Spatial patterns in phytoplankton biomass and pigment distributions in the Ross Sea

The distribution of phytoplankton biomass and pigments was determined in the Ross Sea during late austral summer 1992. Large gradients in biomass were noted both in the east-west and north-south direction, with maximum particulate matter concentrations occurring in the southwest portion of the Ross Sea. Two xanthophyll pigments dominated the profiles, fucoxanthin (indicative of diatoms) and 19' hexanoyloxyfucoxanthin (hex) (indicative of the prymnesiophyte Phaeocystis antarctica). Fucoxanthin concentrations were greatest near the coast of Victoria Land and within the northern transect, whereas hex concentrations were highest offshore in the SE Ross Sea. Particulate carbon:chlorophyll a (POC:chl) ratios in diatom-dominated waters of the western Pass Sea were relatively high (210). The POC:chl ratio far Phaeocystis antarctica populations from the SE Pass Sea was substantially less (92) than the ratios observed in diatom-dominated waters. Pigment C-14 labeling indicated that phytoplankton carbon in the diatom-dominated northern Pass Sea accounted for approximately 30% of the POC, with a phytoplankton C:chl ratio of 130. Short-term (24 hour) vertical fluxes of pigments ranged from 3 to 40 mu g chi a m(-2) d(-1). Diatom-dominated regions had greater fluxes of phaeophorbides, suggesting that metazoans were the most important grazers at these locations. In contrast, the phaeophytin/total phaeopigment ratio was highest in waters dominated by Phaeocystis antarctica. The distribution of phytoplankton biomass and pigments revealed a spatially variable distribution of taxa, one which clearly has important consequences to food-web dynamics, biogeochemical cycles, and vertical flux patterns in the Pass Sea.