Recent biogenic sedimentation on the Antarctic continental margin
Leventer, Amy Ruth
Dunbar, Robert B.
Doctor of Philosophy
Floral and geochemical analyses were conducted on sinking and suspended particulate matter, and on sea ice and recent sediment samples from the northwestern Weddell Sea--northern Antarctic Peninsula area, and McMurdo Sound, in the southwestern Ross Sea. Data from McMurdo Sound reveal that although large numbers of diatom frustules dissolve within the upper water column the decrease in silica mass flux is much smaller. At mid-water depths, increases in the absolute flux of Nitzschia curta and Thalassiosira spp. indicate the influence of lateral advection. Within a near-bottom nepheloid layer additional dissolution occurs. Dilution and preferential dissolution is responsible for production of a surface sediment assemblage dominated by Thalassiosira spp. and Nitzschia curta. The surface sediment diatom assemblage in McMurdo Sound documents the seasonal history of sea ice extent and regional circulation patterns. Thalassiosira spp., indicative of water column primary productivity, is most common in eastern and northwestern McMurdo Sound, the result of advection from areas of open water. Nitzschia curta, a member of the sea ice microbial community and of ice edge blooms in the Ross Sea is most abundant in the southwestern Sound where the northward advection of oligotrophic water results in the dominance of the local flora. Maximum downcore Thalassiosira abundances occurred between 1600-1875 A.D., during the Little Ice Age. Warmer atmospheric temperatures or more persistent winds may have been responsible for more prevalent polynyas, suggesting that within the southwestern Ross Sea, the production of High Salinity Shelf Water, and hence Antarctic Bottom Water, may have been greater at that time. Measurements of water and acid soluble and insoluble phosphate performed on samples of suspended particulate matter from the Antarctic Peninsula region show the concentration of water-soluble, loosely bound organic phosphates decreases rapidly within the upper 100 m, the result of rapid phosphorus regeneration. A gradual decrease in insoluble organic phosphate signifies slower recycling of cell wall material. Acid-soluble phosphatic skeletal parts are transported efficiently. Concentration of insoluble phosphate increases in an eastern and southern direction as a function of increased influence of old Warm Deep Water containing higher levels of refractory organic material.