Water chemistry and diatom occurrences in sediments of Terrasovoje, Radok and Beaver Lake, Amery Oasis, East Antarctica

The diatom flora of three lakes in the ice-free Amery Oasis, East Antarctica, was studied. Two of the lakes are meltwater reservoirs, Terrasovoje Lake (31 m depth) and Radok Lake (362 m depth), while Beaver Lake (>435 m depth) is an epishelf lake. The lakes can be characterized as cold, ultra-oligotrophic and alkaline, displaying moderate (Radok and Terrasovoje lakes) to high (Beaver Lake) conductivities. There was no diatom phytoplankton present in any of the three lakes. While 34 benthic diatom taxa were identified from modern and Holocene sediments of Terrasovoje and Radok lakes, a 30-cm long sediment core recovered in Beaver Lake was barren. Five species (Luticola muticopsis, Muelleria peraustralis, Pinnularia cymatopleura, Psammothidium metakryophilum, P. stauroneioides) are endemic to the Antarctic region. All identified taxa are photographically documented and brief notes on their taxonomy, biogeography and ecology are provided. The most abundant diatom taxa are Amphora veneta, Craticula cf. molesta, Diadesmis spp, M. peraustralis and Stauroneis anceps. This is the first report on the diatom flora in lakes of the Amery Oasis.

Fig. 2. Lithology, water and total carbon content, cumulative grain-size distribution, and quartz, feldspar, and mica contents of core sequence Lz1013 from south-western Beaver Lake

A 100 cm long sediment sequence was recovered from Beaver Lake in Amery Oasis, East Antarctica, using gravity and piston corers. Sedimentological and mineralogical analyses and the absence of micro and macrofossils indicate that the sediments at the base of the sequence formed under glacial conditions, probably prior to c. 12 500 cal. yr BP. The sediments between c. 81 and 31 cm depth probably formed under subaerial conditions, indicating that isostatic uplift since deglaciation has been substantially less than eustatic sea-level rise and that large areas of the present-day floor of Beaver Lake must have been subaerially exposed following deglaciation. The upper 31 cm of the sediment sequence were deposited under glaciomarine conditions similar to those of today, supporting geomorphic observations that the Holocene was a period of relative sea-level highstand in Amery Oasis.