|MadSci Network: Earth Sciences|
The following answer is provided by Dr Kai Bester: There are two ways oxygen gets into the water. If it is a eutrophic ecosystem, there will generally be an oxygen demand, especially in warm summer nights, as the plants cannot produce oxygen without light, thus oxygen has to be imported from the air, which consists of 23% oxygen. Oligotrophic ecosystems and eutrophic systems which can absorb enough light will produce oxygen (chemical reaction from water and bicarbonate) so the worlds oceans deliver much of the oxygen which is in the air. I hope this will answer your question. Cheers kai
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