Rychagov G.I. Fluctuations of the Caspian Sea level: causes, effects, forecast
Fluctuations of the Caspian Sea level: causes, effects, forecast
The article gives brief data about the fluctuations of the Caspian Sea level and their economic effects. The results of geological and geomorphologic investigations provide a basis for the sea level forecast: according to them in the nearest future the Caspian Sea level will not exceed -25 m, and if the economic activities and the coastal relief features are considered it will not exceed -26 m.
Palaeoclimate and evolution of the environment
- Bolikhovskaya N.S. The Holocene evolution of climate and landscapes in the Lower Volga River region
Pollen analysis and radiocarbon dating of the most informative sections of the Holocene sediments allowed a detailed reconstruction of repeated changes of the zonal types of vegetation and transformation of the zonal and intra-zonal plant formations within the Lower Volga River region during the last 10 kyr. Landscape-climatic features and chronological limits of 26 stages of environmental changes during the Holocene were identified. The reconstructed palaeoclimatic stages were correlated with the Holocene transgressions and regressions of the Caspian Sea. The periodical scheme of palaeoclimatic events was elaborated which would provide a climate-stratigraphic basis for further palaeogeographical studies of the Holocene within the northern part of the Caspian Sea region.
Yanina T.A., Svitoch A.A., Wesselingh F.P. Biodiversity of mollusk fauna of the Caspian Sea during the Holocene
Evolution of the biodiversity of mollusk fauna of the Caspian Sea during the last 10 kyr was analyzed using the results of field investigations within two environmentally different areas, i.e. the coastal zone of the Middle Caspian Sea region (the Turali area of the Dagestan coast) and the Volga River delta (the Damchik area of the Astrakhan Biosphere Reserve). Biodiversity of mollusks depends on the parameters of the aquatic environment which reflect climate changes followed by the transformation of regional water balance. The result was the change of thermal conditions, level and salinity of water bodies. Biodiversity of the New Caspian basin and water bodies of the Volga River delta was strongly affected by the anthropogenic factor, i.e. the biological invasion and acclimatization of Azov-Black Sea species which appeared to be much more competitive that the Caspian Sea autochthones. The present-day areals of Caspian endemics are smaller than potential areas of their distribution. Anthropogenic transformation of natural ecosystems of the Caspian Sea region destructs their uniqueness, thus contributing to the global loss of biodiversity.
Kislov A.V. About multi-scale nature of the Caspian Sea level fluctuations
During the last 10 kyr the Caspian Sea experienced several transgressions and regressions with characteristic periodicity of about 2000 years and standard deviation of the sea level σ ≈ 3 m. These “centennial” fluctuations were accompanied by shorter “decade” oscillations resulting in sea level changes during several dozens of years. The article deals with the problem of decade variability dependence on the stage (transgression or regression) of the sea. Theoretical approach is based on the application of the mathematical apparatus of the Brownian motion theory. Analysis and solution of the corresponding stochastic equation (the Langevin equation) provided a formula for the dispersion of decade fluctuations. The dispersion values are poorly dependent on the observed variations of water balance components. Thus, during the Holocene transgressions and regressions sea level fluctuations were mainly “changes of the average values”. Therefore it is possible to use statistical parameters calculated on the basis of present-day data for the estimation of confidence intervals while analyzing the palaeohydrological anomalies of the Holocene.
Toropov V.S., Morozova P.A. Evaluation of the Caspian Sea level fluctuations during the Late Pleistocene cryochrone epoch based on the results of the numerical climate modeling
The results of CNRM climate model adjusted for the Scandinavian glacier melting were the basis for the reconstruction of the Caspian Sea level during the Late Pleistocene cryochrone epoch. The Volga River runoff was calculated for the Late Valdai Ice Age with and without consideration of the Scandinavian glacier melting. The results were used to estimate the Caspian Sea level during that period. The Caspian Sea level after the total glacier degradation within the north-western part of European Russia was calculated as well. The results of calculations were correlated with the data of palaeoreconstructions.
Recent changes of the Caspian Sea hydrology and the coastal zone
Basing on the results of long-term shipboard and coastal observations typical features of the Caspian Sea hydrology response (in terms of its mean water level and thermohaline structure) to climate-induced variations of external factors, such as river runoff, other water balance components, wind etc., are discussed. Of particular interest is the radical change of the regime of long-term variability of hydrological parameters in the second half of 1970-s. It is argued that the increased inflow of fresh water after the regime change resulted in the sea level rise, higher static stability of water stratification, poorer ventilation and overall environmental deterioration of near-bottom water of the Caspian Sea. The shift of wind transfer along the quasi-meridian axis of the sea resulted in the increase of upwelling near the eastern coast of the Caspian Sea. Such regime was persistent during the last 15 years.
The results of landscape-geochemical investigations of the Caspian Sea coastal zone are discussed. Geochemical features of present-day landscapes of accumulative coasts were analyzed, as well as those of transgression complexes of palaeosoils and sediments of the New-Caspian age. Geochemical changes in coastal landscapes during the recent cycle of the sea level fluctuations could become a key for the geochemical indication of palaeoenvironments of formation of the New-Caspian sediments.
The article summarizes the results of a long-term application of remote sensing and GIS methods for investigation of natural and natural-anthropogenic geosystems of the Volga River delta. The examples are mapping of aquatic ecosystems of the delta shallow-water areas and changes in vegetation cover, position of the sea front of the delta and the use of arable lands. A set of methodological approaches is suggested.
River mouth areas under the changing sea level
Mikhailov V.N., Magritsky D.V., Kravtsova V.I., Mikhailova M.V., Isupova M.V. Effects of the Caspian Sea level changes and water management for the hydrological regime and morphology of river mouths .
Response of the Caspian river mouths to the changes of the sea level and river runoff and sediment yield is discussed. Changes of the hydrological regime and morphological structure of the Volga, Terek, Sulak, Ural and Kura river mouths were analyzed for three periods, namely the regression before 1978, the transgression of 1978-1995 and relative stabilization of the sea level during the last 15 years. The river mouths differ in hydrological and morphological processes due to dissimilar sediment yields and inclinations of the delta surface and the near-mouth sea bottom. A number of theoretical and methodological approaches were tested for the analysis and calculation of processes under study. The results are applicable to river mouths in other regions of Russia and the world.
Hydrological and morphological processes within the Volga River delta during 1800-2010 were analyzed. Evolution of the marine edge of the delta and its river network and the morphodynamic types of channels of its water courses were studied. The rate of delta surface changes was estimated in relation to marine and river factors. It was found out that the main component of delta increment is a passive one. Fluctuations of the Caspian Sea level have practically no influence on the river network density and water amount within the delta. The main cause of their changes is the increase of river runoff to the delta area. The distribution of morphodynamic types of river channels within the Volga River delta was also studied. Straight, meandering and branching channels account for 66%, 27% and 7% of the total length of water courses respectively.
Advancement of the Volga River delta started about 2-2,5 kyr ago after the Ulluchai stage of the New-Caspian transgression. At present the delta includes the older ox-bow lake plain and the recent kultuk-floodplain one. During the end of the 18th – the beginning of the 19th century high level of the Caspian Sea (about -25 m) resulted in bay formation in the eastern part of the delta and redistribution of river runoff towards the system of Buzan, Bolda and Bushma water courses. Backwater effect of sea transgression led to the increase of accumulation within delta channels and formation of channel branches. After 1929 sea regression triggered the regressive erosion and the incision of delta channels, thus causing the transformation of channel branches.
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