Carbon monoxide (CO) in the marine boundary layer, surface waters, and water column was measured along the western limb of the North Pacific from the western North Pacific to the Bering Sea during summer 2012. Using these observations, we estimated the CO budget in the surface mixed layer for two distinct regimes: the western North Pacific (NP) and the Bering Sea (BS). CO photochemical production rates were 27 (±3) and 26 (±2) µmol m⁻² d⁻¹, while microbial consumption rates were 24 (±5) and 63 (±19) µmol m⁻² d⁻¹ in the NP and BS, respectively. In both regions, photochemical production and microbial consumption were the dominant components of the marine CO budget, whereas air–sea gas exchange and downward mixing remained negligible. The CO budget in the NP was nearly balanced, whereas microbial consumption exceeded production in the BS, indicating a substantial imbalance. This imbalance is likely compensated by external physical transport processes such as lateral advection, subduction, or ventilation. Moreover, the increase in CO column burden was consistent with the budget imbalance, highlighting the important role of physical transport in regulating marine CO dynamics. These results show that physical transport can be a key control on CO cycling in the western North Pacific and the Bering Sea.

marine carbon monoxide,western North Pacific,the Bering Sea,physical transport,mixed-layer budget