Abstract
Lakes beneath the Antarctic Ice Sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments. However, no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet, and understanding of sediment pathways, processes and structure in subglacial lake environments remains uncertain. Here we present an analysis of seismic data from Subglacial Lake Ellsworth, showing that the lake bed comprises very fine-grained sediments deposited in a low energy environment, with low water- and sediment-fluxes. Minimum sediment thickness is 6 m, the result of prolonged low sedimentation rates. Based on the few available analogues, we speculate this sediment age range is a minimum of 150 ka, and possibly >1 Ma. Sediment mass movements have occurred, but they are rare and have been buried by subsequent sedimentation. We present a new conceptual model of subglacial lake sedimentation, allowing a framework for evaluating processes in subglacial lake environments, and for determining future lake access locations and interpreting subglacial lake samples.
Highlights
More than 400 lakes lie hidden beneath the Antarctic Ice Sheet (Siegert et al, 2016), part of an extensive active subglacial hydrological system that influences ice dynamics and the future evolution of the ice sheet (Bentley et al, 2011)
Two contemporary subglacial lakes have been accessed, Vostok Subglacial Lake (Lukin and Vasiliev, 2014) beneath the East Antarctic Ice Sheet and Subglacial Lake Whillans (SLW; Tulaczyk et al, 2014) beneath Whillans Ice Stream, no sediments were recovered from the former, and those recovered from SLW reflect icestream flow and drainage events, not subglacial lake sedimentation (Hodson et al, 2016)
We used the reflections from the three main interfaces: ice– water, water–bed and ice-bed (Fig. 2), to enable interpretation of the lake bed and surrounding subglacial material
Summary
More than 400 lakes lie hidden beneath the Antarctic Ice Sheet (Siegert et al, 2016), part of an extensive active subglacial hydrological system that influences ice dynamics and the future evolution of the ice sheet (Bentley et al, 2011). Beneath the West Antarctic Ice Sheet, subglacial lake sediments may yield evidence for Pleistocene ice sheet collapses. Subglacial Lake Ellsworth (SLE) lies under the West Antarctic Ice Sheet (Fig. 1) It is approximately 15 km long, 3 km wide, up to 156 m deep, and ice thickness is 2930–3280 m (Woodward et al, 2010). We use our results to develop a new conceptual subglacial lake model, and consider the implications for SLE and for subglacial lakes in general This provides a new framework on which to interpret future samples, and an established sequence of techniques to understand the environments in, and prepare for direct access to, other Antarctic subglacial lakes
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