Über die Tiefenwasserausbreitung im Weddellmeer und in der Scotia-See: Numerische Untersuchungen der Transport- und Austauschprozesse in der Weddell-Scotia-Konfluenz-Zone

Abstract

The deep Scotia Sea is filled with ventilated Weddell Sea Deep Water (WSDW). This in turn is an essential contributor to the ventilation of the World Ocean abyss. A primitive equation, hydrostatic, ocean general circulation model (BRIOS1.1) with terrain-following coordinate is used to investigate the water mass export from the Weddell Sea. The model is circumpolar focusing on the Weddell Sea, with particularly high resolution (~20 km) in the DOVETAIL area. The northern limb of the Weddell Gyre exhibits an eastward Weddell Sea Deep Water transport across 44°W of 24 Sv. Export rates of Weddell Sea Deep Water through gaps in theSouth Scotia Ridge are estimated to be 6.4 Sv with a semi-annual cycle of ± 0.6 Sv, which can be correlated to atmospheric cyclone activity and Weddell Gyre strength. Sensitivity studies considering extreme sea ice conditions in the Weddell Sea show higher (lower) exports in years of minimum (maximum) winter sea ice extent. This can be attributed to the local change of the surface stress achieved by wind and ice. Lagrangian particle trajectories illustrate the pathways of water masses from the inner Weddell Sea into the Scotia Sea through the major gaps in the South Scotia Ridge. They support the existing flow divergence on the northwestern continental shelf with one branch entering Bransfield Strait and the other continuing eastwards subsequently filling the deep Weddell and Scotia seas. Floats highlight the interannual variability of the flow field. Water masses flowing through the major gaps originate from the southwestern and southeastern Weddell Sea continental shelves.Water masses formed east of the Weddell Sea (e.g., Prydz Bay) also seem to feed the deep Scotia Sea. The propagation of dense water masses spreading from the southern continental shelf to the South Atlantic Ocean is estimated to be about 8 years not including residence times on the continental shelf.