Frictional Origin of Slip Events of the Whillans Ice Stream, Antarctica

Abstract

Sea level rise (SLR) is among the most significant long-term consequences of global warming with direct economic, societal, and cultural impacts (Nicholls & Cazenave, 2010). Given the enormous volume of ice sitting in low-elevation basins located below sea level, the Antarctic ice sheet has the potential to become the largest contributor to future SLR. This contribution, however, remains highly uncertain (Alley et al., 2005; Golledge et al., 2019; Oppenheimer, 1998; Pachauri et al., 2014). The single largest source of this uncertainty in most simulations of long-term ice flow is the representation of glacier sliding physics (Cornford et al., 2020). Glacier sliding physics is most often understood through idealized theoretical models (Meyer et al., 2018; Schoof, 2005; Weertman, 1964) and laboratory experiments (Iverson et al., 2003; Tulaczyk et al., 2000; Wu et al., 2008; Zoet & Iverson, 2020). Although these are both important lines of investigation, both theoretical and laboratory results must be validated against field observations to confirm that they capture the correct physical processes. Abstract Ice sheet evolution depends on subglacial conditions, with the ice-bed interface s strength exerting an outsized role on the ice dynamics. Along fast-flowing glaciers, this strength is often controlled by the deformation of subglacial till, making quantification of spatial variations of till strength essential for understanding ice-sheet contribution to sea-level. This task remains challenging due to a lack of in situ observations. We analyze continuous seismic data from the Whillans Ice Plain (WIP), West Antarctica, to uncover spatio-temporal patterns in subglacial conditions. We exploit tidally modulated stick-slip events as a natural source of sliding variability. We observe a significant reduction of the till seismic wave-speed between the WIP sticky-spots. These observations are consistent with a poroelastic model where the bed experiences relative porosity and effective pressure increases of >11% during stick-slips. We conclude that dilatant strengthening appears to be an essential mechanism in stabilizing the rapid motion of fastflowing ice streams.