Oceanographic processes near the Filchner Sill – plans for fieldwork in 2007
Over the Antarctic continental shelves, the focus of attention has been on the export of cold dense
shelf waters to the world’s deep ocean and their contribution to Antarctic Bottom Water (AABW)
production. Far less attention has been given to the import, onto the continental shelves, of surface and warm deep waters, which are key components of the heat, salt and mass budgets for the shelf seas. In order to quantify these budgets, mechanisms that control the rate of cross-shelf
exchange need to be identified if we are to better understand the interactions between the Antarctic shelf seas and adjacent oceans. In the southeastern Weddell Sea, east of 26°W, the water masses over the narrow continental
shelf are separated from the deep ocean by a series of fronts and associated currents. During winter, cooling leads to the formation of Winter Water (WW), while over the continental shelf water masses are freshened by glacial melt from the ice shelves that fringe the region [Fahrbach
et al., 1994]. This cross-shelf density gradient supports a westward slope front current. In addition, the prevailing easterly winds produce a surface Ekman transport, leading to an increase in sea surface elevation toward the coast and a downwelling of the isopycnals that both deepens
the interface between the WW and the underlying Weddell Deep Water (WDW) and supports a westward coastal current. In the southeastern Weddell Sea where the open shelf is very narrow, these currents effectively merge and are referred to as the Antarctic Coastal Current [Fahrbach et
al., 1992]. Once the coastal current passes the Stancomb-Wills Ice Stream, which overhangs the shelf break,
the continental shelf broadens and the current separates into coastal and slope components [Foster and Carmack, 1976]. The coastal component heads south towards Brunt Ice Shelf while the slope component flows west towards the Filchner Sill. North of Helmert Bank, WDW is found below the depth of both the shelf break and the troughs that cut some 200 m deeper into the surrounding shelf. Nevertheless, despite the physical and dynamic barriers associated with the shelf break, WDW is able to upwell and access the continental shelf in a modified form. These intrusions of Modified Weddell Deep Water (MWDW) occur at various locations along the shelf break, although only two persist beyond the shelf break region and extend southwards toward
Filchner Ronne Ice Front. The aim of the forthcoming cruise in early 2007 is to identify the shelf break processes that control the upwelling of MWDW onto the shelf, and determine the flux of heat, salt and mass across the continental shelf break around the Filchner Sill region and along
the Luitpold Coast (Figure 1).
Authors: Makinson, K., Nicholls, K.W., Abrahamsen, E.P.