The effect of water turbidity on the upper-ocean properties and dynamics in the Mediterranean and Black Seas

Marine chlorophyll concentration has an impact on turbidity affecting the upper-ocean properties and regulating the air-sea fluxes. This work aims at assessing the effect of turbidity, as estimated via surface chlorophyll, on the heat content and dynamics of the Mediterranean and Black Seas. We performed twin-simulation experiments using a regional configuration of the NEMO v4.2 ocean model comparing: 1) a run with climatological chlorophyll satellite data to estimate turbidity and shortwave penetration in the water column, with 2) a reference run of fixed turbidity (i.e., chlorophyll concentration fixed at 0.05 mg/m³) corresponding to Yerlov type I clear waters. Interim results for long-term simulations (2008-2018) show that considering the effects of turbidity, as estimated from realistic surface chlorophyll concentrations, increases sea surface temperature, amplifies the seasonal cycle of temperature in the surface layer (0-20 m), and increases the annual heat loss in the Mediterranean Sea by about 1.5 W/m². The latter is explained because the surface warming during summer is more intense than the cooling observed during winter, with differences between the two experiments reaching up to 2 °C in some regions. The increasing turbidity also affects the subsurface layers (20-200 m), with cooler temperatures throughout the year due to less solar radiation penetrating the water column. Ongoing work is currently being undertaken to estimate the indirect atmospheric feedback due to turbidity changes, using a fully-coupled ocean-atmosphere system (NEMO-WRF).