Articles | Volume 10, issue 5
The Cryosphere, 10, 2485–2500, 2016

Special issue: Climate–carbon–cryosphere interactions in the...

The Cryosphere, 10, 2485–2500, 2016

Research article 24 Oct 2016

Research article | 24 Oct 2016

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

Robert B. Sparkes1,2, Ayça Doğrul Selver1,3, Örjan Gustafsson4, Igor P. Semiletov5,6,7, Negar Haghipour8, Lukas Wacker9, Timothy I. Eglinton8, Helen M. Talbot10, and Bart E. van Dongen1 Robert B. Sparkes et al.
  • 1School of Earth and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, University of Manchester, Manchester, UK
  • 2School of Science and the Environment, Manchester Metropolitan University, Manchester, UK
  • 3Balıkesir University, Geological Engineering Department, Balıkesir, Turkey
  • 4Department of Environmental Science and Analytical Chemistry (ACES) and the Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 5Pacific Oceanological Institute Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
  • 6International Arctic Research Center, University of Alaska, Fairbanks, USA
  • 7National Tomsk Research Polytechnic University, Tomsk, Russia
  • 8Geological Institute, ETH Zurich, Zurich, Switzerland
  • 9Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland
  • 10School of Civil Engineering and Geosciences, Newcastle University, Newcastle, UK

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.

Short summary
The permafrost in eastern Siberia contains large amounts of carbon frozen in soils and sediments. Continuing global warming is thawing the permafrost and releasing carbon to the Arctic Ocean. We used pyrolysis-GCMS, a chemical fingerprinting technique, to study the types of carbon being deposited on the continental shelf. We found large amounts of permafrost-sourced carbon being deposited up to 200 km offshore.