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AbruptSLR

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The WAIS Workshop 2013
« on: December 16, 2013, 02:57:39 PM »
The following links are to all of the abstracts, and pdf's of the available session presentations, from the WAIS Workshop 2013.  As I do not have time to comment about all of these abstracts & presentations at the moment, I invite any interested parties to download and comment on any of these downloads either in this new folder, or in any of the other relevant folders.  As time permits, I will comment on the downloads that I think are of most interest:

Abstracts:
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/abstracts

Session 1 (Whillians Ice Stream)
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session1/
Session 2
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session2/
Session 3
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session3/
Session 4
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session4/
Session 5
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session5/
Session 6
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session6/
Session 7
ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session7/

“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: The WAIS Workshop 2013
« Reply #1 on: December 16, 2013, 03:29:43 PM »
To start this thread off, I present the following abstract from Bassis and I attach the accompanying image that illustrates his findings for the Big 4 Antarctic ice shelves: (a) Ross Ice Shelf, RIS; (b) Filchner-Ronne Ice Shelf, FRIS, (c) Amery Ice Shelf, and (d) Larsen C.  This attached image illustrates that most crevasses begin near the grounding line and then undergo local plastic necking damage at widely different rates depending largely on whether the ocean forcing locally beneath a shelf either partially heals the crevasse by accreting basal ice into the basal crevasse, or partially melts ice in the basal crevasse.  The basal melting – plastic necking mechanism should thus be very important for the Pine Island Ice Shelf, PIIS, not explicitly discussed by Bassis (2013), as PIIS has greatest amount of ocean forcing of basal melting of any large ice shelf in Antarctica:


Evolution of basal crevasses links ice shelf stability to ocean forcing
Jeremy N. Bassis
Department of Atmospheric, Oceanic and Space Sciences, University of Michigan
 
"Basal melting and iceberg calving are the primary mechanisms responsible for transferring mass from the ice shelves to the ocean. Although the connection between basal melting and ocean forcing is clear, the effect of ocean forcing on iceberg calving remains more controversial with conflicting hypothesis about whether a warming ocean will increase or decrease iceberg production. Previous theories of iceberg calving have often relied on various flavors of fracture mechanics, assuming that iceberg calving is a brittle process. Here I use a perturbation analysis to show that the strain weakening nature of ice allows initially narrow basal crevasses with width much smaller than the ice thickness to seed a visco-plastic instability that gives rise to locally enhanced ductile deformation and ice shelf thinning over length scales that are comparable to the ice thickness. This process, called plastic necking, widens basal crevasses and allows crevasses to penetrate an increasing fraction of the ice thickness as they advect downstream. This instability, however, is weak and progresses slowly, allowing enhanced melting or accretion of marine ice within basal crevasses to have a strong influence on crevasse geometry. Despite large uncertainty in ice-ocean interaction on the scale of individual crevasses, this model is able to explain the difference between the quasi-steady short (<15 km long) Erebus Glacier Tongue and much longer (>80 km long) Drygalski Ice Tongue. Moreover, application of the model to the four largest Antarctic ice shelves predicts that deep crevasses form downstream of the grounding line that correspond to locations of fractures visible in satellite imagery. However, accumulation of marine ice within basal crevasses can substantially decrease crevasse penetration heights, increasing ice shelf stability, providing a strong link between iceberg calving and ocean-forcing. Moreover, the plastic necking instability amplifies any perturbation to the ice shelf thickness (with appropriate wavelength) allowing perturbations due to, for example, melt channels, to seed the necking instability."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: The WAIS Workshop 2013
« Reply #2 on: December 16, 2013, 04:04:21 PM »
Thanks for this and all the good work you do. But if I may be so presumptuous, I wonder if you might help out those of us less familiar with the wide scope and intimate details of this research by contextualizing these pieces and bringing out what you see as their main contributions. I, at least, would find that enormously helpful. Thanks ahead of time--wili
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #3 on: December 16, 2013, 04:17:26 PM »
wili,

I will provide comments on key articles as I have time, and the next in line is as follows:

Next, I present the following abstract from Clem & Fogt (2013) which is related to the following 2014 peer-reviewed paper (in press):

Clem, K. R., and R. L. Fogt, 2014:  "Varying roles of ENSO and SAM on the Antarctic Peninsula Climate".  J. Geophys. Res, in press.

 ENSO and SAM Relationships Across the Antarctic Peninsula in Contrast to West Antarctica
Kyle R. Clem and Ryan L. Fogt
Scalia Laboratory for Atmospheric Analysis, Department of Geography, Ohio University, Athens, OH
Abstract: "Recent analysis has suggested that the warming trends in West Antarctica and the Antarctic Peninsula are primarily of tropical origin, through atmospheric teleconnections. There is a strong seasonality to these connections, and the relationship also varies in space in time. Here, connections with tropical (specifically, the El Niño-Southern Oscillation, ENSO) and hemispheric circulation patterns (specifically, the Southern Annular Mode, SAM) are contrasted across the Antarctic Peninsula and West Antarctica. We note that during austral winter and spring, ENSO has a persistent relationship across the western Antarctic Peninsula temperatures, while SAM has a persistent relationship with temperatures across the northeastern Antarctic Peninsula. Meanwhile, the ENSO relationship with temperatures across the northeastern Antarctic Peninsula, and the SAM relationship with temperatures along the western Peninsula vary in time, especially in austral spring. In contrast, the relationship of these two climate patterns and temperatures across West Antarctica is more complicated and less persistent. Using the newly reconstructed Byrd temperature time series, we find significant relationships with SAM and temperatures across West Antarctica, but only in certain seasons. The ENSO relationship is weaker and statistically insignificant and varies in time and season as a function of the location and magnitude of the teleconnection to the South Pacific. Together, these results suggest that linking the warming across both the Antarctic Peninsula and West Antarctica to either changes in ENSO or SAM requires careful consideration of temporal and spatial variations in the atmospheric response in the Amundsen-Bellingshausen Seas associated with these patterns."

