Geochemical evidence for cryptic sulfur cycling in salt marsh sediments

Mills, Jennifer V. and Antler, Gilad and Turchyn, Alexandra V. (2016) Geochemical evidence for cryptic sulfur cycling in salt marsh sediments. Earth and Planetary Science Letters, 453. pp. 23-32. ISSN 0012-821X DOI 10.1016/j.epsl.2016.08.001

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Abstract

Cryptic sulfur cycling is an enigmatic process in which sulfate is reduced to some lower-valence state sulfur species and subsequently quantitatively reoxidized; the rate and microbial energetics of this process and how prevalent it may be in the environment remain controversial. Here we investigate sulfur cycling in salt marsh sediments from Norfolk, England where we observe high ferrous iron concentrations with no depletion of sulfate or change in the sulfur isotope ratio of that sulfate, but a 5‰ increase in the oxygen isotope ratio in sulfate, indicating that sulfate has been through a reductive cycle replacing its oxygen atoms. This cryptic sulfur cycle was replicated in laboratory incubations using 18O-enriched water, demonstrating that the field results do not solely result from mixing processes in the natural environment. Numerical modeling of the laboratory incubations scaled to represent the salt marsh sediments suggests that the uptake rate of sulfate during this cryptic sulfur cycling is similar to the uptake rate of sulfate during the fastest microbial sulfate reduction that has been measured in the natural environment. The difference is that during cryptic sulfur cycling, all of the sulfur is subsequently reoxidized to sulfate. We discuss mechanisms for this pathway of sulfur cycling including the possible link to the subsurface iron cycle.

Item Type: Article
Additional Information: The authors regret that the δ18OSO4 axis in Fig. 2 and the y axis in Fig. 6b were mislabelled in the published manuscript. In Fig. 2, the initial δ18OSO4 axis went from 17–27 and should have gone from 7–17. In Fig. 6b, the y axis went from 0–0.12 and should have gone from 0–0.06. The authors would like to apologise for any inconvenience caused. The corrected figures appear below for the reader's convenience.
Uncontrolled Keywords: 2016AREP; IA71
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 453
Page Range: pp. 23-32
Identification Number: 10.1016/j.epsl.2016.08.001
Depositing User: Sarah Humbert
Date Deposited: 15 Dec 2016 17:38
Last Modified: 15 Dec 2016 17:41
URI: http://eprints.esc.cam.ac.uk/id/eprint/3784

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