Dynamic seasonal cycling of inorganic carbon downstream of South Georgia, Southern Ocean

Elizabeth M. Jones, Dorothee C. E. Bakker, Hugh J. Venables, Andrew J. Watson

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The influence of the island mass effect of South Georgia on the seasonal marine carbon cycle was investigated during austral summer (January-February) 2008. South Georgia (54-55°S 36-38°W) lies on the North Scotia Ridge, strongly influencing the passage of the Southern Antarctic Circumpolar Current Front to the south. Surface waters upstream of the island, in the central Scotia Sea, were characterised by relative high-nutrient low-chlorophyll (HNLC) conditions from winter (September) 2007 to summer, as indicated by satellite and shipboard observations. The fugacity of carbon dioxide (fCO2) was slightly supersaturated and the HNLC waters represented a summertime CO2 source of 2.6±1.5 mmol m-2 day-1. Extensive phytoplankton blooms developed in the Georgia Basin, downstream of South Georgia, in October 2007 and persisted until March 2008. The seasonal depletion in dissolved inorganic carbon (DIC) was 94±1 µmol kg-1 and the ?fCO2(sea-air) was -92±21 µatm in the core of the bloom by early February. These conditions created a strong sink for atmospheric CO2 of -12.9±11.7 mmol m-2 day-1. In contrast, wintertime mixing into DIC-rich sub-surface waters created a strong CO2 source of 22.0±14.4 mmol m-2 day-1. These processes drive substantial seasonal changes in DIC of up to -0.7 µmol kg-1 day-1 from winter to summer. Similarly to the blooms of Kerguelen and Crozet, the South Georgia bloom is likely to be fuelled by natural iron fertilisation. A DIC deficit of 2.2±0.3 mol m-2 upstream of South Georgia suggested that the relative HNLC waters were more productive than indicated by satellites. The DIC deficit more than doubled downstream of South Georgia (4.6±0.8 mol m-2) to create the strongest seasonal carbon uptake in ice-free waters of the Southern Ocean to date.
Original languageEnglish
Pages (from-to)25-35
Number of pages11
JournalDeep-Sea Research Part II: Topical Studies in Oceanography
Publication statusPublished - Jan 2011

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