Asked by: Bill Ritchie, by email

In 1992, research by scientists at the US National Centre for Atmospheric Research in Boulder, Colorado showed that oxygen levels do indeed rise and fall with the seasons, reaching a peak in the summer months.

Increased release of oxygen by plants is part of the explanation, along with changes in the solubility of oxygen as the seas warm and cool. The changes are, however, too small for us to notice.

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