Central Arctic Ocean surface–atmosphere exchange of CO 2 and CH 4 constrained by direct measurements

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

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 (inline-formulaCH4) and carbon dioxide (inline-formulaCO2) 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 inline-formulaCO2 flux estimates and no previously reported direct air–sea inline-formulaCH4 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 inline-formulaCH4 and inline-formulaCO2, as well as air–snow fluxes of inline-formulaCO2 in the summertime CAO north of 82.5inline-formula N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021.

Measurements of air–sea inline-formulaCH4 and inline-formulaCO2 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 inline-formulacm h−1 applicable over the observed 10 inline-formulam wind speed range (1–11 inline-formulam s−1). The average observed air–sea inline-formulaCO2 flux was inline-formula−7.6 inline-formula M20inlinescrollmathml unit normal mmol nobreak0.125em normal m - normal 2 0.125emnobreak normal d - normal 1 67pt13ptsvg-formulamathimg6add7475d1c0615a24800106f13ac773 bg-21-671-2024-ie00001.svg67pt13ptbg-21-671-2024-ie00001.png , and the average air–snow inline-formulaCO2 flux was inline-formula−1.1 inline-formula M23inlinescrollmathml unit normal mmol 0.125emnobreak normal m - normal 2 nobreak0.125em normal d - normal 1 67pt13ptsvg-formulamathimg8c4b3213a0a8ab1c445432263e63f72b bg-21-671-2024-ie00002.svg67pt13ptbg-21-671-2024-ie00002.png . Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of inline-formula−1.75 inline-formula M25inlinescrollmathml unit normal mmol 0.125emnobreak normal m - normal 2 nobreak0.125em normal d - normal 1 67pt13ptsvg-formulamathimg7577e0735720859b6cef6768466f7d08 bg-21-671-2024-ie00003.svg67pt13ptbg-21-671-2024-ie00003.png , within the range of previous indirect estimates.

The average observed air–sea inline-formulaCH4 flux of 3.5 inline-formula M27inlinescrollmathml unit normal µ normal mol 0.125emnobreak normal m - normal 2 0.125emnobreak normal d - normal 1 64pt15ptsvg-formulamathimgd4b681ee9159c6466a531df63bb9f062 bg-21-671-2024-ie00004.svg64pt15ptbg-21-671-2024-ie00004.png , accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 inline-formula M28inlinescrollmathml unit normal µ normal mol 0.125emnobreak normal m - normal 2 nobreak0.125em normal d - normal 1 64pt15ptsvg-formulamathimgf92bc3adeb03ab641b77d252d5bbc101 bg-21-671-2024-ie00005.svg64pt15ptbg-21-671-2024-ie00005.png , lower than previous estimates and implying that the CAO is a very small (inline-formula≪ 1 %) contributor to the Arctic flux of inline-formulaCH4 to the atmosphere.



Prytherch, John / Murto, Sonja / Brown, Ian / et al: Central Arctic Ocean surface–atmosphere exchange of CO2 and CH4 constrained by direct measurements. 2024. Copernicus Publications.


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