Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 114, Issue 21, Pages 5355-5360Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1618926114
Keywords
methane; carbon dioxide; greenhouse gas emissions; marine biogeochemistry; Arctic Ocean
Categories
Funding
- USGS
- US Department of Energy [DE-FE0002911, DE-FE0005806]
- University of Tromso - The Arctic University of Norway
- Research Council of Norway
- Research Council of Norway through its Centres of Excellence [223259]
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Continued warming of the Arctic Ocean in coming decades is projected to trigger the release of teragrams (1 Tg = 10(6) tons) of methane from thawing subsea permafrost on shallow continental shelves and dissociation of methane hydrate on upper continental slopes. On the shallow shelves (< 100 m water depth), methane released from the seafloor may reach the atmosphere and potentially amplify global warming. On the other hand, biological uptake of carbon dioxide (CO2) has the potential to offset the positive warming potential of emitted methane, a process that has not received detailed consideration for these settings. Continuous sea-air gas flux data collected over a shallow ebullitive methane seep field on the Svalbard margin reveal atmospheric CO2 uptake rates (-33,300 +/-7,900 mu mol m(-2) . d(-1)) twice that of surrounding waters and similar to 1,900 times greater than the diffusive sea-air methane efflux (17.3 +/- 4.8 mu mol m(-2) . d(-1)). The negative radiative forcing expected from this CO2 uptake is up to 231 times greater than the positive radiative forcing from the methane emissions. Surface water characteristics (e.g., high dissolved oxygen, high pH, and enrichment of C-13 in CO2) indicate that upwelling of cold, nutrient-rich water from near the seafloor accompanies methane emissions and stimulates CO2 consumption by photosynthesizing phytoplankton. These findings challenge the widely held perception that areas characterized by shallow-water methane seeps and/or strongly elevated sea-air methane flux always increase the global atmospheric greenhouse gas burden.
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