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 Sou thern Ocean. From data collected throughout the springs/summers of 1991-199 4, we calculated the proportion of water column Chi a and primary productiv ity within the upper optical attenuation length (K-par(-1),) and the satell ite-weighted depth. The temporal variability was resolved every 2-3 days an d was observed to be greater within years than between years. Three-year av erages (n = 223) revealed that 10.2 +/- 3.6% of total Chi 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-par(-1), 24.1 +/- 8% of total Chi a and 34 +/- 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time sca les of seasonal blooms. We observed that the patterns of Chi a vertical dis tribution within blooms are also subject to taxonomic influence and depende nt upon the physiological state of the phytoplankton. Highest proportions o f water column Chi a in the first optical depth were measured during the ra pid onset of surface cryptophyte blooms each year, i.e. 50% within K-par(-1 ) and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% o f biomass within K-par(-1), and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyse s suggest that satellite-dependent models of Chi a and subsequent chlorophy ll-dependent primary production will be challenging to develop for the near shore Southern Ocean, especially given the potentially high natural variabi lity in the vertical distribution of Chi a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences.