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Abstract Shifting baselines in the Arctic atmosphere‐sea ice‐ocean system have significant potential to alter biogeochemical cycling and ecosystem dynamics. In particular, the impact of increased open water duration on lower trophic level productivity and biological CO₂sequestration is poorly understood. Using high‐resolution observations of surface seawater dissolved O₂/Ar andpCO₂collected in the Pacific Arctic in October 2011 and 2012, we evaluate spatial variability in biological metabolic status (autotrophy vs heterotrophy) as constrained by O₂/Ar saturation (∆O₂/Ar) as well as the relationship between net biological production and the sea‐air gradient ofpCO₂(∆pCO₂). We find a robust relationship between∆pCO₂and∆O₂/Ar(correlation coefficient of −0.74 and −0.61 for 2011 and 2012, respectively), which suggests that biological production in the late open water season is an important determinant of the air‐sea CO₂gradient at a timeframe of maximal ocean uptake for CO₂in this region. Patchiness in biological production as indicated by∆O₂/Arsuggests spatially variable nutrient supply mechanisms supporting late season growth amidst a generally strongly stratified and nutrient‐limited condition.