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1. Weakening of the pinning point buttressing Thwaites Glacier, West Antarctica

   https://doi.org/10.5194/tc-16-397-2022  

   Wild, Christian T. ; Alley, Karen E. ; Muto, Atsuhiro ; Truffer, Martin ; Scambos, Ted A. ; Pettit, Erin C. ( January 2022 , The Cryosphere)

   Abstract. The Thwaites Eastern Ice Shelf buttresses a significant portion of Thwaites Glacier through contact with a pinning point 40 km offshore of the present grounding line. Predicting future rates of Thwaites Glacier’s contribution to sea-level rise depends on the evolution of this pinning point and the resultant change in the ice-shelf stress field since the breakup of the Thwaites Western Glacier Tongue in 2009. Here we use Landsat-8 feature tracking of ice velocity in combination with ice-sheet model perturbation experiments to show how past changes in flow velocity have been governed in large part by changes in lateral shear and pinning point interactions with the Thwaites Western Glacier Tongue. We then use recent satellite altimetry data from ICESat-2 to show that Thwaites Glacier’s grounding line has continued to retreat rapidly; in particular, the grounded area of the pinning point is greatly reduced from earlier mappings in 2014, and grounded ice elevations are continuing to decrease. This loss has created two pinned areas with ice flow now funneled between them. If current rates of surface lowering persist, the Thwaites Eastern Ice Shelf will unpin from the seafloor in less than a decade, despite our finding from airborne radar data that themore »seafloor underneath the pinning point is about 200 m shallower than previously reported. Advection of relatively thin and mechanically damaged ice onto the remaining portions of the pinning point and feedback mechanisms involving basal melting may further accelerate the unpinning. As a result, ice discharge will likely increase up to 10 % along a 45 km stretch of the grounding line that is currently buttressed by the Thwaites Eastern Ice Shelf.« less
2. Rapid retreat of Thwaites Glacier in the pre-satellite era

   https://doi.org/10.1038/s41561-022-01019-9  

   Graham, Alastair G. C. ; Wåhlin, Anna ; Hogan, Kelly A. ; Nitsche, Frank O. ; Heywood, Karen J. ; Totten, Rebecca L. ; Smith, James A. ; Hillenbrand, Claus-Dieter ; Simkins, Lauren M. ; Anderson, John B. ; et al ( September 2022 , Nature Geoscience)

   Understanding the recent history of Thwaites Glacier, and the processes controlling its ongoing retreat, is key to projecting Antarctic contributions to future sea-level rise. Of particular concern is how the glacier grounding zone might evolve over coming decades where it is stabilized by sea-floor bathymetric highs. Here we use geophysical data from an autonomous underwater vehicle deployed at the Thwaites Glacier ice front, to document the ocean-floor imprint of past retreat from a sea-bed promontory. We show patterns of back-stepping sedimentary ridges formed daily by a mechanism of tidal lifting and settling at the grounding line at a time when Thwaites Glacier was more advanced than it is today. Over a duration of 5.5 months, Thwaites grounding zone retreated at a rate of >2.1 km per year—twice the rate observed by satellite at the fastest retreating part of the grounding zone between 2011 and 2019. Our results suggest that sustained pulses of rapid retreat have occurred at Thwaites Glacier in the past two centuries. Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the sea floor.
3. Two decades of dynamic change and progressive destabilization on the Thwaites Eastern Ice Shelf

   https://doi.org/10.5194/tc-15-5187-2021  

   Alley, Karen E. ; Wild, Christian T. ; Luckman, Adrian ; Scambos, Ted A. ; Truffer, Martin ; Pettit, Erin C. ; Muto, Atsuhiro ; Wallin, Bruce ; Klinger, Marin ; Sutterley, Tyler ; et al ( January 2021 , The Cryosphere)

