Abstract. To quantify the air-sea flux of CO₂ in a high-latitude coastal region, we conducted shipboard observations of atmospheric and surface water partial pressures of CO₂ (pCO₂) and total dissolved inorganic carbon (TCO₂) in the Canadian Beaufort Sea (150° W–127° W; 69° N–73° N) in late summer 2000 and 2002. Surface water pCO₂ was lower than atmospheric pCO₂ (2000, 361.0 μatm; 2002, 364.7 μatm), and ranged from 250 to 344 μatm. Accordingly, ΔpCO₂, which is the driving force of the air-sea exchange of CO₂ and is calculated from differences in pCO₂ between the sea surface and the overlying air, was generally negative (potential sink for atmospheric CO₂), although positive ΔpCO₂ values (source) were also found locally. Distributions of surface water pCO₂, as well as those of ΔpCO₂ and CO₂ flux, were controlled mainly by water mixing related to river discharge. The air-sea fluxes of CO₂ were −15.0 and −16.8 mmol m⁻² d⁻¹ on average in 2000 and 2002, respectively, implying that the area acted as a moderate sink for atmospheric CO₂. The air-to-sea net CO₂ flux in an extended area of the western Arctic Ocean (411 000 km²) during the ice-free season (=100 days) was calculated as 10.2±7.7 mmol m⁻² d⁻¹, equivalent to a regional CO₂ sink of 5.0±3.8 Tg C. The estimated buffer factor was 1.5, indicating that the area is a high-capacity CO₂ sink. These CO₂ flux estimates will need to be revised because they probably include a bias due to the vertical gradients of physical and chemical properties characteristic in the region, which have not yet been adequately considered.