| Abstract: | Sediment traps were deployed in the Drake Passage, Bransfield Strait and west of South Orkney Islands (Powell Basin) during December 1980/ January 1981, December 1983, and between March and December 1983, respectively.Most of the trapped material is biogenic opal except in the lower half of the water column in Bransfield Strait where large amounts of resuspended aluminosilicates and quartz grains were present. Frustules and skeletons of siliceous microorganisms (diatoms, silicoflagellates, radiolarians, chrysophycean cysts), fragments and moults of crustaceans and tests of foraminifera were found. Quantitatively diatoms are the dominant constituent of the trapped biogenic material.Alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton. It mainly affects large frustules (e.g. Corethron criophilum Castracane) in the uppermost part of the water column. Dissolution of frustules occurs mostly at the sediment/water interface and leads to the enrichment of strongly silicified valves e.g. Nitzschia kerguelensis (O'Meara) Hasle, Thalassiosira antarctica Comber (resting spores)].At the Bransfield Strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods. The bulk of pellet content consists of fragmented diatom frustules (1–10 μm in size). Most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport: e.g. settling as solitary particles or incorporated into or attached to “Marine Snow” or “Large Amorphous Aggregates”. |
