Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf

Abstract

Abstract. Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis–gas chromatography–mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC) which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river–ocean transects of surface sediments transition from river-dominated to coastal-erosion-dominated to marine-dominated signatures.

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

“…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. This agrees with previous findings reporting the inflow of nutrient-rich Pacific waters westward up to around 160°E (Anderson et al, 2011;Semiletov et al, 2005;Sparkes et al, 2016;Tesi et al, 2014).…”

“…These numbers and patterns are similar to previous estimates of the terrOC contribution in surface water POC (Semiletov et al, 2012). This agrees with previous findings reporting the inflow of nutrient-rich Pacific waters westward up to around 160°E (Anderson et al, 2011;Semiletov et al, 2005;Sparkes et al, 2016;Tesi et al, 2014). They were highest close to the Lena River delta and northward (roughly along 130°E).…”

“…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).…”

Carbonaceous material export from Siberian permafrost tracked across the Arctic Shelf using Raman spectroscopy

“…Additionally, the East Siberian coastline contains large Ice Complex Deposits (ICD; also known as "Yedoma"). These Plio-Pleistocene permafrost deposits are weakly lithified and rich in well-preserved OC, providing a major influx of sediment and carbon to the Arctic Ocean (Bischoff et al, 2016;Lantuit et al, 2013;Schirrmeister et al, 2008Schirrmeister et al, , 2011Strauss et al, 2012Strauss et al, , 2013Sparkes et al, 2016;Vonk et al, 2010Vonk et al, , 2012.…”

“…The seabed consists of permafrost that developed sub-aerially, was flooded during Holocene sea-level rise and is now being buried by sediment sourced from fluvial and coastal erosion (Kienast et al, 2005). Geochemical studies investigating the sources and offshore distribution of organic matter have noted differences between east and west, nearshore and offshore sections of the shelf (Bischoff et al, 2016;Karlsson et al, 2015;Semiletov et al, 2005;Sparkes et al, 2015Sparkes et al, , 2016Tesi et al, 2014).…”