Nella Dan: AAMBER Cruise Chlorophyll a Data

The composition, size and abundance of phytoplankton and microzooplankton were measured across a transect from Prydz Bay to Australia during late March 1987. Phytoplankton populations were low, with concentrations of chlorophyll a ranging from 0.08 to 0.22 mg.m-3. Small cells predominated numerically; nanoplankton consistently represented 55 to 68% of the total cell number while picoplankton represented 27 to 44%. Microplankton never represented more than 3% of cells by number, but constituted 57 to 93% of the total cell volume, and accounted for most of the latitudinal variation in total volume. Small flagellates, not identifiable by light microscopy, were the most numerous cells encountered across the transect, with a five-fold increase in abundance at 47S. Numbers of diatoms (most less than 20 microns in size) increased markedly south of the Antarctic Convergence, with a strong correlation to the concentration of silica. Dinoflagellate numbers were relatively constant across the transect, although somewhat higher north of 50S. Those less than 20 microns in size were most numerous and accounted for most of the numerical variation. HPLC analysis of chlorophyll and carotenoid pigments showed a peak of peridinin which coincided with the flagellate peak at 47S, but not with observed dinoflagellates, suggesting that the flagellate peak included unrecognized dinoflagellates. Chlorophyll b and prasinoxanthin were also associated, suggesting a significant contribution by prasinophytes. Almost no cyanobacteria were observed south of the convergence, although very large numbers, which correlated with the abundance of zeaxanthin, were encountered to the north. Numbers of ciliates and tintinnids were quite variable although they followed each other closely. Numbers of both were low in the region of the Antarctic Convergence.