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Front. Earth Sci. | doi: 10.3389/feart.2019.00140

The sedimentary carbon-sulfur-iron interplay - a lesson from East Anglian salt marsh sediments

  • 1University of Cambridge, United Kingdom
  • 2Department of Environmental Science, Policy, and Management, University of California, Berkeley, United States
  • 3Department of Earth Sciences, Faculty of Earth Sciences & Geography, University of Cambridge, United Kingdom
  • 4Department of Biology, University of York, United Kingdom

We explore the dynamics of the subsurface sulfur, iron and carbon cycles in salt marsh sediments from East Anglia, United Kingdom. We report measurements of pore fluid and sediment geochemistry, coupled with results from laboratory sediment incubation experiments, and develop a conceptual model to describe the influence of bioturbation on subsurface redox cycling. In the studied sediments the subsurface environment falls into two broadly defined geochemical patterns – iron-rich sediments or sulfide-rich sediments. Within each sediment type nearly identical pore fluid and solid phase geochemistries (in terms of concentrations of iron, sulfate, sulfide, dissolved inorganic carbon, and the sulfur and oxygen isotope compositions of sulfate) are observed in sediments that are hundreds of kilometres apart. Strictly iron-rich and strictly sulfide-rich sediments, despite their substantive geochemical differences, are observed within spatial distances of less than five meters. We suggest that this bistable system results from a series of feedback reactions that determine ultimately whether sediments will be sulfide-rich or iron-rich. We suggest that an oxidative cycle in the iron-rich sediment, driven by bioirrigation, allows rapid oxidation of organic matter, and that this irrigation impacts the sediment below the immediate physical depth of bioturbation. This oxidative cycle yields iron-rich sediments with low total organic carbon, dominated by microbial iron reduction and no methane production. In the absence of bioirrigation, sediments in the salt marsh become sulfide-rich with high methane concentrations. Our results suggest that the impact of bioirrigation not only drives recycling of sedimentary material but plays a key role in sedimentary interactions among iron, sulfur and carbon.

Keywords: Bioturbation, Sulfur, Iron, Carbon, salt marsh, Isotopes

Received: 10 Jul 2018; Accepted: 16 May 2019.

Edited by:

Bradley M. Tebo, Oregon Health & Science University, United States

Reviewed by:

Mustafa Yucel, Middle East Technical University, Turkey
Aubrey L. Zerkle, University of St Andrews, United Kingdom  

Copyright: © 2019 Antler, Mills, Hutchings, Redeker and Turchyn. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Gilad Antler, University of Cambridge, Cambridge, United Kingdom, giladantler@gmail.com