| Hydrographic measurements made during the four U.S. Southern Ocean Global OceanEcosystems Dynamics Program survey cruises, which took place from April to June and July to September of 2001 and 2002, provide a description of changes inwater mass distributions and circulation patterns in the Marguerite Bayregion as a result of seasonal variability and offshore forcing by thesouthern boundary of the Antarctic Circumpolar Current. The primary seasonalchange in water mass properties is the reduction in Antarctic Surface Waterand replacement by a thick Winter Water layer. The primary effect of theAntarctic Circumpolar Current is to pump Circumpolar Deep Water (CDW) ontothe continental shelf below 200 m at specific sites that correspond tobathymetric features, such as the Marguerite Trough. The CDW was observed tointrude onto the continental shelf, move across shelf, and enter MargueriteBay. Offshore flow in response to intrusions occurs across the shelf in themiddle of the study area, but does not seem tied to specific bathymetry.This pattern of flow was observed several times and at several sites during thecruises, suggesting that onshelf intrusions of CDW is a frequent occurrence.This circulation has implications for heat, salt and biogenic materialbudgets for the west Antarctic Peninsula region. The hydrographicdistributions also show a narrow southwestward flowing coastal current thatenters Marguerite Bay around Adelaide Island and exits around AlexanderIsland. This current, which may result from seasonal, coastal buoyancyforcing, was well developed in austral fall but appears to be absent inaustral winter. |
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