Long-term hydrodynamic changes in marginal estuarine seas: the role of sea level rise and freshwater fluxes

Significant environmental changes have occurred in marginal estuarine seas in the past, driven by changes in sea level and water and salt balances. Predicting the future evolution of these seas is a scientific challenge because adequate scenario studies are currently hindered by the quality of 3D models on millennial timescales. In this paper, we present relatively simple and efficient models of the Black Sea. This sea connects rivers to the ocean and acts as a 'mixer', diluting inflowing saline ocean water with riverine freshwater to generate brackish water. For such an ocean system, it is crucial to incorporate mixing within the sea and two-layer exchange within the strait into a single framework. This paper demonstrates that the developed models can be used to (1) estimate past and future ocean states resulting from specific combinations of global sea level and freshwater fluxes; (2) critically address the consistency of used water and salt balances; (3) conceptualizing further studies of major environmental trends. Illustrations are provided to show the evolution of stratification of the Black Sea in the Holocene. Application to other ocean environments controlled by two-layer exchange flows is also discussed.