C21D-1271 Summertime Glacial Meltwater Transport near Dotson Ice Shelf

Abstract: Identifying glacial meltwater via oceanographic profiling along West Antarctica’s Amundsen Sea Embayment helps quantify nearby ice shelf basal melt. However, the high variability of exported meltwater and the low resolution of existing observations have led to uncertainties in the exact origin and fate of meltwater found spanning the continental shelf. Here, we use summertime profiles of temperature, salinity, oxygen, and microstructure turbulence to resolve two layers of glacial meltwater within the eastern Amundsen Sea Polynya (110-120°W). We suggest that a deeper meltwater layer originates from basal melt within the Dotson Ice Shelf cavity, while a shallower meltwater layer is largely imported from upstream ice margins to the east. Melt rate calculations derived from a summation of the two layers may thus over-estimate Dotson Ice Shelf mass loss. Furthermore, in situ turbulence measurements of the meltwater layers allow for the validation of general circulation models that typically parameterize how meltwater mixes into the ocean. We determine that the two meltwater layers undergo localized intermixing near the ice shelf but are elsewhere separated by an intermediate layer of remnant Winter Water. Near the interfaces of meltwater and Winter Water, thermal diffusivity varies by up to five orders of magnitude and does not scale well with turbulence intensity, so models that assume either constant diffusivity or constant mixing efficiency may not correctly resolve the diffusion of meltwater back into the coastal ocean. Increases in the basal melt of West Antarctica’s ice shelves may result in reductions in sea-ice volume and Antarctic Bottom Water formation, so it is essential that pathways of heat and meltwater transport are accurately quantified.