On the transport, variability and origin of dense water masses crossing the South Scotia Ridge

Abstract

Abstract The deep Scotia Sea is filled with ventilated Weddell Sea Deep Water. This in turn is an essential contributor to the ventilation of the World Ocean abyss. Depending on the formation process and/or its location along the Weddell Sea periphery, deep and bottom water masses follow different routes to cross the South Scotia Ridge. A primitive equation, hydrostatic, terrain-following coordinate ocean general circulation model (BRIOS-1) 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. Eastward Weddell Sea Deep Water transport of 24×106 m3 s−1 is found in the northern limb of the Weddell Gyre across 44°W. Export rates of Weddell Sea Deep Water through gaps in the South Scotia Ridge are estimated to be 6.4×106 m3 s−1 with a semi-annual cycle of ±0.6×106 m3 s−1, 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. Lagrangian particle trajectories illustrate the pathways of water masses from the inner Weddell Sea into the Scotia Sea through various gaps in the South Scotia Ridge. They highlight 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. Water masses flowing through the major gaps originate from the southwestern and southeastern Weddell Sea continental shelves. However, water masses formed east of the Weddell Sea (e.g., Prydz Bay) also seem to feed the deep Scotia Sea, since a large portion of floats flowing northward through the gaps of the South Scotia Ridge have been in contact with the mixed-layer processes outside the inner Weddell Sea.