Sulfur diagenesis under rapid accumulation of organic-rich sediments in a marine mangrove from Guadeloupe (French West Indies)

Abstract

International audienceThe biogeochemistry of sulfur and carbon during early-diagenetic processes within organic-rich marine mangrove sediments was studied in the “Manche à Eau” lagoon, Guadeloupe, West Indies. These sediments are characterized by a total organic carbon content (TOC) mostly above 11 wt%, δ13CTOC below − 25‰ VPDB and C/Nmolar ratios exceeding 15. Rates of mangrove-derived organic carbon accumulation vary between ~ 200 and 400 gOC·m− 2·yr− 1, with highest rates at the shore of the lagoon. On the lagoon border, where colorless filamentous sulfur-oxidizing bacteria colonize the sediments, active sulfate reduction within the upper 20 cm, with a net removal rate of ~ 0.5 μmol·cm− 3·d− 1, is assumed to be essentially driven by organic carbon oxidation. This is expressed by relatively low apparent sulfur isotope fractionation (34εnet = − 33‰) and a gentle δ18O/δ34Ssulfate apparent slope of 0.36 ± 0.03 (2s). Further inside the lagoon, in the absence of sulfur-oxidizing bacteria, higher apparent sulfur isotope fractionation and a steeper δ18O/δ34Ssulfate slope (0.67 ± 0.20) suggest an overall lower sulfate removal rate that may be coupled to minor sulfur disproportionation. Spatial and vertical variation in sulfur cycling, reflected by oxygen and sulfur isotopic characteristics, seem to be mainly controlled by unsteady to relatively steady organic matter deposition and its reactivity. In all sediments, δ34S values of pyrite are positively correlated with the TOC/TS ratio and negatively correlated with δ13CTOC; suggesting a primary control of the quantity and quality of organic matter on the pyrite isotope records, despite potential iron-limiting conditions for the most active sites. Our results provide insights into the role of organic carbon input on sulfur cycling; stimulating sulfate reduction and in turn the presence of sulfur-oxidizing microbial mats, resulting in an intense cycling of both carbon and sulfur in these marine mangrove sediments

Diagenetic controls on the isotopic composition of carbonate‐associated sulphate in the Permian Capitan Reef Complex, West Texas

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Role of APS reductase in biogeochemical sulfur isotope fractionation

“…Sulfur isotope data from modern environments, shown as a histogram in Fig. 4, were obtained from previous compilations 19,60,78 with addition of the recent environmental studies 79–84 . The data are binned and recalculated in Supplementary Data 1.…”

Geochemical characteristics of iron in sediments from the Sea of Marmara

“…Pore-water data from push cores displayed a deeper sulfate depletion zone in Cinarcik Basin close the Core MRS-CS-16 (Ruffine et al, in press). Crémière et al (2017) found that the sediments would be more reducing and acidic when TOC content is higher or when the hydrocarbon seepage is more intensive. By comparing with the Cinarcik Basin, because the TOC of the Western High were higher and the gases contained a relatively high content of heavy hydrocarbons, there are more electron receptors, leading to a sedimentary environment more reducing and acidic.…”