Regime of water balance components of the Caspian Sea

The results of studying the hydrological regime of the Caspian Sea and its basin climate in observation period 1945–2010 are generalized. The results of analysis of the regime of precipitation, air temperature in the Caspian Sea basin and its level, as well as Volga runoff in periods of Caspian Sea level rise and drop are given. The conformity in variations of the trends in Caspian Sea level its basin climate is demonstrated, and the direction of further studies is substantiated.     

Long-Term variations in water levels in the Volga mouth area and their dependence on the Caspian Sea level variations

Long-term water level variations in the Volga mouth area and the effect exerted on them by the river’s flow and the Caspian Sea’s level variations are considered. Quantitative relationships were identified between the mean annual water levels at different gages in the mouth and the sea level. A backwater component was isolated in the long-term variations in water level in the Volga mouth area. Relationships between the daily water levels in the mouth and the Caspian Sea’s level at fixed water flow in the delta apex are presented. The magnitude and the propagation distance of backwater from the sea into the delta are specified. The responses of the mouth areas of rivers emptying into the Caspian Sea to sea level variations in the past century are compared.     

Current Variations in the Wind Speed Vector and the Rate of Evaporation from the Caspian Sea Surface

Regularities in the rearrangement of the surface atmospheric circulation in the Caspian Sea region are studied. It is found that during the current rise in the Caspian Sea level, a statistically significant decrease in the wind speed modulus occurred (mainly in autumn and winter winds of zonal directions). This caused a decrease in the rate of evaporation in the region. The results of this study testify to a need for developing a deterministic model of current variations in the Caspian Sea water regime at varying global and regional climate.     

A Nonlinear Model of Level Variations in the Caspian Sea

A new thermophysical mechanism of the Caspian Sea level variations is proposed. The mechanism incorporates the effect exerted on the dynamics of the water budget of the Caspian Sea by the nonlinear dependence of the evaporation rate on the moistening of the basin.     

Numerical Simulation of the Caspian Sea Circulation Using the Marine and Atmospheric Research System

The Marine and Atmospheric Research System (MARS) for the Caspian Sea meteorological characteristics is presented, which is implemented in Zubov State Oceanographic Institute. It includes computation of the atmospheric forcing with the Weather Research and Forecasting model, as well as computation of currents, sea level, temperature, salinity and sea ice with the Institute of Numerical Mathematics Ocean Model and the computation of wind wave parameters using the Russian wind-wave model. The results are presented on verification of the hydrometeocharacteristics simulated with the MARS for the Caspian Sea. As well, the retrospective simulation of the thermohydrodynamic characteristics in this basin is performed with MARS for the ice-free period 2003–2013. The important features of the Caspian Sea circulation are shown.     

Nonlinear dynamics of level variations in the Caspian Sea

Caspian Sea level variations, which have several equilibrium states, are studied by the methods of the theory of nonlinear dynamic systems. Normal monthly values of sea level according to data collected at Makhachkala gauge from 1900 to 2000 are considered. The diagnostic characteristics of dynamic chaos are used to show that sea level variations have some properties of series with chaotic behavior. A model of level variations in the Caspian Sea, comprising a system of water balance equations for the sea basin, the dynamics of river runoff, and water balance of the sea itself, is proposed. Equation of a nonlinear oscillator is derived and shown to have solutions with chaotic regimes at some combinations of parameters.     

Elision and Infiltration Waters in the Northern Caspian

Elision and infiltration groundwater of the Northern Caspian basin are described. It is shown that a zone of elision brines with a high formation pressure exists under the Caspian Sea. These brines are shown to penetrate from below the Caspian Sea into the underground beds, carry fluids, and facilitate the formation of hydrocarbon fields.     

The response of river mouths to large-scale variations in sea level and river runoff: Case study of rivers flowing into the Caspian Sea

Regularities in the response of the mouths of major rivers, flowing into the Caspian Sea, to large-scale variations in its level and river water runoff and sediment yield are considered. Changes in the morphological structure and hydrological regime of the Volga, Terek, Sulak, Ural, and Kura mouths have been analyzed in both geological past and separately for three modern periods: a considerable drop in Caspian Sea level before 1978, its abrupt rise in 1978–1995, and a relative stabilization in the subsequent years. Specific features were identified in the hydrological-morphological processes in different mouths, caused by the differences in river sediment yields, and the slopes of delta surface and mouth nearshore beds. Some theoretical and methodological approaches were verified in the analysis and evaluation of the processes under consideration. The obtained results of studies of the mouths of rivers flowing into the Caspian Sea can be regarded as examples and analogues in the assessment of processes, which take place at the mouths of other Russian and world rivers at present and can take place in the future under anticipated natural and anthropogenic variations in sea level and river runoff.     

Studying Long-term Variations in the Caspian Sea with the Use of the Theory of Stochastic Differential Equations

Nonlinear mechanisms of long-term variations in the Caspian Sea level are described. It is shown that with account taken of the dependence of the evaporation depth from the Volga basin surface on soil moisture content and the dependence of the evaporation depth from the sea surface on its level, we obtain a fundamentally new (chaotic) oscillation mechanism with several attraction levels. The stochastic differential equations describing the water budget of the sea basin and the sea proper and the respective solutions of the Fokker–Planck–Kolmogorov equation are shown to have stationary bimodal density of the level probability. The random process, characterizing the sea level variations at a nonlinear dependence between the evaporation rate and the level is found to be non-Gaussian. Noise-induced transitions, caused by nonlinear evaporation processes are described. A new nonlinear stochastic theory describing the Caspian Sea level variations and based on predicted physical effects is suggested.     

