ΔO2/N2′ as a New Tracer of Marine Net Community Production: Application and Evaluation in the Subarctic Northeast Pacific and Canadian Arctic Ocean

We compared field measurements of the biological O2 saturation anomalies, 1O2/Ar and 1O2/N2, from simultaneous oceanographic deployments of a membrane inlet mass spectrometer and optode/gas tension device (GTD). Data from the Subarctic Northeast Pacific and Canadian Arctic Ocean were used to evaluate 1O2/N2 as an alternative to 1O2/Ar for estimates of mixed layer net community production (NCP). We observed strong spatial coherence between 1O2/Ar and 1O2/N2, with small offsets resulting from differences in the solubility properties of Ar and N2 and their sensitivity to vertical mixing fluxes. Larger offsets between the two tracers were observed across hydrographic fronts and under elevated sea states, resulting from the differential time-response of the optode and GTD, and from bubble dissolution in the ship’s seawater lines. We used a simple numerical framework to correct for physical sources of divergence between N2 and Ar, deriving the tracer 1O2/N20. Over most of our survey regions, 1O2/N20 provided a better analog for 1O2/Ar, and thus more accurate NCP estimates than 1O2/N2. However, in coastal Arctic waters, 1O2/N2 and 1O2/N20 performed equally well as NCP tracers. On average, mixed layer NCP estimated from 1O2/Ar and 1O2/N20agreed to within ∼2 mmol O2 m−2 d−1, with offsets typically smaller than other errorsin NCP calculations. Our results demonstrate a significant potential to derive NCP from underway O2/N2 measurements across various oceanic regions. Optode/GTD systems could replace mass spectrometers for autonomous NCP derivation under many oceanographic conditions, thereby presenting opportunities to significantly expand global NCP coverage from various underway platforms