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Abstract

Paleogeographical data give grounds to assert that during the late Quaternary the "Great" Khvalynskaya transgression of the Caspian Sea took place. In the early, maximum transgression stage covering the final deglaciation period (17-13 kyr BP), the sea level was tens meters above the current sea level, and there are significant disagreements in understanding the driving mechanisms of this extraordinary hydrological phenomenon.Earlier, it has been shown (Panin et al., 2005, 2021) that meltwater runoff due to the Scandinavian ice-sheet melting contributed insignificantly to the transgression of the sea. Our study was motivated by the following question: could the Early Khvalynian transgression has been initiated by hydroclimatic factors in the cryoarid climate of the deglaciation period and in the absence of a significant inflow of glacial meltwater? Using a full ocean model INMNIO COMPASS – CICE coupled with the global climate model INMCM4.8, we estimated that the mean river inflow into the sea providing the assigned sea level rise should be as much as 400-450 km³/year (equilibrium value). Then, using a hydrological model ECOMAG forced by the paleo-climate data, we found that the estimated extreme water inflow into the sea could be formed due to the spread of post-glacial permafrost underlying the ancient river catchments. As a result of numerical experiments, we answered “yes” on the aforementioned research question and concluded that the hydroclimatic drivers of the Early Khvalynian transgression could be strengthened by permafrost covered the Caspian Sea catchment area after the Scandinavian glacier has retreated.