Preprints
https://doi.org/10.5194/egusphere-2024-1829
https://doi.org/10.5194/egusphere-2024-1829
01 Jul 2024
 | 01 Jul 2024
Status: this preprint is open for discussion.

Enigmatic Fe-Mn-fueled Anaerobic Oxidation of Methane in sulfidic coastal sediments of the Eastern Arabian Sea

Kalyani Sivan, Aditya Peketi, Aninda Mazumdar, Anjali Zatale, Sai Pavan Kumar Pillutla, Ankita Ghosh, Mohd Sadique, and Jittu Mathai

Abstract. Anaerobic oxidation of methane (AOM) coupled with Fe-Mn reduction (Fe-Mn-AOM) is considered a globally important biogeochemical process in marine sediments in addition to sulfate-driven AOM (SO42−-AOM) responsible for the consumption of methane, a strong greenhouse gas. Most existing studies have emphasized the significance of Fe-Mn-AOM activities in sediments below the depth of the sulfate methane transition zone (SMTZ) with insignificant dissolved sulfide and sulfate concentrations in the porewaters. Here, we report for the first time enigmatic geochemical evidence of focused Fe-Mn-AOM activity across the SMTZ in the presence of high dissolved sulfide concentrations in a sediment core collected within the seasonal coastal hypoxic zone of the Eastern Arabian Sea (West coast of India (WCI)). The Fe-Mn-AOM activity is evident from the concurrent decrease in CH4 concentrations, d13CCH4 and d13CDIC values coupled with the enrichment of porewater Fe2+ and Mn2+ concentrations at multiple depths below the seafloor. Since neither CH4 nor reactive Fe appears to be the limiting factor controlling the Fe-Mn-AOM activity, we hypothesize that the focused Fe-Mn-AOM at multiple depths is likely fueled by the localization of metal-reducing and methanotrophic microbial communities, leading to biogeochemical heterogeneity in a dynamic seasonally hypoxic coastal environment sensitive to climate change. This study highlights new insight into CH4-S-Fe-Mn biogeochemical cycling with far-reaching implications in climate studies linked to the estimation of sedimentary methane production and consumption.

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Kalyani Sivan, Aditya Peketi, Aninda Mazumdar, Anjali Zatale, Sai Pavan Kumar Pillutla, Ankita Ghosh, Mohd Sadique, and Jittu Mathai

Status: open (until 21 Aug 2024)

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Kalyani Sivan, Aditya Peketi, Aninda Mazumdar, Anjali Zatale, Sai Pavan Kumar Pillutla, Ankita Ghosh, Mohd Sadique, and Jittu Mathai
Kalyani Sivan, Aditya Peketi, Aninda Mazumdar, Anjali Zatale, Sai Pavan Kumar Pillutla, Ankita Ghosh, Mohd Sadique, and Jittu Mathai

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Short summary
The present study reports Fe-Mn-driven anaerobic oxidation of methane (Fe-Mn-AOM) in seasonally hypoxic coastal sediments under sulfidic conditions. The Fe-Mn-AOM activity is observed over the entire sediment core at multiple depths above and below the sulfate methane transition zone. We hypothesize that the focused Fe-Mn-AOM activity is possibly controlled by the Fe-Mn reducing microbial population distribution in the sediment core.