Seasonal and Interannual Variations in Hydrographic

Distributions in Marguerite Bay and Environs

Eileen E. Hofmann, John M. Klinck, Robert C. Beardsley, Baris Salihoglu

Hydrographic measurements made during the U.S. Southern Ocean GLOBEC cruises that took place from April to June and July to September of 2001 and 2002, provide a description of changes in water mass distributions and circulation patterns in the Marguerite Bay region as a result of seasonal variability and offshore forcing by the southern boundary of the Antarctic Circumpolar Current (ACC). The primary seasonal change in water mass properties is the reduction in Antarctic Surface Water and replacement by a thick Winter Water layer. The primary effect of the ACC is to pump Circumpolar Deep Water (CDW) onto the continental shelf below 200 m at specific sites that correspond to bathymetric features, such as the Marguerite Trough. The CDW was observed to intrude onto the continental shelf, move across shelf, and enter Marguerite Bay. Offshore flow in response to intrusions occurs across the shelf in the middle of the study area, but does not seem tied to specific bathymetry. This pattern of flow was observed several times during these cruises, suggesting that onshelf intrusions of CDW is likely a frequent occurrence. This circulation has implications for heat, salt and biogenic material budgets for the west Antarctic Peninsula region. The hydrographic distributions also show a narrow southwestward flowing coastal current that enters Marguerite Bay around Adelaide Island and exits around Alexander Island. This current, which may result from seasonal, coastal buoyancy forcing, was well developed in austral fall but appears to be absent in austral winter.