We carried out a 6 month study that aimed to robustly track CO₂ exchange between landfast sea ice and the atmosphere during the winter and spring season. A meteorological mast equipped for eddy-covariance measurements was installed on landfast sea ice near Barrow (Alaska), 1 km off the coast, from the end of January 2009 to the beginning of June 2009, before ice break-up. These data were supported by continuous measurements of solar radiation, snow depth, ice thickness and temperature profile in the ice. Biogeochemical data necessary for the understanding of the CO₂ dynamics in sea ice were obtained through discrete ice coring. Two regimes were detected for the CO₂ exchanges linked with the status of the sea ice: a winter regime and a spring summer regime. From 27 March onwards brine volume at the sea-ice–snow interface was above the threshold of permeability for liquid according to Golden and others (1998). During this period, we observed some conspicuous CO₂ fluxes events tightly linked to wind speed. The flux was directed from the sea ice to the atmosphere and reached up to 0.6 µmol m^–2 s^–1 (51.8 mmol m^–2 d^–1). This flux to the atmosphere is expected as sea ice at the air interface is permeable during a large part of the period and brines are oversaturated compared with the atmosphere. CO₂ may accumulate in the snow layer which thus acts as a buffer that is flushed under occurrence of high wind speeds and associated pressure pumping. During the spring/summer period, i.e. from 27 April onwards, we observed a marked increase in sea-ice temperature. Temperature profiles suggest that convective events occurred within the ice cover between 27 April and 5 May. Within these convective events, two regimes were observed. First, for a period of 5 days, pCO₂ was still above the threshold of saturation and CO₂ fluxes were still mainly positive but lower than in the winter period, ranging from 0.1 to 0.2 µmol m^–2 s^–1. This flux was only moderately controlled by wind speed perhaps due to the reduced snow cover. Further temperature increase led to a second flux regime where pCO₂ of the brines were undersatured and sea ice shifted from a source to a sink of CO₂ for the atmosphere, ranging from 0.0 to 0.1 µmol m^–2 s^–1. These latter fluxes showed a diurnal pattern with no exchange during the night and downward fluxes during the day.