Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica

F O Nitsche,M Jakobsson,J B Anderson,K Gohl,S Jacobs,G Kuhn,C.-D Hillenbrand,J A Smith,R D Larter

doi:10.5194/tc-7-249-2013

Abstract

Abstract. Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.

Highlights

Response of the Antarctic ice sheets to changing climate conditions is one of the largest uncertainties in the prediction of future sea-level (IPCC, 2007)
The grid includes most of the main paleo-ice stream trough while data gaps remain in shallow areas northeast of the trough and around Iceberg B22A, which was formerly an ice tongue extending from Thwaites Glacier
The seafloor morphology of the northernmost study area 1 is characterised by moderate relief with water depths in the range 500–1100 m, gradually shoaling seaward and dominated by linear features (Fig. 2). This pattern continues northward towards the mid-shelf, where it changes into megascale glacial lineations (MSGL) interrupted by grounding zone wedges as described by Graham et al (2010) and Jakobsson et al (2012)

Summary

Introduction

Response of the Antarctic ice sheets to changing climate conditions is one of the largest uncertainties in the prediction of future sea-level (IPCC, 2007). About 25–35 % of the WAIS is currently draining into the Amundsen Sea, mostly through the Pine Island and Thwaites glaciers (Drewry et al, 1982; Rignot et al, 2008). These ice streams are potential weak points in the ice sheet because they occupy troughs that become steadily deeper towards the WAIS interior and are buttressed by relatively small ice shelves (Hughes, 1973; Vaughan et al, 2006). Theoretical studies have concluded that ice grounding lines are unstable on such reverse gradients and, once retreat starts it may proceed rapidly (Weertman, 1974; Schoof, 2007), as recently observed under the Pine Island Ice Shelf (Jenkins et al, 2010)

Results

Discussion

Conclusion