PL14A-2212 Contribution of double-diffusive convection to vertical heat flux across glacial meltwater layers in the coastal Amundsen Sea

Abstract: Meltwater-rich outflows of modified Circumpolar Deep Water from beneath Amundsen Sea ice shelves supply heat to the middle water column, resulting in a seasonal erosion of the overlying Winter Water layer. It is imperative that global circulation models resolve this process in order to accurately represent the alongshore transport of glacial meltwater and its influences on nearby sea ice formation and downstream overturning circulation. The increases in both salinity and temperature between Winter Water and the underlying glacial meltwater suggest that energy dissipation at this depth may be driven by double-diffusive convection (DC), which is thought to increase the efficiency of vertical mixing. However, the paucity of in situ turbulence measurements in this region results in uncertainties regarding the magnitude of vertical heat diffusivity. In this work, we apply a recently developed spice model of energy dissipation during DC (Middleton et al., 2021, https://doi.org/10.1029/2021GL092779) to an array of 2021/2022 summertime ship- and glider-based temperature and salinity profiles from within the Amundsen Sea Polynya (110-120°W). The modeled dissipation rates are validated by in situ vertical microstructure profiles and provide evidence of elevated temperature diffusivity (and thus upward heat flux) throughout the glacial meltwater layer. These results motivate the inclusion of parameterizations of DC in general circulation models of meltwater transport along the West Antarctic coastline, as well as continued efforts into confirming the dependence of mixing efficiency on turbulence intensity, overturn age, and density ratio.