Diatom stratigraphy defining ice sheet grounding chronology, Ross Sea, Antarctica

Evidence of Antarctic ice sheet behavior and paleoenvironment is often approached from proxy records because there is a dearth of direct records from Antarctica itself. The studies presented here seek to augment our knowledge of translations of the West Antarctic Ice Sheet’s (WAIS) marine termination based on direct biostratigraphic evidence. Diatom analyses were conducted from two areas of Ross Sea, Antarctica. In the first study, diatoms were used to constrain the age of diamictons from five seismic units in the Eastern Basin and thus expand our knowledge of WAIS behavior during the Southern Hemisphere Last Glacial Maximum (LGM). All five units have a late Pliocene diatom assemblage. The absence of a late Pleistocene diatom assemblage indicates that the Eastern Basin LGM could not have been at ca. 20 kyrs. Moreover, differences in diatom assemblages indicate that units previously assigned to a single phase of LGM advance and post-LGM retreat must have included two temporally distinct grounding events. In the second study, diatoms were used to assess the uniformity of a till sheet by comparing the assemblage from the topset bed to that of the interior of the till sheet. The analysis suggests that the till sheet as observed from seismic data is homogeneous, and helps support the validity of studies made by using short sediment cores that sample only the upper part of the till sheet. In the third study, diatoms from diatomite units from south of Ross Island were used to provide paleoenvironmental information about the early Pliocene. The diatom assemblages have no modern analogues, but they do indicate that sea surface temperatures were much warmer in the early Pliocene compared to the present, there was enhanced ice sheet ablation, and katabatic winds were absent at least during the diatom growth season