To investigate CO₂ sink capacity in the western Arctic Ocean (north of 65°N), we conducted underway, ship-based observations of partial pressures of CO₂ (pCO₂) and total dissolved inorganic carbon (TCO₂) in surface seawater in early winter (November 2018). From these two properties of the seawater inorganic carbon system, we calculated total alkalinity (TA). In the early winter, surface seawater pCO₂ in most places was lower than atmospheric pCO₂. The weighted mean of the air-sea fluxes of CO₂ were calculated to be -7.5 ± 1.6 mmol m⁻² d⁻¹. The calculated fluxes implied that the area acted as a moderate sink for atmospheric CO₂ in early winter, and its rate of CO₂ uptake was comparable to that (-8.0 ± 1.7 mmol m⁻² d⁻¹) in summer (late August-September 2017). Spatial variations of surface seawater pCO₂ in the early winter could be attributed mostly to conservative changes of TCO₂ and TA, which together accounted for more than 70% of the pCO₂ variations. In the marginal ice zone, however, there was a drawdown of surface seawater pCO₂ by 70-90 matm due to horizontal advection of water with an anomalously high temperature from the Pacific Ocean and its subsequent cooling. We found that TA was an important determinant of the spatial variations of pCO₂ in the western Arctic Ocean because of the conservative nature of the changes of TA and TCO₂ during mixing of water masses. This conservative behavior was observed in both the early winter and summer.