02 Feb 2023
 | 02 Feb 2023
Status: this preprint is currently under review for the journal BG.

Evidence of deep subsurface sulfur cycle in a sediment core from eastern Arabian Sea

Aninda Mazumdar, Aditya Peketi, Namrata Khadke, Subhashree Mishra, Ankita Ghosh, Sai Pavan Pillutla, Mohd Sadique, Kalyani Sivan, and Anjali Zatale

Abstract. Anaerobic microbial sulfate reduction and oxidative sulfur cycling have been studied in long sediment cores mainly acquired as part of IODP explorations. The most remarkable observation in many of these studies is the existence of an active sulfur cycle in the deep subsurface sediments that have very low organic carbon content and are presumably refractory. Here we investigate the interstitial sulfate concentrations and sulfur isotope ratios in a 290 m long core collected from the eastern Arabian Sea at a water depth of 2663 m. Continuous decrease in pore water-sulfate concentrations with depth (up to 75 mbsf) coupled with enrichment in δ34SSO4 values suggests organoclastic sulfate reduction (OSR) processes attributed to the activity of sulfate-reducing bacteria (SRB) and retention of labile organic substrates amenable to the SRBs. Below a depth of 75 mbsf, the absence of a further reduction in sulfate concentrations indicates insufficient labile substrate to drive SRB. An increase in sulfate concentrations at the deeper subsurface (below 128.5 mbsf) coupled with decreasing δ34SSO4 values may be attributed to a ferric-oxyhydroxide driven oxidation of Fe-sulfide. This study reveals that even under deep aerobic water columns, organic matter may continue to be a source of labile organic substrates at significantly deeper subsurface. Enhanced sulfate concentrations in the deeper depths may be attributed to the oxidation of sulfides via ferric-oxyhydroxides buried deep within the sediment. A microbiological investigation may reveal further details of the sulfur cycle at the deep surface.

Aninda Mazumdar et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-3', Anonymous Referee #1, 02 Mar 2023
  • RC2: 'Comment on bg-2023-3', Anonymous Referee #2, 17 Mar 2023

Aninda Mazumdar et al.

Aninda Mazumdar et al.


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Short summary
Deep biospheric processes deal with microbial activities and its influence on chemical-mineralogical changes in the sediments below the surface. These microbial and inorganic processes extend from few meters to several kms below the surface. These processes have been reported from deep mines to ocean sediments. In the present study we have unraveled the evidence of deep biospheric activities in 300 m long sediment core underlined 2500 m of water column from temperature eastern Arabian sea.