I also attach the following three images from the PowerPoint pdf:

The first image shows the range of the Amundsen Bellingshausen Sea Low, ABSL, and it's area of possible influence.

The second image shows correlations between the Southern Oscillation Index (or the El Nino Southern Oscillation: ENSO), the Southern Annular Mode (SAM), the ABSL mean sea level pressure (MSLP), and where SON is the austral spring (or September October November).
The third image shows Clem & Fogt 2013's summary.

This information emphasizes the importance of both the intensity and location of the ABSL with regard to the expected warming in both the Antarctic Peninsula and the West Antarctic; thus as I have stated in other threads, when the ABSL drifts into position to blow warm ocean water into the Amundsen Sea Embayment, ASE, one can expect ice mass loss from the glaciers around the ASE to accelerate.
“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: The WAIS Workshop 2013
« Reply #4 on: December 16, 2013, 05:52:41 PM »
To provide more of the context that wili asked for about the Bassis presentation, I provide the additional background considerations:

(a) All four ice shelves that Bassis focuses on (RIS, FRIS, Amery and Larsen C) are all considered to have "cold" ocean forcing; in that after the basal crevasses are formed near the grounding lines, they tend to be healed by the infill of ice into the basal crevasse due to the "cold" ocean forcing currently present in these shelves.

(b) However, recent calculations shows that warm ocean forcing (water) is currently leaking into areas beneath these cold ice shelves and with expected changes in ocean currents these leaks of warm water inflow should accelerate, see: (i) Mayewski, P.A., Maasch, K.A., Dixon, D., Sneed, S.B., Oglesby, R., Korotkikh, E., Potocki, M., Grigholm, B., Kreutz, K., Kurbatov, A.V., Spaulding, N., Stagger, J.C., Taylor, K.C., Steig, E.J., White, J., Bertler, N.A.N., Goodwin, I., Simões, J.C., Jaña, R., Kraus, S. and Fastook, J. 2013. "West Antarctica’s Sensitivity to Natural and Human Forced Climate Change Over the Holocene", Journal of Quaternary Science 28(1), pp 40-48. DOI: 10.1002/jqs.2593.; and (ii) Hellmer, H.H., Kauker, F., Timmermann, R., Determann, J., and Rae, J. (2012) "Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current" Nature, Vol. 485, May 10, 2012, p. 225. doi: 10.1038/nature11064.

(c) Such warm ocean forcing (as discussed in point (b)) many convert some of these "cold" shelves into "warm" shelves (particularly FRIS after 2050), which could contribute to accelerated calving of such shelves (note that the ice shelves in ASE are considered "warm" and during the 1980's and 1990's there were massive calving events in this area as discussed by: MacGregor, J.A., Catania, G.A., Markowski, M.S., Andrews, A., (2012), "Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011", Journal of Glaciology, Vol. 58, No. 209, doi: 10.3189/2012JoG11J262.

Viewed in this light the current "cold" shelves may not be as stable as previously thought (see my discussion in the FRIS/RIS thread).
“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: The WAIS Workshop 2013
« Reply #5 on: December 17, 2013, 12:43:10 AM »
To provide more of the context that wili requested with regard to the Clem & Fogt 2013 presentation (see my prior post in this thread); I would like to point-out that due both to the El Nino hiatus and the Antarctic ozone hole, the ABSL has migrated westward in the past couple of decades (see: SCOTT HOSKING, J.; ORR, ANDREW; MARSHALL, GARETH J.; TURNER, JOHN; PHILLIPS, TONY, (2013), "The Influence of the Amundsen-Bellingshausen Seas Low on the Climate of West Antarctica and Its Representation in Coupled Climate Model Simulations", Journal of Climate . Sep2013, Vol. 26 Issue 17, p6633-6648).  When the El Nino hiatus period ends and the ozone hole begins to heal itself, one can expect the ABSL to migrate back eastward; where it should more frequently telecommunicate heat from the Pacific into the ASE, thus promoting ice mass loss in this critical area.  I believe that essentially no published estimates of ice mass loss from the ASE glaciers account for this consideration.
“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: The WAIS Workshop 2013
« Reply #6 on: December 17, 2013, 01:36:34 AM »
Next I present the abstract from Schroeder et al 2013:

Radar Scattering Tell Us About the Relative Character of Past and Future Retreats in the Amundsen Sea Embayment?
Dustin Schroeder, Donald Blankenship, Duncan Young
University of Texas Institute for Geophysics

Abstract: "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 apply a new algorithmic approach to measuring the radar scattering function of the ice/bed interface by performing range-migrated SAR focusing using multiple reference functions spanning different ranges of Doppler frequencies for 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 the application of this technique to a gridded airborne radar survey over the entire catchment of Thwaites Glacier, West Antactica. We show how this information can be used to constrain the morphology of basal bedforms and infer the distribution of deformable sediments and crystalline bedrocks across the catchment. We compare this distribution to offshore bedforms and sediment records on the deglaciated inner continental shelf of the Amundsen Sea Embayment. We also discuss the potential implications for the processes and timing of previous, contemporary, and potential grounding line retreats in the region."

