Oceanographic Conditions in the Grounding Zone Region of Thwaites Glacier

Antarctic ice shelves restrain the flow of grounded ice into the ocean, and are thus an important control on Antarctica's contribution to global sea level rise. West Antarctica represents the largest source of uncertainty in future sea level projections, and Thwaites Glacier has the potential to influence sea level more than any other outlet glacier in this region. The future behaviour of Thwaites Glacier is particular sensitive to the oceanographic conditions near the grounding line, where elevated basal melting can drive rapid grounding line retreat. Here we present oceanographic observations taken through a hot-water drilled access hole located approximately 1.1 km downstream of the Thwaites grounding line. Our observations show that the 55 m thick water column is highly salt-stratified, with the strongest stratification within 2-3 m of the ice base. Despite this strong salinity stratification, there is little evidence of a diffusive-convective staircase. Current speeds are very low with velocities between 3 and 5 cm/s. The tidal flow is less than 1 cm/s. Surface based ApRES measurements suggest that the melt rate is approximately 2 m/yr. Ultimately, these observational efforts will allow us to better constrain grounding zone conditions and the rate of basal melting in large-scale numerical models, facilitating more accurate simulations of the Antarctic ice sheet in the changing climate.