95964be55c06e73d53ca8aa72336c940c)

Abstract: "We employ Sentinel-1a C band satellite radar interferometry data in Terrain Observation with Progressive Scans mode to map the grounding line and ice velocity of Pope, Smith, and Kohler glaciers, in West Antarctica, for the years 2014–2016 and compare the results with those obtained using Earth Remote Sensing Satellites (ERS-1/2) in 1992, 1996, and 2011. We observe an ongoing, rapid grounding line retreat of Smith at 2 km/yr (40 km since 1996), an 11 km retreat of Pope (0.5 km/yr), and a 2 km readvance of Kohler since 2011. The variability in glacier retreat is consistent with the distribution of basal slopes, i.e., fast along retrograde beds and slow along prograde beds. We find that several pinning points holding Dotson and Crosson ice shelves disappeared since 1996 due to ice shelf thinning, which signal the ongoing weakening of these ice shelves. Overall, the results indicate that ice shelf and glacier retreat in this sector remain unabated."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: FishOutofWater on September 01, 2016, 04:28:28 PM
While the AABW formation is declining the heat content and sea surface heights are jumping up off of Florida and the southeastern U.S. The recent rate of sea level rise along the south Florida coast is shocking.

Local sea level rise effects from the rapid increase of oceanic heat discussed by Jim Hansen can happen far more suddenly that global SLR. Ultimately, the global effects are much larger but the local effects can combine with hurricanes and intense cold core storms to accelerate coastal damage. I'm watching Hermine closely.

Yes, Hansen's predictions are starting to verify.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Bruce Steele on September 01, 2016, 04:53:21 PM
Fish, Any chance you might chime in over on the Hansen + 3 meter page ? Appreciate your opinion !
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 14, 2016, 03:34:18 PM
The linked reference provides additional background about the recent sensitivity of the PIG to ocean forcing:

Knut Christianson et. al., (12 October 2016), "Sensitivity of Pine Island Glacier to observed ocean forcing", Geophysical Research Letters, DOI: 10.1002/2016GL070500

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070500/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL070500/abstract)

Abstract: "We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice-sheet instability. Following a subsequent 60% drop in ocean heat content from early 2012 to late 2013, ice flow slowed, but by < 4%, with flow recovering as the ocean warmed to prior temperatures. During this cold-ocean period, the evolving glacier-bed/ice-shelf system was also in a geometry favorable to stabilization. However, despite a minor, temporary decrease in ice discharge, the basin-wide thinning signal did not change. Thus, as predicted by theory, once marine ice-sheet instability is underway, a single transient high-amplitude ocean cooling has only a relatively minor effect on ice flow. The long-term effects of ocean-temperature variability on ice flow, however, are not yet known."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 25, 2016, 07:56:04 PM
While solartim27 has already posted this in the "Surge" thread, I figure the more the merrier, and if Pope accelerates this will reduce the stability of Thwaites.  Also, if it is not clear why ice mass loss from Pope's grounding line is occurring faster than for Thwaites, it may be because the grounding line for Pope is deeper than for Thwaites and the freezing temperature of seawater increases with depth, thus Pope's grounding line has more melting potential:

The linked NPR article is entitled: "Antarctica's Ice Sheets Are Melting Faster — And From Beneath".  I cites unbalanced/unstable basal melt rates for several ice shelves draining into the Amundsen Sea Embayment, at a rate that will likely lead to the eventual collapse of the associated ice shelves and a subsequent acceleration of the associated glaciers (Pope, Smith & Kohler, see the attached image).

http://www.npr.org/sections/thetwo-way/2016/10/25/499206005/antarcticas-ice-sheets-are-melting-faster-and-from-beneath (http://www.npr.org/sections/thetwo-way/2016/10/25/499206005/antarcticas-ice-sheets-are-melting-faster-and-from-beneath)

Extract: "A team from JPL has been studying that grounding line in several places along the edge of the West Antarctic ice sheet. They used radar to look beneath the ice. In particular, overflights have targeted ice shelves along the West Antarctic ice sheet known as the Amundsen Sea Embayment.

They've found that the ice is melting faster than they've ever seen. The researchers believe the cause is warm water circulating beneath the ice shelf. The melting was most pronounced from 2002 to 2009. (The influx of warmer water to the region stalled recently, and the rate of melting seems to have slowed somewhat.)

Khazendar says the more the bottom of the shelves melt, the more ice is exposed to warm water. "It becomes a runaway process," he explains, "which makes it unstable."
Where's the warmer water coming from? The team, whose findings appear in the journal Nature Communications, points to global warming that's heating up the oceans. There's been a spate of research lately showing that Antarctic ice is melting faster than previously thought — and raising global sea levels.

Khazendar says the melting process appears to be irreversible. Polar scientists fear that at some point, the shelves will collapse and Antarctica's glaciers will flow into the sea."


For the reference see:
Khazendar et. al. (Oct 25 2016), "Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica", Nature Communications 7, Article no. 13243, doi: 10.1038/ncomms13243

http://www.nature.com/articles/ncomms13243 (http://www.nature.com/articles/ncomms13243)

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 26, 2016, 01:41:46 AM
...  if Pope accelerates this will reduce the stability of Thwaites.  Also, if it is not clear why ice mass loss from Pope's grounding line is occurring faster than for Thwaites, it may be because the grounding line for Pope is deeper than for Thwaites and the freezing temperature of seawater increases with depth, thus Pope's grounding line has more melting potential:

