Hydrodynamics of the Turkish Strait System: Insights from 35 years of three-dimensional numerical model simulation

The Turkish Strait System (TSS), comprising the Bosphorus Strait, Marmara Sea, and Dardanelles Strait, serves as a vital marine corridor connecting the Black Sea and the Mediterranean Sea. Its two-layer stratified flow plays a crucial role in water exchange as well as heat and nutrient transport between these two sea basins. This study utilizes a three-dimensional numerical model to investigate the short- and long-term hydrodynamic behavior of the TSS over a 35-year period (1987–2021) incorporating realistic atmospheric forcing. Model outputs reveal interannual sea level variations primarily governed by net freshwater input to the Black Sea, which is, in turn, modulated by the North Atlantic Oscillation (NAO). Although annual variability in volume fluxes through the straits is generally limited, notable peaks and troughs correspond to periods of increased or decreased freshwater input from the Black Sea. A statistically significant decreasing trend is detected in the upper layer flow, associated with declining sea level differences between the Black Sea and Aegean Sea, potentially driven by increased evaporation in the Black Sea. The long-term mean circulation in the Marmara Sea features a strong westward flow in the central basin, accompanied by anticyclonic eddies to the north and cyclonic eddies to the south, reflecting dipole wind curl pattern. On monthly timescales, circulation patterns exhibit substantial variability in response to the dynamic interplay between wind curl and Bosphorus outflow. This study offers new insights into the coupled atmospheric-hydrodynamic controls shaping the TSS and underscores its sensitivity to climate-driven variability, with implications for regional oceanographic processes and sustainable management strategies.