Deep water formed around the Antarctic continent drives the world ocean circulation. Most of this deep water is formed within only about 10% of the Antarctic circumpolar band: the Weddell Sea. Subtle changes in the circulation of the Weddell Sea can lead to major changes in floating ice-shelves, with critical implications for global sea level, the production of deep water, and the global ocean overturning circulation. Despite these critical climate implications, the Antarctic shelf circulation remains poorly understood.
The 5-year WAPITI project funded by the European Research Council will investigate a range of different aspects of the Weddell Sea circulation, using a combination of targeted observation, existing observation database, and high-resolution models, as well as the use of new, specifically developed autonomous instruments. The ultimate goal of the project is to refine our understanding of the water-mass transformation and pathways in this key region of the worlds ocean.
Existing observation databases will be used to revisit descriptions of the surface layer dynamics, as seen under sea-ice. Using this dataset, the question of the subpolar gyre intensity and variability will also be tackled. Water from the subpolar gyre can be partly injected onto the Antarctic continental shelf and will eventually flow under the ice-shelf to form bottom water. However, the transfer of water-mass across the intense slope current that flows along the Antarctic continental slope is not understood. This question, and the impact of small oceanic features upon this process, will be approached using a specifically designed high-resolution numerical model of the region.
Once water-mass enters the continental shelf, it undergoes large transformation before it is injected under the ice shelves. However, the lack of winter observations prevents us from understanding how water-masses are modified. As part of the WAPITI project, Lagrangian floats measuring water-mass properties will be deployed to drift under sea-ice year-round. They will position themselves by triangulation, using a network of sound sources deployed on the continental shelf. Finally, the turbulence and water-mass changes associated with bottom water overflow will be investigated using specifically designed floats, which will drift in the bottom boundary layer, measuring water-mass characteristics and the vertical profile of currents along their path.