A GEOLIPID CHARACTERIZATION OF ORGANIC LAKE - A HYPERSALINE MEROMICTIC ANTARCTIC LAKE

An organic geochemical study of the benthic sediments taken over a tra nsect of Organic Lake is reported. Fatty acids, hydroxyacids, and ster ols were the three major geolipid classes isolated from the total solv ent extracts. The fatty acid chain lengths range between C-12 and C-28 carbons and show two maxima viz. at C-16-18 and at C-24-26. The first maximum is consistent with a microbial origin which in the context of Organic Lake includes mainly bacteria and some algae. The C-24-26 max imum is also found in other Antarctic lakes and is likely to be bacter ial in origin. Organic Lake differs from other lakes in the region in that sulphate-reducing bacteria and their signature biolipids are abse nt in the lake sediments, but dimethyl sulphide is present. The salini ty is about 19% thus the lake is hypersaline and the biological commun ities present are very simplified, providing a rare opportunity to exa mine a biomarker array in an extreme environment with limited species diversity. The general distribution of fatty acids and sterols in Orga nic Lake is common to other lakes of Antarctica. Organic Lake differs, however, in the presence of unusual hydroxy acid isomers and of Delta 7-sterols. The fatty acid total abundances are much higher and the st erol abundances lower than expected for Antarctic lakes of comparable salinity. The gross analyses of the three geolipid classes suggest tha t the collection sites broadly represent eco-niches across this meromi ctic lake. The deepest site is both anoxic and hypersaline and appears to be presenting organic matter. Analysis of the phospholipid fatty a cids reveals, however, environmental differences in the benthic sedime nts and by using signature fatty acids it has proven possible to sugge st how these benthic bacterial communities differ with depth and oxici ty. Copyright (C) 1996 Elsevier Science Ltd.