Conference:
32nd International Geological Congress, Florence, Italy, 20-28 August, Session: G-19.02 Climate and paleoenvironmental changes during the Quaternary: palynological evidence.
Author:
Philippe Sorrel, Speranta-Maria Popescu, Martin Head.
Abstract:
The Aral Sea in Central Asia was regarded as the world’s fourth greatest lake until as recently as 1960. During the past 40 years, its surface area has decreased by more than 40% and its volume by 60%, constituting one of the most important environmental crises of the last century. Average salinity in the Aral Sea has increased from 9 psu in 1960 to 30 psu in 1990, locally rising to more than 90 psu in 2003. The Holocene evolution of the Aral Sea is closely linked to global and local climatic variations, although human impact through expanding irrigation in the hinterland accounts for recent environmental changes. Dinoflagellate cysts are being investigated from a core in Chernyshov Bay located on the NW margin of the Great Aral Sea in order to reconstruct hydrographic conditions and particularly salinity for the past 1500 yrs. Samples are rich in dinoflagellate cysts and other aquatic palynomorphs, although assemblages are typically low in species richness and dominated by morphotypes of Lingulodinium machaerophorum with reduced processes, and by a new gonyaulacaean species. Also present are Spiniferites spp., cysts related to Spiniferites cruciformis, cysts apparently of Pentapharsodinium dalei, and round brown protoperidiniacean? cysts. Species of Botyrococcusand Pediastrumprobably represent freshwater inflow. Tintiniid loricae and the incertae sedis aquatic palynomorphs Polyasteriumand Radiosperma corbiferumare present in low numbers. The assemblage as a whole reflects brackish conditions with salinities perhaps as low as about 10–15 psu judging from the dominance of Lingulodinium machaerophorumwith reduced processes. Pentapharsodinium dalei is a cool-water spring blooming species that, if definitively identified, would imply cold winter temperatures. Significant erosion of marine Palaeogene deposits, including those of Eocene age, within the hinterland during the Holocene is evidenced by the presence of reworked cysts including Areosphaeridium diktyoplokum, Charlesdownia coleothrypta, Phthanoperidinium comatumand Enneadocysta arcuata.