| Abstrakt: |
The South Scotia Ridge, in the Atlantic sector of the Southern Ocean, is a key region for water mass modification. It is the location of the Weddell‐Scotia Confluence, an area of reduced stratification which separates the Weddell Gyre to the south and the Antarctic Circumpolar Current to the north, and which receives input of shelf waters from the tip of the Antarctic Peninsula. To elucidate the transformations over the ridge, we focus on one of its largest seamounts, Discovery Bank, which has previously been observed as hosting a stratified Taylor column that retains water for months to years, during which time water masses are entrained from north and south of the Weddell Front and steadily mixed. Data from ship‐deployed sensors and autonomous platforms are analyzed to quantify and understand the diapycnal mixing, heat fluxes and water mass transformations over the bank. Ocean glider and free‐profiling drifting float data show that the mid‐depth temperature maximum of the Circumpolar Deep Water (CDW) is eroded between the northern and southern sides of the bank, while diapycnal diffusivity is enhanced by up to an order‐of‐magnitude over its steeply sloping portions. This is accompanied by heat fluxes from the CDW layer being increased by up to a factor of six, which may contribute to a reduction in mid‐depth stratification. Tidal model analysis shows that the southern side of the bank hosts strong barotropic to baroclinic energy conversion (>150 N m−2), emphasizing the role of internal tides in modulating water mass transformations in the Confluence. Plain Language Summary: The Weddell‐Scotia Confluence region, in the South Atlantic sector of the Southern Ocean, is a zone where ocean waters from the Antarctic Circumpolar Current to the north, the Weddell Sea to the south, and the Antarctic Peninsula to the west, come together and interact. In this paper, observations from a research ship, an autonomous underwater glider, and free‐drifting ocean floats are used to characterize the mixing between these different sources of water, and to understand what impact this mixing has on the downstream vertical structure of the water column. The results show that an anticlockwise circulation of waters occurs around a large underwater seamount in the region, causing the waters there to be trapped for months to years. In addition, interaction with the steeply sloping undersea topography generates particularly strong mixing between these different waters through the action of tides, which helps to sustain the characteristic low vertical density gradients present in the region. These processes have important implications for both the movement of mid‐depth waters south into the circulation of the Weddell Sea, and likely also for the supply of nutrients to the productive surface layer of the ocean. Key Points: New observations reveal enhanced mixing rates and mid‐depth heat fluxes over one of the largest seamounts of the South Scotia RidgeThis enhanced mixing may help to sustain the mid‐depth stratification minimum found in the Weddell Scotia ConfluenceResults from a tidal model show high rates of barotropic to baroclinic tidal energy conversion over steeply sloping parts of the bank [ABSTRACT FROM AUTHOR] |
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