[jauntywundrkind]

To me the logical point was that some of the oceanic processes that release oxygen are under-thread by man's effort to pluck up those same resources.

It's true that temperature and salinity both mean less oxygen, which means these oxygenator resources might become moot for the ocean's sake, but the ocean mining work very well could threaten a vital oxygen supply for underwater areas, potentially. I think it's fair to say only that: we have no frigging clue whatsoever.