Peering beneath the ice: observing the ocean under Antarctica’s floating ice shelves

Antarctic ice shelves – the floating extensions of the Antarctic Ice sheet – exert a critical control on Antarctica’s contribution to global sea-level rise by restraining the flow of grounded ice into the ocean. Our inability to reliably predict how the Antarctic Ice Sheet will respond to our warming climate is the largest source of uncertainty in projections of future sea-level rise. The loss of grounded ice is particularly sensitive to the rate at which the floating ice shelves are melted from below by ‘warm’ ocean water. The melt rate is controlled by the turbulent transfer of heat through the last few meters of the ocean. The physics of this ice shelf–ocean boundary layer are not well understood and are poorly represented in climate models. In this talk I will present our work using hot water drilled access holes to directly observe the ice shelf–ocean boundary layer. These observations provide a unique opportunity to understand the turbulent processes responsible for modulating the rate of ice shelf melting. I will show that while existing models of basal melting work well beneath some ice shelves, in the Amundsen Sea sector of West Antarctica, where we have seen huge losses of ice from Pine Island and Thwaites Glacier, existing models dramatically overestimate the rate of melting with unknown consequences. Ultimately, our observations allow us to better constrain representations of basal melting in large-scale climate models, facilitating more accurate simulations of the changing Antarctic Ice Sheet.