EGU2020-3952
https://doi.org/10.5194/egusphere-egu2020-3952
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Exploring the Affinity and Selectivity of Sedimentary Mackinawite (FeS) Towards Natural Organic Matter

Alexandre Tétrault1 and Yves Gélinas2
Alexandre Tétrault and Yves Gélinas
  • 1Concordia University, Montreal, Canada (al_tetra@live.concordia.ca)
  • 2Concordia University, Montreal, Canada (yves.gelinas@concordia.ca)

Marine sediments represent the most important sink for organic matter across geological time spans, in which carbon-containing molecules are sequestered away and can escape remineralization to CO2 by microbial degradation. Strong associations between minerals such as iron oxides and organic matter reaching the seafloor play a fundamental role in this preservation and have been known for some decades. Despite the importance of this protective mechanism in the balances of the global carbon budget, very little is known of the fate of bound organic matter as it is shuttled across the redox gradient into the reducing layers of sediment, particularly with respect to the Fe-OM associations. This study focuses on measuring the selective affinity of ferric and ferrous iron species for various functional groups commonly associated with the degradation products of organic molecules in marine systems as the iron cycles from +3 (oxides: goethite, lepidocrocite and ferrihydrite) to +2 (sulfides: mackinawite) oxidation states. This approach involves following model compounds across an artificial iron redox shuttle while probing Fe-OM bonding via quantitative FTIR and calculating mass balances using elemental analysis. A predicted outcome of this study will be a greater understanding of the fate of mineral-bound organic matter as it traverses the sedimentary redox gradient and the importance of iron sulfides such as mackinawite in their preservation. 

How to cite: Tétrault, A. and Gélinas, Y.: Exploring the Affinity and Selectivity of Sedimentary Mackinawite (FeS) Towards Natural Organic Matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3952, https://doi.org/10.5194/egusphere-egu2020-3952, 2020

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Presentation version 1 – uploaded on 02 May 2020
  • CC1: Comment on EGU2020-3952, Anne-Christin Melcher, 14 May 2020

    Hi, I was hoping you would attend the session during EGU week. I had a question: in regard to part (III) in your methods what do you mean by “cycle to goethite/mackinawite etc)? How do you cycle it? What kind of analysis are you referring to in your scheme 4a,b and c, is it EA-IRMS?

    Are you using different concentration of NaS as sulfide or just one concentration?

    All the best,

    Anne-Christin Melcher

    • AC1: Reply to CC1, Alexandre Tétrault, 14 May 2020

      Hi Anne-Christin,

      Thanks for your comment!  I felt terrible about missing the discussion but I had issues with my connection. 

      To cycle goethite to mackinawite I use Na2S as an abiotic reductant/coprecipitate while maintaining a seawater pH.  I use a slightly more concentrated solution than the stoichiometric 3:2 sulfide/iron ratio just to make sure the reaction proceeds in a reasonable amount of time.

       

      As far as analyses, elemental analysis - isotope ratio mass spec (EA-IRMS) allows us to use 13C as a label and gives us the accuracy to detect very small changes in solid phase carbon concentrations.  I'm also looking at FTIR to try to distinguish bonding mechanisms. 

      I hope that is more clear, thanks again!

      • AC2: Reply to AC1, Alexandre Tétrault, 14 May 2020

        Oh and I meant to ask, do you also work with sediments?

        :)