Artificial island construction exacerbates storm-induced loss of buried estuarine carbon

Storm deposition is critical for burying estuarine sedimentary organic carbon (OC), yet how this process responds to artificial island construction remains unclear. We examined this issue by comparing lithology, elemental and organic geochemistry, and ²¹⁰Pb and ¹³⁷Cs profiles of two sediment cores retrieved 1 yr apart near the newly constructed Zhoushan Green Petrochemical Base (ZGPB) in Hangzhou Bay, China. We identified a post-construction storm deposit of unprecedented thickness, likely formed by high-turbidity flows linked to a storm-triggered submarine landslide near ZGPB. The associated substantial OC burial during storm's waning phase was far outweighed by OC loss due to severe erosion during its waxing phase. This net OC loss was further exacerbated by enhanced remineralization within the thick deposit. These findings underscore the necessity for holistic planning of artificial islands, as their construction may amplify coastal vulnerability to emerging geohazards and undermine estuarine carbon storage capacity.