Meteoric water and glacial melt in the southeastern Amundsen Sea: a time series from 1994 to 2020

Abstract

Ice sheet mass loss from Antarctica is greatest in the Amundsen Sea sector, where “warm” modified Circumpolar Deep Water moves onto the continental shelf and melts and thins the bases of ice shelves hundreds of meters below the sea surface. We use nearly 1000 paired salinity and oxygen isotope analyses of seawater samples collected on seven expeditions from 1994 to 2020 to produce a time series of glacial meltwater inventory for the southeastern Amundsen Sea continental shelf. Deep water column salinity–δ18O relationships yield freshwater end-member δ18O values from -31.3±1.0‰ to -28.4±1.0‰, consistent with the isotopic composition of local glacial ice. We use a two-component meteoric water end-member approach that accounts for precipitation in the upper water column, and a pure glacial meteoric water end-member is employed for the deep water column. Meteoric water inventories are comprised of nearly pure glacial meltwater in deep shelf waters and of >74 % glacial meltwater in the upper water column. Total meteoric water inventories range from 8.1±0.7 to 9.6±0.8 m and exhibit greater interannual variability than trend over the study period, based on the available data. The relatively long residence time in the southeastern Amundsen Sea allows changes in mean meteoric water inventories to diagnose large changes in local melt rates, and improved understanding of regional circulation could produce well-constrained glacial meltwater fluxes. The two-component meteoric end-member technique improves the accuracy of the sea ice melt and meteoric fractions estimated from seawater δ18O measurements throughout the entire water column and increases the utility for the broader application of these estimates.