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.

今天的海洋在水体中储存的溶解有机碳 (DOC)与大气中的CO ₂一样多，因此溶解有机物质 (DOM) 是全球碳循环的重要组成部分。结果表明，在缺氧海洋沉积物中，硫物质（例如 H ₂S) 与有机物发生非生物反应，有助于碳保存。尚不清楚这些过程是否也有助于保存海水中的 DOM。在这里，我们通过结合元素、同位素和分子分析来展示黑海硫化水中的 DOM 硫化。溶解有机硫 (DOS) 主要在水体中形成，而不是来自沉积物或外来非海洋来源。我们的研究结果表明，在大规模缺氧事件中，DOM 可能通过与还原硫物质的非生物反应积累，通过增强有机碳封存对全球气候产生长期影响。