Preprints
https://doi.org/10.5194/gmd-2020-312
https://doi.org/10.5194/gmd-2020-312

Submitted as: model description paper 14 Nov 2020

Submitted as: model description paper | 14 Nov 2020

Review status: a revised version of this preprint was accepted for the journal GMD and is expected to appear here in due course.

Anoxic iron and sulphur cycling in the cGENIE.muffin Earth system model (v0.9.16)

Sebastiaan J. van de Velde1,a, Dominik Hülse1, Christopher T. Reinhard2, and Andy Ridgwell1 Sebastiaan J. van de Velde et al.
  • 1Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
  • 2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • acurrent address: Bgeosys, Geoscience, Environment & Society, Université Libre de Bruxelles, Brussels, Belgium; Operational Directorate Natural Environment, Royal Belgian Institute of Natural Sciences, Brussels, Belgium

Abstract. The coupled biogeochemical cycles of iron and sulphur are central to the long-term biogeochemical evolution of Earth's oceans. For instance, before the development of a persistently oxygenated deep ocean, the ocean interior likely alternated between states buffered by reduced sulphur (euxinic) vs. buffered by reduced iron (ferruginous), with important implications for the cycles and hence bioavailability of dissolved iron (and phosphate). Even after atmospheric oxygen concentrations rose to modern-like values, the ocean continued, episodically, to develop regions of euxinic or ferruginous conditions, such as associated with past key intervals of organic carbon deposition (e.g. during the Cretaceous) as well as extinction events (e.g. at the Permian/Triassic boundary). A better understanding of the cycling of iron and sulphur in an anoxic ocean, how geochemical patterns in the ocean relate to the available spatially heterogeneous geological observations, and quantification of the feedback strengths between nutrient cycling, biological productivity, and ocean redox, requires a spatially-resolved representation of ocean circulation together with an extended set of (bio)geochemical reactions.

Here, we extend the muffin release of the intermediate-complexity Earth system model cGENIE, to now include an anoxic iron and sulphur cycle, enabling the model to simulate ferruginous and euxinic redox states as well as the precipitation of reduced iron and sulphur minerals (pyrite, siderite, greenalite) and attendant iron and sulphur isotope signatures, which we describe in full. While we cannot make direct model comparison with present-day (oxic) ocean observations, we use an idealized ocean configuration to explore model sensitivity across a selection of key parameters. We also present the spatial patterns of concentrations and δ56Fe isotope signatures of both dissolved and solid-phase Fe species in an anoxic ocean as an example application. Our sensitivity analyses show how the first-order results of the model are relatively robust against the choice default kinetic parameters within the Fe-S system, and that simulated concentrations and reaction rates are comparable to those observed in process analogues for ancient oceans (i.e., anoxic lakes). Future model developments will address sedimentary recycling and benthic iron fluxes back to the water column, together with the coupling of nutrient (in particular phosphate) cycling to the iron cycle.

Sebastiaan J. van de Velde et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Sebastiaan J. van de Velde et al.

Model code and software

cGENIE.muffin model release v0.9.16 Ridgwell, A. et al. https://doi.org/10.5281/zenodo.4033262

Sebastiaan J. van de Velde et al.

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Short summary
Biogeochemical interactions between iron and sulphur are central to the long-term biogeochemical evolution of Earth's oceans. Here, we introduce an iron-sulphur cycle in a model of Earth's ocean. Our analyses show how the results of the model are robust towards parameter choices and that simulated concentrations and reactions are comparable to those observed in ancient oceans analogues (anoxic lakes). Our model presents an important step forward in the study of iron-sulphur cycling.