Carbon starvation enhances microbiologically influenced corrosion in marine offshore infrastructures

In offshore wind foundations, microbiologically influenced corrosion (MIC) is a critical concern in the mud zone, where steel is embedded in sediment characterized by limited oxygen availability and pronounced redox gradients. Although marine sediments contain substantial total organic carbon, only a small fraction is readily bioavailable to microorganisms. The limited availability of labile substrates can influence microbial metabolic strategies, potentially promoting alternative electron-transfer pathways, including metal-dependent electron acquisition associated with MIC. Consequently, microbial activity and corrosion are often assumed to be limited under such conditions; however, this assumption remains insufficiently validated. Here, we investigated how carbon availability shapes microbial community structure and corrosion behavior in biofilms relevant to offshore infrastructure. Sediment from the North Sea was used as inoculum, and steel coupons were exposed under blank (no added carbon), lactate, and yeast extract conditions. Corrosion was assessed by weight loss and 3D profiling, while microbial communities were analyzed using 16S rRNA gene sequencing. Dissolved sulfide and metabolomics were used to evaluate metabolic activity. Despite higher sulfide concentrations in nutrient-amended systems, the highest pitting occurred under carbon-limited conditions. These findings suggest that carbon limitation can promote alternative MIC pathways that may lead to more aggressive degradation of offshore wind foundation.