An examination of double-diffusive processes in a mesoscale eddy in the Arctic Ocean

Temperature and salinity measurements of an Atlantic Water mesoscale eddy in the Arctic Ocean's Canada Basin are analyzed to understand the effects of velocity shear on a range of double-diffusive processes. Double-diffusive structures in and around the eddy are examined through the transition from low shear (outside the eddy and within its solid body core) to high geostrophic shear zones at the eddy flanks. The presence or absence of a double-diffusive staircase structure (in regions where the vertical gradients in temperature and salinity are double-diffusively unstable) can be predicted by a Richardson number criterion, with low Richardson numbers (high shear) coinciding with the absence of a well-formed staircase. A double-diffusive staircase is not observed at the eddy flanks, where shear-driven turbulent mixing dominates; a Thorpe scale analysis is used to estimate turbulent diffusivities in these regions. Double-diffusive and turbulent heat, salt and buoyancy fluxes from the eddy are computed, and used to place bounds on the timescale for eddy decay. Estimated lateral variations in vertical fluxes across the eddy allow for speculation that double diffusion speeds up the eddy decay, having important implications to the transfer of Atlantic Water heat in the Arctic Ocean.