SUBSTANTIAL OPEN-OCEAN PHYTOPLANKTON BLOOMS TO THE NORTH OF SOUTH GEORGIA, SOUTH-ATLANTIC, DURING SUMMER 1994

Substantial open-ocean phytoplankton blooms in the Antarctic Zone to t he northwest of South Georgia, South Atlantic are described. Chlorophy ll a, nutrient and physical oceanography data, collected between 2 and 5 January 1994 and again 1 mo later between 2 and 4 February along a 450 km transect comprising 14 stations, are presented. The transect cr ossed the Subantarctic and the Polar Front. During the January transec t survey, in 2 locations to the south of the Polar Front, average surf ace mixed-layer chlorophyll a concentrations were >8 and >13 mg m(-3), and were associated with silicate, nitrate and phosphate depletions ( <2.0, <11.0 and 1.0 mmol m(-3) respectively), and nitrite and ammonium enhancement (>0.3 and >1.4 mmol m(-3) respectively). One of the phyto plankton blooms was associated with the nearby Polar Front, but the or igin of a bloom further south, well within the Antarctic Zone, was not clear. Phytoplankton production predicted by nutrient drawdown was fa r greater than the observed biomass on both surveys. If a common Antar ctic Zone origin is accepted for the southern bloom, a decline in biom ass of similar to 2.7 mol C m(-2) occurred in the upper 50 m of the wa ter column between the 2 surveys, which cannot be accounted for by zoo plankton grazing. If the bloom had originated in Subantarctic water ad vected to the south of the Polar Front, initial nutrient concentration s would have been lower and consequently predicted production was clos er to the observed biomass values. Nevertheless, the area may be one o f intense but local carbon export.