Deep-Sea Research I 49 (2002) 2183–2202 The Southern Antarctic Circumpolar Current Front: physical and biological coupling at South Georgia Peter Ward a, *, Mick Whitehouse a , Mike Meredith a , Eugene Murphy a , Rachael Shreeve a , Rebecca Korb a , Jon Watkins a , Sally Thorpe a , Rachel Woodd-Walker a , Andrew Brierley b , Nathan Cunningham a , Sharon Grant a , Doug Bone a a British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge CB3 0ET, UK b Gatty Marine Laboratory, University of St Andrews, St. Andrews, Fife KY16 8LB, UK Received 31 December 2001; received in revised form 25 July 2002; accepted 26 August 2002 Abstract 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 (1.81C and 0.51C, 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 (o1 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 copepods Calanoides acutus and Rhincalanus gigas at stations within the front suggested that rather than simply resulting from entrainment and concentration within the jet, increased copepod abundance was the result of development in situ. Estimates of bloom duration, based on silicate and carbon budget calculations, set the likely duration between 82 and 122 d, a figure supported by the development schedule of the two copepod species. Given this timescale, model outputs from FRAM and OCCAM indicated that particles that occurred on the north *Corresponding author. E-mail address: pwar@nerc-bas.ac.uk (P. Ward). 0967-0637/03/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0967-0637(02)00119-X