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

• Published in: Nature
• Main Authors: Hilton, Robert G., Galy, Valier, Gaillardet, Jérôme, Dellinger, Mathieu, Bryant, Charlotte, O'Regan, Matt, Gröcke, Darren R., Coxall, Helen, Bouchez, Julien, Calmels, Damien
• Other Authors: Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Arctic Ocean; Mackenzie River; Mackenzie river; permafrost
• Online Access: https://insu.hal.science/insu-03579674; https://insu.hal.science/insu-03579674/document; https://insu.hal.science/insu-03579674/file/Hilton-RG-etal_revised-for-Nature-DRO.pdf; https://doi.org/10.1038/nature14653

International audience 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 (CO 2 ) 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 CO 2 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 teragrams of carbon per year from the Mackenzie River, which is three times the CO 2 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 CO 2 sink.