THE EFFECTS OF SEA ICE ON GAS TRANSFER VELOCITIES AND GAS PARTITIONING BETWEEN WATER AND SEA ICE

Abstract

Sea ice is a defining feature of the polar geochemical ecosystem. It is a critical substrate for marine biota and it regulates ocean-atmosphere exchange, including the exchange of biogenic gases such as CO2 and CH4. In this study, we are concerned with determining the rates and pathways that govern gas transport around sea ice. N2O, SF6 and 3He were used as inert tracers of the transport and exchange processes taking place between the water, ice and air in a laboratory sea ice experiment. Using gas budgets and gradients we were able to estimate these transport rates as a function of both water current speed and wind speed. We observed divergence in the mass balance of each gas, but most of these patterns follow consistent behavior based on differences in gas solubility and molecular diffusivity as well as the molecular size of each gas. Diffusive flux of the gases into the ice was found to be on the scale of 10-6 cm2 s-1, which is nearly the same as molecular diffusion in water and too slow to be of consequence for air-sea gas transport. In contrast, we observed increasing trends in the air-sea gas transfer velocities (keff) as a function of increased forcing. Gas transfer rates responded positively to both wind and water current speed as well as the combination of the two, indicating that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice.