LATE QUATERNARY INTERGLACIAL AND SUBGLACIAL ENVIRONMENTS IN AN EASTERN ANTARCTIC OASIS

Information on late Quaternary environments in Antarctica is primarily derived from ice cores from the interior and marine sediment cores from the continental shelf. Ice cores permit temperature reconstructions derived from changes in atmospheric composition and marine cores can document changes in biological production. However, there is limited information on environmental changes in terrestrial and freshwater environments of the late Quaternary era in Antarctica due to removal of stratigraphic records by glacial erosion. Recent evidence suggests that some east Antarctic coastal oases had limited ice cover through the Last Glacial Maximum. In one of these oases, the Larsemann Hills, a sediment core was collected from a 38 m deep lake and studied for geochronology, sedimentology, biological and biochemical markers. Results suggest that the first sediments were deposited during the Eemian interglacial. Diatoms and pigments reveal a productive biological community consistent with warmer conditions at this time. This was followed by a subglacial period resulting in almost complete suppression of biological activity in the lake. Whilst we cannot exclude that life persisted under these subglacial conditions, it would have done so under an extremely impoverished light, oxygen and nutrient regime. Just over 4500 years ago the lake re-emerged from under the ice and biological production resumed but with a lower biological diversity, lower rates of pigment production and a different species assemblage compared with the preceding interglacial. This suggests cooler conditions during the Holocene than the Eemian interglacial and a high degree of species turnover. The sediment sequence gives scientists an opportunity not only to compare environments of the last two interglacials but also to examine the biological consequences of a lake becoming subglacial.