Ünderstanding the Caspian Sea Erratic Fluctuations". Part II: Late Pleistocene-Holocene environmental changes
by
Françoise Gasse
CEREGE, UMR CNRS 6635, Aix-en-Provence, France
Coauthors: The INCO-Copernicus Contract IC15-CT96-0112 Consortium

The Caspian Sea (CS), the world largest inland waterbody, is poorly understood and interpretation of its recent, short-term level fluctuations is still controversial. For a better understanding of the CS behaviour, we conducted in parallel (EU INCO-Copernicus Contract IC15-CT96-0112): (I) a geochemical approach of the modern CS system (Cf Part I); (II) a study of Late Quaternary CS sediments, summarized here.

The analysis of Kullenberg (8-10 m long) and short pilote (1-2 m) sediment cores, retrieved from the Southern and Central CS basins, includes: mineralogy and elemental chemistry, mineral magnetic parameters, total organic carbon (TOC), diatom-, ostracod-, pollen- and dinoflagellates-analyses, stable isotope composition of bulk carbonates, chemistry and isotope composition of interstitial waters. Because of low TOC contents, AMS 14C chronology is based on authigenic inorganic or biogenic carbonates. Some aging should be suspected due to influx of dead carbon to the waterbody (see Part I). More accurate absolute age control is still needed to properly establish a detailed chronological framework.

The major environmental change is recorded by all environmental indicators at the onset of the Holocene period. Unit I (Late Glacial) is characterised by laminated, detrital sediments, lower water content, lower ionic concentration and lower bottom water oxygenation than today, and very high sedimentation rate. Unit II (Holocene) is characterised by a homogeneous, carbonate-rich mud, mesosaline water, oxic bottom conditions, lowsedimentation rate. The abrupt transition between Units I and II is attributed to the end of ice meltwater inflows from the northern ice sheet and from the Caucasus and Elburz glaciers, inducing a major modification of the CS hydrodynamics.

The regular lamination of Unit I is remarkable by the couplet thickness (7-8 mm). Laminae correspond to changes in the iron monosulphide/ion oxide ratio, interpreted as having an early diagenetic origin. They reflect rythmic geochemical variations in the uppermost sediments. They suggest annual deposits (to be confirmed), as the 14C ages of in situ ostracods remain almost constant (ca. 10.5 14C kyr BP) in the laminated sections.

Holocene sedimentary fluctuations are interpreted in terms of climate when they fit pollen-inferred climatic changes. However, some features can only be explained by "erratic" deep water influxes, and/or abrupt tectonic-induced events generating changes in the drainage network of the eastern rivers (Amu Darya-Uzboi).

The consortium includes : Françoise Chalié & Sophie Bieda (CEREGE, Aix-en-Provence, France), Alina Jelinowska & Piotr Tucholka (Université Paris-Sud, Orsay, France), Denise Badaut-Trauth & Pierre-Jean Giannesini (MNHN, Paris, France), François Guichard & Uli von Grafenstein (LSCE, Gif-sur-Yvette, France), Norbert Clauer & Marie-Claire Pierret (CGS, Strasbourg, France), Gérard Blanc (DGO, Bordeaux, France), Guy Seret & Santi Giralt (UCL, Louvain, Belgium), Vassili I. Ferronsky & Pavel Kuprin (Water Problems Institute, R.A.S., Moscow, Russia), Gian--Maria Zuppi & Anna Conti (Universita ca' Foscari di Venezia, Scienze Ambientali, Venezia, Italy), Michael Antipov (Geological Institute, R.A.S., Moscow, Russia), Suzanne Leroy (Brunel University, London, UK), Fabienne Marret (School of Ocean Sciences, Bangor, UK), Ian Boomer (Department of Geography, Newcastle University, UK.

Date received: May 15, 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-02.