Carbon starvation enhances microbiologically influenced corrosion in marine offshore infrastructures.

INTRODUCTION: 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. In marine sediments, the limited availability of labile substrates can influence microbial metabolic strategies, potentially promoting alternative electron-transfer pathways. Here, we performed an exploratory mechanistic study to investigate how carbon availability influences microbial community structure and corrosion behavior in multispecies biofilms relevant to offshore infrastructure. METHODS: 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. RESULTS AND DISCUSSION: The findings illustrated that nutrient regime strongly shaped microbial and chemical conditions. Yeast extract produced the highest total sulfide concentrations (9 mM), but corrosion severity did not scale with bulk sulfide accumulation. The highest corrosion rate occurred under carbon-limited conditions (0.55 mm yr-1), compared with 0.122 and 0.072 mm yr-1 for lactate and yeast extract, respectively. Pitting rate was also most pronounced under carbon-limited conditions (0.65 mm yr-1). These findings suggest that the test conditions for offshore foundation materials should include low-labile-carbon scenarios to better reflect sediment zones and highlight the need for further mechanistic investigation.