A Topography-Aware Eddy Parameterization Improves Warm Water Transport Across the Cape Darnley Continental Slope

Abstract

The onshore transport of warm Circumpolar Deep Water determines the properties of Antarctic shelf waters and drives the melting of the Antarctic ice shelves. The largest net onshore transport of CDW coincides with regions of dense water export, such as the Cape Darnley region in the East Antarctic, one of the major sources of Antarctic Bottom Water. In an eddy-resolving regional ocean model of the Cape Darnley region, the winter downslope flow of dense water produces an eddy-driven transport of warm modified Circumpolar Deep Water across the shelf break. At coarse resolution typical for climate models, this warm water transport is absent and needs to be parameterized. The Gent and McWilliams/Redi (GM/Redi) scheme improves the simulated hydrographic fields and recovers a transport of warm water across the shelf break. With high constant GM/Redi coefficients that improve the mean hydrography the most, however, the on-shelf transport of warm water is overestimated. This is because the dynamical suppression of eddy-driven transports across sloping bottom topography is not considered in the GM/Redi scheme. Therefore, we implement a topography-aware version of the GM/Redi scheme that reduces the coefficients over steep continental slopes, representing the eddy-suppressive effect of sloping bottom topography. The topography-aware GM/Redi scheme outperforms the traditional version by simultaneously improving the mean hydrographic fields and the cross-slope warm water transports. Eddy parameterizations remain important for the representation of onshore tracer transports and shelf water masses in ocean models provided they incorporate regional and local physics as in our example of a topography-aware scheme.