Net Community Production derived from DeltaO2/Ar measurements and N2O-based corrections for vertical mixing in the Subarctic Northeast Pacific

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 (DeltaO2/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 DeltaO2/Ar measurements. After correcting for the mixing flux, all coastal stations showed autotrophic signatures, with maximum NCP exceeding 100 mmol O2 m-2 day-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 co-occurrence of N2O minima and O2 maxima resulted in biased (over-estimated) 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. Data in this submission include the ancillary components required to replicate all calculations, and conclusions made in the main manuscript.本研究首次将基于一氧化二氮（N₂O）的方法应用于现场实验，用于校正由混合层氧浓度观测值估算净群落生产力（NCP）过程中的垂直混合效应。依托东北亚北极太平洋海域获取的船测一氧化二氮及生物氧饱和度异常值（ΔO₂/Ar）新观测数据，我们针对不同水文环境优化了混合层净群落生产力估算结果，并对该方法的技术考量与局限性开展了全面评估。通过一氧化二氮观测推算得到的混合层底部垂直混合系数增大的时段，与风速升高及沿岸上升流发生时期相吻合。在沿岸区域，低氧水的垂直补给会通过负ΔO₂/Ar观测值错误地指示净异养状态，此时校正效果最为显著。校正混合通量后，所有沿岸测站均呈现自养特征，春夏季节的最大净群落生产力超过100 mmol O₂ m⁻² d⁻¹。陆架外海域的垂直通量较低，但通常占校正后净群落生产力的50%以上。但在部分大洋测站，一氧化二氮极小值与氧浓度极大值的同步出现会导致一氧化二氮校正结果出现偏差（高估）。对这些区域的垂直通量进行评估仍是船测研究面临的挑战。尽管如此，相较于未校正的结果，我们优化后的净群落生产力估算值与表层叶绿素浓度、水温及混合层深度的相关性更佳。混合层中潜在的一氧化二氮生成过程会为本方法带来一定不确定性，但误差量级通常较小。综上，本研究为采用一氧化二氮校正方法优化净群落生产力估算提供了理论依据，在沿岸海域尤为适用。本投稿附带的数据包含复现所有计算及主文稿结论所需的全部配套数据集。