View source for Continuous dissolved oxygen (DO) optodes

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! O<sub>2</sub> optode method
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| '''Approach:''' continuous O<sub>2</sub> measurement by luminescent optode, light and dark bottles
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| '''Context:''' incubation, simulated ''in situ''
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| '''Spatial scale:''' point sample
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| '''Temporal scale:''' hours to one day
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| '''Units:''' µmol O<sub>2</sub> L<sup>-1</sup> d<sup>-1</sup>; convertible to µmol C L<sup>-1</sup> d<sup>-1</sup>
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| '''Community captured:''' all
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| '''Co-measurements:''' temperature, PAR, salinity, pressure; photosynthetic quotient (PQ) for C conversion
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== Method Overview ==

Luminescent optical oxygen sensors (optodes) are mounted inside incubation bottles, allowing dissolved O<sub>2</sub> to be logged continuously throughout the incubation rather than at a single endpoint. The same light-dark bottle design as the Winkler method is used: light bottles capture NCP (net O<sub>2</sub> production); dark bottles capture community respiration (CR). GPP = NCP + CR. Because O<sub>2</sub> is measured continuously, the method can resolve short-term dynamics and diel patterns within a single incubation, and non-linear responses in the dark bottles can be detected and accounted for.

Optodes respond to the partial pressure of dissolved O<sub>2</sub> via a luminescence lifetime that decreases as O<sub>2</sub> quenches a fluorescent dye embedded in the sensor membrane. Temperature and salinity corrections are required for accurate O<sub>2</sub> concentration calculations.

=== Scale of measurement ===

As a bottle-based incubation, the method provides a point measurement in space. Larger bottle volumes (> 1 L) compared to Winkler bottles reduce the relative contribution of wall effects and increase the signal-to-noise ratio for low-productivity waters.

=== Data generated ===

The method yields time-resolved O<sub>2</sub> concentration trajectories, from which GPP, NCP, and CR are estimated as linear rates over selected time windows. Conversion to carbon requires PQ (for GPP and NCP) and RQ (for CR).

=== Units & currency ===

Units are µmol O<sub>2</sub> L<sup>-1</sup> d<sup>-1</sup>, or µmol C L<sup>-1</sup> d<sup>-1</sup> after conversion. The currency is oxygen (carbon is derived).

=== Sample size ===

Typical samples are > 1 L in volume.

=== Repositories & databases ===

== Limitations ==

Sensor drift over longer incubations must be monitored and corrected. Response times of optodes can lag behind rapidly changing O<sub>2</sub> concentrations. Gas permeability of some incubation vessel materials can introduce artefacts in the O<sub>2</sub> mass balance. The same biological bottle effects (grazer exclusion, altered physico-chemical environment) apply as in the Winkler method. Light-dependent O<sub>2</sub> consumption reactions can cause overestimation of GPP.

== Example Applications & Protocols ==

=== Classic examples ===
*

=== Recent applications ===
*

=== Common calculations/conversions ===
* GPP (µmol O<sub>2</sub> L<sup>-1</sup> d<sup>-1</sup>) = rate of O<sub>2</sub> increase in light bottle − rate of O<sub>2</sub> decrease in dark bottle.
* GPP (µmol C L<sup>-1</sup> d<sup>-1</sup>) = GPP<sub>O2</sub> / PQ.

== References ==

[[Category:Main Pages|Model types]]