Ross Sea diatoms: Modern assemblage distributions and their relationship to ecologic, oceanographic, and sedimentary conditions

Abstract

Marine diatoms from surface sediments of the Ross Sea were studied to determine the modern distributions of important assemblages. Factor analysis of diatom data distinguished four significant assemblages which account for 96.6% of the raw data. Diatom factor assemblages provide a means of understanding modern oceanographic, ecologic, and sedimentary conditions because they show the response of this floral group to different environments. Assemblage 1 consists primarily of epontic diatoms and is most important in areas where undisturbed sedimentation of diatoms occurs. Assemblage 2 contains abundant Eucampia balaustium, a heavily silicified species, which is indicative of lag deposits where lighter, more fragile diatoms have been selectively winnowed by bottom currents. Diatom species in Assemblage 3 have widely differing stratigraphic ranges (from greater than 3.3 m.y.B.P. to Recent) and probably represent reworked older sediments mixed with more recent material. Assemblage 4 contains oceanic diatom species characteristic of open waters north of the Antarctic Divergence. In Ross Sea sediments higher relative abundances of diatoms are encountered in the western portion of the region, probably reflecting earlier seasonal breakup of sea ice there than occurs in the east. Lowest relative abundances occur in regions where available data suggest high rates of deposition of terrestrial material, in regions where the reworked assemblage (Assemblage 3) predominates, and in regions with strong bottom currents.