Observations of turbulent mixing and ocean currents in Dotson Ice Shelf cavity

Adjacent to Thwaites Ice Shelf in the Amundsen Sea, Antarctica, Dotson Ice Shelf is experiencing rapid grounding line retreat and high melt rates. Here we present oceanographic observations from a propeller-driven autonomous underwater vehicle sent into the Dotson Ice Shelf cavity, to study the inflow of relatively warm water into the cavity.

In February 2022, during the TARSAN research voyage on RV Nathaniel B Palmer, an Autosub Long Range (ALR) completed four missions under Dotson Ice Shelf. The mission tracks ventured ~20km into the eastern cavity (inflow region) and ~40km into the central cavity (central trough), with one mission travelling along the ice-shelf front. During its missions, the ALR recorded seawater temperature and salinity, chlorophyll concentration and turbidity, current velocity, and turbulent microstructure approximately 80 m above the seabed. 

We present an analysis of this unique dataset. Turbulent energy dissipation rate (ε) in the cavity is on the order of 10^-10 to 10^-8 W/kg. Outside of the cavity ε is higher, with values ranging from 10^-9 to 10^-8 W/kg.  These values are similar to ε values measured under Pine Island Ice Shelf. We are able to show that turbulent mixing is higher in the inflow and bottom intensified, it is influenced by interactions with bathymetry and current speed. Our measurements are able to resolve the warm, dense inflow of water in the eastern cavity with average southward velocities of -7 cm/s at the ice shelf front and variable flow patterns deep into the central cavity. We show the near-bed currents in context with water-mass properties, turbulence, and conditions in the embayment immediately in front of Dotson. This dataset opens up exiting opportunities for collaboration, including with other datasets collected in the Dotson Ice Shelf cavity during the TARSAN campaign and with modelling efforts.