Spatio-Seasonal Hypoxia/Anoxia Dynamics and Sill Circulation Patterns Linked to Natural Ventilation Drivers, in a Mediterranean Landlocked Embayment: Amvrakikos Gulf, Greece

Amvrakikos Gulf is a Mediterranean landlocked, fjord-like embayment and marine protected area suffering from natural, human-induced hypoxia/anoxia massive fish mortality events. Seasonal geophysical oceanographic surveys were conducted focusing on the water-circulation patterns at sill spatial-seasonal distribution of dissolved oxygen (DO) in gulf. Detailed sill, only communication route between gulf open sea, revealed two-layer water circulation pattern (top brackish outflow–bottom seawater inflow) role tide daily exchange. Statistical analysis known natural drivers DO (density difference Ionian Sea Amvrakikos, river inflow, wind) that horizontal density gradients strongly affect anoxia reduction seafloor oxygenation, while inflow wind mainly oxygenate volume/areas located above or within pycnocline range, with concentrations > 2 mg/L. Complex geomorphology well-formed internal basins contributes to development preservation low conditions below pycnocline. Finally, 43% 36% gulf’s total volume are permanently hypoxic, reach maximum 70% 62%, respectively, September July. This work tailored future ecosystem management plans, decisions, research coastal ecosystems.