Distribution of kinetic energy in the Weddell Sea gravity current

Abstract

The Weddell Sea is the largest contributor to deep water formation in the Southern Hemisphere. Dense and cold waters form during sea ice production on the continental shelves of the southern and western Weddell Sea, and are subsequently exported into the deep ocean via a dense near-bottom gravity current.  The current then propagates along the continental slope for several hundred kilometers. The gravity current is important for the global ocean circulation, although not all details are understood, as observations are sparse in this heavily ice-covered region. Furthermore, the current is likely modified by small-scale processes, which are generally unresolved by global ocean models. In this work, we use multi-year velocity measurements from 2017 to 2019 from moorings on the southern and northwestern Weddell Sea continental shelf and slope to quantify the relevant energy sources within the gravity current. Specifically, we investigate barotropic and baroclinic tidal energy, internal wave background and their dependence on location and time. Stronger internal waves up-slope coincide with the position of the gravity current main cores, which suggests that the bulk amount of mixing of the dense water with the ambient water occurs in shallower areas. Although the energy contained in waves with periods of several days varies throughout the year, the internal wave background on hourly time-scales seems to be largely unaffected. Our work is mainly aimed at the understanding of local energy levels within the dense gravity current, which may ultimately benefit a more accurate representation of dense water formation in global models.