Abstract
Abstract. Decadal variability in Caspian Sea thermohaline properties is investigated using a high-resolution ocean general circulation model including sea ice thermodynamics and air–sea interaction forced by prescribed realistic atmospheric conditions and riverine runoff. The model describes synoptic, seasonal and climatic variations of sea thermohaline structure, water balance, and sea level. A reconstruction experiment was conducted for the period of 1961–2001, covering a major regime shift in the global climate during 1976–1978, which allowed for an investigation of the Caspian Sea response to such significant episodes of climate variability. The model reproduced sea level evolution reasonably well despite the fact that many factors (such as possible seabed changes and insufficiently explored underground water infiltration) were not taken into account in the numerical reconstruction. This supports the hypothesis relating rapid Caspian Sea level rise in 1978–1995 with global climate change, which caused variation in local atmospheric conditions and riverine discharge reflected in the external forcing data used, as is shown in the paper. Other effects of the climatic shift are investigated, including a decrease in salinity in the active layer, strengthening of its stratification and corresponding diminishing of convection. It is also demonstrated that water exchange between the three Caspian basins (northern, middle and southern) plays a crucial role in the formation of their thermohaline regime. The reconstructed long-term trends in seawater salinity (general downtrend after 1978), temperature (overall increase) and density (general downtrend) are studied, including an assessment of the influence of main surface circulation patterns and model error accumulation.
Highlights
The Caspian Sea is the largest enclosed water body on earth with a surface area of more than 370 000 km2 and a catchment area almost 10 times greater
sea surface salinity (SSS) evolution in the entire sea correlates with river discharge and air humidity, and the results presented here are consistent with the observations (Tuzhilkin et al, 2011)
We have considered a long-term numerical reconstruction of the Caspian Sea thermohaline circulation in 1961–2001
Summary
The Caspian Sea is the largest enclosed water body on earth with a surface area of more than 370 000 km and a catchment area almost 10 times greater. It is highly sensitive to variations in the global and regional climate systems as well as economic activities that include major schemes of river regulation This is vividly reflected in the evolution of the Caspian Sea level, which is subject to large fluctuations on seasonal and decadal timescales. The increasing production of global atmospheric reanalysis datasets and their availability over several decades have made possible retrospective studies of the longterm evolution of the marine environment based on numerical reconstruction of its response to external forcing, as will be done in the present paper This approach was applied in our previous work (Dyakonov and Ibrayev, 2018) with emphasis on the long-term variability of the Caspian Sea water balance and its sensitivity to external factors. In the following figures vertical dashed lines mark instances in which climatic shifts occur
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