For those who do not remember the relationship of the PSK glacial basin to the Thwaites glacial basin I re-post the three attached images.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 28, 2016, 01:18:06 AM
Here is a gif of the Thwaites area for 2014, 2015, and today.  After comparing it to the Larsen B gif I made I do not have a warm fuzzy feeling in my gut.  I am leaving it full size because the white on white detail is hard to pick up, so click to animate. 
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 28, 2016, 05:08:58 PM
I found a sentinel from march, so here is a gif of the southern part of Thwaites, closest to PIG, versus today

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg)

and S1A_EW_GRDM_1SSH_20160331T045150_542F_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 07, 2016, 06:37:47 PM
The linked reference is entitled: "A 125-year record of climate and chemistry variability at the Pine Island Glacier ice divide, Antarctica".  The reference find a distinct seasonality to the mineral dust & sea salt in the ice cores.  It will be interesting to see how this seasonal behavior interactions with the risks of hydrofracturing & cliff failure mechanisms if/when GMSTA approaches 2.7C (a threshold identified by DeConto 2016):

Schwanck, F., C. Simões, J., Handley, M., A. Mayewski, P., D. Auger, J., T. Bernardo, R., and E. Aquino, F.: A 125-year record of climate and chemistry variability at the Pine Island Glacier ice divide, Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-242, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-242/ (http://www.the-cryosphere-discuss.net/tc-2016-242/)


Abstract. The Mount Johns (MJ) ice core (79º55' S; 94º23' W) was drilled near the Pine Island Glacier ice divide on the West Antarctic Ice Sheet during the 2008–2009 austral summer, to a depth of 92.26 m. The upper 45 m of the record covers approximately 125 years (1883–2008) showing marked seasonal variability. Trace element concentrations in 2,137 samples were determined using inductively coupled plasma mass spectrometry. In this study, we reconstruct mineral dust and sea salt aerosol transport and investigate the influence of climate variables on the elemental concentrations to the MJ site. The ice core record reflects changes in emissions as well as atmospheric circulation and transport processes. Our trajectory analysis shows distinct seasonality, with strong westerly transport in the winter months and a secondary northeasterly transport in the summer. During summer months, the trajectories present slow-moving (short) transport and are more locally influenced than in other seasons. Finally, our reanalysis trace element correlations suggest that marine derived trace element concentrations are strongly influenced by sea ice concentration and sea surface temperature anomalies. The results show that seasonal elemental concentration maxima in sea-salt elements correlate well with the sea ice concentration winter maxima in the West Amundsen and Ross Seas. Lastly, we observed an increased concentration of marine aerosols when sea surface temperature decreased.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 09, 2016, 05:15:17 PM
The linked reference discusses progress being made in modeling iceberg calving from Thwaites:

Yu, H., Rignot, E., Morlighem, M., and Seroussi, H.: Iceberg calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics, The Cryosphere Discuss., doi:10.5194/tc-2016-249, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-249/ (http://www.the-cryosphere-discuss.net/tc-2016-249/)
http://www.the-cryosphere-discuss.net/tc-2016-249/tc-2016-249.pdf (http://www.the-cryosphere-discuss.net/tc-2016-249/tc-2016-249.pdf)

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that match the distribution of crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of calving events. It is more prominent for glaciers with rapid calving rates than glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining crevasse formation and iceberg calving.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 25, 2016, 02:48:33 PM
Here is a gif of a small calving at the northern end of Thwaites near Haynes glacier.  Oct 28 to Nov 23.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161123T042739_CF1E_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161123T042739_CF1E_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 28, 2016, 06:51:21 PM
The linked reference indicates that the PIIS is calving further upstream than in the past due to oceanic driven disintegration of the northern shear margin mélange and intensified melting with basal crevasses.  As the ocean in this area will remain relatively warm for a long time, this indicates that the PIIS will continue to calve more rapidly than in the past and will calve further and further upstream, with time.  This will cause the buttressing on the SW Tributary Glacier to be reduced, which will help to trigger the acceleration of ice velocities for Thwaites:

Seongsu Jeong, Ian M. Howat & Jeremy N. Bassis (28 November 2016), "Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL071360

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full (http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full)

Abstract: "Pine Island Glacier has undergone several major iceberg calving events over the past decades. These typically occurred when a rift at the heavily fractured shear margin propagated across the width of the ice shelf. This type of calving is common on polar ice shelves, with no clear connection to ocean-ice dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the ice shelf, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the ice mélange that filled the northern shear margin, resulting in ice sheet detachment from this margin. Examination of ice velocity suggests that this internal rifting resulted from the combination of a change in ice shelf stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing."

See also:

http://www.csmonitor.com/Environment/2016/1128/Why-this-Antarctic-ice-shelf-is-breaking-up-from-the-inside-out (http://www.csmonitor.com/Environment/2016/1128/Why-this-Antarctic-ice-shelf-is-breaking-up-from-the-inside-out)

Extract: "The evidence of a deep subsurface rift indicates that a warming ocean likely contributed to the breakup and will likely lead to more significant breaks in the near future."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 01, 2016, 05:46:53 PM
As a follow-on to my last post, the linked Climate Central article is entitled: "Odd Rifts in Antarctic Ice Could Mean ‘Sayonara, Glacier’", and it cites an ocean-ice interaction mechanism that could accelerate the loss of the PIIS and subsequently the loss of the PIG (beyond current consensus projections):

http://www.climatecentral.org/news/rifts-antarctic-ice-sayonara-glacier-20923 (http://www.climatecentral.org/news/rifts-antarctic-ice-sayonara-glacier-20923)

Extract: "The key question for the future of Pine Island Glacier is whether rifts will keep forming in these valleys further and further inland. If they do, more and more icebergs could calve off at a quicker pace than is typical, diminishing the ice shelf and speeding the retreat of the glacier.
The study shows “a new mechanism for potentially rapid collapse,” Mankoff said. “It’s a little bit scary.”
Or, as Howat put it, if this mechanism does continue like this, “then it’s going to be, ‘Sayonara, glacier.’”"
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 03, 2017, 06:23:13 PM
The linked reference is entitled: "In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica", and it provides field data (in the 2008 to 2014 timeframe) to help better understand ice mass loss trends for the PIG.

