A Comprehensive Assessment of Dissolved Oxygen Fluctuations and Biocorrosion Trends in the Sea of Marmara

Izmit Bay (IZ17) and Cınarcık Basin (45C) are the important points where low dissolved oxygen (DO) is observed in the Sea of Marmara. Investigating oxygen levels is essential regarding the sustainability of marine environments and evaluating possible microbiologically influenced corrosion (MIC) risks. Sulfate-reducing bacteria (SRB) play a pivotal role in the biogeochemical cycle, and they are the most aggressive group for MIC. In this study, suboxic and anoxic conditions in the Sea of Marmara were evaluated for the first time with SRB and other heterotrophic bacteria. The physicochemical parameters of seawater, nutrient analysis, hydrogen sulfide (H2S), and sulfate measurements were performed. Total SRB and aerobic heterotrophic bacteria (AHB) cells were determined along the water column. Also, the MIC tests were performed. Results showed that the corrosion rate of Al7075 alloy was increased by SRB biofilm in real seawater. Also, suboxic conditions were observed in the bottom waters of IZ17 and 45C stations and the transition zone from suboxic to anoxic conditions at deeper depths was detected in IZ17. It indicated that the suboxic and anoxic conditions exhibit a variable profile in the Sea of Marmara. This study highlights the supportive role of examining microorganisms to better understand the biogeochemical cycles.