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

We compared net community production determined from an in situ O-2/Ar mass balance (O-2/Ar-NCP) with incubation measurements of new and primary production in the subarctic northeast Pacific. In situ O-2/Ar-NCP was strongly correlated to new production from 24-h (NO3-)-N-15 uptake integrated over the mixed layer (N-15-NewP), if measurements were separated into high and low-productivity conditions. Under high-productivity conditions, O-2/Ar-NCP estimates were similar to N-15-NewP, whereas under low productivity conditions O-2/Ar-NCP was up to two times higher than N-15-NewP. The relationship between O-2/Ar-NCP and 24-h C-13 primary production (C-13-PP) was more variable, but with a consistent mean O-2/Ar-NCP: C-13-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 O-2/Ar mass balance in winter in the subarctic Pacific, preventing the determination of NCP by the O-2/Ar method at that time, except for one unusual stratification event in February 2007.