Physical processes in Subglacial Lake Whillans, West Antarctica: Inferences from sediment cores

Abstract

25The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the 26 dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the 27 ice sheet. Despite considerable interest in understanding this subglacial network and its affect on 28 ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the 29 first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial 30 Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice 31Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no 32 evidence of erosion or deposition by flowing water. By inference, these floods must have 33 insufficient energy to erode or transport significant volumes of sediment coarser than silt. 34Consequently, water flow beneath the region is probably incapable of incising continuous 35 channels into the bed and instead follows preexisting subglacial topography. Sediment on the 36 lake floor consists of till deposited during intermittent grounding of the ice stream following 37 flood events. The fabrics within the till are weaker than those thought to develop in thick 38 deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and 39 unlikely to have a large stabilizing effect on the ice stream's grounding zone. 40Text 41 42

Poststagnation Retreat of Kamb Ice Stream's Grounding Zone

“…Sediment flux to the GZW due to subglacial deformation ( Q t ) is a function of the average till velocity ( ), and the thickness of the deforming layer ( h t ): per meter width, where ϕ till and ϕ GZW denote porosity of the subglacial till and GZW, respectively (Alley et al, ; Larter & Vanneste, ). Estimates of the depth of mobilization ( h t ) beneath the Siple Coast ice streams vary between the several centimeters to several tens of centimeters estimated by Engelhardt and Kamb () (see also Hodson et al, ), to the 6–8 m estimated by Rooney et al () and Blankenship et al ().…”

Biogeochemical Connectivity Between Freshwater Ecosystems beneath the West Antarctic Ice Sheet and the Sub‐Ice Marine Environment

“…However, quantification of Antarctic subglacial organic matter stores and their significance to regional biogeochemical processes is limited by a paucity of data and direct observations. Whillans Subglacial Lake (SLW) was the first Antarctic subglacial lake that was directly sampled using specialized clean access technology (Priscu et al, ) and characterized through physical, chemical, and microbiological investigations (Achberger et al, ; Christner et al, ; Hodson et al, ; Michaud et al, ; Michaud et al, ; Mikucki et al, ; Purcell et al, ; Tulaczyk et al, ; Vick‐Majors, Mitchell et al, ). SLW is a relatively small body of fresh water (~0.13 km 3 ; Christner et al, ; Fricker & Scambos, ) located ~800 m beneath the West Antarctic Ice Sheet (Fricker et al, ).…”

Sedimentary processes at ice sheet grounding‐zone wedges revealed by outcrops, Washington State (USA)

“…Upon depositing at the grounding line, sediment is subjected to remobilization by sediment failures, gravity flows, and reworking by meltwater discharge (King et al, 1991;Powell and Alley, 1997;Horgan et al, 2013). Limited estimates of sediment flux have been reported, with values ranging from 40 m 3 a -1 near the modern Whillans Ice Stream grounding line (Hodson et al, 2016) to 8000 m 3 a -1 for the paleo-Norwegian Channel Ice Stream (Nygård et al, 2007). Limited estimates of sediment flux have been reported, with values ranging from 40 m 3 a -1 near the modern Whillans Ice Stream grounding line (Hodson et al, 2016) to 8000 m 3 a -1 for the paleo-Norwegian Channel Ice Stream (Nygård et al, 2007).…”