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AbruptSLR

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Surge of WAIS Ice Mass Loss
« on: February 21, 2013, 12:12:09 AM »
I suspect that the WAIS may have sustained a surge of ice mass loss from Summer to Fall of 2012 indicated by the attached image from the GRACE satellite (http://grace.jpl.nasa.gov/data/gracemonthlymassgridsoverview/) indicating that in that time frame the adjoining sea level dropped by about 7cm (due to the fingerprint effect of ice mass loss).  MODIS Rapidfire images (http://rapidfire.sci.gsfc.nasa.gov/subsets/?project=antarctica) at the same time indicate that the Thwaites Ice Tongue surges as did the Ferrigno Ice Tongue.  Also, over the same period the SLR indicated by NOAA (http://ibis.grdl.noaa.gov/SAT/SeaLevelRise/LSA_SLR_timeseries_global.php) in the North Pacific was significantly higher than the increase in global mean SLR, while NOAA also shows that the SLR in the Souther Ocean was well below the global mean; all of which are indications of a surge of ice mass loss from WAIS.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #1 on: February 21, 2013, 01:09:31 AM »
I believe that the surge of the Thwaites Glacier was triggered by the Summer 2012 ice mass loss from GIS which would raise the local Amundsen Sea level by a mm (or more); which would then raise the glacial ice at the Thwaites grounding line enough to trigger its surge; which would be facilitated by the lubrication action of the Subglacial melt water drainage system shown in the NASA figure (which according to the Dec. 2012 AGU presentation "C43C-0630: Configuration of Subglacial Water and Sediments Beneath Thwaites Glacier, West Antarctica: Context for a Potential Basal-Water-Triggered Grounding-Line-Retreat" by Dustin M Schroeder, Donald D Blankenship, Duncan A Young, Evelyn Powell, contains numerous Subglacial lakes).  The Subglacial lakes can act as pressurized water accumulators than once the grounding line is lifted can supply a reserve of basal water to lubricate the motion of the glacier during its surge.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #2 on: February 21, 2013, 01:31:40 AM »
I also think that warm circumpolar deep water, CDW, carved a cavity through the ice at the threshold of the Thwaites Glacier from the possible groundling line shown in the figure (from Rignot 2009) back to the indicated ridge/gate leading to the Byrd Subglacial Basin, BSB, by the Summer of 2012.  If so the previously discussed Thwaites 2012 ice surge would thin the glacial ice (which should have re-grounded during the Fall of 2012 as the subglacial lakes drained and as the local sea level dropped [due to the ice mass finger print effect]).  Thus in the Summer of 2013 when GIS melt water raises the Amundsen Sea level again, then it will be easier to possibly trigger another surge (provided that the subglacial lakes have re-charged by then), which would then thin the glacial ice more, possibly enough to open a cavity for warm CDW to gradually flow down into the BSB by extending the cavity by means of advection.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #3 on: February 21, 2013, 01:44:14 AM »
Here is a figure from Tamisiea and Mitrovica (2011) illustrating the ice mass loss finger print effect that could help to establish a mechanism to support periodic surges of selected (Thwaites, Ferrigno, etc.) WAIS glaciers as the Amundsen Sea level raises in the Summer due to GIS melt water and then drops in the Fall if/when the selected WAIS glaciers surge (and then re-ground again).
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #4 on: February 21, 2013, 02:17:08 AM »
Attached is an illustration of the basal lubrication from subglacial lakes for the Byrd Glacier (which flows from the EAIS into the Ross basin).  If such a mechanism were to be periodically triggered for the Thwaites Glacier, the associated ice mass loss would be much more significant, not only because Thwaites is bigger but also because the Byrd Glacier flow down a relatively narrow (1D) trough, while if I am right that a cavity at the threshold of the Thwaites Glacier has reached the lip of the BSB then the Thwaites Glacier ice movement would be 2D flowing both laterally and down into the BSB.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #5 on: February 21, 2013, 02:36:32 AM »
Attached is a figure of output from a hydraulic circulation model [taken from numerical simulations conducted at CCPO (St-Laurent, Klinck and Dinniman)] for the Amundsen Sea Embayment, ASE, indicating that warm CDW flows through a trough in the continental shelf from the Amundsen Sea to the Pine Island Glacier, PIG, ice shelf, a portion of this water then flows Westward through a submerged rift valley that parallels the coast down to the postulated cavity at the threshold of Thwaites, where I believe that the warm CDW bottom water flows into the cavity beneath fresher seawater (diluted by melt water from the glacier), and I believe that the colder fresher water continues flowing to the Northwest.  If so this would set-up both vertical and horizontal saline pumping actions for the combine PIG/Thwaites glacial system; which would promote this inflow of warm CDW flow to accelerate the melting of the glacial ice at the groundling line of both PIG and Thwaites.
« Last Edit: February 27, 2013, 11:22:39 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #6 on: February 21, 2013, 02:58:33 AM »
Attached is a figure from Gladstone et. al 2012 of the output from a box model of sub ice shelf advective circulation of CDW into (and out of) the PIG subglacial cavity for SRES A1B until 2100.  Note that the blue histogram indicates the likehood that the groundling line will reteat to the indicated rectangle by 2100, while the green histogram indicates that the groundling line retreat might temporarily stall in area indicated by the associated rectangles.  Note also that this model indicates a meaningful chance that the PIG subglacial cavity may extend 350 km to the WAIS divide by 2100 (where it might possibly run into a postulate subglacial cavity extending beneath the Ferrigno Glacier).  Also note that: (a) the Gladstone model does not consider the circulation synergy between the PIG and Thwaites Glacial systems [which could accelerate advective ice melting beyond that indicated in the figure] and (b) Currently the world is following SRES A1FI and the CDW is warming faster than the SRES A1B case reported by Gladstone et al.  I also postulate that a similar advective action is initiating for at least Thwaites (and soon for Ferrigno) Glacier, and recept that for Thwaites the subglacial cavity will branch to follow the various branches that the subglacial basal melt water follows beneath Thwaites.  Also accompanying is a figure from from Park et al. 2011 showing a plan view of projected grounding line retreat for PIG only considering advection within the subglacial cavity for PIG.
« Last Edit: February 23, 2013, 01:29:11 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #7 on: February 21, 2013, 03:25:30 AM »
Attached is a figure from Bingham et al 2012 showing the rate of decrease in elevation of glaciers around the WAIS, together with the submerged troughes in the WAIS continental shelf that guide warm CDW directly to the bases of numerous WAIS glaciers thus promoting grounding line retreat due to advection driving melting and associated grounding line retreat.  Note that there is a black rectangle around the Ferrigno Glacier which is the subject of Bingham el al's findings.  This is the last post/reply for tonight, to be followed by numerous new topic threads that taken together should indicate that the risk of abrupt SLR from the collapse of the WAIS this century is much more likely than many researchers are prepared to state publicaly at this time.
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Re: Surge of WAIS Ice Mass Loss
« Reply #8 on: February 21, 2013, 12:40:58 PM »
Yes, great stuff, AbruptSLR. The Antarctic is also one of the reasons to start this Forum, as I couldn't fit that in on an Arctic Sea Ice Blog, and didn't feel like starting a second blog. Maybe I should some day. After I close down the Arctic Sea Ice Blog due to ice-free conditions.  ;)
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #9 on: February 21, 2013, 03:56:47 PM »
Lodger & Neven,