   Abstract. The Thwaites Eastern Ice Shelf (TEIS) buttresses the eastern grounded portion of Thwaites Glacier through contact with a pinning point at itsseaward limit. Loss of this ice shelf will promote further acceleration of Thwaites Glacier. Understanding the dynamic controls and structuralintegrity of the TEIS is therefore important to estimating Thwaites' future sea-level contribution. We present a ∼ 20-year record of change onthe TEIS that reveals the dynamic controls governing the ice shelf's past behaviour and ongoing evolution. We derived ice velocities from MODIS andSentinel-1 image data using feature tracking and speckle tracking, respectively, and we combined these records with ITS_LIVE and GOLIVE velocityproducts from Landsat-7 and Landsat-8. In addition, we estimated surface lowering and basal melt rates using the Reference Elevation Model of Antarctica (REMA) DEM in comparison to ICESat andICESat-2 altimetry. Early in the record, TEIS flow dynamics were strongly controlled by the neighbouring Thwaites Western Ice Tongue (TWIT). Flowpatterns on the TEIS changed following the disintegration of the TWIT around 2008, with a new divergence in ice flow developing around thepinning point at its seaward limit. Simultaneously, the TEIS developed new rifting that extends from the shear zone upstream of the ice rise andincreased strain concentration within thismore »shear zone. As these horizontal changes occurred, sustained thinning driven by basal melt reduced icethickness, particularly near the grounding line and in the shear zone area upstream of the pinning point. This evidence of weakening at a rapid pacesuggests that the TEIS is likely to fully destabilize in the next few decades, leading to further acceleration of Thwaites Glacier.« less
4. Pathways and modification of warm water flowing beneath Thwaites Ice Shelf, West Antarctica

   https://doi.org/10.1126/sciadv.abd7254  

   Wåhlin, A. K. ; Graham, A. G. ; Hogan, K. A. ; Queste, B. Y. ; Boehme, L. ; Larter, R. D ; Pettit, E. C. ; Wellner, J. ; Heywood, K. J. ( April 2021 , Science Advances)

   null (Ed.)

   Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat.
5. New gravity-derived bathymetry for the Thwaites, Crosson, and Dotson ice shelves revealing two ice shelf populations

   https://doi.org/10.5194/tc-14-2869-2020  

   Jordan, Tom A. ; Porter, David ; Tinto, Kirsty ; Millan, Romain ; Muto, Atsuhiro ; Hogan, Kelly ; Larter, Robert D. ; Graham, Alastair G. ; Paden, John D. ( January 2020 , The Cryosphere)

   Abstract. Ice shelves play a critical role in the long-termstability of ice sheets through their buttressing effect. The underlyingbathymetry and cavity thickness are key inputs for modelling future icesheet evolution. However, direct observation of sub-ice-shelf bathymetry istime-consuming, logistically risky, and in some areas simply not possible.Here we use new compilations of airborne and marine gravity, radar depthsounding, and swath bathymetry to provide new estimates of sub-ice-shelfbathymetry outboard of the rapidly changing West Antarctic Thwaites Glacierand beneath the adjacent Dotson and Crosson ice shelves. This region is ofspecial interest, as the low-lying inland reverse slope of the ThwaitesGlacier system makes it vulnerable to marine ice sheet instability, withrapid grounding line retreat observed since 1993 suggesting this process maybe underway. Our results confirm a major marine channel >800 mdeep extends tens of kilometres to the front of Thwaites Glacier, while theadjacent ice shelves are underlain by more complex bathymetry. Comparison ofour new bathymetry with ice shelf draft reveals that ice shelves formedsince 1993 comprise a distinct population where the draft conforms closelyto the underlying bathymetry, unlike the older ice shelves, which show a moreuniform depth of the ice base. This indicates that despite rapid basalmelting in some areas, these recently floated parts ofmore »the ice shelf are notyet in dynamic equilibrium with their retreated grounding line positions andthe underlying ocean system, a factor which must be included in futuremodels of this region's evolution.« less