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

• Published in: Biogeosciences
• Main Authors: Prytherch, John, Murto, Sonja, Brown, Ian, Ulfsbo, Adam, Thornton, Brett F., Brüchert, Volker, Tjernström, Michael, Hermansson, Anna Lunde, Nylund, Amanda T., Holthusen, Lina A.
• Format: Text
• Language: English
• Published: 2024
• Subjects: Arctic; Arctic Ocean; oden; Sea ice
• Online Access: https://doi.org/10.5194/bg-21-671-2024; https://bg.copernicus.org/articles/21/671/2024/

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 ( CH 4 ) and carbon dioxide ( CO 2 ) 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 CO 2 flux estimates and no previously reported direct air–sea CH 4 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 CH 4 and CO 2 , as well as air–snow fluxes of CO 2 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 CH 4 and CO 2 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 CO 2 flux was − 7.6 mmol m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="6add7475d1c0615a24800106f13ac773"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00001.svg" width="67pt" height="13pt" src="bg-21-671-2024-ie00001.png"/> </svg:svg> , and the average air–snow CO 2 flux was − 1.1 mmol m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="8c4b3213a0a8ab1c445432263e63f72b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00002.svg" width="67pt" height="13pt" ...