Thank you very much for the warm welcome to this new forum; which seems well suited for my single topic focus (and for me personnally as I have much more information on this topic than I have time to post).  By the way, in my previous replies I stated that Summer ice melt from GIS would raise sea level at Thwaites by about one mm; however, the GRACE Satellite indicates that from January 2012 to September 2012 GIS lost about 700 Gt of ice mass loss which equates to approximately 2mm of eustatic SLR; however, due to the finger print effect this equates to roughly 2.5 mm of RSLR in the Bellingshausen Sea (for the Ferrigno Glacier) and about 2.4 mm of RSLR for the Amundsen Sea Embayment, ASE.  Which I think when added to astronomical tides may have triggered the postulated surge of Thwaites and Ferrigno Glaciers.
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Re: Surge of WAIS Ice Mass Loss
« Reply #10 on: February 21, 2013, 06:21:43 PM »
For those who did not go through the MODIS photographic history (see previous link) of the Thwaites Ice Tongue, the accompanying figure shows the ice tongue before and after the September 2012 surge event, note the non-yellow arrows are in the same location in both images, while the yellow arrows point out the location of the iceberg tongue (which is normally pinned to two submerged peaks) before and after the surge event.
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Re: Surge of WAIS Ice Mass Loss
« Reply #11 on: February 21, 2013, 06:31:37 PM »
The accompanying figure from NASA's Operation IceBridge website, indicates that shortly after the September surge event that a IceBridge plane flew the indicated path and used ground penetrating radar that may well indicate the formation of the subglacial cavity and the grounding line retreat that I am postulating for the Thwaites Glacier.  A few weeks ago, I e-mailed NASA to ask for the results of this October 2012 aerial survey, however, I have not heard back from them.  When this information is released it should provide critical insight into the current stability of the Thwaites Glacier (the soft underbelly of WAIS).
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #12 on: February 21, 2013, 06:39:05 PM »
The accompanying figure from MODIS shows the condition of the Thwaites Ice Tongue in December 2012, indicating that after the September 2012 surge event that the new iceberg tongue was not immediately pinned by the two submerged peaks, and that it continued to extend for several months (indicating that the old pinning mechanism is becoming less effective).  Since December the Thwaites Ice Tongue appears to have become pinned again but the portion of the tongue that in December 2012 extended beyond the two submerged peaks has since calved away.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #13 on: February 21, 2013, 07:47:37 PM »
The accompanying figure from Tinto & Bell 2011 shows several key features for Thwaites including: (a) the two pinning points from the two peaks of the indicated submerged ridge (Tinto & Bell stated that they believed that the Thwaites Ice Tongue would become unpinned within 20 years from 2011, and I am postulating that this happened in Sept 2012); (b) the subglacial trough leading into the Byrd Subglacial Basin, BSB; note that the pink shading indicates that Tinto & Bell were not certain whether a subglacial cavity had already formed in the trough as of 2009, which if so would have positioned the local ground line at the indicated ridge lip leading into BSB, thus exposing the ice at the grounding line to several years of advective melting from warm CDW.  Furthermore, not that the angle of the subglacial trough lines-up precisely with the direction of the CDW following the submerged rift valley paralleling the coast between PIG and Thwaites (see replies from February 20). Note that you need to go to Page 2 to see the next posts.
« Last Edit: February 21, 2013, 08:58:09 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #14 on: February 21, 2013, 08:48:40 PM »
The accompany figure show results of a 2008 underwater survey conducted by Rignot that shows a "hollow" in precisely the same location as the trough/subglacial cavity noted by Tinto and Bell (2011).  While many researchers show the 1996 grounding line shown in the figure, it is clear that by direct underwater survey (by a submersible) advection was already forming a subglacial cavity by 2008, and the figure in my next reply will show box model results indicating how advection could have extended this "hollow" into a subglacial cavity extending all the way back to the ridge/lip leading down into the BSB.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #15 on: February 21, 2013, 08:55:44 PM »
The accompanying figure from Goldberg et al. 2012 shows results from an advective model for a case with conditions of those at the 2008 threshold into the Thwaites Subglacial cavity which indicate the rapid potential for extending the "hollow" identified by Rignot (2008) back to the ridge/lip leading to the BSB.
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Re: Surge of WAIS Ice Mass Loss
« Reply #16 on: February 21, 2013, 10:13:22 PM »
While the surge of the Ferrigno Ice Tongue was less dramatic than for the Thwaites Ice Tongue, the accompanying figure (from MODIS images) shows that Ferrigno Ice Tongue surged in late Summer of 2012 and had calved back to its equilbrium condition by Feb 2013.
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Re: Surge of WAIS Ice Mass Loss
« Reply #17 on: February 21, 2013, 10:41:16 PM »
Accompanying is a cross-section and topography for the Ferrigno Glacier which I believe was made prior to about (or during) 2009, and I believe that the grounding line has retreated considerable since then as the adjoining Bellingshausen Sea is warming very rapidly.
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Re: Surge of WAIS Ice Mass Loss
« Reply #18 on: February 21, 2013, 10:49:22 PM »
The accompanying figure (which I believe is from either 2009 or 2010) shows the measured bottom ocean water potential temperatures (indicating the potential to melt ice at a given depth); which indicates that the bottom ocean water temperatures offshore of ASE and the Ferrigno Glacier have shown some of the highest such temperatures in the Southern Ocean; which is driving the melting of the ice at the base of glaciers in these areas, resulting in rapid grounding line retreat.
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Re: Surge of WAIS Ice Mass Loss
« Reply #19 on: February 22, 2013, 04:03:08 PM »
As I have the feeling that not all readers have taken the time to go the the NOAA SLR site in order to see the "finger print" SLR trend that I mentioned in the opening post I have assembled the accompanying figure of filtered NOAA SLR trend graphs for the Southern Ocean, the Global (eustatic) Ocean, and the North Pacific Ocean, SLR rise trends by Dec. 2012.  You will note that the rise in SLR for the North Pacific Ocean was so large by Dec 2012 that NOAA needed to change the scale as compared to all other graphs that they produce; while at the same time the SLR trend for the Southern Ocean decreased.  These three graphs clearly show that large amounts of ocean water have been transferred from around the WAIS in accordance with the ice mass loss "finger print" effect.  Also, note that the SLR in the North Pacific was several standard deviations above the usual trend line.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #20 on: February 22, 2013, 04:32:39 PM »
As the accompanying figure indicates one issue that makes the WAIS unique in that the crust beneath WAIS is very thin due both to the weight of the WAIS and also because of the local tectonic activity (volcanoes, rift valleys, faults, and earthquakes).  This thin crust transmits significant amounts of geothermal heat from the mantle to the base of the WAIS causing basal ice melting rates that are much higher than researchers thought even one year ago.  Note that in December 2011, measurements made at the WAIS Divide ice core site in the central portion of the WAIS; which indicate that the basal melting rate is extraordinarily high, 1.5~cm a-1, and this high heat flow is likely to be the regional value for the Byrd Subglacial Basin rather than the 0.5 cm  a-1, estimated by Tulaczk & Hossainzadeh.  These extraordinary basal melting rates rapidly recharge the subglacial melt water drainage and subglacial lake system (previously discussed) so that surges of ice particularly from the Thwaites Glacier can be expected to occur with greater frequency than researchers previously thought.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #21 on: February 22, 2013, 05:04:22 PM »
I am providing this figure from Willis and Church 2012, not only to provide an overview to those not familar with key interactions between ice, ocean and atmosphere for the Bellingshausen, and Amundsen, Sea portions of the WAIS but also in order to briefly reiterate here some additional interactions that most researchers have not yet fully factored into their risk consideration for ice mass loss from this portion of the WAIS.  Such additional considerations include: (a) While this figure shows how advection from a vertical salient gradient beneath an ice shelf can form a subglacial cavity pushing back the grounding line of glaciers like PIG, and Thwaites; this figure does not consider the horizontal advective interaction between PIG and Thwaites previously discussed that will acceleration cavity formation from current models; (b) The basal melting rates and subglacial lake/drainage network is more substantial than previously modeled; (c) the local CDW and local atmosphere, are warming faster (which is a relative term) than models previously assumed; (d) the buttressing action of both ice shelves and of submerge ridges is degrading faster than previously assumed; (e) the influence of annual ice mass loss from GIS raising sea levels in the West Antarctic, thus promoting increase frequency of surging of such WAIS glaciers; and (f) the initiation of greater rates of acceleration of non-ice mass loss from such WAIS glacier is happening earlier than previously assumed which will result in greater internal friction within the glaciers resulting in more basal melt water which will further accelerate movement of the glaciers
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #22 on: February 23, 2013, 02:22:18 AM »
The accompaning figure of ARGO measured ocean water potential temperatures at El -995.5m around the Southern Ocean illustrate how warm eddies from the South Pacific Current can periodically become entrained in the CDW offshore of the WAIS.  Such entrainments can contribute to warming the CDW at the base of glaciers particularly those adjoing the Bellingshausen and Amundsen Seas.  It is probable that with climate change such eddy entrainments will become more refrequent and more significant.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #23 on: February 23, 2013, 05:58:13 PM »
I am reposting the following summary of a presentation by Schroder et al. which elaborates on a basal melt water mechanism to support the intensive grounding line retreat of the Thwaites Glacier.  I firmly believe that this cited mechanism is complementary with the warm CDW advective mechanisms (both vertical with a sub ice shelf/glacier and horizontal between PIG and Thwaites) for intensive grounding line retreat.  It is important to note that as these complementary mechanisms (together with regional SLR from: thermal expansion of the local water as the OHC increases, and from ice mass loss from GIS and GIC) trigger the intensive grounding line retreat; then the outflowing glacial ice with thin which will eventually allow the outflowing ice shelf/tongue to float over the top of the various submerged ridges and mounts that are currently working to buttress the Thwaites Glacier.

