Size-fractionated biomass and productivity of phytoplankton and particulate organic carbon in the southern ocean

During the austral summer of 1989/1990, surface samples were obtained of size-fractionated biomass, and the productivity of phytoplankton, its cell abund ance, the composition of the dominant species, the concentration of particulate organic carbon (POC) and the related environmental surface parameters were measured in a large-scale survey primarily of the Atlantic and Indian Sectors. The results showed that the southern atlantic sector is the most fertile; chlorophylla (Chl a) concentration averaged over 2 g l^–1, average cell abundance was about 41.0×10³ cell l^–1, and average POC concentration was also the highest (> 100 g l^–1), but was lower in the Drake Passage and the southern Indian sector. The results for size fractionated Chla showed that netplankton (> 20m) in the South Atlantic Ocean, having abundant nutrients, accounted for the highest proportion (average 65%) of biomass. In the infertile South Indian Ocean, picoplankton (< 2 m) accounted for the highest proportion, averaging 47%. The results for size-fractionated productivity showed that the contribution of picoplankton to total productivity was the largest in the South Atlantic Ocean and Drake Passage, those of nanoplankton (2–20 m) and netplankton being about equal. The relatively high photosynthesis assimilation number of picoplankton demonstrates their importance in the marine ecosystems of Antarctic water. In comparison with the Antarctic water, the subantarctic and subtropical waters are infertile.