Diatom assemblages in surface sediments of the northwestern Weddell Sea, Antarctic Peninsula

A study of 42 surface sediment samples from the northwestern Weddell Sea documents the relationship between the modern distribution of diatom assemblages and present oceanographic conditions in the region. Three diatom assemblages were identified using R-mode principal components analysis and cluster analysis, while Q-mode cluster analysis was used to distinguish two geographically distinct biofacies. Based on the relative abundance of diatom species, the biofacies of the former Larsen A Ice Shelf (LAIS) is more closely associated with a sea ice diatom assemblage, while the biofacies of the Prince Gustav Channel/Northern Peninsula (PGC/NP) is associated with two open coastal diatom assemblages. This division is consistent with variance observed in the current oceanographic setting, whereby the LAIS is generally characterized by a longer seasonal duration of sea ice coverage and lower primary productivity relative to the PGC/NP which is marked by a shorter seasonal duration of sea ice coverage and greater surface water productivity. This relationship is further reflected in the distribution of the paleoenvironmentally significant diatom species Fragilariopsis curta, Thalassiosira antarctica, and Chaetoceros subg. Hyalochaete spp. as well as in absolute abundance data. Specifically, F. curta and the morphological form T. antarctica T1 are representative of greater seasonal duration of sea ice coverage and lower productivity. Chaetoceros subg. Hyalochaete spp. and the morphological form T. antarctica T2 are associated with decreased seasonal duration of sea ice cover and greater surface water productivity, a setting that is further reflected in high absolute diatom abundances. These findings provide a basis for future paleoceanographic work in the region, especially as studies of surface sediment diatom assemblages are vital to establishing a link between downcore diatom assemblages and those presently found in the water column.