Estimating Erosion Rates from the Western Greenland Ice Sheet Using Proglacial Lake Sediment Volumes

Abstract:

Glacial erosion by the Greenland Ice Sheet (GrIS) is evident from the carved relief and deposited sediments on and around its margins. The processes involved in glacial erosion, the rate at which erosion occurs, and how it evolves in a changing climate, however, are poorly constrained. Significant efforts have been made to calculate glacier erosion rates from temperate mountain glaciers and ice fields using quantification of sediment budgets in proglacial lakes, however, very few studies have focused on the polar ice sheets to date. This study adapts sediment volume quantification methods traditionally used for calculating erosion rates from mountain valley glacier systems, and applies it to a partially deglaciated basin at the western margin of GrIS. In 2018, we collected cores, bathymetry and imaged the volume of sediments deposited in two proglacial lakes in the Eqaluit Taserssuat drainage basin using 2-D acoustic reflection profiles. Sediment accumulation rates were determined using radiocarbon dating from the cores, and converted to varying sediment fluxes delivered to the lakes over the Holocene. The corresponding glacial erosion rate could then be calculated by dividing the sediment fluxes by the contributing basin area. The area contributing this sediment from under the GrIS was modeled using BedMachine V3 sub-ice topography. From these results we estimate an erosion rate ranging from 0.05-0.12 mm/yr under this sector of the GrIS. We treat this range as a minimum, time-averaged abrasion rate, and not a total erosion rate because: (1) not all sediment produced by this sector of the GrIS was trapped in the study lakes, (2) any coarser material deposited in deltas and along the lake margins could not be quantified due to lack of penetration by the sub-bottom profiler, and (3) other, subaerial sediment traps (landforms, braidplains) within the watershed were not measured. Nevertheless, the minimum abrasion rate we found is similar to other estimates of basin-averaged erosion rates from GrIS and other outlet glaciers in similar polar climatic regimes. This study is a step forward in measuring erosional processes under ice sheets over the Holocene, and provides a methodological framework for interpretation of proglacial sediments as paleoclimatic records.