Eddies and instabilities in downslope flows in the Weddell Sea, Antarctica

• Main Author: Buck, Justin James Henry
• Published: University of Manchester 2009
• Subjects: 551.462173
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507219

The Weddell Sea, Antarctica is a significant area of down welling water in the world large scale ocean circulation. When water descends a slope it is subject to instabilities forming mesoscale features such as eddies in the plume. This thesis is a study of the source of the plume of Ice Shelf Water (ISW) that flows down the Filchner Slope and the downslope flow via the Ronne Depression into the cavity beneath the Ronne Ice Shelf. Oceanographic observations and laboratory experiments simulating the influence of an ice shelf on such a flow are used in this study. The oceanographic data sets used for the Filchner slope are mooring records and research cruise data. The study includes the analysis of novel yoyo casts where the plume of ISW is observed for periods of up to 15 hours. Although the flows observed could not be fully classified, the analysis demonstrated the ability of such a data set to observe the plume. The data analysed from the Ronne Ice Front are two mooring records with an emphasis on eddies in the flows. Eddies were observed at the ice front in both moorings with stronger signals observed during the winter freezing season when the water column is unstratified. The question arose as to whether eddies can propagate across the topographic barrier the ice shelf presents and what effect does ambient two layer stratification have? The experiments in the rest of the thesis were conducted to answer this question. The experimental work uses small 1.2 m and a large 14 m diameter rotating table considering the effect that an ice shelf has on the propagation of eddies. In all but one experiment eddies are generated in the flows though a barotropic mechanism initiated through vortex stretching. It is shown that a relatively small change in ice shelf thickness is required to impede the propagation of eddies into the cavity beneath the ice shelf. However, when two-layer stratification is present and the interface is near to the base of the ice shelf eddies appear to propagate into the ice shelf cavity. The results are then compared to observations and it is concluded that the oceanographic implication of this work is that eddies are unlikely to propagate across the barrier that the ice shelf represents. This is even when stratification is present during summer because the vorticity of eddies is weak and the stratification level is located above the ice shelf base.