@Marine Scientist, I thought this was contested and were not actually sure, because we keep finding new sources that pretty much claim to solely keep the world oxygen genrated. Why are you so certain?
@Marine Scientist, everyone got upset when the Japanese were killing whales, but since plankton are a large contribution to oxygen production, and whales consume literal tons of plankton daily, the Japanese were only trying to help the environment!
The ocean produces roughly 2/3 of the oxygen on the planet, fun fact!