PALEOENVIRONMENTAL 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 sout h-western Asia. It is diminishing in size and the salinity of the wate r is increasing due to excessive withdrawal of water for irrigation fr om the two main rivers flowing into it. The biota of the lake has been decimated and the chemical composition changed dramatically since 196 0. Three short sediment profiles, two cores and one section, are exami ned with a view to reconstructing the most recent history of the Sea f rom microfossil assemblages. Historical and geological records indicat e that since its formation Aral Sea levels have changed. Such variatio n may have been accompanied by changes in the chemistry of the Sea thr ough increased evaporation or precipitation. In the present work analy ses of the Mg/Ca and Sr/Ca molar ratios, particularly the latter, of b enthonic Ostracoda from the aforementioned cores indicate that althoug h present salinity levels were never attained during the period of dep osition of the sections studied past saalinity variation can be inferr ed. Oxygen and carbon isotope analyses of Ostracoda and Mollusca from one of the sections, however, indicates two possible periods of relati ve salinity increase.