View source for Net community production (NCP) - O₂/Ar

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* [[Page authors|Page authors]]: [[PRIMO]], [[User:Kate Evans|Kate Evans]]
* [[Responsible curator|Responsible curator]]:  [[User:Kate Evans|Kate Evans]]
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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Oxygen production
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| '''Approach:''' tracer quantification
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| '''Context:''' ''in situ''
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| '''Spatial scale:''' meters<sup>2</sup>
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| '''Temporal scale:''' days
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| '''Units:''' mmol O<sub>2</sub> m<sup>-2</sup> day<sup>-1</sup>
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| '''Community captured:''' all
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| '''Co-measurements:''' temperature, salinity, wind speed history
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== Method Overview ==

O₂/Ar compares the gas concentrations of oxygen and argon to determine the net community production (NCP) (a.k.a. net ecosystem production, or NEP) of oxygen within the depths of interest. This measurement relies on argon being biologically inert, but physically nearly identical to oxygen, such that any deviations from the standard ratio of O₂/Ar are due to biological activity <ref name = "Craig1987">Craig, H., & Hayward, T. (1987). Oxygen supersaturation in the ocean: Biological versus physical contributions. Science, 235(4785), 199–202. https://doi.org/10.1126/science.235.4785.199
</ref>.

=== Scale of measurement ===

Generally, this approach is used in ''in situ'' measurements to determine areal (m<sup>2</sup>) rates of net oxygen changes. Because this approach relies on wind speed to determine mixing rates of the mixed layer, it yields units of d<sup>-1</sup>, but these are based on the average length of time water within the mixed layer has been away from contact with the atmosphere, so they are more of the daily overage of the past few days to few weeks.

It has also been used at higher sampling resolution to track diel level changes in the O₂/Ar ratio <ref name = "Ferron2021"> Ferrón, S., Barone, B., Church, M. J., White, A. E., & Karl, D. M. (2021). Euphotic Zone Metabolism in the North Pacific Subtropical Gyre Based on Oxygen Dynamics. Global Biogeochemical Cycles, 35(3). https://doi.org/10.1029/2020GB006744
 </ref>. This approach still requires knowledge of wind speed for mixing rates, but allows for dial-level estimates of both O₂ production and consumption.

=== Data generated ===

Direct yield is the degree of biologically-mediated oxygen over or undersaturation in (typically) the mixed layer of a body of water. This saturation, when coupled with wind speed and mixing rate estimates, thus yields the average daily change to the oxygen concentration, which is converted into the daily consumption or production of total O<sub>2</sub>. Typically, mixed layer NCP estimates in units of oxygen.

=== Units & currency ===

Units are in days<sup>-1</sup>, but they represent the average NCP of the days to weeks, depending on the wind speed and mixing rate, before sampling.

=== Sample size ===

Small volume water samples, often order of 5 mL.

== Limitations ==

Requires the assumption of steady-state dynamics, and that physical transport does not influence mixed layer O₂ dynamics. Most people interested in NCP or NEP measurements want units of carbon, but this yields oxygen and must be converted via some O:C ratio.

It does, however, do a much better job of removing physical interference than most NCP/NEP estimates are capable of.

== Example Applications & Protocols ==

=== Classic examples ===
* Craig & Hayward (1987) ''Oxygen supersaturation in the ocean: Biological versus physical contributions.'' <ref name="Craig1987" />

=== Recent applications ===
* Ferrón et al. (2021) ''Euphotic Zone Metabolism in the North Pacific Subtropical Gyre Based on Oxygen Dynamics. '' <ref name="Ferron2021" /> Protocol: Link to an actual protocol document if possible, can be any document type, e.g. [[:File:TestWD.docx|Example]]

=== Common calculations/conversions ===
* E.g. conversion to standard units

== References ==

[[Category:Main Pages|Model types]]