Water Budget of the Caspian Sea in the Last Glacial Maximum by Data of Experiments with Mathematical Models

Variations of Caspian Sea water budget in the epoch of the Last Glacial Maximum (LGM, ~21 thousand years ago) relative to the preindustrial conditions (~1850 CE) are considered using data of climatic modeling under PMIP4-CMIP6 projects. The variations of evaporation from the Caspian Sea surface and the volumes of river flow required to maintain the equilibrium state of the lake under various climate conditions and under various lake levels were also evaluated with the use of a regional configuration of the eddy-resolvingoceanic model INMIO-CICE. The boundary conditions in the oceanic model were derived from experiments with INMCM climate model reproducing LGM climate and the climate of preindustrial period. According to the data of PMIP4 simulation, both Volga runoff and evaporation from the Caspian Sea surface decreased in LGM epoch compared with the control experiment. The difference between the estimates by different models is rather high: from −5 to −50% for the Volga, and from −2 to −20% for the Caspian Sea. Such results are not enough to make unambiguous conclusions about whether the position of the Caspian in the LGM period was regressive or transgressive; however, deep regression of the Caspian is excluded. Even if the Caspian level is estimated with the use of the results of the model that has demonstrated the maximal decrease in the Volga runoff, the volume of river runoff from the territory of the Caspian basin will be enough to prevent the sea level dropping below –45 m above sea level.