Configuration of Subglacial Water and Sediments Beneath Thwaites Glacier, West Antarctica:
Context for a Potential Melt-Water-Intensive Grounding-Line-Retreat

By Schroeder, D.M., Blankenship, D.D., Young, D.A.
Presented at the 2nd Annual Jackson School Research Symposium, Feb. 2, 2013
Abstract
Thwaites Glacier, in the Amundsen Sea Embayment of the marine West Antarctic Ice Sheet (WAIS) is one of the largest and most rapidly changing glaciers on earth. Thwaites Glacier has a sloping bed that reaches deep into the WAIS interior, so a retreat started at its grounding-line has the potential to spread to the rest of the ice sheet, making its behavior and stability the subject of significant interest and study. Although sub-ice-shelf melting by warm ocean water is a leading hypothesis for the observed changes in Thwaites Glacier, its dynamic subglacial water system offers an alternative or complementary trigger for potential ice sheet acceleration and grounding line retreat. Subglacial water systems have been observed to cause significant accelerations in large Antarctic outlet glaciers and marine bathymetry of collapsed paleo-ice-streams show evidence of large volumes of melt-water and outbursts. However, the observational challenges in characterizing catchment-scale subglacial water systems have prevented the assessment of basal water as a potential trigger of unstable retreat for Thwaites Glacier. Using recent advances in focused coherent radar sounding data analysis, we show that the subglacial hydrology of Thwaites Glacier contains significant volumes of water ponding behind a damming bedrock ridge in a distributed canal system that is feeding a system of concentrated channels downstream. We show that the hydrologic dynamic state of these water systems is coupled to ice flow with the transition from a distributed to a concentrated water system co-located with an increase in basal shear stress. We also use the anisotropy of the radar echo specularity to identify flow-aligned sedimentary bedforms consistent with mega-scale glacial lineations underlying most of the glacier tributaries and a transition from sediment to crystalline bedrock in the trunk upstream of the grounding line. We compare the configuration of sedimentary bedforms beneath Thwaites Glacier with marine bathymetric observations of paleo-icestreams and conclude that its configuration is consistent with the large melt water volumes and outbursts associated with the collapses of those ice streams. Finally, we offer a mechanism by which the configuration of subglacial water and sediments beneath Thwaites Glacier could facilitate a basal-watertriggered grounding-line-retreat.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #24 on: February 23, 2013, 08:04:24 PM »
The accompanying figure from MacGregor 2011 presents later shear strain in the Thwaites Glacier for conditions in approximately 2010.  As Schroeder et al 2012 state: "We show that the hydrologic dynamic state of these water systems is coupled to ice flow with the transition from a distributed to a concentrated water system co-located with an increase in basal shear stress."  Therefore, this figure may provide some idea of the transition of the Thwaites Glacier subglacial water network from a distributed to a concentrated system in 2010.  Presumably this subglacial water network is essentially the same after the Summer of 2012 surge event (discussed in this thread); however, it is postulated that as warm CDW extends and widens the Thwaites subglacial cavity leading down into the BSB that the CDW will follow this concentrated basal water flow paths until the CDW reaches the distributed system at which time it is postulated that the CDW will branch out along the paths of least resistance.  Furthermore, I postuate that the fresh melt water from the subglacial water will work synergistically with the fresh ice water melted by the CDW thus resulting in enhanced advection that will more effectively draw-in more CDW to melt still more ice at the Thwaites grounding line thus accelerating its retreat as well as leading to an eventual branchin of the grounding line at the location where the distributed subglacial water system begins.
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Re: Surge of WAIS Ice Mass Loss
« Reply #25 on: February 24, 2013, 03:38:01 PM »
As the only water circulation data that I have cited to date is from model results.  Therefore,  I am presenting the accompanying figures from Arneborg et al, 2012, regarding channels into (and out of) the Amundsen Sea Embayment, ASE, and measured (from the Western Channel shown in the figure) ocean water temperature - salinity profiles.  A key real world observation that Arneborg et al make is that: "The data show persistent inflow towards the ice shelf of relatively warm and salty water at the bottom of the trough throughout the year, and outflow of colder water above."  This peristent flow is superimposed on natural fluctuations from the ocean current.
The persistent outflow of colder/fresher water above can only mean that ice mass loss occurs year round, and this colder/fresher water above must include (in various proportions depending on which channels we are considering and what season and what weather, and what surge events are happening with Thwaites, we are considering) both the ice melt water from CDW and the basal ice melt water (measured to be 1.5~cm a-1 in the BSB below Thwaites).  As I have said previously: I believe that some of the CDW directed towards PIG (in the Eastern Branch of the Eastern Channel) branches off to the west and follows a rift that parallels the coast directly into the subglacial cavity at the threshold of the Thwaites Glacier and that this portion of CDW induces some ice melting which combines with the somewhat episodic outflow of subglacial melt water from the BSB water drainage network; and that I believe that most of this combined colder/fresher water heads out through the Western Branch of the Eastern Channel thus forming a horizontal advective circulation pattern that is specific to the ASE (and superimposed on the normal vertical advective processes within the subglacial cavities such as for the PIG ice shelf).
« Last Edit: February 25, 2013, 12:10:00 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #26 on: February 24, 2013, 04:08:13 PM »
