Dynamic (in)stability of Thwaites Glacier, West Antarctica

Abstract

[1] Thwaites Glacier, West Antarctica, has the potential to directly contribute 1 m to sea level and currently is losing mass and thinning rapidly. Here, we report on regional results for the Sea-level Response to Ice Sheet Evolution (SeaRISE) experiments and investigate the impact of i) spatial resolution within existing data sets, ii) grounding-zone processes, and iii) till rheology on the dynamics of this outlet glacier. In addition to the SeaRISE data sets, we use detailed aerogeophysical and satellite data from Thwaites Glacier as input to a coupled ice stream/ice-shelf/ocean-plume model that includes oceanic influences across a several kilometers wide grounding zone suggested by new, high-resolution data. Our results indicate that the ice tongue provides limited stability, and that while future atmospheric warming will likely add mass to the surface of the glacier, strong ice stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone. However, we find that stability is significantly enhanced by effectively plastic till beds. Accurate projections of future sea level change relies on correct understanding of the till rheology as well as local basal processes near the grounding line.

Uneven onset and pace of ice‐dynamical imbalance in the Amundsen Sea Embayment, West Antarctica

“…Some localized patches of faster surface lowering might have been related to drainage of subglacial lakes as observed by Smith et al [2016] at higher resolution. In contrast to PIG and the PSK glaciers, THG is not constrained by a relatively narrow bedrock trough, has a greater lateral extent, and the less confined floating glacier tongue and ice shelf provide less buttressing to the grounded ice, making THG less susceptible to an increase in subshelf melting [Parizek et al, 2013;Nias et al, 2016]. Consequently, if the episodic surface lowering was of ice-dynamical origin, it could have been due to temporally well-defined events of ungrounding and a relatively abrupt response of the fast-flowing sections.…”

The sensitivity of West Antarctica to the submarine melting feedback

“…Modeled retreat rates can be sensitive to how melting is applied at the grounding line [Parizek et al, 2013;Golledge et al, 2015]. We implemented a subgrid melting parametrization and performed two sets of simulations, either applying melt to partially grounded cells in proportion to their floating area fraction or restricting all submarine melting to fully floating cells.…”

“…Physically, some interaction between melting and basal drag may be expected [Parizek et al, 2013]. Retreat rates may prove to be sensitive to whether oceanic melting can thin the ice upstream of discrete pinning points that support basal drag, allowing them to go afloat.…”

Glacier change along West Antarctica's Marie Byrd Land Sector and links to inter-decadal atmosphere–ocean variability

“…That is, the potentially rough and shoaling topography upstream of the 2008 GL may require prolonged, continuously high, or increased rates of thinning to permit GL retreat -a process that has been modelled across both idealized and physically constrained grounding zone geometries over other parts of West Antarctica (cf. Schoof et al, 2007;Durand et al, 2011;Parizek et al, 2013;Nias et al, 2016). Until more comprehensive knowledge of Getz Ice Shelf's grounding zone bed structure exists, glacier/ice-stream-specific internal variability, moderated by bed conditions at the 2010-2015 grounding zone, cannot be reliably dismissed as an additional control on the slowdown of GL retreat rate during the CryoSat-2 era.…”