Oxygen

Oxygen enters the Ocean from the atmosphere (principally in polar regions) and is also produced by photosynthesis in phytoplankton in the upper layers of the sea. Oxygen is expended during respiration by marine organisms and by processes of oxidation (including bacterial activity). The oxygen-holding capacity of sea water depends on temperature. When temperature decreases, oxygen solubility increases. Oxygen saturation of the Ocean surface layers can occur during periods of intense photosynthesis, or when the surface temperature rises. In deep layers, the oxygen content is mainly determined by processes of intermixing and transport of water masses by basin- scale currents. The entire ocean content of oxygen is 158 times less than in the atmosphere. In addition, while the atmospheric concentration of oxygen is about 20% (by volume), the concentration of oxygen in the sea is well under 1% (by volume). Typically there is an "oxygen minimum" layer in the sea, at depths ranging from 300 m to well over 1500 m, created by opposing processes of biological uptake and supply from deeper layers.

Units of Measurement

Oxygen has been measured as milliliters per liter (ml/l), micromoles per liter (umol/l), and micromoles per kilogram (umol/kg). Archaic literature refers to moles as gram- atoms, so such units as "microgram-atoms/l" and "microgram- atoms/kg" can also be found.
 

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