Abrahamsen, Einar Povl
Oceanographic conditions beneath Fimbul Ice Shelf, Antarctica
University of Southampton, School of Ocean and Earth Science,
Antarctic ice shelves play a key role in the global climate system, acting as important sites for the cooling of shelf waters, thereby facilitating deep and bottom water formation. Many of the processes that take place under large ice shelves can be observed more conveniently beneath smaller ice shelves such as Fimbul Ice Shelf, an ice shelf in the eastern Weddell Sea. Fimbul Ice Shelf and nearby ice shelves might also play a significant regional role: although no bottom water is produced in this area, it is thought that Fimbul Ice Shelf and nearby ice shelves precondition the shelf waters that ultimately are converted to Weddell Sea Deep Water (WSDW) in the southern Weddell Sea. Using the first data ever to be collected beneath an ice shelf from an autonomous underwater vehicle (AUV), as well as data from the vicinity of the ice shelf using traditional oceanographic methods, this thesis discusses the circulation and processes occurring beneath the ice shelf. This has been supplemented by using a coupled ice shelf/ocean model, POLAIR, to simulate the circulation, melting, and tides under Fimbul Ice Shelf and in the surrounding area. Data from the ice shelf cavity show relatively large variability in temperatures, but all within approx. 0.25 °C of the freezing point. Melt rates are found to be lower than some previous model studies, but in better agreement with observations and glaciological models. The base of the ice shelf was found to be rough in places, corresponding to `flow traces' visible in satellite imagery. This could have implications for mixing beneath the ice shelf, at least in these limited areas. The Autosub AUV was found to be a useful platform for measuring hydrography and ice shelf cavity geometry with spatial coverage and resolution not available from surface measurements.
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