Palaeoenvironmental indicators from Late Holocene and contemporary ostracoda of the Aral Sea

The Aral Sea is a large terminal lake, i.e. having no outflow, in south-western Asia. It is diminishing in size and the salinity of the water is increasing due to excessive withdrawal of water for irrigation from the two main rivers flowing into it. The biota of the lake has been decimated and the chemical composition changed dramatically since 1960. Three short sediment profiles, two cores and one section, are examined with a view to reconstructing the most recent history of the Sea from microfossil assemblages. Historical and geological records indicate that since its formation Aral Sea levels have changed. Such variation may have been accompanied by changes in the chemistry of the Sea through increased evaporation or precipitation. In the present work analyses of the Mg/Ca and Sr/Ca molar ratios, particularly the latter, of benthonic Ostracoda from the aforementioned cores indicate that although present salinity levels were never attained during the period of deposition of the sections studied past saalinity variation can be inferred. Oxygen and carbon isotope analyses of Ostracoda and Mollusca from one of the sections, however, indicates two possible periods of relative salinity increase.