At the risk of being both repetative and overly simplistic, I provide this figure where I draw simple arrows (red for warm CDW and blue for cold ice melt water) on top of the bathymetry (and annotations) by Rignot; in order to hopefully clarify by postulation that a synergistic and persitent (year round) horizontal circulation pattern in ASE exists driven by ice meter water (both from CDW induced melting and from basal melt water) which promotes the formation of subglacial cavities both for the PIG and the Thwaites Glacier.  Besides accelerating advective ice melting in this are, order implications of this horizontal circulation pattern include that: (a) Goldberg et al 2012 indicate that the bottom geometry indicates that the extension of the subglacial cavity for PIG may slow-down (or stall) sometime between 2020 and 2030 on some local bottom ridges; however it is possible that this horizontal circulation pattern may prevent the stalling of the extension of the PIG subglacial cavity at this time/location; and (b) there is no clear deep trough infront of Thwaites (similar to that leading to PIG) and this horizontal circulation pattern could explain how the CDW gets into the BSB below Thwaites while the thin floating ice tongues and cold/fresh ice melt water flow over the tops of the somewhat shallow seafloor features headed toward the Western Channel without creating (gouging) a deep trough leading into Thwaites in past periods (such as the Eemian).  It should be noted that in the accompanying figure the term "Western Channel" means the Western Branch of the Eastern Channel" and the term "Eastern Channel" means the Eastern Branch of the Eastern Channel.
« Last Edit: February 25, 2013, 12:12:11 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #27 on: February 25, 2013, 12:42:16 AM »
Some may not be familiar with the fact that in previous ice ages (including the Eemian) there use to be numerous marine ice sheets (of which the WAIS is the last remaining example) including in the Arctic Sea such as indicated by the accompany figure illustration of the Barents Sea Marine Ice Sheet with the associated Byornoy trough and renna.  I believe that the Byonrnoy trough system has several parallels with the Thwaites Glacier situation including: (a) the Byonrnoy trough has a large amount of sediment deposited at the base of the renna (flow stream or channel in Norwegian) in a similar manner to the sediment in and around the Thwaites grounding line (now assumed to be past the ridge leading into the BSB) which allows the glacial ice to form a periodic seal with the sediment which periodical opens to allow burst of basal water to currently flow out for apparently periods of months; and (b) the upstream channel system branches quickly after this sediment filled area.  It should be noted while the Byornoy renna system slopes uphill while the Thwaites system: (i) first slopes downward before sloping up; and (ii) the Thwaites Basin connects directly to both the Siple Coast Ice Stream and the Weddell Sea Ice Streams, and both of these consideration make the Thwaites system less stable than the Barents Sea Marine Ice Sheet was.
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Re: Surge of WAIS Ice Mass Loss
« Reply #28 on: February 25, 2013, 01:00:49 AM »
I probably should have posted this image early, but nevertheless, it presents the measured monthly variations of the thickness of the CDW flow on the ASE shelf.  As the maximum thickness of CDW flow falls in September of each year, and as the regional sea level rise around the ASE due to the northern hemisphere summer melt of Greenland ice sheets; this implies that the most likely month for the Thwaites (and nearby glaciers) to surge is September (as is what is expected to have happend during the Northern Summer of 2012).
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Re: Surge of WAIS Ice Mass Loss
« Reply #29 on: February 25, 2013, 05:11:41 PM »
I propose that the now disintergated Thwaites Iceberg Tongue (not the current Thwaites Tongue) provides evidence that the Thawites Glacier has "surged" repeatedly in the past as indicated by the surge pattern exhibited by the Thwaites Iceburg Tongue (see accompanying photo circa the winter of 2000 and the subsequent history of the evolution of the ASE coastline from 1972 to 2011 by MacGregor et al. 2012).  The Thwaites Iceberg Tongue was first noted in the 1930's, & I propose that it represents evidence that the subglacial melt water network beneath Thwaites had be periodically triggered even before the 1930's and would surge forward periodically.  I further propose that the presence of warm CDW in the ASE since the 1990's directly lead to the rapid disintergation of the Thwaites Iceberg Tongue and also created a subglacial cavity at the threshold of Thwaites leading to the lip that decends into the BSB.  Furthermore, I propose that the synergy between the subglacial melt water network and the advection of the warm CDW in the subglacial cavity will cause the frequency of the periodic surges to accelerate (possibly once a year) until the elevation of the surface of the ice at the threshold of the Thwaites Glacier has decrease sufficiently (see PIG) to allow the bottom of the glacial ice at the threshold of Thwaites to float up off of the various submarine mounds and ridges that are currently pinning it from surging forward over a broad front (see previously shown bathymetry). These images are presented as evidence to support my proposed surging mechanism which may take several decades to set-up the postulated future surge over a broad front, but this process should be accelerated by the extension of the subglacial cavity down the negative slope leading to the BSB by the continued advection of warm CDW.
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Re: Surge of WAIS Ice Mass Loss
« Reply #30 on: February 26, 2013, 01:30:34 AM »
I thought it would be good to note that:  Last year an NSF-ANT award has been made to "... isolate essential physical processes affecting Thwaites Glacier, TG, ice mass outlet using a suite of existing numerical models in conjunction with existing and International Polar Year (IPY)-proposed data sets. In the NSF-ANT study four different models will be utilized to explore the effects of embayment geometry, ice-shelf buttressing, basal-stress distribution, surface mass balance, surface climate, and inland dynamic perturbations on the present and future dynamics of TG.   Simplifications of the stress field (shallow-ice, shelf-stream, and higher-order), system geometry, and mass-momentum-energy coupling (mechanical and thermo-mechanical), will be made. The models will be constrained and validated by data sets (including regional maps of ice thickness, surface elevation, basal topography, ice surface velocity, and potential fields) and geophysical data analyses (including increasing the spatial resolution of surface elevations, improving regional estimates of geothermal flux, and characterizing the sub-glacial interface of grounded ice as well as the grounding-zone transition between grounded and floating ice)."

It is noted that after the collapse of the Thwaites Ice Tongue (which could happen within a few years time given the Sept 2012 surge and presumed degradation of the Tongue pinning mechanism) many researchers have estimated that the rate of ice mass loss from the Thwaites Glacier will likely double.
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Re: Surge of WAIS Ice Mass Loss
« Reply #31 on: February 26, 2013, 06:27:12 PM »
As I believe that many readers are not grasping the implications of my reported "surge" behavior for Thwaites (and Ferrigno) Glacier, I will soon open several new threads including one devoted to using hazard analysis to delineate the future ice mass loss for the coupled PIG and Thwaites glacial systems during their initiation stage until about 2040 to 2050; and a new thread with an overview critique of the current IPCC WG1 position on abrupt SLR (including a critique of Pfeffer et al).  Until then I will close my planned input to this thread (unless readers ask questions) by presenting the attached image of how the Ross Sea Embayment's, RSE, grounding line has retreated continuously since the LGM (Eemian).  While the Ross Ice shelf is a cold ice shelf without warm CDW circulation still the prior glacier has been undermined by both the sinking of cold salinity Antarctic Bottom Water (due to the annual formation of sea ice) and due to tide water exchange beneath the ice shelf.  While this underming process has taken at least 100,000 years for RSE, I propose that a similar action will happen for the Thwaites Glacier form a new Thwaites Ice Shelf over the current BSB by 2050 to 2060, due to the combined action of warm CDW advection and the associated CDW subglacial cavity formation with the existing subglacial melt water network (streams and lakes) beneath Thwaites; and that this phenomena will thereafter accelerate ice mass loss in the PIG/Thwaites drainage basins by combined advective ice melting beneath the ice shelf and the float-out of icebergs out of the PIG and Thwaites Glacier gateways.
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Re: Surge of WAIS Ice Mass Loss
« Reply #32 on: March 03, 2013, 05:24:57 AM »
Dear AbruptSLR,

