title: Erosion of organic carbon in the Arctic as a geological carbon dioxide sink.
abstract: Soils of the northern high latitudes store carbon over millennial timescales (thousands of years) and contain approximately double the carbon stock of the atmosphere. Warming and associated permafrost thaw can expose soil organic carbon and result in mineralization and carbon dioxide (CO2) release. However, some of this soil organic carbon may be eroded and transferred to rivers. 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 sink. 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 Ocean, and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios to correct for rock-derived POC. 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 rivers. From the measured biospheric POC content and variability in annual sediment yield, we calculate a biospheric POC flux of 2.2(+1.3)(-0.9) teragrams of carbon per year from the Mackenzie River, which is three times the CO2 drawdown by silicate weathering in this basin. 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.
authors.affiliation: Department of Geography, Durham University, South Road, Durham DH1 3LE, UK.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Hilton
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543-1050, USA.
authors.forename: Valier
authors.initials: V
authors.lastname: Galy
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Universite Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Gaillardet
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Universite Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Dellinger
authors.affiliation: NERC Radiocarbon Facility, East Kilbride G75 OQF, UK.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Bryant
authors.affiliation: Department of Geological Sciences, Stockholm University, Stockholm, SE-106 91, Sweden.
authors.forename: Matt
authors.initials: M
authors.lastname: O'Regan
authors.affiliation: Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK.
authors.forename: Darren R
authors.initials: DR
authors.lastname: Gröcke
authors.affiliation: Department of Geological Sciences, Stockholm University, Stockholm, SE-106 91, Sweden.
authors.forename: Helen
authors.initials: H
authors.lastname: Coxall
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Universite Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Bouchez
authors.affiliation: Université Paris-Sud, Laboratoire GEOPS, UMR 8148-CNRS, Orsay, F-91405, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Calmels
mesh_terms: D001110:Arctic Regions; D001272:Atmosphere / Q000737:chemistry; D002244:Carbon / Q000032:analysis*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000032:analysis*; D057965:Carbon Sequestration; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D052638:Particulate Matter / Q000032:analysis / Q000737:chemistry; D045483:Rivers / Q000737:chemistry; D017640:Silicates / Q000032:analysis; D012987:Soil / Q000737:chemistry; D013997:Time Factors; D014329:Tropical Climate
chemical_list: D052638:Particulate Matter; D017640:Silicates; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon