Annual cycle of air‐sea CO 2 exchange in an Arctic Polynya Region

During the Canadian International Polar Year projects in the Cape Bathurst polynya region, we measured a near–complete annual cycle of sea surface CO 2 ( p CO 2 sw ), atmospheric CO 2 ( p CO 2 atm ), sea surface temperature (SST), salinity (S), and wind speed ( U ). In this paper, we combine these data with ancillary measurements of sea ice concentration ( C i ) to estimate the mean annual (September 2007–September 2008) air–sea CO 2 exchange for the region. For the non–freezing seasons the exchange was calculated using a standard bulk aerodynamic approach, whereas during the freezing seasons we extrapolated eddy covariance measurements of CO 2 exchange. Our results show that in 2007–08 the region served as a net sink of atmospheric CO 2 at a mean rate of ‐10.1 ± 6.5 mmol m − 2 d − 1 . The strongest calculated uptake rate occurred in the fall when wind velocities were highest, p CO 2 sw was significantly lower than p CO 2 atm , and ice was beginning to form. Atmospheric CO 2 uptake was calculated to occur (at lower rates) throughout the rest of the year, except for a brief period of outgassing during late July. Using archival U , C i , and p CO 2 sw data for the region, we found that winds in 2007–08 were 25–35 % stronger than the decadal mean and were predominately easterly, which appears to have induced a relatively late freeze–up (by ∼ 3 weeks relative to mean conditions) and an early polynya opening (by ∼ 4 weeks). In turn, these conditions may have given rise to a higher CO 2 uptake than normal. Estimated winter CO 2 exchange through leads and small polynya openings made up more than 50% of the total CO 2 uptake, consistent with recent observations of enhanced CO 2 exchange associated with open water components of the winter icescape. Our calculations for the Cape Bathurst polynya region are consistent with past studies that estimated the total winter CO 2 uptake in Arctic coastal polynyas to be on the order of 10 12 g C yr − 1 .