I now refer to the first attached image from Schroeder et al 2013 which makes the case that the contemporary/extant bed conditions beneath the Thwaites Glacier are similar to those beneath the Paleo-Pine Island Glacier, Paleo-PIG (now in the middle of the ASE); and this comparison is re-enforced by the second accompany image which presents Schroeder et al 2013's conclusion (see additional evidence for their conclusions in their presentation pdf).  While the authors of this presentation must be circumspect, I do not need to be so; therefore, in order to provide the context that wili asked for, I point out that it is likely that the Paleo-PIG collapsed abruptly during Meltwater Plus 1A, when SLR rose at an abrupt rate (see: Deschamps, P., Durand, N., Bard, E., Hamelin, B., Camoin, G., Thomas, A.L., Henderson, G.M., Okuno, J., and Yokoyama, Y., (2012), " Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago", Nature, Vol. 483, 559, doi:10.1038/nature10902).  Thus by extension Schroeder et al 2013, are hinting that with similar bed conditions, that the Thwaites Glacier may also collapse in an abrupt fashion (once the groundling retreats past the transition line shown in the first attached image).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: The WAIS Workshop 2013
« Reply #7 on: December 17, 2013, 10:32:15 AM »
"I will provide comments on key articles as I have time"

Thanks, ASLR. I really do appreciate all you do here.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #8 on: December 17, 2013, 03:45:00 PM »
As a follow-up to the Schroeder et al 2013 presentation I next post the Kirshner et al 2013 abstract, which explicitly warns that the Thwaites Glacier is poised for a meltwater-intensive retreat similar to the three documented such retreats in the Pine Island Bay during the Holocene:

"The Sedimentary Record of Meltwater Intensive Glacial Erosion in Pine Island Bay, West Antarctica and Implications for Glacial Dynamics
Alexandra E. Kirshner 1, Carolyn M. Branecky 1, John B. Anderson 1, Witold Szczuciński 2, Dustin Schroeder 3, Don Blankenship 3, and Martin Jakobsson 4
1 Rice University, Department of Earth Sciences, 6100 Main Street, Houston, TX 77005, USA
2 Adam Mickiewicz University, Institute of Geology, Maków Polnych 16, 61-606 Poznań, Poland 3 University of Texas Institute of Geophysics, Austin, TX
4 Stockholm University, Department of Geological Sciences, Stockholm, Sweden
Here we show that the uppermost sediments in Pine Island Bay were deposited from a meltwater plume, a plumite, which episodically occurred during the late stages of ice sheet retreat since ~7-8.6 k cal yr BP and most recently during modern times. It is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line. The most recent release of sediment coincides with rapid retreat of the grounding line, and has an order of magnitude greater flux relative to the entire unit, indicating episodic sedimentation. These observations are consistent with recent results from Smith et al. (2012) for rapid subglacial erosion beneath Pine Island Glacier.
Our identification of a meltwater-derived deposit has profound implications for understanding glacial instability and numerically modeling ice sheet dynamics for more accurate predictions. This study demonstrates that punctuated meltwater-intensive glacial retreat may have occurred at least three times in the Holocene in this region. We further suggest that the modern Thwaites Glacier is poised for a meltwater-intensive similar retreat.
Reference
Smith, A.M., Bentley, C.R., Bingham, R.G., and Jordan, T.A., 2012, Rapid subglacial erosion beneath Pine Island Glacier, West Antarctica, Geophysical Research Letters, 39, 1-5."

To put this research into context, the WAIS Divide bole-hole has found basal geothermal heat flux beneath Thwaites Glacier that is several times what was previously assumed (resulting in a well-developed subglacial hydrological system beneath the Thwaites Glacier, (see the subglacial hydrological thread), and a shift of the ABSL combined with a warm austral summer could easily result in considerable future surface melt in the Thwaites Gateway that could flow into the numerous surface crevasses in the Thwaites Gateway that could trigger rapid calving and groundling retreat in a manner recently projected for the Jakobshavn Glacier.  Furthermore, as cited in the EAIS thread the Recovery Glacier/Ice Stream also has a well-developed subglacial hydrological system and a high basal geothermal heat flux, and thus is likely also poised for a meltwater-intensive groundling line retreat after 2070.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: The WAIS Workshop 2013
« Reply #9 on: December 17, 2013, 09:44:17 PM »
Re:Thwaites

The Joughin and Smith presentation ends with:

"• Formation of a strong ice shelf as the grounding line recedes is crucial
for maintaining small losses over the next 2.5 centuries.
• A weakened shelf (50%B) could increase losses by more than order of
magnitude (5+ mm/yr).
• Complete inability to form an ice shelf (i.e., a grounded terminus) would
yield a rapid collapse (10+ mm/yr)."

Watch the shelf.

sidd

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #10 on: December 17, 2013, 11:14:50 PM »
Sidd,

It is great to see you posting in the Antartic folder again, and congratulations on making over 100 posts.  Obviously, from Joughin & Smith's findings a SLR contribution from Thwaites of 10+ mm/r if its ice shelf collapses would result in the NRC 2013's definition of abrupt SLR.