Shean, D. E., Christianson, K., Larson, K. M., Ligtenberg, S. R. M., Joughin, I. R., Smith, B. E., and Stevens, C. M.: In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-288, in review, 2017.


http://www.the-cryosphere-discuss.net/tc-2016-288/ (http://www.the-cryosphere-discuss.net/tc-2016-288/)

Abstract. In the last two decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to ice-shelf basal melt and marine ice-sheet instability. To better understand these processes, we analyzed 2008–2010 and 2012–2014 in-situ GPS records for PIG to constrain surface mass balance, firn compaction, and basal melt. We computed time series of horizontal velocity, strain rate, antenna height, surface elevation, and Lagrangian elevation change (Dh/Dt). The antenna height time series show a surface elevation increase of ~ 0.7–1.0 m/yr, which is consistent with model estimates for surface mass balance (SMB) of ~ 0.7–0.9 mwe/yr and ~ 0.7–0.8 m/yr downward velocity due to firn compaction. An abrupt ~ 0.2–0.3 m surface elevation decrease, likely due to surface melt, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dh/Dt for all PIG shelf sites is highly linear, with trends of −1 to −4 m/yr and residuals of < 0.4 m. Corresponding basal melt rate estimates range from ~ 10 to 40 m/yr, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo DEM records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (transverse surface depressions, rifts). Basal melt rates for the 2012–2014 period show limited temporal variability, despite significant changes in ocean heat content, suggesting that sub-shelf melt rates may be less sensitive to ocean heat content than previously reported, at least for these locations and time periods.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 06, 2017, 04:27:13 PM
The linked reference indicates that the PIIS is calving further upstream than in the past due to oceanic driven disintegration of the northern shear margin mélange and intensified melting with basal crevasses.  As the ocean in this area will remain relatively warm for a long time, this indicates that the PIIS will continue to calve more rapidly than in the past and will calve further and further upstream, with time.  This will cause the buttressing on the SW Tributary Glacier to be reduced, which will help to trigger the acceleration of ice velocities for Thwaites:

Seongsu Jeong, Ian M. Howat & Jeremy N. Bassis (28 November 2016), "Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL071360

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full (http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full)

Also see: Lipuma, L. (2017), West Antarctic ice shelf breaking up from the inside out, Eos, 98, doi:10.1029/2017EO064743. Published on 04 January 2017.

https://eos.org/research-spotlights/west-antarctic-ice-shelf-breaking-up-from-the-inside-out?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz010617

Extract: "Although this is the first time researchers have witnessed a deep subsurface rift opening within Antarctic ice, they have seen similar breakups in the Greenland Ice Sheet, in spots where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath. The satellite images provide the first strong evidence that these large Antarctic ice shelves respond to changes at their ocean edge in a way similar to that observed in Greenland.

The researchers note that this kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that there may be a significant collapse of the West Antarctic Ice Sheet in the next century.  They point out that there are many similar valleys farther up the glacier. If these sites are prone to rifting, we could potentially see more accelerated ice loss in Antarctica."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: oren on January 06, 2017, 04:58:21 PM
The linked reference is entitled: "In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica"
Very interesting. Note the article relates to the PIG ice shelf, rather than the glacier itself.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on January 21, 2017, 12:43:34 AM
nice paper by Millain et al in GRL doi:10.1002/2016GL072071 on better bedmaps for PIG,Thwaites,Smith,Kohler. Fearsome holes down there. I attach panels from fig2, PIG, Thwaites and Smith-Kohler

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on February 01, 2017, 05:37:27 PM
Southern Thwaites shelf had a decent size calving.  the big chunk is around 10 km, around the same size as the last small PIG calving, overall about 20 km.  Jan 25 to Feb 1

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170201T044350_123E_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170201T044350_123E_S_1.final.jpg) (30 MB)

S1A_EW_GRDM_1SSH_20170125T045155_2FA4_S_1.final.jpg (34 MB)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on February 03, 2017, 04:19:44 PM
Just a screen shot of the new bergs.  I suppose extent just got a bump up.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170203T042736_5EF7_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170203T042736_5EF7_S_1.final.jpg) (27MB)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: DrTskoul on February 09, 2017, 12:02:38 AM
"Hidden lakes drain below West Antarctica's Thwaites Glacier" (https://m.phys.org/news/2017-02-hidden-lakes-west-antarctica-thwaites.html)

Quote
Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency's CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier's long-term movement is fairly oblivious to trickles at its underside.

"This was a big event, and it confirms that the long-term speed-up that we're observing for this glacier is probably driven by other factors, most likely in the ocean," said corresponding author Ben Smith, a glaciologist with the UW's Applied Physics Laboratory. "The water flow at the bed is probably not controlling the speed."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 17, 2017, 09:00:09 PM
The linked article is entitled: "A New Theory Explains What's Driving Antarctica's Fastest Melting Glacier".

http://www.seeker.com/a-new-theory-explains-whats-driving-antarcticas-fastest-melting-glacie-2268234317.html (http://www.seeker.com/a-new-theory-explains-whats-driving-antarcticas-fastest-melting-glacie-2268234317.html)

Extract: "Researchers previously pinpointed continental winds as the force pushing warm ocean waters underneath West Antarctica's Pine Island Glacier, but now they say local weather patterns are to blame.

