Eddy/tidal mixing and transport at the Antarctic margins

Abstract: 

Ocean processes occurring along the Antarctic continental slope admit shoreward transport of heat toward the continent's marine-terminating glaciers and export newly-formed dense waters from the continental shelf. Recent modeling studies indicate that both eddies and tides may modulate these processes in all sectors of the Antarctic margins. However, due the computational cost of resolving the small (~20km) scales of Antarctic shelf/slope eddies, previous analyses have been limited to regional models and idealized process studies. In this study we analyze the relative contributions of eddies and tides to shoreward heat transport around the entire Antarctic shelf break using output from recent global ECCO2 simulations run at 1/24th and 1/48th degree horizontal resolutions. We show that both tides and eddies effect shoreward heat transport across the continental slope, whereas the heat transport associated with the time-mean flow tends to be directed offshore because it is associated with an Ekman overturning circulation driven by near-continental easterly winds. We discuss the localization of shoreward heat transport relative to troughs in the continental shelf, and variations of these heat transport processes between different sectors of Antarctica. To provide insight into the processes controlling cross-slope heat transport, we use energy and vorticity budgets to characterize the eddy/tidal-mean flow interaction in the Antarctic Slope Current (ASC). We show that tidal forcing produces a distinct dynamical regime in which the core of the ASC flows at almost exactly the same speed as the overlying sea ice, resulting in vanishing surface momentum input that is accommodated by lateral eddy/tidal momentum fluxes.