Eddy Generation and Jet Formation via Dense Water Outflows across the Antarctic Continental Slope

Abstract

AbstractAlong various stretches of the Antarctic margins, dense Antarctic Bottom Water (AABW) escapes its formation sites and descends the continental slope. This export necessarily raises the isopycnals associated with lighter density classes over the continental slope, resulting in density surfaces that connect the near-freezing waters of the continental shelf to the much warmer circumpolar deep water (CDW) at middepth offshore. In this article, an eddy-resolving process model is used to explore the possibility that AABW export enhances shoreward heat transport by creating a pathway for CDW to access the continental shelf without doing any work against buoyancy forces. In the absence of a net alongshore pressure gradient, the shoreward CDW transport is effected entirely by mesoscale and submesoscale eddy transfer. Eddies are generated partly by instabilities at the pycnocline, sourcing their energy from the alongshore wind stress, but primarily by instabilities at the CDW–AABW interface, sourcing their energy from buoyancy loss on the continental shelf. This combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth CDW layer, sustaining a local maximum in the eddy kinetic energy over the slope and balancing the Coriolis force associated with the shoreward CDW transport. The resulting slope turbulence self-organizes into a series of alternating along-slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets. Cross-shore variations in the potential vorticity gradient cause the jets to drift continuously offshore, suggesting that fronts observed in regions of AABW down-slope flow may in fact be transient features.