Summary
The depth distributions of eight groups of phytoplankton were determined along eight north-south transects between longitudes 80„aE and 150„aE, from 63„aS to the sea ice edge or beyond. Phytoplankton stocks were estimated from the distribution of marker chlorophylls and carotenoids as interpreted by CHEMTAX software. This allocated the algal marker, chlorophyll a, into the following groups, as defined by their pigment content: Diatoms, Cryptophytes, Prasinophytes, Chlorophytes, Dinoflagellates, Cyanobacteria, and two types of haptophytes, Hapto3s and Hapto4s, with pigment patterns typical of coccolithophorids and Phaeocystis antarctica, respectively. Consistent patterns were noted across the eight transects. Highest concentrations of most algal groups were usually found at the pycnocline, except in low chlorophyll transects, where populations of Hapto4s and Prasinophytes were found in the Tmin layer. Hapto4s and Prasinophytes were often found below the Tmin layer where the transects passed north of the Antarctic Divergence, while in the south, they were subducted from the Tmin layer at the Antarctic Slope Front. Highest chlorophyll concentrations were associated with regions of thermally stratified water. Under the ice, there was little stratification and populations were usually more dispersed in the upper water column. Concentration minima were typically found in the algal distributions at or near the ice edge and were associated with patches of krill or salps found on this cruise. These minima often corresponded with local maxima in concentrations of Cryptophytes, often with additional Dinoflagellates and/or some Cyanobacteria, possible remnants of selective grazing. High concentrations of chlorophyll a degradation products were often observed beneath melting sea ice, probably representing sedimenting detritus and zooplankton faecal pellets, and occasionally in open water corresponding to minima in concentrations of Chl a.