Sack Lunch Seminar (SLS)

The Antarctic Slope Front (ASF) almost completely encircles the Antarctic continent, separating cold shelf waters from relatively warm Circumpolar Deep Water (CDW) at mid-depth offshore. Exchanges across the ASF transport CDW toward marine-terminating glaciers, and export Antarctic Bottom Water (AABW) to the abyssal ocean. Recent studies indicate that this exchange may be modulated by mesoscale eddies, which facilitate cross-slope exchanges via stirring along isopycnals and eddy bolus transports. In this seminar I will discuss physical controls over the rates of cross-slope water mass exchange, and examine the dynamical balances governing cross-slope eddy transfer.

I will first present a recently-developed eddy-resolving process model of the Antarctic continental shelf and slope. The model enforces realistic offshore ocean stratification over idealized shelf/slope bathymetry, in order to provide a realistic representation of the water masses in a configuration that can be analyzed cleanly. The model forcing includes a westward wind stress over the continental slope and buoyancy loss on the continental shelf, consistent with prevailing Antarctic easterly winds and brine rejection in coastal polynyas.

I will use this model to explore the sources of eddy kinetic energy (EKE) over the continental slope, and its resulting impact on the cross-slope transport of mass and tracers. I will show that the upper-ocean dynamics resemble the Antarctic Circumpolar Current, with wind-driven northward shoaling of the pycnocline resisted by baroclinic conversion of potential energy to EKE. By contrast, close to the ocean bed (at the CDW/AABW interface) potential energy is removed by both the wind-driven mean overturning and the generation of baroclinic eddies, and is instead sourced from the buoyancy loss on the continental shelf. This EKE source turns out to be sensitive to variations in the model surface forcing and bathymetry. Consequently, relatively small changes in the forcing and geometry can produce a substantial rearrangement of the water mass pathways and volume transports across the continental slope. These findings suggest that shoreward eddy transport of CDW should be localized to a few favorable locations around the Antarctic shelf break, and that future changes in the easterly wind strength or coastal polynya productivity could significantly alter the shoreward heat transport and the properties of the outflowing AABW.