Hydrological and climatic characteristics of the Caspian Sea during the Last Glacial Maximum, mid-Holocene and preindustrial conditions according to numerical modelling data

Components of the water balance of the Caspian Sea are calculated for a wide range of lake levels (–85–50 m. a. s. l.) and for the two most contrasting climatic epochs over the last several tens of thousands of years: the middle Holocene (6 ka b. p.) and the Last Glacial Maximum (21 ka b. p.), as well as for the pre-industrial conditions (~1850). The eddy-resolving ocean general circulation model INMIO coupled with the CICE ice model are used for the calculations. Climate data of the INM–CM4.8 model for the indicated periods are used as boundary conditions. It is found that the volumes of river inflow required to maintain the lake level at various marks for the Holocene era are lower than the corresponding pre-industrial values by 6–7%. For the Last Glacial Maximum this decrease is 13–14% for regressive states and 20–21% for transgressive ones. Sensitivity of the results is studied to the temporal resolution of boundary meteorological data and to the locations of fresh water inflow into the Caspian Sea. It is shown that excluding the diurnal and intramonthly variability in input data leads to an underestimation of evaporation from the surface of the sea. The greatest influence on this value is exerted by the exclusion of intramonthly variability of the dynamic wind field: this leads to a decrease in the equilibrium runoff by 35%. To correctly simulate the duration of the ice coverage season, it is necessary to take into account the diurnal cycle of incoming radiation and air temperature. The melting period is significantly lengthened when using data at daily or monthly resolution, which has the greatest impact during transgressive states of the Caspian Sea. The redistribution of river mouth locations along the coast does not significantly affect the value of the total equilibrium inflow, which makes it possible to most likely exclude the uncertainty of this value associated with the lack of data on the mutual ratio of discharge of ancient rivers. In addition, estimates of hydroclimatic characteristics of the Caspian region for the middle Holocene and late Pleistocene are provided based on climate modeling carried out within the framework of the PMIP4 project. 

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