Drivers of abrupt Holocene shifts in West Antarctic ice stream direction determined from combined ice sheet modelling and geologic signatures

C.J Fogwill,R Wieler,L Wacker,D.H Rood,R.S Jones,K Hippe,N.R Golledge,C.S.M Turney,E.B Rainsley

doi:10.1017/s0954102014000613

Abstract

AbstractDetermining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here high-resolution ice sheet modelling was combined with new terrestrial geological constraints (in situ14C and 10Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.

Highlights

Recent observations of rapidly accelerating West Antarctic outlet glaciers have prompted a radical shift in the way the sensitivity of marine-terminating ice sheets to ocean forcing is viewed (Rignot et al 2014)
Decadal-scale changes consistent with this mechanism have been implicated in several key outlets of the West Antarctic Ice Sheet (WAIS) (Rignot et al 2014), suggesting that even small changes at the margins of the Antarctic ice sheets may trigger far-reaching changes in the interior of the Antarctic ice sheet through ice streams, narrow corridors of enhanced ice flow, which control the mass balance of the Antarctic ice sheets (Cuffey 2011, Golledge et al 2012, Rignot et al 2014)
Ice flux is greatest at the head of the deep Thiel Trough and its tributaries, ice from both the Rutford Ice Stream and Institute Ice Stream continue to discharge through the Rutford Trough and the extended Evans Trough on the western side of the Weddell Sea embayment (WSE)

Summary

Introduction

Recent observations of rapidly accelerating West Antarctic outlet glaciers have prompted a radical shift in the way the sensitivity of marine-terminating ice sheets to ocean forcing is viewed (Rignot et al 2014). Evidence for this comes from interpretations of airborne radar-echo sounding (RES), marine geophysical investigations and satellite imagery, which suggests there has been substantial late Holocene reconfiguration of the ice streams in the Weddell Sea; the timing and, critically, the mechanisms driving these changes remain uncertain (Siegert et al 2013). Understanding these mechanisms is critical given twenty-first century projections of ocean warming in the region (Hellmer et al 2012, Fogwill et al 2014), and the presence of extensive subglacial basins upstream of the present-day grounding line (Ross et al 2012)

Results

Discussion

Conclusion