Persistent Meltwater Discharge from Thwaites Glacier Recorded in Offshore Sediments.

Abstract:

Investigations into the effects of subglacial meltwater on ice-sheet and ice-shelf behavior have yielded nebulous, even contrasting, results. Distributed subglacial drainage drives increased ice-flow velocity on sub-seasonal to multi-annual scales, while efficient channelized drainage effectively increases basal friction and can reduce ice-flow velocities. Additionally, meltwater expulsion at the grounding zone can enhance localized basal melt, incise channels in the ice-shelf base – both of which reduce the ice shelf’s ability to buttress grounded ice – and inhibit grounding-zone sediment deposition.

We investigate evidence for subglacial meltwater discharge from Thwaites Glacier (TG), West Antarctica to evaluate the nature of subglacial plumbing and its role in recent (i.e., pre-satellite) grounding-line retreat. Sediment cores recovered during expedition NBP19-02 under the International Thwaites Glacier Collaboration record recent processes and dynamics of the TG grounding zone. Two sediment cores, one recovered from a bathymetric high on which TG was recently pinned and the other from within an adjacent trough, were analyzed using laser-particle size and shape, and the bulk trace-metal geochemistry was measured using x-ray fluorescence. Applying principal component analysis to these sedimentological and geochemical data, we identify fundamental similarities between these two sediment cores, as well as down-core continuity in their sediment characteristics. Similarities between these sediments and meltwater facies from the western Ross Sea and the Amundsen Sea suggest analogous depositional processes.

We find that recent unpinning of TG was punctuated by meltwater discharge and that sediment-laden meltwater plumes continue to influence modern sediment deposition. Ongoing work will integrate radiocarbon and Pb-210 age models to constrain sedimentation rates of these meltwater-influenced intervals and quantify meltwater discharge volumes. Understanding the role meltwater has played in the recent retreat of TG will help clarify the complex relationship between subglacial hydrology and ice-sheet dynamics.