The Southern Antarctic Circumpolar Current Front: physical and biological coupling at South Georgia

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Ward, Peter, Whitehouse, Mick, Meredith, Mike, Murphy, Eugene, Shreeve, Rachael, Korb, Rebecca, Watkins, Jon, Thorpe, Sally, Woodd-Walker, Rachel, Brierley, Andrew, Cunningham, Nathan, Grant, Sharon, Bone, Doug
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2002
• Subjects: Antarctic; South Georgia Island; Antarc*
• Online Access: http://nora.nerc.ac.uk/id/eprint/17512/; http://www.sciencedirect.com/science/article/pii/S096706370200119X

The coupling of physics and biology was examined along a 160 km long transect running out from the north coast of South Georgia Island and crossing the Southern Antarctic Circumpolar Current Front (SACCF) during late December 2000. Surface and near surface potential TS properties indicated the presence of three water types: a near-shore group of stations characterised by water which became progressively warmer and fresher closer to South Georgia, an offshore grouping in which sea surface temperatures and those at the winter water level were relatively warm (1.8°C and 0.5°C, respectively), and a third in which surface and winter water temperatures were cooler and reflected the presence of the SACCF. The transect bisected the SACCF twice, revealing that it was flowing in opposite directions, north-westward closest to South Georgia and south-eastwards at its furthest point from the island. The innermost limb was a narrow intense feature located just off the shelf break in 2000–3500 m of water and in which rapid surface baroclinic velocities (up to 35 cm s−1) were encountered. Offshore in the outermost limb, shown subsequently to be a mesoscale eddy that had meandered south from the retroflected limb of the SACCF, flow was broader and slower with peak velocities around 20 cm s−1. Chlorophyll a biomass was generally low (<1 mg m−3) over much of the transect but increased dramatically in the region of the innermost limb of the SACCF, where a deepening of the surface mixed layer was coincident with a subsurface chlorophyll maximum (7.4 mg m−3) and elevated concentrations down to 100 m. The bloom was coincident with depleted nutrient concentrations, particularly silicate, nitrate and phosphate, and although ammonium concentrations were locally depleted the bloom lay within an elevated band (up to 1.5 mmol m−3) associated with the frontal jet. Increased zooplankton abundance, higher copepod body carbon mass and egg production rates all showed a strong spatial integrity with the front. The population structure of the ...