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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AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #11 on: December 18, 2013, 02:45:49 AM »
I would like to the first image to Sidd's post about Joughin & Smith's 2013 presentation about Thwaites sensitivity to its ice shelf.  This first image shows the measured change in surface elevation for the Thwaites Gateway between January 2012 and January 2013, showing up to a 6m drop in surface elevation in one year.  While the second attached image shows a Landsat 7 photograph of the surface cracking of the Thwaites Ice Tongue in January 2013, in the area indicating a 6m drop in surface elevation in the first image.  Looking at the deteriorated condition of the Thwaites Ice Tongue it is very easy to imagine that the Thwaites Ice Shelf could easily deteriorate or collapse altogether in the not too distant future (say a decade or two from now).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: The WAIS Workshop 2013
« Reply #12 on: December 18, 2013, 05:34:02 AM »
Fig 6. from Joughin and Smith, (the second image from Landsat, Jan 2013, in the preceding post) exhibits the tight correlation between the width of the icebergs (along flow direction, right to left) with the distance between topo induced ripples that run cross flow (up to down)

But staring at that picture, i see that the crevassing (indicated by the black arrows at the right) which run along flow have a spacing that seems to determine the length of the icebergs (top to down, across flow)

so between them the spacing of the topo induced ripples across flow and the crevassing along flow quite precisely determine the (ice air interface) area of incipient iceberg prior to calving. After calving they fall over, cant see this clearly in the separated pack.

I speculate the crevasses are caused, as in PIG, by meltwater plumes, the spacing between them determined by the hydrology, including heat flux. Getting this right is a very difficult calculation, but perhaps we can use the number (the spacing between crevasses is roughly twice the spacing between topo ripples, so say 2Km) to constrain the models.

There is similar data from PIG presented at this workshop which gives the size of the crevasse spacing, and they have verified now that the crevasses are caused my meltwater plume below, but i have not the time to dig it out right now.

sidd

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Re: The WAIS Workshop 2013
« Reply #13 on: December 18, 2013, 07:53:00 AM »
The PIG spacing between crevasses is about 1km, see the Bindschadler pdf session 4 pg 6

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #14 on: December 18, 2013, 04:44:11 PM »
Sidd,

Regarding your reply #12 to my reply #11, I was previously too busy to provide the referenced source for the second image in my reply #11, which is (as previously provided in the "Surge" thread):

A novel method for predicting fracture in floating ice
by: Liz LOGAN, Ginny CATANIA, Luc LAVIER, Eunseo CHOI; Journal of Glaciology, Vol. 59, No. 216, 2013 doi:10.3189/2013JoG12J210

"ABSTRACT. Basal crevasses may play an important precursory role in determining both the location and propagation of rifts and iceberg dimensions. For example, icebergs calved recently from Thwaites Glacier, Antarctica, have the same width as surface undulations, strengthening the connection between basal crevasses, rifting and calving. We explore a novel method for estimating the heights of basal crevasses formed at the grounding lines of ice shelves and ice streams. We employ a thin-elastic beam (TEB) formulation and tensional yielding criterion to capture the physics of flexed ice at grounding lines. Observations of basal crevasse heights compare well with model predictions in the Siple Coast region of the Ross Ice Shelf. We find that the TEB method is most accurate in areas of low strain rate. We also test the method in other areas of Antarctica to produce order-of-magnitude maps of grounding-line basal crevasses and find general agreement with reported observations assuming basal crevasses develop in spatio-temporal sequence and are advected downstream. This method is computationally cheap and could be relatively easy to implement into damage-oriented large-scale ice models which aim at physically simulating calving and fracture processes."

The following passage (and the attached image) from the article describes the mechanisms for active calving from the Thwaites Glacier in January 2013:

"A Landsat-7 image from January 2013 (Fig. 6) shows undulated topography which we believe may indicate the onset of basal crevasses. Measurements of the surface depression spacing (yellow bars) were compared to measurements of the freshly calved icebergs (red bars). The average spacing of the surface depressions is 1034 m, and the average width of the freshly calved icebergs is 1035m (standard deviations 217 and 224 m, respectively). This suggests that, at least in areas where basal crevasses persist long enough to reach the calving front, iceberg geometry can be controlled to a first order by the spacing of basal crevasses."

To this I would like to add that I believe that when the Thwaites Ice Tongue become ungrounded in September 2012, this caused the ice stream to the south (in the trough leading to the BSB) to "surge" northward causing the 6m surface elevation drop (indicated in the first image in my reply #11), and I believe that the vertical restraint from the sides of the trough caused the surface crevasses shown by the black arrows (upstream of the grounding line), rather than due to sub-iceshelf meltwater plumes as appears to be the case for the PIIS crevasses.  I could be wrong but it appears to me that there as several different mechanisms by which the ASE ice shelves can be disrupted.
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AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #15 on: December 18, 2013, 06:51:51 PM »
I believe that the tectonics of the West Antarctic will have a fundamental impact on future ice mass loss (which have not yet been fully accounted for yet) as indicated by the Wiens et al 2013 presentation (see abstract below).  The first figure shows the highly uncertain past estimates of basal geotechnical heat flux in West Antarctic, which shows some possible indication of high basal geotechnical heat flux beneath the Recovery Glacier.  The second image shows the very thin crust beneath the PIG/Thwaites basins indicating the likely high glacial isostatic rebound in this area; which is reinforced by the third image which shows the very low viscosity in the upper mantle beneath the BSB, indicating that this area can rebound much more quickly than most past models have estimated:


"The Structure and Seismicity of West Antarctica and Implications for the Evolution of the West Antarctic Ice Sheet
Douglas A. Wiens1, Andrew Lloyd1, David Heeszel1, Xinlei Sun1, Amanda Lough1, Andy Nyblade2, Sridhar Anandakrishnan2, Richard C. Aster3, Julien Chaput3, Audrey Huerta4, Paul Winberry4, Terry Wilson5
1Dept. of Earth & Planetary Sci., Washington University, St. Louis, MO
2 Dept of Geosciences, Penn State University, State College, PA
3 Dept of Earth & Environ. Sci, New Mexico Inst of Mining and Tech, Socorro, NM
4 Dept of Geological Sciences, Central Washington Univ, Ellensburg, WA
5 Dept of Geological Sciences, Ohio State University, Columbus, OH
New seismic results from the POLENET/ANET seismic deployment provide strong evidence that the solid earth structure of West Antarctica (WA) exerts important controls on the development of the West Antarctic Ice Sheet (WAIS). The POLENET/ANET deployment, begun in 2007, involved installation of 33 seismographs across West Antarctica and surrounding regions, including a 16 station transect from Marie Byrd Land (MBL) to the Whitmore Mountains during 2010-2012. The stations operated continuously over the Antarctic winter using insulated boxes, power systems, and modified instrumentation developed in collaboration with the IRIS PASSCAL Instrument Center. We analyze the data using several different techniques to develop high-resolution models of WA seismic structure. We use Rayleigh wave phase velocities at periods of 20-180 s determined using the two-plane wave analysis of teleseismic Rayleigh waves to invert for the three dimensional shear velocity structure. In addition, Rayleigh wave group and phase velocities obtained by ambient seismic noise correlation methods provide constraints at shorter periods and shallower depths. Receiver functions provide precise estimates of crustal structure beneath the stations, and P and S wave tomography provides models of upper mantle structure down to ~ 500 km depth along transects of greater seismic station density.
Results show that topographic lows such as the Bentley Trench and Byrd Basin are characterized by slow uppermost mantle velocities and thin (20-25 km) crust. These results confirm previous suggestions that the basins represent Cenozoic rift systems. Slow seismic velocities in the shallow mantle indicate that the thermal perturbation associated with the rifting has not yet dissipated, consistent with the inference that these basins were active during the last phase of WA tectonism [Granot et al. 2010]. Thermal anomalies from late Cenozoic rifting may provide an explanation for extremely high heat flow values inferred from the nearby WAIS drilling site and suggests that anomalously high heat flow may exert a profound influence on WAIS evolution. Slow mantle seismic velocities beneath MBL at somewhat deeper asthenospheric depths suggest a major thermal anomaly, possibly due to a mantle plume. The entire WA region shows thin lithosphere and slow seismic velocities, suggesting high upper mantle temperatures and low mantle viscosity. Using realistic rheological models we infer several orders of magnitude difference in viscosity between East and West Antarctica, with lowest viscosities found beneath MBL and the WA Rift System. The low WA upper mantle viscosities suggest that GIA occurs very rapidly in WA and must be taken into account in developing ice sheet models from GPS and GRACE constraints.
We also find evidence for currently active subglacial volcanism in MBL. Swarms of volcanic deep long period (DLP) earthquakes at 25-40 km depth coincide with subglacial highs approximately 55 km south of Mt. Sidley and Mt Waishe in the Executive Committee Range and demonstrate the existence of deep magmatic activity in this region. Subglacial eruptions may routinely provide sudden release of large quantities of water at the ice sheet base far from the coastline, and perturb the hydrological and glaciological conditions within the hydrological catchments of several of the major ice streams."
“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: The WAIS Workshop 2013
« Reply #16 on: December 18, 2013, 11:54:36 PM »
The following link leads to a free access pdf of a paper for the Cochran et al presentation about the Abbot Ice Shelf:

http://www.the-cryosphere-discuss.net/7/5509/2013/tcd-7-5509-2013.pdf


J. R. Cochran, S. S. Jacobs, K. J. Tinto, and R. E. Bell (2013), "Tectonic and oceanographic controls on Abbot Ice Shelf thickness and stability", The Cryosphere Discuss., 7, 5509–5540, 2013
www.the-cryosphere-discuss.net/7/5509/2013/, doi:10.5194/tcd-7-5509-2013
“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: The WAIS Workshop 2013
« Reply #17 on: December 19, 2013, 03:54:38 PM »
The following abstract by Zoet et al 2013 discusses seismically recorded calving events mostly from March 1-3 2011 near the gateway to the Thwaites Glacier near 75.09S 107.82W (see accompanying figure).  Besides being a very interesting use of the POLENET seismic array, due to the proximity of this calving event to the east base of the Thwaites Ice Tongue, I wonder whether this March 2011 calving event may have weakened the Ice Tongue sufficiently so that the Ice Tongue formed a collapse mechanism by Sept 2012 leading to the "surge" event that I discussed in the "Surge" thread:


Calving events near the terminus of Thwaites Glacier, Antarctica
Lucas Zoet1,2, Sridhar Anandakrishnan1, and Richard Alley1
1 Penn State University, Department of Geosciences
2 Iowa State University, Department of Geologic and Atmospheric Sciences
Using The Polar Earth Observing Network’s (POLENET) seismic array, Repeating seismic events at the terminus of Thwaites Glacier, Antarctica, likely caused by calving, were recorded on the Polar Earth Observing Network (POLENET) seismic array. Repeating events occurred in three separate episodes, with the majority of events occurring from March 1-3 2011. The events have a monochromatic signal. A seismogenic calving mechanism is proposed that would result in these observed 2 Hz signals through resonance (“ringing”) of energy within a calving ice block. Calving generates broadband noise, but the block size and seismic velocity select for only those frequencies that constructively interfere.
The events are close to the surface near 75.09S 107.82W, where radar data indicate an ice thickness of ~420 m. For a shear-wave velocity of 1840 m/s, this yields a resonance at 2.2 Hz, in good agreement with the observed ~2 Hz signals, especially if the velocity is lowered slightly to include the effects of the firn. During repeating episodes the mean interevent time is 18 +/- 6 min with a mean magnitude of Ml=1.4. Satellite imagery is not available during the time of repeating ruptures; however, during other periods icebergs of both sizes have been observed to break of the calving front of Thwaites glacier."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

johnm33

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Re: The WAIS Workshop 2013
« Reply #18 on: December 31, 2013, 03:19:29 PM »
I've been watching this
 ftp://ftp-projects.zmaw.de/seaice/AMSR2/Ant_latest_yesterday_AMSR2_3.125km.gif
for the last couple of weeks thinking the pacific side was starting to look very vulnerable, todays snapshot ftp://ftp-projects.zmaw.de/seaice/AMSR2/Ant_latest_yesterday_AMSR2_3.125km.png Compared to  http://www.iup.uni-bremen.de:8084/ssmis/antarctic_SSMIS_nic.png and last years http://www.iup.uni-bremen.de:8084/ssmisdata/asi_daygrid_swath/s6250/2012/dec/asi-SSMIS17-s6250-20121230-v5_nic.png suggests to me lots of weather could hit that coastline in the following weeks.

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #19 on: December 31, 2013, 09:51:26 PM »
johnm33,

The fact that the weather is currently bad in this area is confirmed by the news report in the following link about how bad weather is preventing rescue options for the trapped Russian icebreaker:

http://worldnews.nbcnews.com/_news/2013/12/30/22096342-bad-weather-thwarts-rescue-of-stranded-antarctica-ship
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

johnm33

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Re: The WAIS Workshop 2013
« Reply #20 on: January 01, 2014, 09:30:39 PM »
AbruptSLR On this image ftp://ftp-projects.zmaw.de/seaice/AMSR2/Ant_latest_yesterday_AMSR2_3.125km.png that ship is somewhere around '5 oclock'. Whereas I'm looking at the signs of turbulence in the ocean along the pacific coast of the peninsular across to, and including Ross sea, but more pronounced in Amundsen and close to the peninsular, here the ice looks disconnected from the coast and in the process of disintegrating. There's too much cloud to see it clearly from satellite, but what is visible is shattered, of course the winds could change and drive it all back to consolidate on the coast. If that doesn't happen soon I'm guessing it could be an interesting few weeks.

AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #21 on: January 02, 2014, 03:35:30 PM »
johnm33,

Thanks for pointing out that the researcher ship is down near Mertz Glacier (not in the Pacific sector).  I like the following website for checking the Antarctic weather:

http://www.weather-forecast.com/maps/Antarctica

I agree that the next few weeks and months will be interesting.
“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: The WAIS Workshop 2013
« Reply #22 on: January 06, 2014, 04:47:57 PM »
The following link indicates that while the Antarctic sea ice area in general has been increasing in the past several years, the sea ice area off of the critical West Antarctic has been decreasing; which should expose the ice shelves in this area to increased storm wave, and infragravity wave, action:

http://www.smh.com.au/environment/climate-change/chilly-warning-from-scientists-on-impact-of-antarctica-changes-20140106-30dmr.html
“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: The WAIS Workshop 2013
« Reply #23 on: January 07, 2014, 02:31:25 AM »
The presentation by Schroeder in the WAIS 2013 Workshop is closely related to the following linked paper:


Alexandra E. Witus, Carolyn M. Branecky, John B. Anderson, Witold Szczuciński, Dustin M. Schroeder, Donald D. Blankenship, Martin Jakobsson; (2014), "Meltwater intensive glacial retreat in polar environments and investigation of associated sediments: example from Pine Island Bay, West Antarctica" Quaternary Science Reviews, Volume 85, 1 February 2014, Pages 99–118, http://dx.doi.org/10.1016/j.quascirev.2013.11.021

Abstract
"Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are among the fastest changing portions of the cryosphere and the least stable ice streams in Antarctica. Here we show that the uppermost sediment unit in Pine Island Bay was deposited from a meltwater plume, a plumite, during the late stages of ice sheet retreat ∼7–8.6 k cal yr BP and argue that this deposit records episodes of meltwater intensive sedimentation.

