GDGT distributions on the East Siberian Arctic Shelf: implications for organic carbon export, burial and degradation

Abstract

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 "ice complex" 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 not only that OC on the shelf is sourced from fluvial erosion but also 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.

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

“…They were highest close to the Lena River delta and northward (roughly along 130°E). This also agrees with the patterns reported for terrestrial biomarkers such as lignin phenols (e.g., Bröder, Tesi, Andersson, et al, 2016;Karlsson et al, 2014;Tesi et al, 2014) and solvent-extractable lipids (e.g., Bischoff et al, 2016;Bröder, Tesi, Andersson, et al, 2016;Doğrul Selver et al, 2015;Karlsson et al, 2011Karlsson et al, , 2014Sparkes et al, 2015). The comparison of the distribution of bulk OC with terrOC revealed that the high OC concentrations on the outer eastern East Siberian Sea shelf are probably to a large part caused by marine primary production, since terrOC concentrations in that area are rather low.…”

“…Earlier investigations of terrOC in Arctic margin surface sediments reported a strong decrease of terrigenous biomarker concentrations with increasing water depth/distance from the shore for the East Siberian Arctic Shelf (Bischoff et al, 2016;Bröder, Tesi, Salvadó, et al, 2016;Doğrul Selver et al, 2015;Sparkes et al, 2015Sparkes et al, , 2016Tesi et al, 2014;Vonk et al, 2010) and parts of the North American Arctic margin (Goni et al, 2013). The extent of terrOC degradation appears to be depending on its exposure to oxygen, which in turn is a function of the sediment transport time (e.g., Keil et al, 2004;Mollenhauer et al, 2007).…”

Distribution of branched GDGTs in surface sediments from the Colville River, Alaska: Implications for the MBT′/CBT paleothermometer in Arctic marine sediments

“…[] observed increasing contributions of shoreline‐derived TOC (total organic carbon) with distance from the Colville Delta (ranging from 15% at SL2 to 85% at SL6); however, temperature reconstructions within Simpson Lagoon do not exhibit significant changes with distance from the river mouth. Furthermore, recent investigations of East Siberian Arctic Shelf sediments and the adjacent terrestrial environments have demonstrated that brGDGT concentrations in the Arctic shoreline bluffs are significantly lower than concentrations present in catchment soils, rivers, and marine sediments [ Peterse et al ., ; Dogrul Selver et al ., ; Sparkes et al ., ]. Sparkes et al .…”

“…Sparkes et al . [] found that despite large contributions of organic carbon delivered to the East Siberian Arctic Shelf via coastal erosion (comprising ~50% of marine sediment TOC), nearly 75% of brGDGTs delivered to the shelf were river derived, leading the authors to suggest that brGDGTs may be applicable as a tracer for fluvial TOC in complex Arctic environments. However, marine sediments in the Yenisei Gulf that are removed from the direct influence of the Yenisei River outflow have been found to display brGDGT distributions comparable to the Arctic shoreline sediments [ De Jonge et al ., ].…”

“…In such systems aquatic brGDGT production is likely to be minimized, leading to a signal that is dominated by terrigenous brGDGT contributions. However, the use of the MBT/CBT paleothermometer in fluvial and marine sediments may also be complicated by the influx of sediment eroded from aged sediment deposits containing brGDGT distributions characteristic of the temperature/pH conditions at the time of soil formation [ De Jonge et al ., ; Dogrul Selver et al ., ; Sparkes et al ., ]. The contribution of these aged‐brGDGTs to nearshore marine sediments may be particularly significant in the Arctic, as the rates of shoreline retreat/coastal erosion are among the highest in the world [ Rachold et al ., ; Jones et al ., ].…”