Weakening of the pinning point buttressing Thwaites Glacier, West Antarctica

• Main Authors: Wild, Christian T., Alley, Karen E., Muto, Atsuhiro, Truffer, Martin, Scambos, Ted A., Pettit, Erin C.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Thwaites Glacier; West Antarctica; Western Glacier; Antarc*; Antarctica; Ice Shelf
• Online Access: https://doi.org/10.5194/tc-2021-130; https://tc.copernicus.org/preprints/tc-2021-130/

The Thwaites Eastern Ice Shelf continues to 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 break-up of the Thwaites Western Glacier Tongue in 2009. Here we use Landsat-8 feature tracking of ice velocity in combination with 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 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 entire Thwaites Eastern Ice Shelf will unpin from the seafloor in less than a decade, despite our finding from airborne radar data that the 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 along a 45 km stretch of the grounding line that is currently buttressed by the Thwaites Eastern Ice Shelf.