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

• Published in: Global biogeochemical cycles Vol. 26; no. 3
• Main Authors: Giesbrecht, Karina E., Hamme, Roberta C., Emerson, Steven R.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.09.2012; American Geophysical Union
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; carbon export; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects; Geochemistry; method comparison; ocean productivity; subarctic northeast Pacific; Synecology; Pacific Ocean; Northeast Pacific; North Pacific; mass balance; Incubation; stratification; mixing; Net production; Subpolar zone; in situ; Biological productivity; Offshore; Bloom; argon; iron; Ratio; primary productivity
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2012GB004349

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. Key Points Diapycnal mixing dominates oxygen mass balance as the mixed layer nears oxycline In situ net community production was similar to or exceeded nitrate uptake Net community production was about half of primary production in summer