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\begin{document}

\title{\selectlanguage{greek}Δ\selectlanguage{english}O2/N2' as a Tracer of Mixed Layer Net Community Production: Theoretical
Considerations and Proof-of-Concept\selectlanguage{english}}



\author[1,1]{Robert W. Izett}%
\author[1,1]{Philippe D. Tortell}%
\affil[1]{University of British Columbia}%


\vspace{-1em}



  
  \date{May 08, 2024}


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\selectlanguage{english}
\begin{abstract}
The biological oxygen (O2) saturation anomaly \selectlanguage{greek}Δ\selectlanguage{english}O2/Ar is a tracer for net
community production (NCP) in marine surface waters, with argon (Ar)
normalization used to correct for physical effects on O2
supersaturation. Ship-board mass spectrometry has been used for \selectlanguage{greek}Δ\selectlanguage{english}O2/Ar
measurements, but this approach may not be accessible to many research
groups. Here, we present a proof-of-concept for NCP estimates based on
underway measurements of \selectlanguage{greek}Δ\selectlanguage{english}O2/N2, which can be obtained from deployments
of O2-Optodes and gas tension devices (GTD). We used a one-dimensional
mixed layer model, validated against field observations, to evaluate
divergence in \selectlanguage{greek}Δ\selectlanguage{english}O2/Ar and \selectlanguage{greek}Δ\selectlanguage{english}O/N2 resulting from differences in the
sensitivity of Ar and nitrogen (N2) to various physical processes.
Changes in sea surface temperature and responses in air-sea exchange
most strongly decouple surface Ar and N2 with additional excess N2
associated with bubble-injection during high-wind conditions and
vertical mixing in regions of elevated subsurface N2. In contrast,
biological N2-fixation has a negligible contribution to the observed
divergence between Ar and N2. Based on readily available environmental
data, we present an approach to correct for Ar and N2 differences,
yielding a new tracer, N2', that is a near analog of Ar. We show that
\selectlanguage{greek}Δ\selectlanguage{english}O2/N2' provides an excellent approximation to \selectlanguage{greek}Δ\selectlanguage{english}O2/Ar, and that
uncertainty and biases in \selectlanguage{greek}Δ\selectlanguage{english}O2/N2' are small relative to other errors in
NCP calculations. Our results demonstrate the potential for \selectlanguage{greek}Δ\selectlanguage{english}O2/N2'
measurements to expand NCP estimates from oceanographic research
surveys, vessels of opportunity or autonomous surface vehicles.%
\end{abstract}%



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