I am a new comer to this forum, because I live in Tasmania I am particularly interested in what you have  to say about Antarctica.  Do you think there will be noticeable effects on surrounding land masses from these events ? If so what do you think they might be?

Thanks

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Re: Surge of WAIS Ice Mass Loss
« Reply #33 on: March 03, 2013, 02:00:13 PM »
Hello SG,

My collapse hazard scenario for the WAIS is based on the assumption that we remain close to the Recommended Concentration Pathway, RCP 8.5 50% Confidence Level (CL) radiative forcing scenario developed by the IPCC at least until approximately 2045 (as the thermal inertia of the ocean will continue delivering heat to the Antarctic long after anthropogenic radiative forcing [eg: greenhouse gas emissions] are brought under control.  Therefore, some people will say that following RCP 8.5 50% CL until 2045 is not likely and that you have nothing to worry about, while others will say that if we follow RCP 8.5 50% CL until 2045 you will have more to worry about from extreme weather and global economic/military consequences, than from the risk of abrupt sea level rise, ASLR, in your lifetime; however, I believe that ASLR will compound these other problems and will definitely have large negative affects on the next generation.  Nevertheless, to give a more straight forward response to your question, the accompanying "Finger Print" map of the Greenland Ice Sheet, GIS, and the West Antarctic Ice Sheet, WAIS, ice mass loss contributions to regional SLR indicates that for Tasmania will not have any regional multiplier effect from the "Finger Print" effect for ice mass loss from WAIS, therefore, according to the graphs that I provide in the "philosophical" thread for the RCP 8.5 50% CL collapse scenario Tasmania may experience about a 0.5m SLR by the year 2060 and about a 3m SLR by 2100 (including all SLR contributions around the world not just from the WAIS).  To get the final local effect on your risk of flood you would need to add on to of these values the short-term sea level factors such as tides, storm surge, storm tide, local land elevation changes, and regional variability in sea level (such as ENSO events or multi-decadal variations in sea level), as indicated in the second attached figure.
Good luck down under!
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Re: Surge of WAIS Ice Mass Loss
« Reply #34 on: March 04, 2013, 11:13:47 PM »
Thank you for your reply AbrupSLR,

You may be interested to heat about the local weather changes occurring here.  It is getting warmer.
Traditionally, say 100 years ago, Apples were exported from the far south, Port Huon, Cygnet etc.  There are stories for ice being so thick the horses carts could not safely work in the docks and they where unloaded and carried to the ships by men.  This means extremely thick ice and black ice  about March April.

If ice occurred now in March April it would be extremely surprising.  Now It is the end of, usually very dry summer seasons and a peak bush fire season.  This year has been quite bad for bush fires.  No ice yet!

Cheers

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Re: Surge of WAIS Ice Mass Loss
« Reply #35 on: March 05, 2013, 12:54:35 AM »
sg,

Thanks for the update on the recent weather changes in Tasmania.  If you read through my posts in the "Collapse Main Period" thread, then you will see that around 2065 when enough ice melts from Antarctica to cool large parts of the Southern Ocean, then according to Hansen and Sato 2012, the cyclones around the Southern Ocean will increase in frequency and intensity (due to the severe thermal gradient in the ocean and the projected high humidity in the atmosphere), and I hope that any such cyclone miss Tasmania in the distant future.

Good day, ASLR
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Re: Surge of WAIS Ice Mass Loss
« Reply #36 on: March 07, 2013, 08:53:04 PM »
While I realize that it may take at least ten more years of data to even indicate a new trend line for NOAA's global SLR trend line; nevertheless, if my postulation of a surge event in the summer of 2012 is correct, then it is possible that a new trend line has been established due to accelerated ice mass loss from the WAIS as indicated by my hypothetical new trend line superimposed on the attached image from NOAA showing the global SLR trend through the end of February 2013.
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Re: Surge of WAIS Ice Mass Loss
« Reply #37 on: March 09, 2013, 11:58:14 PM »
AbruptSLR,

Thanks for all of your efforts to give us a comprehensive picture of what is in store for us as the Antarctic continues to suffer the effects of AGW, even if much of what you post sails a bit above my aging grey matter.

