High-resolution reconstruction of the KaraBogazGol - Caspian Sea water level evolution for the last 200 years based on mineralogical changes
by
S. Giralt
Department of Geology, Royal Museum for Central Africa, Leuvensesteenweg, 13 B-3080 Tervuren, Belgium
Coauthors: R. Julià (Institute of Earth Sciences "Jaume Almera" CSIC, Lluís Solé i Sabarís, s/n, E-08028 Barcelona, Spain), S. Leroy (Dept. of Geography and Earth Sciences, Brunel University, Uxbridge, Middlesex, UB8 3PH, U.K.), F. Gasse (CNRS-CEREGE, BP 80, 13545 Aix-en-Provence Cedex 04, France), F. Chalié (CNRS-CEREGE, BP 80, 13545 Aix-en-Provence Cedex 04, France)

Endorheic lakes located in arid and semi-arid environments are highly sensitive to climate oscillations since small variations in their environmental conditions induce dramatic changes within the lake. The Kara-Bogaz Gol, located in the western zone of the Republic of Turkmenistan, represents the natural evaporation basin of the Caspian Sea waters. The climate of this region is severe-continental and extremely dry (less than 90 mm), with important temperature oscillations (4.5°C (January) - 29.8°C (August)). This bay is more than 160 kilometers long, 137 kilometers wide, and covers approximately 18, 000 km2. Present-day level of the water of the Kara-Bogaz-Gol is 28 m below sea level. The water chemistry of this bay records a predominance of Cl- among the anions and Na+ and Mg++ among the cations, with a high density (> 1000 g/l), thus it is hypersaline. pH values ranges between 7.9 and 8.9. Usually calcite and aragonite precipitate during the spring, gypsum forms during the summer, and huge amounts of mirabilite and halite precipitate in the shores of the bay during the winter. In November of 1999, a drill campaign of this bay was carried out using a raft and several sequences were recovered (up to 4 m long). The recovered sediments are mainly composed of a centimetric to decimetric alternation of dark greyish silty-clay and light sandy layers, with some intercalations of whitish layers of salt and several levels of Cerastoderma sp. The mineralogical record of the upper meter of one of these sequences (KBG02-1) has been studied using x-ray diffractions and thin sections, and dated using the 210Pb technique. The mineralogical changes of this core have been used in order to reconstruct the lake level oscillations following the methodology of Giralt et al. (1998). Here we present a high-resolution reconstruction of the lake level variations of the last 200 years. This reconstruction has been compared with the instrumental lake level measurements, with a good agreement between both. This project is developed in the framework of the PEP-III (Pole-Equator-Pole) transect (contract number IC15-CT96-0112 “Understanding the Caspian Sea erratic fluctuations”).

Reference: Giralt, S., Julià, R., Burjachs, F., Rodó, X. and Comín, F.A. 1998. Reconstruction of playa-lake level changes based on mineralogical composition of sediments. In: Cañaveras, J.C., García del Cura, M.A. and Soria, J. (Eds.). Sedimentology at the dawn of the third millennium. Publ. Univ. Alicante. Alicante. 386-388.

Date received: May 30, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahr-25.