[A-CG50] Biogeochemical linkages between the surface ocean and atmosphere

[ACG50-P03] Seasonal variation of the air−sea ice CO₂ flux during MOSAiC expedition in the Central Arctic Ocean

*Daiki Nomura¹, Chamber Team Member MOSAiC (1.Hokkaido University)

Keywords:Sea ice, CO2, Gas exchange

Air–sea ice CO₂ fluxes were measured using an enclosed chamber system several times a month during the MOSAiC Expedition over the ice floe in the Central Arctic Ocean from the end of October 2019 to the end of September 2020. If any new lead ice formation or melt pond water surface was observed, measurements were carried out as "event" on another day of ice coring. We obtained data through the duration of MOSAiC (total 492 measurements). For air−sea ice CO₂ flux, a clear seasonal cycle was observed: during the cold season (<−20°C, March), the frozen lead surfaces were a strong source for atmospheric CO₂, presumably due to high permeability and high CO₂ concentration in lead ice with respect to that of the atmosphere. However, during the warm season ( >0°C, August to September), the melt ponds were a strong sink due to the open water surface providing direct exchange with the atmosphere and a comparatively lower CO₂ concentration with respect to that of atmosphere. The MOSAiC ice floe was a sediment-laden, originating from the Siberian shelf and in second year ice. The ice surface was impermeable, supporting the low magnitude of observed air-ice CO₂ flux. While near zero, a slightly positive trend suggests the degradation of organic matter and high CO₂ concentration in sea ice.