Currents and convection cause enhanced gas exchange in the ice-water boundary layer

The presence of sea ice acts as a physical barrier for air-sea exchange. On the other hand it creates additional turbulence due to current shear and convection during ice formation. We present results from a laboratory study that demonstrate how shear and convection in the ice-ocean boundary layer can lead to significant gas exchange. In the absence of wind, water currents beneath the ice of 0.23m s^-1 produced a gas transfer velocity (k) of 2.8m d^-1, equivalent to k produced by a wind speed of 7m s^-1 over the open ocean. Convection caused by air-sea heat exchange also increased k of as much as 131%compared to k produced by current shear alone. When wind and currents were combined, k increased, up to 7.6m d^-1, greater than k produced by wind or currents alone, but gas exchange forcing by wind produced mixed results in these experiments. As an aggregate, these experiments indicate that using a wind speed parametrisation to estimate k in the sea ice zone may underestimate k by ca. 50 % for wind speeds < 8m s^-1.