Abstract
Abstract. Ice shelves play a critical role in the long-term stability of ice sheets through their buttressing effect. The underlying bathymetry and cavity thickness are key inputs for modelling future ice sheet evolution. However, direct observation of sub-ice-shelf bathymetry is time-consuming, logistically risky, and in some areas simply not possible. Here we use new compilations of airborne and marine gravity, radar depth sounding, and swath bathymetry to provide new estimates of sub-ice-shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier and beneath the adjacent Dotson and Crosson ice shelves. This region is of special interest, as the low-lying inland reverse slope of the Thwaites Glacier system makes it vulnerable to marine ice sheet instability, with rapid grounding line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel >800 m deep extends tens of kilometres to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves, which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these recently floated parts of the ice shelf are not yet in dynamic equilibrium with their retreated grounding line positions and the underlying ocean system, a factor which must be included in future models of this region's evolution.
Highlights
The Thwaites Glacier system is a globally important region of change in the cryosphere system (Fig. 1a) (Scambos et al, 2017)
Many of the isolated pinning points seaward of Thwaites Glacier and beneath the Crosson Ice Shelf shown by InSAR-derived grounding lines (Rignot et al, 2014) are revealed by our study as being situated on broader bathymetric highs
In these areas our recovered topography predicts that the ice shelf is grounded, or within 100 m of grounding
Summary
The Thwaites Glacier system is a globally important region of change in the cryosphere system (Fig. 1a) (Scambos et al, 2017) In this region the marine based West Antarctic Ice Sheet comes into direct contact with upwelling modified Circumpolar Deep Water (mCDW), which is warm relative to the typical cool dense shelf water on Antarctic continental shelves (Jenkins et al, 2018). The inland reverse slope of the bed beneath Thwaites Glacier and some of the adjacent glaciers means that marine ice sheet instability may occur (Schoof, 2007; Weertman, 1974) In this case a feedback is setup where grounding line retreat exposes a progressively larger cross-sectional area of ice; more ice fluxes into the ocean leading to further glacial retreat. Satellite observations revealing an increase in the velocity of ∼ 100 ma−1 extending ∼ 100 km inland from the Thwaites grounding line and a surface draw down of over 1 ma−1 indicate that this region is changing (Gardner et al, 2018; Milillo et al, 2019)
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