Researchers have described the Pine Island Glacier as the "plug" that holds back the expansive West Antarctic Ice Sheet, the melting of which contributes to sea-level rise."

Also see the associated reference entitled: "Mechanisms driving variability in the ocean forcing of Pine Island Glacier" (doi: 10.1038/ncomms14507).

http://www.nature.com/articles/ncomms14507 (http://www.nature.com/articles/ncomms14507)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 21, 2017, 04:02:27 AM
The linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf (http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf)

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on May 21, 2017, 05:28:52 AM
That Webber 2017 article, (open, read all about it)

http://www.nature.com/articles/ncomms14507 (http://www.nature.com/articles/ncomms14507)

documents a cold spell just b4 the drainage. I wonder ...

I notice Dutrieux and Jenkins on the author list of Webber article. Keep on truckin.

sidd

P.S. More specifically, i wonder if the ocean cooling in 2011 decreased shelf bottom melt slowing discharge, thickening ice inland; thus clamping down on interior bottom melt water efflux until pressure build caused submarine jokulhaup as seen in 2013-14 in Smith et al.

Whew, that was a long sentence, even with the semi colon.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 23, 2017, 12:07:21 AM
The linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf (http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf)

Here is more information on the June 2013 to Jan 2014 drainage of four subglacial lakes beneath the Thwaites Glacier.  The article is entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/ (http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/)

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 23, 2017, 12:11:48 AM
See also the attached image from 2016 data (release Feb 8 2017):

http://www.esa.int/spaceinimages/Images/2017/02/Glacier_speed_West_Antarctica (http://www.esa.int/spaceinimages/Images/2017/02/Glacier_speed_West_Antarctica)

Extract: "This image from Sentinel-1 and geographic base map shows the speed of ice flow in West Antarctica. Reaching speeds of over 3 km per year, Thwaites and Pine Island are two of the fastest receding glaciers on the Western Antarctic Ice Sheet. Applying interferometric synthetic aperture swath processing techniques to CryoSat data revealed that four lakes beneath Thwaites drained into the Amundsen Sea."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on June 25, 2017, 08:22:39 PM
More calving, with continued rift development and sea ice dispersal at Thwaites.  22 May to 25 Jun, Click to animate.  (1.7 Mb)
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SDH_20170625T044410_9CB6_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SDH_20170625T044410_9CB6_S_1.final.jpg)
S1A_EW_GRDM_1SSH_20170522T042748_981A_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on June 28, 2017, 02:41:25 AM
Whoa!  Looks like there's more on the way!
S1A_EW_GRDM_1SDH_20170627T042750_486D_S_1.final.jpg
S1A_EW_GRDM_1SDH_20170622T041938_79D0_S_1.final.jpg
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on July 06, 2017, 05:40:05 PM
The calving continues at Thwaites, 22 Jun to 4 July
S1A_EW_GRDM_1SDH_20170704T041939_6046_S_1.final.jpg
S1A_EW_GRDM_1SDH_20170622T041938_79D0_S_1.final.jpg

Great video from Sep 2016 to May here:
http://www.cesbio.ups-tlse.fr/multitemp/?p=10666&utm_source=rss&utm_medium=rss&utm_campaign=watching-ice-shelfs-break-up-with-sentinel-1-2 (http://www.cesbio.ups-tlse.fr/multitemp/?p=10666&utm_source=rss&utm_medium=rss&utm_campaign=watching-ice-shelfs-break-up-with-sentinel-1-2)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 20, 2017, 08:03:53 PM
I would just like to note that in my opinion the force required by the Pine Island Ice Shelf, PIIS, to change the ice flow direction of the Southwest (SW) Tributary Glacier by about 90 degrees will soon (before the boreal summer of 2018) cause a new splitting tension crack across the PIIS by the mechanism illustrated in the first attached image.  Furthermore, it is my opinion that the reaction to such a crack formation in the PIIS will cause a major calving of the SW Tributary Glacier's Ice Shelf as suggested by the growth of the major crack in the SW Tributary Ice Shelf illustrated in the second attachment of a gif sequence provided by solartim27.  If so, this should cause the ice flow velocities of the SW Tributary Glacier to accelerate; which should reduce the boundary shear restrain from the associate border with the Thwaites Glacier.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 26, 2017, 01:53:42 PM
The linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1 (https://doi.org/10.1175/JCLI-D-16-0891.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 01, 2017, 05:09:07 PM
The linked reference concludes that the groundling line for the PIG has a several km wide "flush zone" where seawater intrudes beneath the glacier on high tides and where there is "… continuous draining/filling of subglacial lakes proximal to the grounding line."  Further, it concludes that: "At present, numerical models of ice flow do not account for a flush zone. The existence of a flush zone should make the glacier more prone to retreat in response to warmer ocean waters."

Pietro Milillo, Eric Rignot, Jeremie Mouginot, Bernd Scheuchl, Mathieu Morlighem, Xin Li & Jacqueline T. Salzer (31 August 2017), "On the short-term grounding zone dynamics of Pine Island glacier, West Antarctica observed with COSMO-SkyMed interferometric data", Geophysical Research Letters, DOI: 10.1002/2017GL074320 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074320/abstract?utm_content=buffer19afa&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/2017GL074320/abstract?utm_content=buffer19afa&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract: "Using radar satellite data from the Italian COSMO-SkyMed (CSK) constellation and the German TanDEM-X formation, we present comprehensive measurements of the bi-weekly grounding line dynamics of Pine Island Glacier, West Antarctica, from August to December 2015. The one-day repeat cycle of CSK reveals tidally-induced, grounding line migration on the scale of kilometers and extensive seawater intrusion within the grounding zone, which significantly exceeds that predicted for a stiff bed but are consistent with that calculated for a deformable bed. The deformable bed also explains the continuous draining/filling of subglacial lakes proximal to the grounding line. After correction for oceanic tides, we estimate a retreat rate for 2011-2015 of 0.3 km/yr at the glacier center and 0.5 km/yr on the sides, which is three times slower than for 1994-2011 (1.2 km/yr at the center). We attribute the decrease in retreat rate to colder ocean conditions in 2012-2013 relative to 2000-2011."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 12, 2017, 11:07:30 PM
The linked open access reference discusses variability of the ocean forcing on PIG and PIIS.

