Phytoplanktonic and bacterial carbon pools and productivities in the Gerlache Strait, Antarctica, during early austral spring

Phytoplankton and bacterial biomass and productivities were investigated at four depths in the upper 500 m of the water column in the Gerlache Strait, Antarctica during the prebloom period of early austral spring, from Octobe r 13 to November 4, 1995. The concentrations of all carbon pools were low, with the total particulate organic carbon (POC) concentration averaging 1.9 +/- 0.9 mu M. Bacterial, protozoan, and phytoplankton carbon accounted for 21% of the total POC, indicating that detritus or unenumerated organisms c omprised the bulk of the POC during this period. Larger zooplankton or prot ozoa, such as ciliates, may account for this difference, since microzooplan kton can represent a significant fraction of the total microbial biomass. P rimary and bacterial secondary production rates were also low, less than 30 0 and 30 ng C L-1 h(-1), respectively. However, when production was normali zed to either chlorophyll or bacterial cell number, rates were similar to t hose recorded during the spring bloom periods. This indicates that the cell s were metabolically active during the prebloom period. Chlorophyll specifi c primary production averaged over the upper 80 m of the water column was 1 .28 +/- 0.84 mu g C mu g chl(-1) h(-1), whereas the mean bacterial specific growth rate over the same depth interval was 0.34 +/- 0.24 d(-1). The over all production rates were low only because of the low abundance of cells du ring the prebloom period. When the site was reoccupied the following year, all measures of biomass and productivity were higher [36], emphasizing the large interannual variability in the Gerlache Strait.