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Selected physico-chemical and biological properties were compared between shelf and deep oceanic waters in the vicinity of Bouvet and the South Sandwich Islands during the austral summers of 1982-1983 and 1990-1991. On 3 of these occasions circuminsular chlorophyll a levels were 3 to 7 mg chl a m-3, an increase of 3 to 4 times over off-shore stations. At South Sandwich in 1990-1991 high phaeopigment levels indicated senescence of the phytoplankton bloom and primary production on this occasion was not markedly greater than in off-shore waters. On 2 occasions (Bouvet 1990, South Sandwich 1982 high chlorophyll concentrations were associated with a marked increase in production (up to ca 280 mg C m-' h-' in 1982-1983 and ca 1.5 mg C m-3 h- ' in 1990-1991). This combination of high chl a and production levels was associated with depletion of dissolved nutrients. Size fractionation during summer 1990-1991 indcated dominance (ca 70 % of total chl) by netphytoplankton (20 to 200 pm) at Bouvet and by nanoplankton (1 to 20 ym, 70 % of total chl) at South Sandwich. Sharp drops in temperature and salinity over the island shelves, and spatial covariance between upper mixed layer depth and chl a concentration, suggest that stabilisation by meltwater may be the main cause of phytoplankton bloom formation. The present and published data suggest a longitudinal trend of decreasing phytoplankton production from Antarctic Peninsula archipelagos to islands in the Indian Ocean sector of the Southern Ocean. This may have implications for the estimation of total carbon f l u in Antarctic waters.

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