Webber et al (2017), "Mechanisms driving variability in the ocean forcing of Pine Island Glacier", Nat. Commun. 8, 14507, doi: 10.1038/ncomms14507

http://www.nature.com/articles/ncomms14507 (http://www.nature.com/articles/ncomms14507)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on October 15, 2017, 05:48:40 PM
The linked reference finds limited ice-stream bed erosion beneath the PIG in recent decades:

Davies, D., Bingham, R. G., King, E. C., Smith, A. M., Brisbourne, A. M., Spagnolo, M., Graham, A. G. C., Hogg, A. E., and Vaughan, D. G.: How dynamic are ice-stream beds?, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-214, (https://doi.org/10.5194/tc-2017-214,) in review, 2017.

https://www.the-cryosphere-discuss.net/tc-2017-214/ (https://www.the-cryosphere-discuss.net/tc-2017-214/)

Abstract. Projections of sea-level rise contributions from West Antarctica's dynamically thinning ice streams contain high uncertainty because some of the key processes involved are extremely challenging to observe. An especially poorly observed parameter is sub-decadal stability of ice-stream beds. Only two previous studies have made repeated geophysical measurements of ice-stream beds at the same locations in different years, but both studies were limited in spatial extent. Here, we present the results from repeat radar measurements of the bed of Pine Island Glacier, West Antarctica, conducted 3–6 years apart, along a cumulative ~ 60 km of profiles. Analysis of the correlation of bed picks between repeat surveys show that 90 % of the ice-stream bed displays no significant change despite the glacier increasing in speed by up to 40 % over the last decade. We attribute the negligible detection of morphological change at the bed of Pine Island Glacier to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state, such that sediment is transported along the basal interface without inducing morphological change to the radar-sounded bed. Significant change was only detected in one 500 m section of the bed where a change in bed morphology occurs with a difference in vertical amplitude of 3–5 m. Given the precision of our measurements, the maximum possible erosion rate that could go undetected along our profiles is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1000 mm a-1 previously reported from repeat geophysical surveys in West Antarctica.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on October 15, 2017, 10:23:31 PM
The Davies paper is interesting in that it shows evidence for a deformable till bed in steady state.

"The absence of detectable morphological change to the bed over the majority of the ~60 km of bed profiles on PIG could be interpreted in three ways: (1) that no sediment erosion/transport/deposition is occurring at the measured sites; (2) that erosion/deposition is occurring but at rates too low to be detected within the vertical range resolution of the radar; or (3) that thesubglacial till flux is in a steady state wherein sediment transport is active but is not altering the shape of the bed."

They plump for 3).

"We attribute the negligible detection of morphological change at the bed of Pine Island Glacier on the sub-decadal timescale to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state such that sediment is transported along the basal interface without inducing measurable vertical displacement to the radar-sounded basal interface."

Another point of interest is that they see no tidal influence at all.

Hmmm. I shall have to think on this, and I eagerly await comments on the paper on the cryo-discuss site. Thanks for the reference.

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on October 16, 2017, 06:19:15 AM
Some more thoughts:

1) deformable till is helpful, modelled glacial retreat  is slower on deformable bed.
2) the finding that the bed is in steady state for more than a decade is also a good sign
3) it would be useful to find the tidal range in Pine Island Bay as compared to that at the mouth of the Rutland glacier to which they compare. The latter has much stronger tidal variation upstream.

sidd

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: steve s on October 16, 2017, 10:20:40 AM
From the paper:
"... the maximum possible erosion rate that could go undetected along our profiles is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1000 mm a-1 previously reported from repeat geophysical surveys in West Antarctica."

The PIG has been transporting water under the ice for a long time. Given that fact, I find 20" per year -- 5 meters per decade -- of erosion of the bed to be rapid. It seems to me, admittedly poorly educated in this research area, that better instruments are needed before claiming minimal bed erosion.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on October 19, 2017, 08:20:18 PM
Phys.org on forams in PIG and Margurite Bay indicating last appearance of CDW beneath iceshelves was 7Kyr ago. But,alas, no journal reference or even author names.

https://phys.org/news/2017-10-antarctic-ice-shelves-years.html

sidd
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on October 25, 2017, 07:28:01 AM
An amazing video at the link
https://mobile.twitter.com/sgascoin/status/922938968152461312/video/1
Thwaites glacier ice shelf from 214 Sentinel-1 HH images (Feb 2015 to Sep 2017) @ESA_EO @CopernicusEU
Update of (link: http://www.cesbio.ups-tlse.fr/multitemp/?p=10666) cesbio.ups-tlse.fr/multitemp/?p=1…
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 20, 2017, 05:04:21 PM
If one only considers basal slide of the PIG, then the basal roughness of PIG's bed identified (see image) in the linked reference is good news, as it may slow future ice mass loss.  On the other hand, such basal roughness may do little to slow ice mass loss associated with any future cliff failures that PIG may experience in the coming decades:

