Effects of snow, snowmelting and refreezing processes on air–sea-ice CO₂ flux

The air–sea-ice CO 2 flux was measured in the ice-covered Saroma-ko, a lagoon on the northeastern coast of Hokkaido, Japan, using a chamber technique. The air–sea-ice CO 2 flux ranged from −1.8 to +0.5 mg C m −2 h −1 (where negative values indicate a sink for atmospheric CO 2 ). The partial pressure of CO 2 (pCO 2 ) in the brine of sea ice was substantially lower than that of the atmosphere, primarily because of the influence of the under-ice plume from the Saromabetsu river located in the southeastern part of the lagoon. This suggests that the brine had the ability to take up atmospheric CO 2 into the sea ice. However, the snow deposited over the sea ice and the superimposed ice that formed from snowmelting and refreezing partially blocked CO 2 diffusion, acting as an impermeable medium for CO 2 transfer. Our results suggest that the air–sea-ice CO 2 flux was dependent not only on the difference in pCO 2 between the brine and the overlying air, but also on the status of the ice surface. These results provide the necessary evidence for evaluation of the gas exchange processes in ice-covered seas.