Sulfurization of dissolved organic matter in the anoxic water column of the Black Sea

Today's oceans store as much dissolved organic carbon (DOC) in the water column as there is CO2 in the atmosphere, and as such dissolved organic matter (DOM) is an important component of the global carbon cycle. It was shown that in anoxic marine sediments, reduced sulfur species (e.g., H2S) abiotically react with organic matter, contributing to carbon preservation. It is not known whether such processes also contribute to preserving DOM in ocean waters. Here, we show DOM sulfurization within the sulfidic waters of the Black Sea, by combining elemental, isotopic, and molecular analyses. Dissolved organic sulfur (DOS) is formed largely in the water column and not derived from sediments or allochthonous nonmarine sources. Our findings suggest that during large-scale anoxic events, DOM may accumulate through abiotic reactions with reduced sulfur species, having long-lasting effects on global climate by enhancing organic carbon sequestration.

Automated summary

Dissolved organic carbon in today's oceans is an important component of the global carbon cycle, with anoxic marine environments possibly contributing to its preservation through reactions with sulfur species. Studies show that in the sulfidic waters of the Black Sea, dissolved organic sulfur is largely formed within the water column, indicating potential long-lasting effects on global climate.