The plumite is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line. The uppermost sediment unit is interpreted as a product of non-steady-state processes in which low background sedimentation in large bedrock-carved basins alternates with episodic purging of sediment-laden water from these basins. The inner part of Pine Island Bay contains several basins that are linked by channels with a storage capacity on the order of 70 km3 of stagnant water and significant sediment storage capacity. Purging of these basins is caused by changes in hydraulic potential and glacial reorganization. The sediment mobilized by these processes is found here to total 120 km3."
“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: The WAIS Workshop 2013
« Reply #24 on: February 12, 2014, 02:06:24 AM »
The final sentence of the following abstract b Behrendt, indicates that high rates of basal melting in the area of the WAIS Divide, and possibly increase volcanic activity due to isotatic rebound, may be increase future ice mass loss rates from the WAIS: "These various lines of evidence lead to the general interpretation that the ice divide area of the WAIS overlies present to recent subglacial volcanic activity that may have an influence on the past and future behavior of the WAIS.":

"Evidence for Subglacial Volcanic Activity Beneath the area of the Divide of the West Antarctic Ice Sheet
John C. Behrendt
INSTAAR University of Colorado, Boulder

There is an increasing body of aeromagnetic, radar ice–sounding, heat flow, subglacial volcanic earthquakes, several exposed active and subglacial volcanoes and other lines of evidence for volcanic activity associated with the West Antarctic Rift System (WR) since the origin (~25 Ma) of the West Antarctic Ice Sheet (WAIS), which flows through it. Exposed late Cenozoic, alkaline volcanic rocks, 34 Ma to present concentrated in Marie Byrd Land (LeMasurier and Thomson, 1990), but also exposed along the rift shoulder on the Transantarctic Mountains flank of the WR, and >1 million cubic  kilometers, of mostly subglacially erupted “volcanic centers” beneath the WAIS inferred from aeromagnetic data, have been interpreted as evidence of a magmatic plume. About 18 high relief, (~600-2000 m) “volcanic centers“ presently beneath the WAIS surface, probably were erupted subaerially when the WAIS was absent, based on the 5-km orthogonally line spaced Central West Antarctica aerogeophysical survey. All would be above sea level after ice removal and isostatic adjustment. Nine of these high relief peaks are in the general area beneath the divide of the WAIS. This high bed relief topography was first interpreted in the 1980s as the volcanic “Sinuous Ridge “ based on a widely spaced aeromagnetic –radar ice sounding survey (Jankowski et al,. 1983). A 70-km wide, circular ring of interpreted subglacial volcanic rocks was cited as evidence of a volcanic caldera underlying the ice sheet divide based on the CWA survey (Behrendt et al., 1998). A broad magnetic “low” surrounding the caldera area possibly is evidence of a shallow Curie isotherm. High heat flow reported from temperature logging (Clow et al., 2012) in the WAISCORE and a thick volcanic ash layer in the core (Dunbar et al., 2012) are consistent with this interpretation. A 2 km-high subaerially erupted volcano (subglacial Mt Thiel, ~78.5 degrees S, 111 degrees W) ~ 100 km north from the WAISCORE could be the source of the ash layer if it has been recently active. Models by Tulaczyk and Hossainzadeh (2011) indicate >4mm/yr Basal melting in the general area of the WAIS, again supportive of high heat flow and the presence of subglacial lakes in West Antarctica. These various lines of evidence lead to the general interpretation that the ice divide area of the WAIS overlies present to recent subglacial volcanic activity that may have an influence on the past and future behavior of the WAIS."
“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: The WAIS Workshop 2013
« Reply #25 on: February 12, 2014, 06:14:42 PM »
The following abstract indicates that due to a deeper bed in Marie Byrd Land (particularly near the Executive Committee Mountains that have shown recent seismic/volcanic activity) that the WAIS has an additional 4.94 cm of SLE contribution to future SLR, if the entire WAIS were to collapse.  Note also that ice mass loss from the Executive Committee Mountain area would feed both through the Thwaites and the Siple Coast drainage basins.

"Consequences of a Deeper Bed for Marie Byrd Land Stability"
Nicholas Holschuh, David Pollard, Richard Alley, Sridhar Anandakrishnan 
The Pennsylvania State University, University Park, PA 16802

Abstract: "Stability of the West Antarctic Ice Sheet (WAIS) has been a subject of much research since the marine ice sheet instability was proposed. Data collection and analysis have focused primarily on the Amundsen Sea embayment and the Siple Coast, coastal regions whose retreat will ultimately provide the avenue for ice loss from the continent’s interior. Despite having only limited geophysical data collected inland from the coast, Marie Byrd Land (MBL) has been treated as a regional high in bed topography in all major mapping efforts of Antarctica. This high reduces the long term variability of ice over MBL; models using the currently prescribed bed show little change in ice volume or its spatial distribution on MBL in the last 5 million years. RES data collected by Operation Ice Bridge during the 2009-2010 Antarctic field season show ice thicknesses that locally exceed previous estimates by more than a kilometer, and indicate a much deeper and more complex bed for the region surrounding the Executive Committee Mountains. Improved ice thickness measurements indicate an additional 19,400 km3 of ice (4.94 cm SLE) within WAIS. Using new bed topography generated from these data, along with the model outlined in Pollard and DeConto (2012), we refine the estimates of ice retreat into Marie Byrd Land, providing new insight into the sea-level contribution of WAIS in the event of complete collapse."
“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: The WAIS Workshop 2013
« Reply #26 on: February 12, 2014, 07:15:14 PM »
In general terms, I agree with the approach presented by Wikman-Svahn in the linked pdf and accompanying abstract (from the WAIS 2013 Workshop).  I believe that the value of the Robust Decision Making approach regarding the outlook for SLR from ice sheets is borne-out by considerations such as, since the AR5 report was released: (a) it has been shown that climate sensitivity cannot be less than 3 degrees C, and that climate sensitivity is likely closer to 4.5 degrees C, and (b) work on El Nino events and the PDO cycle show that prior GCM's need to use higher climate sensitivity values if they are going to match the observed recent ENSO, and ocean heat content behavior, and (c) the UN has finally admitted that RCP 2.6 is not likely to be achievable.  Hopefully, when the UN/IPCC develop new guidance to replace the old RCP scenarios/pathways, they will include more believable radiative forcing inputs (including methane emissions from the permafrost) and more accurate values for climate sensitivity.

