AUTHOR=Izett Robert W. , Hamme Roberta C. , McNeil Craig , Manning Cara C. M. , Bourbonnais Annie , Tortell Philippe D. 

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

JOURNAL=Frontiers in Marine Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.718625

DOI=10.3389/fmars.2021.718625

ISSN=2296-7745

ABSTRACT=<p>We compared field measurements of the biological O<sub>2</sub> saturation anomalies, ΔO<sub>2</sub>/Ar and ΔO<sub>2</sub>/N<sub>2</sub>, 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 ΔO<sub>2</sub>/N<sub>2</sub> as an alternative to ΔO<sub>2</sub>/Ar for estimates of mixed layer net community production (NCP). We observed strong spatial coherence between ΔO<sub>2</sub>/Ar and ΔO<sub>2</sub>/N<sub>2</sub>, with small offsets resulting from differences in the solubility properties of Ar and N<sub>2</sub> 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 N<sub>2</sub> and Ar, deriving the tracer ΔO<sub>2</sub>/N<sub>2</sub>′. Over most of our survey regions, ΔO<sub>2</sub>/N<sub>2</sub>′ provided a better analog for ΔO<sub>2</sub>/Ar, and thus more accurate NCP estimates than ΔO<sub>2</sub>/N<sub>2</sub>. However, in coastal Arctic waters, ΔO<sub>2</sub>/N<sub>2</sub> and ΔO<sub>2</sub>/N<sub>2</sub>′ performed equally well as NCP tracers. On average, mixed layer NCP estimated from ΔO<sub>2</sub>/Ar and ΔO<sub>2</sub>/N<sub>2</sub>′ agreed to within ∼2 mmol O<sub>2</sub> m<sup>–2</sup> d<sup>–1</sup>, with offsets typically smaller than other errors in NCP calculations. Our results demonstrate a significant potential to derive NCP from underway O<sub>2</sub>/N<sub>2</sub> 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.</p>