Spatial and temporal distribution of assemblages of the diatom Corethron criophilum in the Polar Frontal region of the South Atlantic

Morphometric data in the form of frequency distributions of valve widths (transapical measurements) of the diatom Corethron criophilum have been plotted for stations between 50 and 47°S on transects 5, 11 and 12 of cruise ANT X/6 to the Atlantic sector of the Southern Ocean. The profiles largely confirm the picture of sharp differences between the waters as revealed by hydrological, pigment and other biological data. The assemblages to the north, which lie in the southern part of the Polar Frontal Zone water, are more congruent with those in water to the south, that is presumed to have eddied off the PFZ water, than with interlaying, Antarctic Circumpolar Current water. The profiles also show how assemblages of this species can be recognised over space and time. Furthermore, they reveal how a sexual event in the life cycle can lead to a rapid change in the character of the assemblage due to rapid loss of gametangial cell walls from the water column.