Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean

Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of 1991-1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K^sup -1^^sub par^) and the satellite-weighted depth. The temporal variability was resolved every 2-3days and was observed to be greater within years than between years. Three-year averages (n=223) revealed that 10.2±3.6% of total Chl a and 14.8±6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values were twice as high within K^sup -1^^sub par^, 24.1±8% of total Chl a and 34±9% of production respectively. Masked in these long-term averages are very large changes occurring on short time scales of seasonal blooms. We observed that the patterns of Chla vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within K^sup -1^^sub par^ and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K^sup -1^^sub par^ and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean, especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences.[PUBLICATION ABSTRACT]