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  • 1. Broder, Lisa
    et al.
    Tesi, Tommaso
    Andersson, August
    Eglinton, Timothy I.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Roos, Per
    Gustafsson, Orjan
    Historical records of organic matter supply and degradation status in the East Siberian Sea2016In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 91, p. 16-30Article in journal (Refereed)
    Abstract [en]

    Destabilization and degradation of permafrost carbon in the Arctic regions could constitute a positive feedback to climate change. A better understanding of its fate upon discharge to the Arctic shelf is therefore needed. In this study, bulk carbon isotopes as well as terrigenous and marine biomarkers were used to construct two centennial records in the East Siberian Sea. Differences in topsoil and Pleistocene Ice Complex Deposit permafrost concentrations, modeled using delta C-13 and Delta C-14, were larger between inner and outer shelf than the changes over time. Similarly, lignin-derived phenol and cutin acid concentrations differed by a factor of ten between the two stations, but did not change significantly over time, consistent with the dual-carbon isotope model. High molecular weight (HMW) n-alkane and n-alkanoic acid concentrations displayed a smaller difference between the two stations (factor of 3-6). By contrast, the fraction for marine OC drastically decreased during burial with a half-life of 19-27 years. Vegetation and degradation proxies suggested supply of highly degraded gymnosperm wood tissues. Lipid Carbon Preference Index (CPI) values indicated more extensively degraded HMW n-alkanes on the outer shelf with no change over time, whereas n-alkanoic acids appeared to be less degraded toward the core top with no large differences between the stations. Taken together, our results show larger across-shelf changes than down-core trends. Further investigation is required to establish whether the observed spatial differences are due to different sources for the two depositional settings or, alternatively, a consequence of hydrodynamic sorting combined with selective degradation during cross-shelf transport. (C) 2015 Elsevier Ltd. All rights reserved.

  • 2. Selver, Ayca Dogrul
    et al.
    Sparkes, Robert B.
    Bischoff, Juliane
    Talbot, Helen M.
    Gustafsson, Orjan
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Boult, Stephen
    van Dongen, Bart E.
    Distributions of bacterial and archaeal membrane lipids in surface sediments reflect differences in input and loss of terrestrial organic carbon along a cross-shelf Arctic transect2015In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 83-84, p. 16-26Article in journal (Refereed)
  • 3. Wilson, Rachel M.
    et al.
    Tfaily, Malak M.
    Rich, Virginia I.
    Keller, Jason K.
    Bridgham, Scott D.
    Zalman, Cassandra Medvedeff
    Meredith, Laura
    Hanson, Paul J.
    Hines, Mark
    Pfeifer-Meister, Laurel
    Saleska, Scott R.
    Crill, Patrick
    Cooper, William T.
    Chanton, Jeff P.
    Kostka, Joel E.
    Hydrogenation of organic matter as a terminal electron sink sustains high CO2:CH4 production ratios during anaerobic decomposition2017In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 112, no Supplement C, p. 22-32Article in journal (Refereed)
    Abstract [en]

    Abstract Once inorganic electron acceptors are depleted, organic matter in anoxic environments decomposes by hydrolysis, fermentation, and methanogenesis, requiring syntrophic interactions between microorganisms to achieve energetic favorability. In this classic anaerobic food chain, methanogenesis represents the terminal electron accepting (TEA) process, ultimately producing equimolar CO2 and CH4 for each molecule of organic matter degraded. However, CO2:CH4 production in Sphagnum-derived, mineral-poor, cellulosic peat often substantially exceeds this 1:1 ratio, even in the absence of measureable inorganic TEAs. Since the oxidation state of C in both cellulose-derived organic matter and acetate is 0, and CO2 has an oxidation state of +4, if CH4 (oxidation state −4) is not produced in equal ratio, then some other compound(s) must balance CO2 production by receiving 4 electrons. Here we present evidence for ubiquitous hydrogenation of diverse unsaturated compounds that appear to serve as organic TEAs in peat, thereby providing the necessary electron balance to sustain CO2:CH4>1. While organic electron acceptors have previously been proposed to drive microbial respiration of organic matter through the reversible reduction of quinone moieties, the hydrogenation mechanism that we propose, by contrast, reduces CC double bonds in organic matter thereby serving as (1) a terminal electron sink, (2) a mechanism for degrading complex unsaturated organic molecules, (3) a potential mechanism to regenerate electron-accepting quinones, and, in some cases, (4) a means to alleviate the toxicity of unsaturated aromatic acids. This mechanism for CO2 generation without concomitant CH4 production has the potential to regulate the global warming potential of peatlands by elevating CO2:CH4 production ratios.

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