Letter | Published:

Erosion of organic carbon in the Arctic as a geological carbon dioxide sink

Nature volume 524, pages 8487 (06 August 2015) | Download Citation

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Abstract

Soils of the northern high latitudes store carbon over millennial timescales (thousands of years) and contain approximately double the carbon stock of the atmosphere1,2,3. Warming and associated permafrost thaw can expose soil organic carbon and result in mineralization and carbon dioxide (CO2) release4,5,6. However, some of this soil organic carbon may be eroded and transferred to rivers7,8,9. If it escapes degradation during river transport and is buried in marine sediments, then it can contribute to a longer-term (more than ten thousand years), geological CO2 sink8,9,10. Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers at high latitudes remains poorly constrained. Here, we quantify the source of POC in the Mackenzie River, the main sediment supplier to the Arctic Ocean11,12, and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios to correct for rock-derived POC10,13,14. Our samples reveal that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5,800 ± 800 years, much older than the POC in large tropical rivers13,14. From the measured biospheric POC content and variability in annual sediment yield15, we calculate a biospheric POC flux of teragrams of carbon per year from the Mackenzie River, which is three times the CO2 drawdown by silicate weathering in this basin16. Offshore, we find evidence for efficient terrestrial organic carbon burial over the Holocene period, suggesting that erosion of organic carbon-rich, high-latitude soils may result in an important geological CO2 sink.

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Acknowledgements

Radiocarbon measurements were funded by the Natural Environment Research Council (NERC), UK (Allocation 1611.0312) to R.G.H and C.B. Fieldwork was funded by CNRS (OXYMORE and CANNIBALT) to J.G. and R.G.H., the Woods Hole Oceanographic Institution Arctic Research Initiative to V.G. and an Early Career Research Grant by the British Society for Geomorphology to R.G.H. V.G. was supported by the US National Science Foundation (OCE-0928582) and H.C. by a Royal Society University Fellowship. The research was carried out under Scientific Research Licence No. 14802 issued by the Aurora Research Centre, who we thank for logistical support (in particular D. Ross and J. Gareis). We also thank I. Peters for preparation of offshore borehole samples, C. Johnson, X. Philippon and M. Bollard for analytical assistance, E. Tipper and K. Hilton for field assistance and discussions and D. Ofukany, G. Lennie, R. Wedel and R. Pilling of Environment Canada for loan of equipment.

Author information

Affiliations

  1. Department of Geography, Durham University, South Road, Durham DH1 3LE, UK

    • Robert G. Hilton
  2. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543-1050, USA

    • Valier Galy
  3. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Universite Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France

    • Jérôme Gaillardet
    • , Mathieu Dellinger
    •  & Julien Bouchez
  4. NERC Radiocarbon Facility, East Kilbride G75 OQF, UK

    • Charlotte Bryant
  5. Department of Geological Sciences, Stockholm University, Stockholm, SE-106 91, Sweden

    • Matt O'Regan
    •  & Helen Coxall
  6. Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK

    • Darren R. Gröcke
  7. Université Paris-Sud, Laboratoire GEOPS, UMR 8148–CNRS, Orsay, F-91405, France

    • Damien Calmels

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Contributions

R.G.H., V.G. and J.G. conceived the study and R.G.H., J.B., D.C., V.G. and M.D. designed the fieldwork and collected the river samples. M.O. and H.C. collected sediment and carbonate data from the offshore borehole. R.G.H., V.G., M.D., C.B. and D.G. processed the samples and carried out the geochemical analyses. R.G.H. wrote the manuscript with input from all co-authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Robert G. Hilton.

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https://doi.org/10.1038/nature14653

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