Refined Estimates of Net Community Production in the Subarctic Northeast Pacific Derived From ΔO₂/Ar Measurements With N₂O-Based Corrections for Vertical Mixing
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 Northeas...
Published in: | Global Biogeochemical Cycles |
---|---|
Main Authors: | , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2018
|
Subjects: | |
Online Access: | http://hdl.handle.net/2429/64864 https://doi.org/10.1002/2017GB005792 |
Summary: | 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. Science, Faculty of Non UBC Botany, Department of Earth, Ocean and Atmospheric Sciences, Department of Reviewed Faculty Postdoctoral Graduate |
---|