This study investigates the role of seafloor cold seeps in mercury (Hg) biogeochemical cycling. Sediment cores from the Haima cold seep in the South China Sea showed significant Hg and methylmercury (MMHg) enrichment in active seep areas compared to inactive and reference areas. Analysis of Hg isotopic composition and metagenomic data revealed the presence of microbes capable of Hg methylation, demethylation, and reduction. The study estimates a substantial global Hg and MMHg storage in cold seeps, suggesting they act as a previously unrecognized sink for Hg and source for MMHg in the deep ocean.
