Alterations of the Physical and Biochemical Structure in the İzmit Bay Following the Blockage Events at the İstanbul Strait

In December 2021 and March 2022, synoptic-scale weather systems triggered blockages in the & Idot;stanbul 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 & Idot;zmit 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 & Idot;zmit Bay, as evidenced by Acostic Poppler Current Profiler (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 & Idot;zmit Bay.