Alterations of the Physical and Biochemical Structure in the Izmit Bay Following the Blockage Events at the Istanbul Strait

In December 2021 and March 2022, synoptic-scale weather systems triggered blockages in the Istanbul Strait, resulting in a notable alteration of the water dynamics of the upper layer of the northeastern Marmara Sea. The blockages resulted in the disruption of water mass exchanges between İzmit Bay and the eastern Marmara basin, driven by intensified hydrodynamic forces and severe wind conditions. The blockage of the two-layer flow in the strait led to an intensification of upper layer dynamics, resulting in an elevation of nutrient levels through mixing with nutrient-rich lower waters and/or the redistribution of nutrient fluxes via an enhanced jet current. This study demonstrates the occurrence of rapid changes in the biochemical structure of İzmit Bay, as evidenced by ADCP measurements and near-weekly temperature and salinity profiles. The analyses demonstrate significant shifts in flow dynamics, with salinity serving as an indicator of enhanced mixing. This mixing enabled the transport of nutrient-rich deep waters to the upper productive layer, thereby stimulating increased biological activity. The findings highlight that the altered dynamics resulted in a notable surge in nutrient concentrations and biochemical activity, potentially fostering the expansion of mucilage-forming species in İzmit Bay.