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

• Published in: Chemical Geology
• Main Authors: Crémière, Antoine, Strauss, Harald, Sebilo, Mathieu, Hong, Wei-Li, Gros, Olivier, Schmidt, Sabine, Tocny, Jennifer, Henry, Françoise, Gontharet, Swanne, Laverman, Anniet M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2017
• Subjects: VDP::Matematikk og Naturvitenskap: 400::Geofag: 450; VDP::Mathematics and natural science: 400::Geosciences: 450; Microbial sulfate reduction; Organic carbon-rich sediments; Sulfur and oxygen isotopes; Sulfur oxidizing microbial mats; Early diagenesis; Marine mangrove; Arctic
• Online Access: https://hdl.handle.net/10037/13430; https://doi.org/10.1016/j.chemgeo.2017.02.017

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.chemgeo.2017.02.017 . Accepted manuscript version, licensed CC BY-NC-ND 4.0. The 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%, δ 13 C TOC below − 25‰ VPDB and C/N molar 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 ( 34 εnet = − 33‰) and a gentle δ 18 O/δ 34 S sulfate 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 δ 18 O/δ 34 S sulfate 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, δ 34 S values of pyrite are positively correlated with the TOC/TS ratio and negatively correlated with δ 13 CTOC; 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.