A study on Holocene foraminifera from the Aral Sea and West Siberian lakes and its implication for migration pathways

Late Holocene cored sediments from the Aral Sea were examined in respect of foraminiferal diversity and the tests of 4 species of foraminifera were differentiated. The species are listed and documented by SEM photographs. All of the identified species from the Aral Sea belong to the Ponto-Caspian faunal complex. Another Ponto-Caspian foraminiferal species is found in the mid-Holocene sediments of Kushmurun Lake located in the Turgai Valley in the southern part of the West Siberian Lowland. During the Holocene neither the water level of the Caspian Sea nor that of the Aral Sea was high enough to create a northern connection with West Siberia via the Turgai Valley. During the late glacial such a waterway may have existed due to overflowing of huge proglacial lakes in northern West Siberia. The water flow, however, would have been directed to the south preventing foraminiferal migration to the north. Moreover, the freshwater conditions would not have allowed foraminifers to survive. Thus, foraminifera were transported to the West Siberian lakes from the Caspian Sea or from the Aral Sea by water birds. Avian-mediated colonization of lacustrine ecosystems by foraminifera is not an exception, but a regular process. The Aral Sea was re-colonized during the Holocene several times with the aid of water birds from the Caspian Sea.