SEDIMENT TRAP DIATOM ASSEMBLAGES FROM THE NORTHERN ANTARCTIC PENINSULA REGION

Quantitative floral analyses were performed on 29 samples collected during approximately 24-h deployments of floating sediment traps. Traps were deployed at five sites in the northern Antarctic Peninsula region during December 1986 to March 1987. These analyses and comparison to surface sediment data provide information concerning the influence of primary production, spore formation, post-bloom mass sedimentation, advection, and resuspension on the sinking and sedimented floral assemblage. At three of the five sites, absolute diatom flux decreased by more than an order of magnitude from January to February, the result of the sinking of bloom populations and subsequent decreased levels of primary productivity. These data indicate that at least to 200 m, grazing and pelletization did not obscure the primary signal. Relatively low and uniform diatom flux in Drake Passage was indicative of a deeply mixed surface layer in which peak levels of biomass were not permitted to accumulate. Conversely, uniformly high diatom fluxes at a final site may have resulted from initially high productivity followed by a resuspension event during February, perhaps the result of storm mixing that was documented by the increased relative percentage of benthic diatoms. The utility of diatoms as water mass tracers is demonstrated by the distribution of three floral assemblages, both in the sediment traps and surface sediment samples. A distinct circumpolar assemblage dominated by Nitzschia kerguelensis was observed in Drake Passage. A diatom assemblage comprised of moderate to high abundances of Chaetoceros resting spores, Nitzschia curta, and Thalassiosira antarctica was broadly distributed through Bransfield Strait and Livingston Island continental shelf. Diatom flux in Gerlache Strait was dominated by resting spores of Chaetoceros. Northeastward advection distributed these spores into Bransfield Strait where high Chaetoceros fluxes were observed at depth. Chemical data suggest the possibility that spore formation resulted from nutrient depletion. In neritic Antarctic waters, significant production and mass sinking of resting spores appears to be characteristic of the final stages of an intense phytoplankton bloom.