| High latitude oceans are major sinks for atmospheric carbon dioxide (CO2) but so far the extensive sea ice cover has been considered inert with respect to gas exchange with the atmosphere. There are growing observations that sea ice exchanges CO2 directly with the atmosphere, highlighting the need in understanding CO2 dynamics within sea ice. In spring ice, at least 6 processes can affect CO2 dynamics, namely: (1) temperature change and (2) related melting of ice crystal, (3) biological activity, (4) dissolution of carbonate minerals, (5) internal convection and (6) air-ice gases exchanges. Each process can significantly impact inorganic carbon dynamics with opposing and compensating effects.
To explore the relationships between sea ice-specific biogeochemical processes and spring CO2 dynamics, we carried out 5 surveys in Antarctic and Arctic land fast sea ice, and first year and multiyear pack ice. We tried to assess the role played by none-transport processes and give some clues of the impact of the others. In sea ice, intense growth of microalgae is commonly observed and acts to significantly decrease the partial pressure of CO2 (pCO2) and promote the uptake of atmospheric CO2 by Antarctic sea ice. Biological mediated decrease of pCO2 is significantly enhanced by superimposed none-transport abiotic processes (temperature change and related melting of ice crystals, dissolution of carbonate minerals) while transport processes (internal convection and air-ice gas exchange) counteract the observed decrease of pCO2.
Independent and indirect estimates of the potential CO2 fluxes driven by these processes are consistent with measurements of air-ice CO2 exchanges and indicate that air-ice CO2 transfer contribute significantly to the overall CO2 sink of the Southern Ocean. |