Sensitivity of Antarctic Bottom Water Formation and Export to Horizontal Model Resolution

Abstract

The formation of Antarctic Bottom Water (AABW) is a key process in the global ocean circulation, but modeling the formation and downslope flow of AABW represents an ongoing challenge for ocean and climate models due to the high horizontal resolution required. Here, we assess the formation and export of AABW to the abyss and its sensitivity to horizontal model resolution in a circumpolar ocean-sea ice model available at horizontal resolutions of 1/10°, 1/20°, and 1/40°. The formation of Dense Shelf Water (DSW), the precursor of AABW, reduces with increasing model resolution in most formation regions due to shelf freshening. Increased eddy activity with higher model resolution flattens the isopycnals in the open Southern Ocean and enables access of lighter, fresher waters onto the continental shelf. Despite the decrease in DSW formation, the total offshore AABW transport increases with increasing model resolution, especially across the 2,500 m isobath, due to less diapycnal mixing during the downslope flow. This resolution dependency is strongest in the Ross and Weddell Seas, the two most important regions of AABW formation. We conclude that a horizontal resolution of 1/10° is sufficient to simulate AABW export from East Antarctica, in agreement with theory of the downslope flow of dense plumes, but finer resolutions of up to 1/40° increase the offshore transport and may be required to resolve the AABW export in the Weddell and Ross Seas.