Hydrodynamic responses of the Caspian Sea and Black Sea to greenhouse warming in a high-resolution ocean-atmosphere coupled climate model

The Caspian Sea and Black Sea are the two earth's largest inland seas. Projections of their temperature, circulation and water balance responses to greenhouse warming remain largely uncertain. We investigated hydrodynamic changes of the two water bodies in a high-resolution CESM1 simulation, in which both the Caspian Sea and Black Sea are simulated by the ocean model (POP2). It turns out the mean surface water temperature of the two seas will increase by about 2.5°C in response to CO₂ doubling in the atmosphere. Meanwhile, reduction of wind stress curl will lead to a spin-down of the main gyre circulations particularly in the Black Sea, which was also evidenced by a two-dimensional ocean model with joint effect of baroclinicity and bottom relief being considered. Our results also show that future evaporation enhancement due to surface warming will lead to a negative water balance for both seas, which is equivalent to a mean sea level trend of -0.1 m/year when CO₂ concentration in the atmosphere doubles. These hydrodynamic changes are likely to exert large impacts on the aquatic ecosystems, fisheries, and human societies in the coastal areas.