Size structure of phytoplankton carbon and primary production in the Southern Ocean south of Australia during the summer of 1983-84

The size structure of phytoplankton carbon content and primary production were examined in the upper 125-m water column in the Southern Ocean south of Australia during the summer of 1983-84. At the surface, total phytoplankton carbon was 13.8±1.6μg/l in the Subantarctic Ocean and 45.6±27.4μg/l in the Antarctic Ocean. Phytoplankton in the 8 to 16-μm size class accounted for a large portion of phytoplankton carbon in the Subantarctic Ocean, whereas >64-μm forms were dominant in the Antarctic Ocean. The mean primary production was 0.952mgC/m^3/h in the Subantarctic Ocean and 0.400 in the Antarctic Ocean; the >20-μm fraction accounted for a major part of the total production in both areas. Geographically, both phytoplankton carbon and primary production in the small cell size classes (16 and >5μm, respectively) which were composed mainly of diatoms varied largely, determining the magnitude of the total values. Such large variation of biomass in netplankton as found in the surface water was also found down to the 125-m depth at all stations investigated. The importance of netplankton as primary producers in the Southern Ocean was discussed