Spatio-Seasonal Hypoxia/Anoxia Dynamics and Sill Circulation Patterns Linked to Natural Ventilation Drivers, in a Mediterranean Landlocked Embayment: Amvrakikos Gulf, Greece
Nikos Georgiou,
Elias Fakiris,
Constantin Koutsikopoulos,
George Papatheodorou,
Dimitris Christodoulou,
Xenophon Dimas,
Maria Geraga,
Zacharias G. Kapellonis,
Konstantinos-Marios Vaziourakis,
Alexandra Noti,
Dimitra Antoniou,
George Ferentinos
Affiliations
Nikos Georgiou
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Elias Fakiris
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Constantin Koutsikopoulos
Department of Biology, University of Patras, 26500 Rio Patras, Greece
George Papatheodorou
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Dimitris Christodoulou
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Xenophon Dimas
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Maria Geraga
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Zacharias G. Kapellonis
Hellenic Centre for Marine Research, Institute of Marine Biological Resources and Inland Waters, 576A Vouliagmenis Ave., 16452 Athens, Greece
Konstantinos-Marios Vaziourakis
Department of Ecology and Genetics/Limnology, Uppsala University, 75236 Uppsala, Sweden
Alexandra Noti
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Dimitra Antoniou
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
George Ferentinos
Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, 26500 Rio Patras, Greece
Amvrakikos Gulf is a Mediterranean landlocked, fjord-like embayment and marine protected area suffering from natural, human-induced hypoxia/anoxia and massive fish mortality events. Seasonal marine geophysical and oceanographic surveys were conducted focusing on the water-circulation patterns at the sill and the spatial-seasonal distribution of dissolved oxygen (DO) in the gulf. Detailed surveys at the sill, the only communication route between the gulf and the open sea, revealed a two-layer water circulation pattern (top brackish outflow–bottom seawater inflow) and the role of the tide in the daily water exchange. Statistical analysis of the known natural drivers of DO distribution (density difference between the Ionian Sea and Amvrakikos, river inflow, wind) revealed that horizontal density gradients strongly affect anoxia reduction and seafloor oxygenation, while river inflow and wind mainly oxygenate volume/areas located above or within the pycnocline range, with DO concentrations > 2 mg/L. Complex geomorphology with well-formed internal basins contributes to the development and preservation of low DO conditions below the pycnocline. Finally, 43% of the seafloor and 36% of the gulf’s total water volume are permanently hypoxic, and reach a maximum of 70% and 62%, respectively, in September and July. This work is tailored to future ecosystem management plans, decisions, and future research on coastal ecosystems.
