UBC Faculty Research and Publications

Refined Estimates of Net Community Production in the Subarctic Northeast Pacific Derived From ΔO₂/Ar Measurements With N₂O-Based Corrections for Vertical Mixing Izett, Robert W.; Manning, Cara C.; Hamme, Roberta C.; Tortell, Philippe Daniel, 1972-

Abstract

We present the first field application of a N₂O-based approach to correct for vertical mixing in the estimation of net community production (NCP) from mixed layer O₂ measurements. Using new ship-based observations of N₂O and biological oxygen saturation anomalies (ΔO₂/Ar) from the Subarctic Northeast Pacific, we provide refined mixed layer NCP estimates across contrasting hydrographic regimes and a comprehensive assessment of the methodological considerations and limitations of the approach. Increased vertical mixing coefficients at the base of the mixed layer, derived using N₂O measurements, corresponded with periods of heightened wind speed and coastal upwelling. Corrections were most significant in coastal regions where the vertical supply of low-O₂ water can otherwise falsely imply net heterotrophy from negative ΔO₂/Ar measurements. After correcting for the mixing flux, all coastal stations showed autotrophic signatures, with maximum NCP exceeding 100 mmol O₂ m⁻² d⁻¹ in the spring and summer. Vertical fluxes were lower in off-shelf waters but often contributed more than 50% to corrected NCP. At some oceanic stations, however, the cooccurrence of N₂O minima and O₂ maxima resulted in biased (overestimated) N₂O corrections. Evaluating vertical fluxes in these regions remains a challenge for ship-based studies. Nonetheless, our refined NCP estimates show better coherence with surface chlorophyll, temperature, and mixed layer depth than uncorrected values. Potential mixed layer N₂O production introduces some uncertainty in the approach, but errors are likely to be small. Ultimately, this work provides rationale for the adoption of the N₂O correction to refine NCP estimates, particularly in coastal waters.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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