According to Soviet researcher Vassilli Bgatov, most of the oxygen in the atmosphere comes from the heart of the Earth and not from the photosynthesis of plants, which was previously thought. According to this geologist, cracks on the surface of the ocean floor emerge magma and thereby oxygen. Oxygen-saturated cold waters rise to the surface and release excess oxygen when heated in it.
This hypothesis can give oceanists a way to explain why the seabed water contains so much oxygen. However, the oxygen richness of surface waters is due to plankton.
Another fact in favor of the Bgatov hypothesis may be that the sea and surface waters present a different proportion of isotopes. The source of this difference must be somewhere.