In oceanography, it is a key parameter to trace physical dynamics and to better understand biogeochemical processes in the World Oceans. Actually, O2 concentration is always the balance between biological terms (production by phytoplankton, consumption through respiration by all organisms) and ocean-atmosphere O2 exchanges (so-called ventilation processes). Observations in several parts of the world ocean show a general decrease in O2. Models also predict an overall decline in O2 under global warming, mostly in extra-tropical regions. That decline is likely associated with an expansion of tropical Oxygen Minimum Zones (OMZ), with far reaching consequences on coastal ecosystems, and this appears to be confirmed by observations, which require to be re-inforced, in particular thanks to combination O2-sensor-autonomous platforms.
2) How is it measured ?
Several methods exist to determine the oceanic O2 concentration :
> In situ (sensor): electrochemical and optical methods.
> In vitro (in the lab), on discrete samples: chemical titration method, the so-called Winkler method.
The chemical method is the most appropriate method to calibrate the in situ sensors.
3) Where is more information available ?
Gruber et al. (2007). The Argo-oxygen program: A white paper to promote the addition of oxygen sensors to the international Argo float program. (access to paper online)