GDGT distributions in the East Siberian Sea: implications for organic carbon export, burial and degradation

R. B. Sparkes, A. DogŸrul Selver, J. Bischoff, H. M. Talbot, O– Gustafsson, I. P. Semiletov, O. V. Dudarev, Bart Van Dongen

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    Abstract

    Siberian permafrost contains a globally-significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate-carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in "Yedoma" permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the Branched and Isoprenoidal Tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting that OC on the shelf is not only sourced from fluvial erosion, but that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43% of the OC and 87% of the mineral sediment to the ESAS, but that rivers deliver 72% of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.
    Original languageEnglish
    Pages (from-to)3753-3768
    Number of pages15
    JournalBiogeosciences
    Volume12
    DOIs
    Publication statusPublished - 12 Jan 2015

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