A Procedure for Calculating Extreme Characteristics of the Northern Caspian Sea Level

A procedure is proposed for calculating extreme characteristics of the level of a sea with allowance for positive and negative setups. Analysis is made of past storm events in the Northern Caspian Sea that have caused strong setups. Sixty-three storm weather patterns are chosen from a period of 45 years. Time ring synoptic maps are used to digitize the atmospheric pressure fields and calculate the field of its gradient and the wind near water surface. Based on these data, the sea level values and currents are calculated through two- and three-dimensional hydrodynamic models. A probabilistic model along with computer-aided data treatment procedures are used to calculate the fields of extreme characteristics of the sea level at the Lagan gage with the occurrence of once per N years at the average Caspian Sea level of 27 m below SL.     

Variations in wind direction and speed from arctic to the Caspian Sea as a manifestation of modern climate changes

The regularities in present-day variations in the wind speed vector are examined at 18 stations along the section from Kola Peninsula to the Caspian Sea. Data on long-term variations in the major climate-forming factors and climatic parameters are generalized. The statistically significant tendency toward a considerable decline in the wind speed with a maximum module and the most frequent wind speeds of zonal, mostly western, directions (this tendency has been revealed earlier for the eastern coast of the middle and southern Caspian Sea) was found to hold for the greater part of the European Russia. Possible causes of present-day climate changes and their manifestations at the regional level are analyzed. A possible mechanism of present-day climate changes is proposed     

Hydrological and morphological processes at river mouths of the Caspian Sea Region as possible analogs of expected changes of mouths of other rivers in Russia and the world

Present changes in the regime and structure of mouths of rivers, which empty into the Caspian Sea, are discussed. The similarities and differences of these processes at the mouths of different rivers of the Caspian Region were revealed. Assessment was made of the impact of changes in river water runoff and sediment load and in the Caspian Sea level as well as the nearshore zone relief and local hydraulic engineering activities on the processes under study. Anomalous features of the processes occurring at the mouths of the Volga and Terek rivers were revealed and explained. Hydrological and morphological processes typical of the present mouths of the rivers of Ural, Sulak, and Kura were revealed; these processes could be accepted as universal and possible analogs in assessing the expected changes at the mouths of other rivers in Russia and the world in the XXI century.     

Regime of Low-Frequency Wave Motion in the Coastal Zone of the Northwestern Caspian Sea

Regime characteristics of infragravitational and wind-induced waves for the northwestern Caspian Sea are given. The role of infragravitational waves in the dynamics of the northern Caspian coastal zone is determined based on empiric regional relationships, used to improve the conventional methods, and wind wave calculations.     

Long-Term Variations in the Vertical Thermohaline Structure in Deep-Water Zones of the Caspian Sea

Long-term variability in water temperature and salinity in August has been determined for deep-water segments of standard profiles in the Central and Southern Caspian Sea based on data of on-board observations carried out in 1956–2000. Estimates of parameters of the vertical thermohaline structure of waters were obtained for four time intervals. These estimates have been compared to the variability in the main external factors governing the formation of thermohaline regime. Appreciable long-term variations in the vertical thermohaline structure of waters, caused by a nonperiodic alternation of two main types of hydrological processes in the Caspian Sea are revealed. Qualitative characteristics of these two types are presented.     

Present-day changes in water consumption in the Caspian Sea basin

Indices characterizing the withdrawal of water resources in the basins of rivers flowing into the Caspian Sea and the use of these resources in different economic sectors in 1970–2003 are analyzed. The dynamics of disposal of wastewaters and collector-drainage waters is discussed. Tendencies in changes in the volumes of consumptive water use in the basins of individual rivers and the Caspian Sea as a whole are identified.     

Geographical and Ecological Characteristics of the Caspian Sea and Modern Tendencies in the Evolution of Its Ecosystem

The Caspian Sea is characterized in the geographic and ecological aspects, and the state of its ecosystem is estimated. The natural and anthropogenic processes that control the formation of the environmental conditions in the Caspian Sea and the distribution of principal commercial hydrobionts and their food items are analyzed. Data on modern tendencies in changes in the abiotic and biotic parameters of the ecosystem, their causes and mechanisms are summarized. Prospects of further changes related to the development of shelf fields of petroleum hydrocarbons are assessed.     

Macro- and microelements in the interstitial water of deep-water areas of the Southern and Middle Caspian Sea

The results of determinations of macro- and microelement concentrations (Mn, Fe, Ba, Sr, Rb, Si, Pb, and U) in the interstitial water in four cores of bottom sediments sampled in the deep-water areas of the Southern and Middle Caspian Sea are compared with the concentrations of these elements in the free water of the Caspian Sea. The data obtained amplify the present-day concept on the geochemical and ecological states of the sea.     

Probabilistic Estimates of Water Level in the Ural River Mouth Reach at Interaction between the River Runoff and Positive Setups

A probabilistic technique is developed for assessing water level in the mouth reach of the Ural River in the course of interaction between the river runoff and irregular rises in the Caspian Sea level (positive setups) at the predicted background sea levels of –26.5 and –26.0 m abs.     

Variations in the Caspian Sea Level in the Historic Epoch

Reconstruction of variations in the Caspian Sea level is proposed based on the results of investigations of deposits in the Agrakhan sand bar and bays (or former bays) of the eastern sea coast. The history of sedimentation in particular regions is reconstructed by the radiocarbon dating. Generalized data on the age of deposits are used to construct the most likely temporal course of variations in the sea level within the historic epoch.