Rapid fragmentation of Thwaites Eastern Ice Shelf, West Antarctica

Abstract

Abstract. Ice shelves play a key role in the dynamics of marine ice sheets, by buttressing grounded ice and limiting rates of ice flux to the oceans. In response to recent climatic and oceanic change, ice shelves fringing the West Antarctic Ice Sheet (WAIS) have begun to fragment and retreat, with major implications for ice sheet stability. Here, we focus on the Thwaites Eastern Ice Shelf (TEIS), the remaining pinned floating extension of Thwaites Glacier. We show that TEIS has undergone a process of fragmentation in the last five years, including brittle failure along a major shear zone, formation of tensile cracks on the main body of the shelf, and release of tabular bergs on both eastern and western flanks. Simulations with the Helsinki Discrete Element Model (HiDEM) show that this pattern of failure is associated with high backstress from a submarine pinning point at the distal edge of the shelf. We show that a significant zone of shear upstream of the main pinning point developed in response to the rapid acceleration of the shelf between 2002 and 2006, seeding damage on the shelf. Subsequently, basal melting and positive feedbacks between damage and strain rates weakened TEIS, allowing damage to accumulate. Thus, although backstress on TEIS has likely diminished through time as the pinning point has shrunk, accumulation of damage has ensured that the ice in the shear zone has remained the weakest link in the system. Experiments with the BISICLES ice sheet model indicate that additional damage to or unpinning of TEIS are unlikely to trigger significantly increased ice loss from WAIS, but the calving response to loss of TEIS remains highly uncertain. It is widely recognised that ice-shelf fragmentation and collapse can be triggered by hydrofracturing and/or unpinning from ice shelf margins or grounding points. Our results indicate a third mechanism, backstress-triggered failure, that can occur when ice ffractures in response to stresses associated with pinning points. In most circumstances, pinning points are essential for ice shelf stability, but as ice shelves thin and weaken the concentration of backstress in damaged ice upstream of a pinning point may provide the seeds of their demise.

Mapping Antarctic Crevasses and their Evolution with Deep Learning Applied to Satellite Radar Imagery

“…5 i). This closely mirrors a feature that was identified by Benn et al (2021), using an ice sheet model to infer changes to material properties of the ice as the aforementioned slip plane developed. The benefit of using crevasse maps to assess structural change is that they can be used to derive quantitative information beyond that which can be gained by looking directly at satellite images.…”

“…5 fracturing decreasing around its western end, and increasing to the south and east. This is due to crevasses/rifts opening up in-situ, perpendicular to the orientation of the pinning point on the main body of the shelf in response to increased shear stress in the latter half of the 2010's in a region running south-west from the pining point's eastern tip (Benn et al, 2021).…”

“…An analysis of satellite images over the Thwaites Glacier terminus shows the Eastern Ice Shelf loosening from the pinning point and a shear plane developing between the two (Benn et al, 2021). The fracture density change map we see is consistent with a picture of an ice shelf transitioning from one that is slow-moving and heavily pinned, where fracturing occurs due to compressive stresses originating from the pinning point, to a freely-floating ice shelf with crevasses forming and propagating perpendicular to flow by the action of internal stresses.…”

Last Interglacial subsurface warming on the Antarctic shelf triggered by reduced deep-ocean convection

“…A subsurface ocean warming has contributed to the melting and thinning of West Antarctic ice shelves in recent decades [34,35]. While Southern Ocean sea-ice extent has increased slowly at the end of the 20th century and until 2016, it has abruptly decreased since then [36], hinting at an accelerated warming of the Southern Ocean.…”

Ocean variability beneath Thwaites Eastern Ice Shelf driven by the Pine Island Bay Gyre strength

“…2 , and up to 1.6 km yr -1 since 2017; ref. 5 ) support that Thwaites Glacier and TEIS are in the early stages of a rapid mass loss and retreat that may persist for decades to centuries 6 . However, the pace of such retreat is uncertain and dependent on future trends in climate and ocean conditions [7][8][9] .…”