High-resolution estimates of net community production and air-sea CO₂ flux in the northeast Pacific

[1] Rates of net community production (NCP) and air-sea CO₂ flux in the Northeast Pacific subarctic, transition zone and subtropical regions (22°N–50°N, 145°W–152°W) were determined on a cruise in August–September 2008 by continuous measurement of surface values of the ratio of dissolved oxygen to argon (O₂/Ar) and the partial pressure of CO₂ (pCO₂). These estimates were compared with simultaneous measurements of sea surface temperature (SST), chlorophyll-a (chl-a), flow cytometry, and discrete surface nutrient concentrations. NCP and CO₂ influx were greatest in the subarctic (45°N–50°N, 25.8 ± 4.6 and 4.1 ± 0.9 mmol C m⁻² d⁻¹) and northern transition zone (40°N–45°N, 17.1 ± 4.4 and 2.1 ± 0.5 mmol C m⁻² d⁻¹), with mean NCP ∼6–8× greater than mean CO₂ invasion (error estimates reflect 1 σ confidence intervals). Contrastingly, the southern transition zone (32°N–40°N) and subtropics (22°N–32°N) had lower mean NCP (5.4 ± 1.8 and 8.1 ± 2.1 mmol C m⁻² d⁻¹, respectively) and mean CO₂ efflux (3.0 ± 0.5 and 0.1 ± 0.0 mmol C m⁻² d⁻¹, respectively). In the subarctic and transition zone, NCP was highly correlated with surface chl-a and CO₂ influx, indicating strong coupling between the biological pump and CO₂ uptake. Meridional trends in our NCP estimates in the transition zone and subtropics were similar to those for integrated summertime NCP along the cruise track determined using an upper ocean climatological carbon budget.