Robert G. Bingham et al. (2017), "Diverse landscapes beneath Pine Island Glacier influence ice flow", Nature Communications, DOI: 10.1038/s41467-017-01597-y

https://www.nature.com/articles/s41467-017-01597-y

Abstract: "The retreating Pine Island Glacier (PIG), West Antarctica, presently contributes ~5–10% of global sea-level rise. PIG’s retreat rate has increased in recent decades with associated thinning migrating upstream into tributaries feeding the main glacier trunk. To project future change requires modelling that includes robust parameterisation of basal traction, the resistance to ice flow at the bed. However, most ice-sheet models estimate basal traction from satellite-derived surface velocity, without a priori knowledge of the key processes from which it is derived, namely friction at the ice-bed interface and form drag, and the resistance to ice flow that arises as ice deforms to negotiate bed topography. Here, we present high-resolution maps, acquired using ice-penetrating radar, of the bed topography across parts of PIG. Contrary to lower-resolution data currently used for ice-sheet models, these data show a contrasting topography across the ice-bed interface. We show that these diverse subglacial landscapes have an impact on ice flow, and present a challenge for modelling ice-sheet evolution and projecting global sea-level rise from ice-sheet loss."

See also:

Title: "Antarctic landscape insights keep ice loss forecasts on the radar"

https://phys.org/news/2017-11-antarctic-landscape-insights-ice-loss.html

Extract: ""These bedforms, which have been the focus of my research for many years, represent a considerable resisting element to, and therefore a crucial control on, the flow of ice. Models of ice stream flow should attempt to incorporate the variable topography we have shown to exist under the ice to improve their reliability.""

&
http://www.bbc.com/news/science-environment-42052072
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 20, 2017, 05:12:21 PM
While this reference has been cited/discussed elsewhere, it also belongs here:

Wise et al. (2017), "Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks", Nature 550, 506-510, doi:10.1038/nature24458

https://www.nature.com/articles/nature24458

Extract: "From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels.
...
Our findings demonstrate the effective operation of Marine ice-cliff instability (MICI) in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet."

See also:

http://glacierhub.org/2017/11/20/roundup-ice-cliff-instability-buffers-glacial-retreat/

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: steve s on November 20, 2017, 10:05:41 PM
Perhaps current basal roughness reflects past cliff fracturing with shallow bergs and little bed erosion. If so, rough beds may be a sign of rapid glacial retreat.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: jai mitchell on November 21, 2017, 04:22:15 PM
Article today that discusses the implication of wise et al. described above by ASLR and the previous DeConto paper describing Thwaites and PIG SLR potentials.

https://grist.org/article/antarctica-doomsday-glaciers-could-flood-coastal-cities/
Doomsday on Ice

Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century.

By Eric Holthaus   on Nov 21, 2017

Quote
The only place in the world where you can see ice-cliff instability in action today is at Jakobshavn glacier in Greenland, one of the fastest-collapsing glaciers in the world. DeConto says that to construct their model, they took the collapse rate of Jakobshavn, cut it in half to be extra conservative, then applied it to Thwaites and Pine Island.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on November 23, 2017, 11:04:43 AM
Perhaps current basal roughness reflects past cliff fracturing with shallow bergs and little bed erosion. If so, rough beds may be a sign of rapid glacial retreat.

I concur with your hypothesis.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 01, 2017, 04:39:04 AM
The linked article is a nice summary for anyone new to this topic (the two attached images from the article show the cumulative ice mass loss from 1980 to 2016 for the PIG and the Thwaites Glacier, respectively):

Title: "In Antarctica, Two Crucial Glaciers  Accelerate Toward the Sea"

https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html

(Hint for those who want to learn more, no one knows more about these two glaciers than Eric Rignot)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on December 07, 2017, 05:31:51 PM
The linked reference indicates that ice shelf melt rates in the ASE requires complex modeling but indicates that this issue will likely contribute to an acceleration of grounding line retreats for both PIG and Thwaites, in coming decades:

Marion Donat-Magnin et al. (6 December 2017), "Ice-Shelf Melt Response to Changing Winds and Glacier Dynamics in the Amundsen Sea Sector, Antarctica", JGR Oceans, DOI: 10.1002/2017JC013059

http://onlinelibrary.wiley.com/doi/10.1002/2017JC013059/abstract?utm_content=buffer9d542&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "It has been suggested that the coastal Southern Ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds, with potential adverse effects on West Antarctic glaciers. However, using a 1/12° ocean regional model that includes ice-shelf cavities, we find a more complex response to changing winds in the Amundsen Sea. Simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the SAM projected trend. The buoyancy-driven circulation induced by ice-shelf melt transports this cold offshore anomaly onto the continental shelf, leading to cooling and decreased melt below 450 m. In the vicinity of ice-shelf fronts, Ekman pumping contributes to raise the isotherms in response to changing winds. This effect overwhelms the horizontal transport of colder offshore waters at intermediate depths (between 200 and 450 m), and therefore increases melt rates in the upper part of the ice-shelf cavities, which reinforces the buoyancy-driven circulation and further contributes to raise the isotherms. Then, prescribing an extreme grounding line retreat projected for 2100, the total melt rates simulated underneath Thwaites and Pine Island are multiplied by 2.5. Such increase is explained by a larger ocean/ice interface exposed to CDW, which is then amplified by a stronger melt-induced circulation along the ice draft. Our main conclusions are that (1) outputs from ocean models that do not represent ice shelf cavities (e.g. CMIP5 models) should not be directly used to predict the thermal forcing of future ice shelf cavities; (2) coupled ocean/ice sheet models with a velocity-dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 22, 2018, 11:01:37 PM
The linked reference finds that with regards to ice mass loss from the BSB that: " Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary."  This indicates that it is a very bad idea to continue following a BAU forcing pathway as mankind has been doing since the pre-industrial era.

M. S. Waibel, C. L. Hulbe, C. S. Jackson & D. F. Martin (16 January 2018), "Rate of mass loss across the instability threshold for Thwaites Glacier determines rate of mass loss for entire basin", Geophysical Research Letters, DOI: 10.1002/2017GL076470

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076470/abstract?utm_content=buffer0799e&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed. We use a high-resolution ice sheet model to examine the mechanics of TG self-sustained retreat by nudging the grounding line just past the point of instability. We find that by modifying surface slope in the region of the grounding line, the rate of the forcing dictates the rate of retreat, even after the external forcing is removed. Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary. Retreat is sensitive to short-duration re-advances associated with reduced external forcing where the bathymetry allows re-grounding, even when an instability is invoked."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: wili on January 23, 2018, 03:38:36 AM
"Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed"

I hadn't heard it put quite that way in writing in the scientific literature yet, but I obviously have not been paying close enough attention.

This sounds kind of...bad...
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on January 23, 2018, 03:55:24 AM
"Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed"

I hadn't heard it put quite that way in writing in the scientific literature yet, but I obviously have not been paying close enough attention.

This sounds kind of...bad...

I would have thought that the "Ice Apocalypse" thread would have given some idea of how much at risk that the TG is of crossing a threshold:

https://forum.arctic-sea-ice.net/index.php/topic,2205.0.html

However, if that thread is not sufficient I re-post the following from the Potential Collapse Scenario for the WAIS" thread

"Based on my interpretation of the two linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the four images) will begin sometime 2025 and 2033, and will be initiated due to influences from Super El Nino events in that timeframe:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017

https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdf
https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017-assets.html

Abstract. "Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades.  Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing.  We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA’s Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations.  We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving."

Extract: "In our simulations, we find that crevasses propagate significantly faster near the ice front when the ice shelf is shortened.

The reason for the propagation of crevasses is the existence of a nonhydrostatic condition of ice immediately downstream of the grounding line, which is not accounted for in simplified models that assume hydrostatic equilibrium everywhere on the ice shelf.  We also find that calving is enhanced in the presence of pre-existing surface crevasses or shorter ice shelves or when the ice front is undercut.  We conclude that it is important to consider the full stress regime of ice in the grounding line region to replicate the conditions conducive to calving events, especially the nonhydrostatic condition that is critical to propagate the crevasses."

&

The second linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent.""
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: wili on January 23, 2018, 04:49:31 AM
Thanks for the added info, ASLR.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Sigmetnow on January 24, 2018, 04:47:58 PM
“Looking at these two glaciers as a system involved a time-consuming process of building algorithms that interpret airborne data gathered from planes flying at different heights with unique radar systems.”

Stanford researcher: Interacting Antarctic glaciers may cause faster melt and sea level contributions
Quote
A new study shows that a large and potentially unstable Antarctic glacier may be melting farther inland than previously thought and that this melting could affect the stability of another large glacier nearby – an important finding for understanding and projecting ice sheet contributions to sea-level rise.

The findings, by a Stanford-led team of radar engineers and geophysical glaciologists, came from radar data collected at the same locations in 2004, 2012 and 2014, each revealing details of the glaciers miles below the surface. The surveys show that ocean water is reaching beneath the edge of the Pine Island Glacier about 7.5 miles further inland than indicated by previous observations from space.

The team also found that the Southwest Tributary of Pine Island Glacier, a deep ice channel between the two glaciers, could trigger or accelerate ice loss in Thwaites Glacier if the observed melting of Pine Island Glacier by warm ocean water continues down the ice channel. The results were published online in the Annals of Glaciology. ...
https://earth.stanford.edu/news/stanford-researcher-interacting-antarctic-glaciers-may-cause-faster-melt-and-sea-level
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on February 23, 2018, 06:05:02 PM
For the sake of completeness, I provide the linked reference, which considers possible interactions between the PIG and Thwaites glacier:

Dustin M. Schroeder et al. Ocean access beneath the southwest tributary of Pine Island Glacier, West Antarctica, Annals of Glaciology (2017). DOI: 10.1017/aog.2017.45

https://www.cambridge.org/core/journals/annals-of-glaciology/article/ocean-access-beneath-the-southwest-tributary-of-pine-island-glacier-west-antarctica/EFF449338C7D7D088CCB7BC48D40B150

Abstract: "The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line."
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on April 27, 2018, 07:35:08 PM
The two attached Sentinel1 images from April 27 & 26, respectively, make it very clear that as the Pine Island Ice Sheet flows, it will soon break-off a large portion of the Southwest Tributary Ice Shelf.  This will reduce the buttressing action of the Southwest Tributary Ice Shelf on the Southwest Tributary Glacier; which in-turn will reduce the shear stress on Thwaites Glacier's eastern shear margin (which will reduce the stability of Thwaites).

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on May 14, 2018, 07:32:05 PM
The first attached Sentinel-1 image of the SW Tributary Ice Shelf, from May 14 2018, makes it clear that a major piece of the ice shelf has now become an iceberg and that the ice shelf upstream of the iceberg is crumbling to the point that its buttressing action is continuing to degrade.

