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Sci Adv. 2018 Jan 17;4(1):eaao4842. doi: 10.1126/sciadv.aao4842. eCollection 2018 Jan.

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf.

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Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA.
Department of Environmental Science and Analytical Chemistry, Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory, Department of Earth System Science, University of California, Irvine, Irvine, CA 92697, USA.
Large Lakes Observatory, University of Minnesota Duluth, Duluth, MN 55812, USA.
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA.
U.S. Geological Survey, Woods Hole, MA 02543, USA.
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA.
Global Monitoring Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA.
Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA.


In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon-sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere.

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