Central Arctic Ocean surface–atmosphere exchange of CO2 and CH4 constrained by direct measurements
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Published:2024-02-02
Issue:2
Volume:21
Page:671-688
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Prytherch JohnORCID, Murto SonjaORCID, Brown Ian, Ulfsbo AdamORCID, Thornton Brett F.ORCID, Brüchert VolkerORCID, Tjernström MichaelORCID, Hermansson Anna Lunde, Nylund Amanda T.ORCID, Holthusen Lina A.ORCID
Abstract
Abstract. The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air–sea CO2 flux estimates and no previously reported direct air–sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air–sea flux of CH4 and CO2, as well as air–snow fluxes of CO2 in the summertime CAO north of 82.5∘ N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of air–sea CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden, and air–snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 cm h−1 applicable over the observed 10 m wind speed range (1–11 m s−1). The average observed air–sea CO2 flux was −7.6 mmolm-2d-1, and the average air–snow CO2 flux was −1.1 mmolm-2d-1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of −1.75 mmolm-2d-1, within the range of previous indirect estimates. The average observed air–sea CH4 flux of 3.5 µmolm-2d-1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 µmolm-2d-1, lower than previous estimates and implying that the CAO is a very small (≪ 1 %) contributor to the Arctic flux of CH4 to the atmosphere.
Funder
Knut och Alice Wallenbergs Stiftelse Svenska Forskningsrådet Formas Hasselbladstiftelsen National Science Foundation
Publisher
Copernicus GmbH
Reference80 articles.
1. Ahmed, M. M. M., Else, B. G. T., Capelle, D., Miller, L. A., and Papakyriakou, T.: Underestimation of surface pCO2 and air–sea CO2 fluxes due to freshwater stratification in an Arctic shelf sea, Hudson Bay, Elementa: Science of the Anthropocene, 8, 084, https://doi.org/10.1525/elementa.084, 2020. 2. Bastviken, D., Ejlertsson, J., Sundh, I., and Tranvik, L.: METHANE AS A SOURCE OF CARBON AND ENERGY FOR LAKE PELAGIC FOOD WEBS, Ecology, 84, 969–981, https://doi.org/10.1890/0012-9658(2003)084[0969:maasoc]2.0.co;2, 2003. 3. Bates, N. R. and Mathis, J. T.: The Arctic Ocean marine carbon cycle: evaluation of air-sea CO2 exchanges, ocean acidification impacts and potential feedbacks, Biogeosciences, 6, 2433–2459, https://doi.org/10.5194/bg-6-2433-2009, 2009. 4. Bates, N. R., Moran, S. B., Hansell, D. A., and Mathis, J. T.: An increasing CO2 sink in the Arctic Ocean due to sea-ice loss, Geophys. Res. Lett., 33, L23609, https://doi.org/10.1029/2006gl027028, 2006. 5. Bigdeli, A., Hara, T., Loose, B., and Nguyen, A. T.: Wave Attenuation and Gas Exchange Velocity in Marginal Sea Ice Zone, J. Geophys. Res.-Oceans, 123, 2293–2304, https://doi.org/10.1002/2017jc013380, 2018.
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