Edit, the second attached image from Sentinel-1 of the SW Tributary Ice Shelf from June 3 2018, makes it clear that due to the calving of the downstream portion of the shelf, the buttressing from the PIIS on the SW Tributary Ice Shelf has moved in the Northwest direction, which in my opinion will contribute to the calving upstream for future PIIS calving events.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on July 06, 2018, 12:20:47 AM
Thwaites is continuing to break up.  I noticed this roller pretty far in. Anyone seen recent grounding line info?
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on July 09, 2018, 04:40:51 PM
The attached image of both the SW Tributary Ice Shelf and the PIIS calving front, from July 8 2018, indicates that these ice shelves are progressively degrading:
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: AbruptSLR on September 24, 2018, 08:50:20 PM
The attached image from Sept 24 2018 gives me the impression that: 1) the SW Tributary Glacier ice flow velocity is increasing and that 2) the PIIS may undergo a major calving event this coming austral summer.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on November 17, 2018, 07:33:48 PM
A very small, nothing to worry about calving at Thwaites, of only about 10 miles.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on December 14, 2018, 05:54:12 PM
The ice shelf west of the Thwaites ice tongue has lost its tip last week. Eyeballing the area it has lost around 60 km². The remains were rapidly transported to the lower left (W-NW direction). See attached images, the upper one from Dec 05, 2018, the lower one from Dec 13, 2018. Both are from EOSDIS worldview. The black line represents the borders of the ice shelf around 2010.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on December 18, 2018, 09:46:34 PM
Even more breakdown of the fast ice N of the Thwaites glacier tongue. EOSDIS worldview from Dec 05 (top) and Dec 18 (bottom). The dark signature that goes from the tip of the broken fast ice to the Thwaites ice tongue is probably partly open water (??)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on December 29, 2018, 11:41:50 AM
A new big crack goes through the fast ice west of the Thwaites ice tongue. See the three figures from dec 15, dec 22 (first visible thin line) and dec 28, 2018 (unfortunately partly cloud-covered)
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on January 02, 2019, 06:03:47 PM
It looks like the whole thing (ca. 20 km x 60 km) is breaking apart. I marked the "calving fronts" in red. It is not only sea ice, but in the "calving area" are also icebergs from the Smith/Kohler glaciers. New open water (marked in blue) has also appeared.
Picture taken from EOSDIS worldview Jan 01, 2019.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: solartim27 on January 02, 2019, 10:54:05 PM
The area you have circled is just sea ice now that it has separated from the glacier, though it might qualify as an ice shelf.  The calving front is about 20 miles further in.  Gif from Nov 29 to Jan 1, lots of motion visible. I wonder where the grounding line is these days.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: steve s on January 02, 2019, 11:25:24 PM
Iceberg b-35 (I think that's the number) has been grounded for the last couple of years, blocking movement of sea ice west of the Thwaites' tongue. It may be breaking up and starting to move, thereby allowing the crack to propagate to the west.

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: sidd on January 03, 2019, 08:37:21 AM
Shean et al., on PIG basal melt: Joughin and Dutrieux among the authors

"Mean 2008–2015 basal melt rates for the full PIG ice shelf were ~82–93 Gt/yr. Local basal melt rates were ~200–250 m/yr near the grounding line, ~10–30 m/yr over the outer main shelf, and ~0–10 m/yr over the North and South shelves, with notable exception of ~50–100 m/yr near the grounding line of a fast-flowing tributary on the South shelf."

Nice pics, i attach two. Scale on the right  is rate of surface height decrease for the first and bed depth on the second.  That huge hole behind the grounding line (white) says that doom is nigh.
 
open access, read all about it:

https://www.the-cryosphere-discuss.net/tc-2018-209/

Then we have the glaciers next door: Pope,Smith,Kohler aint doin so good either. Sutterly et al. on those, PIG, and Crosson, Dotson ice shelves, open access:

https://www.the-cryosphere-discuss.net/tc-2018-186/

And Getz goin fast: Rippin sounding alarm

" ... the vast majority of the ice shelf (where data is available) is undergoing basal thinning at a mean rate of nearly 13m/a, which is several times greater than recent modelling estimates ... t these measurements represent changes that are significantly greater than modelling outputs, it is also clear that we still do not fully understand how ice shelves respond to warming ocean waters."

open access:

https://www.the-cryosphere-discuss.net/tc-2018-163/

sidd

Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on January 03, 2019, 05:39:15 PM
Shean et al., on PIG basal melt: Joughin and Dutrieux among the authors

[...]
sidd
Thanks for posting these links. Interesting (although worrying) papers.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: Stephan on January 08, 2019, 06:52:40 PM
New development also at the fast ice west of the Thwaites ice tongue.
It looks loke a complete collapse of the fast sea ice. See the two images from Dec 09, 2018 and Jan 08,2019 from EOSDIS worldview.
Title: Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
Post by: gerontocrat on July 09, 2019, 04:28:52 PM
One for those who know what they are talking about (not me)
The word "irreversible" is used.
They quote a time frame (200-600 years) but.......

https://www.pnas.org/content/early/2019/07/02/1904822116
Marine ice sheet instability amplifies and skews uncertainty in projections of future sea-level rise
PDF @ https://www.pnas.org/content/pnas/early/2019/07/02/1904822116.full.pdf

Guardian article for ordinary people (me)
https://www.theguardian.com/world/2019/jul/09/glacial-melting-in-antarctica-may-become-irreversible
Glacial melting in Antarctica may become irreversible
Thwaites glacier is likely to thaw and trigger 50cm sea level rise, US study suggests

Quote
Antarctica faces a tipping point where glacial melting will accelerate and become irreversible even if global heating eases, research suggests.

A Nasa-funded study found instability in the Thwaites glacier meant there would probably come a point when it was impossible to stop it flowing into the sea and triggering a 50cm sea level rise. Other Antarctic glaciers were likely to be similarly unstable.

Recent research found the rate of ice loss from five Antarctic glaciers had doubled in six years and was five times faster than in the 1990s. Ice loss is spreading from the coast into the continent’s interior, with a reduction of more than 100 metres in thickness at some sites....
...Hélène Seroussi, a jet propulsion laboratory scientist at Nasa, said: “It could happen in the next 200 to 600 years. It depends on the bedrock topography under the ice, and we don’t know it in great detail yet.”