Analysis of phytoplankton of the Australian sector of the Southern Ocean: Comparisons of microscopy and size frequency data with interpretations of pigment HPLC data using the 'CHEMTAX' matrix factorisation program

A new matrix factorization program 'CHEMTAX' was used to interpret high-performance liquid chromatography (HPLC) pigment data from a transect between Prydz Bay, Antarctica, and Australia during March 1987. The program calculated the abundance of diatoms, dinoflagellates, haptophytes resembling Emiliania huxleyi, haptophytes resembling Phaeocystis antarctica, cyanobacteria, prasinophytes, chlorophytes and cryptophytes along the transect. The results were compared with those of microscopy and particle size analysis. The transect was dominated by small cells: particle size analysis showed that particles <2 mu m represented 27 to 44% of the total by number while particles 2 to 20 mu m represented 55 to 68%. Particles >20 mu m never represented more than 3% by number but constituted 57 to 93% of the total volume. Microscopic analysis showed that small flagellates were the most abundant cells along the transect, with a 5-fold increase in abundance at 47 degrees S. Numbers of diatoms (most <20 mu m in size) increased markedly south of the Polar Front, correlating with the concentration of silica. Dinoflagellate numbers were relatively constant along the transect, although somewhat higher north of 50 degrees S. Those <20 mu m in size were most numerous and accounted for most of the latitudinal variation. interpretation of HPLC pigment data using the CHEMTAX program was consistent with microscopical analysis. The computed abundances of diatoms and dinoflagellates correlated more strongly with the numbers of small (<20 mu m) diatoms and dinoflagellates, respectively, than with large ones. Computed cyanobacterial abundances correlated well with microscopical observations except for small errors where cyanobacteria were absent, probably due to misallocation of zeaxanthin from chlorophytes and prasinophytes. The program was able to distinguish 2 populations of haptophytes along the transect, representing Phaeocystis antarctica and coccolithophorids, even though their pigment compositions were qualitatively (though not quantitatively) identical. It also indicated the separate distributions of chlorophytes and prasinoxanthin-containing prasinophytes, and showed the presence of cryptophytes where none were observed by microscopy.