Regarding your last figure, showing a potential new trend line,  I have several questions:

1.  Does that include the GIS mass loss in 2012?
2.  What was the SLR contributions (or mass loss) from the WAIS in 2012?
3.  What was the Net SLR contributions (or mass loss) from Antarctica in 2012?
4.  If your hypothetical new SLR trend line holds to be true, what do you estimate the current global SLR/year to be?

FYI, I just posted a video. on the Cryospheric Contributions to SLR, from the American Geophysical Union  (December 2012), on the Greenland  & Arctic Circle board:

https://forum.arctic-sea-ice.net/index.php/topic,109.0.html 

This presentation showed that Greenland and Antarctica contributed 0.27mm/yr to SLR in the 1990s and had increased to 0.95mm/yr between 2005 & 2010.  This is almost a quadrupling of the combined contributions in less than 20 year.

THANKS
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Re: Surge of WAIS Ice Mass Loss
« Reply #38 on: March 10, 2013, 01:43:53 AM »
OldLeatherneck,

First, yes the NOAA eustatic SLR data includes SLR contributions from GIS for 2012 (the NOAA data is measured directly from the ocean surface and not a number derived from various different contributing sources).  As indicated in the attached figure of GRACE satellite measured ice mass loss for the GIS loss about 700 Gt of ice mass from March to Sept 2012, and typically gains about 150 Gt of ice mass from a typical Oct to a typical Feb (inclusive).  As eustatic SLR increase about 0.28 mm per 100 Gt of ice mass contributed, this means that from March to September 2012 the GIS contributed about 2mm to SLR, and probably subtracted about 0.42mm from Oct 2012 to Feb 2013 (not the data for this period has not yet been made public).  As I cannot find the corresponding GRACE data for the same timeframe on the internet for either the AIS or the WAIS, I can only estimate the atypical contribution from the AIS (assumed to be dominated by the WAIS contribution) as follows:  From January 2012 to January 2013 eustatic sea level rose about 7mm, while for a typical year the rise should be 2.8 mm (per NOAA) which in a typical year should include a 0.7mm contribution from the GIS, but last year included a contribution of about 1.58mm, this means that the AIS contribution (dominated by WAIS) last year was about 7-2.8-(1.58-0.7) = 3.32mm.
Regarding the slope of my estimated possible new trend line (the rate of SLR/yr) it is 4.7 mm/yr (vs. NOAA's value of 2.8 mm/yr); which if maintained would support my hazard analysis. 

If someone with direct access to GRACE satellite data could post this information it would be helpful, otherwise, this is as accurate as I can be for now.
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Re: Surge of WAIS Ice Mass Loss
« Reply #39 on: March 10, 2013, 05:43:23 AM »
AbruptSLR,

Thanks  for  you prompt and informative response.  You have, as always, provided valuable information.

May I make a recommendation.  While I have been following AGW/CC for many years and very closely for the past year, your posts include terminology, references and acronyms that are far behond the comprehension of the nominal citizen searching for information regarding the future impacts of AGW/CC.  It might help, time permitting, if you were to create another topic with a glossary of terms and definitions.
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Re: Surge of WAIS Ice Mass Loss
« Reply #40 on: March 10, 2013, 09:24:40 AM »
ASLR,
Does your 3.3 mm estimate from AIS include potential extra water from La Nina stored on the continents flowing back into the ocean? See Hansen et al 2011 for this suggestion:
http://pubs.giss.nasa.gov/docs/2011/2011_Hansen_etal.pdf

I don't know how much this effect could have contributed, maybe about 0.5 mm? Still, if so, 2.8 mm from AIS would be a very large increase from the average over the past 5-10 yrs.

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Re: Surge of WAIS Ice Mass Loss
« Reply #41 on: March 10, 2013, 01:03:50 PM »
OldLeatherneck,

It is true that as I write these posts that I am imagining writing to expects in this field, such as those in IPCC WG1; but nevertheless, per your request I will post an incomplete glossary in the "Critique" thread where it seems to be most appropriate.

Lennart,

I attach two images from NASA illustrating how the extra water from La Nina got stored on the continents creating the indicated sharp 6mm drop in sea level until March 2011; however, I assume that by January 2012 almost all of this water has returned to the ocean as the "dip" in the NOAA SLR trend line has completely infilled by that time.  Therefore, I am seriously proposing that a 2012 surge in ice mass loss from the WAIS was on the order of 3.3 mm in one year; indicating how non-linear/non-stationary systems can accelerate quite rapidly.
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Re: Surge of WAIS Ice Mass Loss
« Reply #42 on: March 10, 2013, 03:09:41 PM »
ok, so with this La Nina-rebound fully included, this would indeed be a very remarkable surge; some peer review would be useful now :)

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Re: Surge of WAIS Ice Mass Loss
« Reply #43 on: March 10, 2013, 04:53:38 PM »
Lennart,

The most useful peer review would be if you could bring this matter to a qualified scientist's attention (as I am an engineer) who has access to the GRACE satellite data for 2012, and the IceBridge ground penetrating radar survey data of the Thwaites Glacier gateway from Oct 2012.  Ever since July 2012 NASA has stopped updating the GRACE ocean graphics (from JPL) such as the one that I am re-posting here from the start of this thread, showing a 7cm hole in the ocean north of the WAIS as of July 2012 (and if I am right this hole in the Amundsen/Bellingshausen/Weddell Seas has got bigger since then). 

