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Author Topic: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe  (Read 99252 times)

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #50 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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #51 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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #52 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


"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."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #53 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


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."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #54 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


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."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #55 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).  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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #56 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

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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #57 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



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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #58 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #59 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
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #60 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
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.
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #61 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.
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #62 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #63 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

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #64 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #65 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
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), 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
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #66 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #67 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

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #68 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
We do not err because truth is difficult to see. It is visible at a glance. We err because this is more comfortable. Alexander Solzhenitsyn

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #69 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #70 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

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)."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #71 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
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #72 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

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

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #73 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,
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #74 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

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), 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."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #75 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

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."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #76 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/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
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #77 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

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."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #78 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://phys.org/news/2014-01-giant-antarctic-glacier.html

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 "
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #79 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.

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #80 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
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #81 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

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."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #82 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
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #83 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/

The Ocean2ice goals are stated at the following link:

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/dynamic-ice-istar-c/
http://www.istar.ac.uk/projects/ice-loss-istar-d/
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #84 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

"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."
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #85 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:
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #86 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. 
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #87 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


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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #88 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

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
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #89 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/

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

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #90 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
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nukefix

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #91 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?

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #92 on: April 21, 2014, 04:22:50 PM »
nukefix,

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

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ASLR
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #93 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/

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
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sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #94 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

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #95 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
« Last Edit: April 26, 2014, 05:56:19 PM by AbruptSLR »
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sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #96 on: April 26, 2014, 04:32:27 AM »
yes, Bassis was the one. thanx

sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #97 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.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #98 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

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."
« Last Edit: May 30, 2014, 12:38:09 AM by AbruptSLR »
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #99 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson