Biological productivity along Line P in the subarctic northeast Pacific: In situ versus incubation-based methods

[1] We compared net community production determined from an in situ O₂/Ar mass balance (O₂/Ar-NCP) with incubation measurements of new and primary production in the subarctic northeast Pacific. In situ O₂/Ar-NCP was strongly correlated to new production from 24-h¹⁵NO₃⁻ uptake integrated over the mixed layer (¹⁵N-NewP), if measurements were separated into high and low-productivity conditions. Under high-productivity conditions, O₂/Ar-NCP estimates were similar to¹⁵N-NewP, whereas under low productivity conditions O₂/Ar-NCP was up to two times higher than¹⁵N-NewP. The relationship between O₂/Ar-NCP and 24-h¹³C primary production (¹³C-PP) was more variable, but with a consistent mean O₂/Ar-NCP:¹³C-PP ratio of 0.52 ± 0.17 when only low-productivity, summer measurements were considered. This relationship with primary production is perturbed by high productivity events such as a late-summer, iron-stimulated bloom observed at the offshore stations. Finally, we show that diapycnal mixing usually dominates the O₂/Ar mass balance in winter in the subarctic Pacific, preventing the determination of NCP by the O₂/Ar method at that time, except for one unusual stratification event in February 2007.