Details

Autor(en) / Beteiligte

• Abdulla, Hussain A.
• Burdige, David J.
• Komada, Tomoko

Titel

Abiotic formation of dissolved organic sulfur in anoxic sediments of Santa Barbara Basin

Ist Teil von

• Organic geochemistry, 2020-01, Vol.139, p.103879, Article 103879

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2020

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• •Abiotic sulfurization is a major pathway that forms DOS in anoxic pore waters.•Nucleophilic addition reactions are the major abiotic sulfurization pathways.•Abiotic reactions may explain the formation of oxidized DOS in anoxic pore waters.•CRAM molecules could play an important role in the formation of abiotic DOS. Sulfurization has been found to enhance organic matter preservation and petroleum formation in marine sediments. However, we do not yet have a comprehensive understanding of sulfurization mechanisms. In this study, we investigated several possible mechanisms of dissolved organic sulfur (DOS) formation in the top 4.5 m of anoxic sediments of Santa Barbara Basin (SBB), California Borderland. Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS), we identified chemical formulas of potential dissolved organic matter (DOM) precursors to these DOS compounds. We also examined how the formulas of abiotically formed DOS changed as a function of depth across a major redox gradient. Results show that abiotic nucleophilic addition reactions involving bisulfide (HS−) and polysulfide (HSx−) are the major sulfurization pathways that form DOS in anoxic pore waters of SBB sediments. We identified 2124 unique DOS formulas that could be generated from the addition of HS− and HSx− to 2203 DOM formulas, and this accounted for ∼70% of all DOS formulas detected in these pore waters. Examining the DOM formulas that served as reactants in the abiotic sulfurization reactions, we found that 64% contained only carbon, hydrogen, and oxygen (CHO formulas) while the remainder (34%) included nitrogen (DON formulas). Our results revealed high reactivity toward sulfurization among many of the CHO and DON formulas that have H/C and O/C elemental ratios that overlap with those of carboxyl-rich alicyclic molecules (CRAM). This specific class of formulas could play an important role in the formation of organic sulfur compounds in sulfidic marine ecosystems, and in the formation of sulfur-containing protokerogen in marine sediments. Our results further suggest that anoxic sediments are a source of DOS compounds to the oceans.