Preprints
https://doi.org/10.5194/bg-2023-82
https://doi.org/10.5194/bg-2023-82
22 May 2023
 | 22 May 2023
Status: a revised version of this preprint is currently under review for the journal BG.

Central Arctic Ocean surface-atmosphere exchange of CO2 and CH4 constrained by direct measurements

John Prytherch, Sonja Murto, Ian Brown, Adam Ulfsbo, Brett F. Thornton, Volker Brüchert, Michael Tjernström, Anna Lunde Hermansson, Amanda T. Nylund, and Lina A. Holthusen

Abstract. The Central Arctic Ocean’s (CAO) current and future role in the exchange of climate-forcing trace gases with the atmosphere is highly uncertain, in particular the effect of sea ice on the exchange. There are no previously reported direct air-sea methane (CH4) flux estimates from the CAO. We present direct measurements of the air-sea flux of CH4 and carbon dioxide (CO2), as well as air-ice 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. Fluxes and dissolved gas concentrations from surface water were used to determine gas transfer velocities that exhibited a weaker wind speed dependence than existing parameterisations, with a median gas transfer rate in sea-ice leads 2.5 cm hr−1. Average observed CO2 air-sea flux were −7.6 mmol m−2 day−1, and the average air-snow flux −1.1 mmol m−2 day−1. Extrapolating these fluxes and the corresponding sea ice concentrations gives an August and September flux for the CAO of −1.75 mmol m−2 day−1 and a corresponding annual CAO uptake of 126.6 Tg yr−1.

Average observed air-sea CH4 flux of 3.5 μmol m−2 day−1, accounting for sea ice concentration, equates to a CAO flux of 0.35 μmol m−2 day−1, or 9.2 Gg yr−1, lower than previous estimates and implying that the CAO is a very small, << 1 %, contributor to the flux of CH4 to the atmosphere from the Arctic.

John Prytherch et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-82', Richard Sims, 24 Jul 2023
    • AC1: 'Reply on RC1', John Prytherch, 01 Oct 2023
  • RC2: 'Comment on bg-2023-82', B.G.T. Else, 04 Aug 2023
    • AC2: 'Reply on RC2', John Prytherch, 01 Oct 2023

John Prytherch et al.

John Prytherch et al.

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Short summary
We used chamber-flux systems to directly measure methane and carbon dioxide exchange between the ocean or sea ice and the atmosphere during an icebreaker-based expedition to the Central Arctic Ocean in summer 2021. These measurement-based constraints inform climate modeling and carbon budgets. The methane exchange measurements, the first such made in the CAO, are lower than previous estimates and imply that the CAO is an insignificant contributor to Arctic methane emission.
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