In the way of other evidence that you can submit for peer review I post the second image from NOAA of the SLR trend for the North Pacific which shows a Jan-Feb 2013 cummulative sea level rise (from 2000) of about 49mm which is approximately 1.5 to 2mm above its traditional maximum seasonal fluctuation.  Now according to the "Finger Print" map shown in the third image the North Pacific Ocean sea level should increase by about 30% more than the eustatic sea level rise (note that the fourth image from Jan/Feb 2013 only shows a eustatic/global cummulative sea level rise of 42mm since 2000) associated with ice mass loss from the WAIS, and as I estimated a 3.32mm eustatic sea level rise from the postulated 2012 WAIS surge, this should account for 3.32x 0.3 = 1mm of the regional sea level rise in the North Pacific Ocean beyond that which can reasonably be accounted for by a conservative estimate of seasonal/interannual sea level fluctuations.
« Last Edit: March 10, 2013, 05:09:08 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #44 on: March 10, 2013, 07:54:08 PM »
The accompanying figure may support the idea that as WAIS surge began in the Summer of 2012, accelerated in the Fall of 2012 and then stablized by the beginning of 2013, which is also the pattern indicated by the surging of ice tongues for the Thwaites and Ferrigno Glaciers (see earlier posts)
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Re: Surge of WAIS Ice Mass Loss
« Reply #45 on: March 11, 2013, 11:11:15 AM »
ASLR,
Do you know why the NOAA-global mean sea level figure seems to differ from the Colorado one? The NOAA-trend is 2.8 mm/yr, while the Colorado-one is 3.2 mm/yr:
http://sealevel.colorado.edu/content/2013rel2-global-mean-sea-level-time-series-seasonal-signals-removed

As to peer review: who would be the right experts to approach? I suppose Tinto & Bell and Mauri Pelto would maybe want to comment, since they've predicted and observed this Thwaites surge. Maybe Jim Hansen would be interested as well. As for GRACE-experts, I would have to look them up, but maybe you already know who they are?

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Re: Surge of WAIS Ice Mass Loss
« Reply #46 on: March 11, 2013, 12:01:40 PM »
Lennart,

The difference in the 2.8 mm/yr SLR trend rate for NOAA and the 3.2mm/yr value from University of Colorado, is the Glacial Isostatic Adjustment, GIA, factor of about 0.3 to 0.4 mm/yr.  The GIA is due to on-going deepening of the oceans as magma flows from beneath the seafloor to under the continents (due to rebound from past & present glacial retreats), and is explained in detail on the University of Colorado's website.  This GIA factor is not relevant to the discussion of whether a surge occurred or did not.  Your choice of scientists sounds fine, and I believe that John Wahr of the University of Colorado should have access to any GRACE data needed for this discussion.
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Re: Surge of WAIS Ice Mass Loss
« Reply #47 on: March 11, 2013, 02:57:40 PM »
ASLR,

I just sent out this email:

Dear Robin Bell, Kirsteen Tinto, Mauri Pelto, John Wahr, and Jim Hansen,

I would like to point your attention to this Antarctica-page on the new Arctic Sea Ice Forum:
https://forum.arctic-sea-ice.net/index.php/topic,21.0.html

On this page an apparently well-informed engineer discusses the surge/unpinning of Thwaites Glacier in Sept-Oct 2012, with reference to Tinto & Bell 2011 and Mauri Pelto's Glacierchange-blog, amongst others.

His estimate is that this surge has contributed about 3.3 mm to global mean SLR. That would imply this surge would have shed about 1200 Gton of ice to the ocean, if I'm not mistaken. That would seem like a very large surge, so I'm wondering if you maybe have more info on this.

Do you know if GRACE-data, or maybe other data (e.g. on the La Nina-rebound effect that Hansen et al 2011 on earth's energy imbalance mentions), can confirm or falsify this estimate? Or if not yet, when is such information to be expected?

And do you think this surge could indeed have been the start of faster ice loss from Thwaites Glacier, as Tinto & Bell 2011 seems to have predicted? If so, to what extent would such acceleration have been included in SLR-projections for this century?

Thank you for any reply, with kind regards,

Lennart van der Linde
The Hague Environmental Center
Netherlands

If you send me a mail at lennart.vanderlinde[at]haagsmilieucentrum.nl I can forward and/or carbon copy any replies to you directly.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #48 on: March 11, 2013, 03:50:05 PM »
Lennart,

Thank you very much (I will contact you later by e-mail from my other account).  However, to avoid some misunderstanding regarding what I have loosely referred to as a "Surge" event during the Summer and Fall of 2012 for WAIS; I was referring to ice mass loss contribution to SLR from all of the WAIS not just ice export out of the Thwaites Glacier gateway.  This distinction is important because:
(a) As stated in the "Surge" thread I postulate that the export of ice out of the Thwaites Glacier gateway was accompanied by an outburst of a significant quantity of ice meltwater from the Thwaites Subglacial meltwater network.  This outburst probably not only lubricated the export of ice out of the Thwaites Glacier gateway (thus reshaping the Thwaites Ice Tongue), but also probably dropped the surface elevation of the Thwaites Glacier over the areas where the subglacial meltwater drained from.
(b) As stated in the "Surge" thread I postulate that the Ferrigno Glacier also surged in the same timeframe, probably also exporting some subglacial meltwater together with the ice export that reshaped its ice tongue.
(c) Although less significant I also mentioned that some melting of grounded ice at the grounding line of the Filchner Ronne Ice Shelf, FRIS, and the Pine Island Ice Shelf, PIIS, could have made smaller contributions, each.

Of these, certainly the ice mass loss contribution from the Thwaites drainage basin is most likely to have made the largest contribution.
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Re: Surge of WAIS Ice Mass Loss
« Reply #49 on: March 11, 2013, 03:59:18 PM »
ASLR,

Thanks for the correction of my mail to the experts, that I will forward to them. This of course makes more sense, so I should have worded my mail more carefully. Let's see if they reply.