ftp://sidads.colorado.edu/pub/projects/waisworkshop/2013/presentations/session2/Wikman-Svahn.pdf


"When Assessing the Outlook for the Ice Sheets"
Per Wikman-Svahn
Earth and Environmental Systems Institute
Pennsylvania State University

Abstract: "Managing and communicating uncertainty in policy-relevant scientific assessments is connected to deep philosophical issues. These issues can have important practical and ethical implications for society. It is therefore of high importance to discuss implicit assumptions and value judgments that are made in policy-relevant scientific assessments, such as the future contribution to sea level rise from the great ice sheets.

The view that science should be free of social and ethical considerations (sometimes called "the value-free ideal of science") is examined. It is showed that this view in itself assumes an ethical standpoint, which becomes particularly important when making scientific assessments that are policy-relevant.

An alternative to the value-free ideal for policy-relevant assessments is proposed, in which scientific assessments that are used to inform societal decision-making should try to anticipate applications and aim to construct statements that characterize knowledge and uncertainty in a way that are most useful for those anticipated applications.

This alternative ideal means that scientific assessments should take into account the context in which the information will be used. In particular, the recent development of decision-making tools that are able to work with great uncertainty, such as bottom-up" and "robust" decision-making frameworks, are presented. It is showed how these tools introduces new demands but also new opportunities for making policy-relevant scientific assessments of the future of the ice sheets."
“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: The WAIS Workshop 2013
« Reply #27 on: May 15, 2014, 01:52:38 AM »
"WAIS 2014, the International Workshop on Advances in Information Security, is the 8-th of a series of meetings focusing on the latest research in the area of Information Security and it will be held in July 2nd - July 4th, 2014, Birmingham City University, Birmingham, UK."

Anyone in the UK then might want to attend; otherwise, I will download the abstracts when they are available in a new thread.
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AbruptSLR

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Re: The WAIS Workshop 2013
« Reply #28 on: June 11, 2014, 05:36:13 PM »
We should all remember that most of the headline news reports recently about the stability (or lack there-of) of the WAIS, is based on research from a year ago, including Rignot et al 2014 statements used ISSM results; which is the topic of the following WAIS Workshop 2013 report (I hope you quickly review the other posts in this thread as they highlight other research relevant to today's headlines including geothermal heat in the BSB, subglacial meltwater systems, etc):

"Controlling mechanisms of fast flowing glaciers in West Antarctica"
Helene Seroussi1, Ala Khazendar1, Mathieu Morlighem2,
Eric Larour1 and Eric Rignot 1,2
1 Jet Propulsion Laboratory, Pasadena. CA
2 University of California, Irvine, CA

Abstract: "Ice shelves play a major role in the stability of fast flowing ice streams in Antarctica, by exerting buttressing on inland ice and controlling the discharge of ice into the ocean. However, the mechanisms at work remain poorly understood and interactions between floating and grounded ice need to be better characterized in order to estimate the impact of climate change on the ice sheets. Glaciers in West Antarctica experienced significant changes over the past decades.
Pine Island Glacier, for example, has been thinning and accelerating since the 1970’s at least and its grounding line has been retreating inland at a rate of about 1 km/yr. Initiation of these changes is usually attributed to warmer ocean waters in the Amundsen Sea affecting the floating part of Pine Island. By buttressing grounded ice flow and controlling the discharge of inland ice to the ocean, the ice shelf of Pine Island plays a major role in the stability of the glacier. Thwaites Glacier features a small and heavily fractured ice shelf that provides limited back stress pressure on inland ice but is pinned on the eastern part on a prominent ridge. Contrary to Pine Island Glacier, Thwaites Glacier has maintained a consistently high velocity and negative mass balance for at least 20 years. Recent observations show a widening of its fast flowing area as well as a sustained acceleration since 2006 and a rapid retreat of its grounding line in the center of the glacier.
We use the Ice Sheet System Model (ISSM) and a three-dimensional higher-order model to simulate the evolution of the glacier for the next fifty years and assess the effect of changes in several climate forcings and model parameters, namely basal melting under the floating part, ice front position, atmospheric conditions and grounding line retreat. Simulation results show the dominant effect of basal melting and of grounding line retreat. Results also show that changes are not limited to the ice shelf and the grounding line area but propagate far inland, almost to the ice divide. We find that enhanced basal melting or grounding line retreat are each associated with a distinct pattern of ice thinning and acceleration. We compare the simulation results with remote sensing observations of velocity changes and grounding line evolution to elucidate which forcing is more likely to have caused the recent changes observed on these glaciers.
This work was performed at the California Institute of Technology's Jet Propulsion Laboratory and the University of California Irvine under a contract with the National Aeronautics and Space Administration, Cryospheric Sciences and Modeling, Analysis and Prediction Programs."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson