The regulation of sea ice thickness by double-diffusive processes in the Ross Gyre

New fine-scale observations from the central Ross Gyre reveal the presence of double-diffusive staircase structures underlying the surface mixed layer. These structures are persistent over seasons, with more developed mixed layers within the double-diffusive staircase in winter months. The sensitivity of the ice formation rate with respect to mixing processes within the main pycnocline (double-diffusive versus purely turbulent mixing) is investigated with the 1D model. A scenario with purely turbulent mixing results in significant underestimates of sea ice thickness. However, a scenario when double-diffusive mixing operates in the presence of weak shear yields plausible ranges for sea ice thickness that agrees well with the observations. The model results and observations suggest a peculiar feedback mechanism that promotes the self-maintenance of double-diffusive staircases. Suppression of the vertical heat fluxes due to the presence of a double-diffusive staircase, compared to purely turbulent case, allows Upper Circumpolar Deep Water to be more exposed to surface buoyancy fluxes. Our results shed light on the process - double diffusion - that might account for estimated rates of winter water mass transformation in the central Ross Gyre.