Preprints
https://doi.org/10.5194/bg-2020-399
https://doi.org/10.5194/bg-2020-399

  06 Nov 2020

06 Nov 2020

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

Technical Note: Uncovering the influence of methodological variations on the extractability of iron bound organic carbon

Ben J. Fisher1,a, Johan C. Faust1, Oliver W. Moore1, Caroline L. Peacock1, and Christian März1 Ben J. Fisher et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
  • acurrent address: School of GeoSciences, University of Edinburgh, EH9 3FE, UK

Abstract. Association of organic carbon (OC) with reactive iron (FeR) represents an important mechanism by which OC is protected against remineralisation in soils and marine sediments. Recent studies indicate that the molecular structure of organic compounds and/or the identity of associated FeR phases exerts a control on the ability of an OC-FeR complex to be extracted by the citrate-bicarbonate-dithionite (CBD) method. While many variations of this method exist in the literature, these are often uncalibrated to each other, rendering comparisons of OC-FeR values extracted by different method iterations impossible. Here, we created a synthetic ferrihdyrite sample coprecipitated with simple organic structures and subjected these to modifications of the most common CBD method. Method parameters (reagent concentration, time of the extraction and sample preparation methods) were altered and FeR recovery measured to determine which (if any) modifications resulted in the greatest release of FeR from the sediment sample. We provide an assessment of the reducing capacity of Na dithionite in the CBD method and find that the concentration of dithionite deployed can limit OC-FeR extractability for sediments with a high FeR content. Additionally, we show that extending the length of any CBD extraction offers no benefit in removing FeR. Finally, we demonstrate that for synthetic OC-FeR samples, the almost universal technique of freeze drying samples can significantly reduce OC-FeR extractability and we offer insight into how this may translate to environmental samples using Arctic Ocean sediments. These results provide a valuable perspective on how the efficiency of this extraction could be improved to provide a more accurate assessment of sediment OC-FeR content. Accurate determinations of OC-FeR in sediments and soils represents an important step in improving our understanding of, and ability to model, the global carbon cycle.

Ben J. Fisher et al.

 
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Status: closed
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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

Ben J. Fisher et al.

Ben J. Fisher et al.

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Short summary
One way to remove carbon dioxide from the atmosphere is to store it in the seafloor, minerals can act to preserve seafloor carbon by preventing microbes from breaking it down. We can use a chemical method to tell us how much of this seafloor carbon is protected by iron minerals (how much will be preserved). However, different scientists use different versions of this method which makes results hard to compare. Here we make an assessment of these various methods to determine the best approach.
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