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- Title
Placing an upper limit on cryptic marine sulphur cycling.
- Authors
Johnston, D. T.; Masterson, A.; Beirne, E.; Gill, B. C.; Casciotti, K. L.; Knapp, A. N.; Berelson, W.
- Abstract
A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is required to explain the role of oxygen-minimum zones (OMZs) in controlling the fixed nitrogen inventory of the global ocean. Apparent imbalances in geochemical nitrogen budgets have spurred numerous studies to measure the contributions of heterotrophic and autotrophic N2-producing metabolisms (denitrification and anaerobic ammonia oxidation, respectively). Recently, 'cryptic' sulphur cycling was proposed as a partial solution to the fundamental biogeochemical problem of closing marine fixed-nitrogen budgets in intensely oxygen-deficient regions. The degree to which the cryptic sulphur cycle can fuel a loss of fixed nitrogen in the modern ocean requires the quantification of sulphur recycling in OMZ settings. Here we provide a new constraint for OMZ sulphate reduction based on isotopic profiles of oxygen (18O/16O) and sulphur (33S/32S, 34S/32S) in seawater sulphate through oxygenated open-ocean and OMZ-bearing water columns. When coupled with observations and models of sulphate isotope dynamics and data-constrained model estimates of OMZ water-mass residence time, we find that previous estimates for sulphur-driven remineralization and loss of fixed nitrogen from the oceans are near the upper limit for what is possible given in situ sulphate isotope data.
- Subjects
SULFUR cycle; OXYGEN content of seawater; NITROGEN content of seawater; REDUCTION of sulfates; ISOTOPE geology
- Publication
Nature, 2014, Vol 513, Issue 7519, p530
- ISSN
0028-0836
- Publication type
Article
- DOI
10.1038/nature13698