Earlier quoted context omitted.
Can you explain further, please? I don't doubt what you are saying, but don't know why it is "obvious". Is it, because the amount of sea water is so large, relative to the amount of 'pollution'? The abstract of the paper linked in the article seems to support your statement, though. "For the past several hundred million years, oxygen concentrations in Earth's atmosphere have been comparatively high[..]. Yet, the ocea…
Is a complex theme To start anoxia is a relative term. It depends on how much oxygen do you spent respect to how fast you replace it. Is also a buffered event, and the problem corrects itself automatically [1]. Therefore, things like "the edge of anoxia" have moving boundaries and are difficult to define [1] When some area is lacking oxygen, marine life response migrating or is simply killed. The result is that more…
Water will be filled with high concentrations of things that love to release oxygen. Bazillions of oxygen. Thus throwing fertilizer in the ocean equals to oxygen increase, not decrease... in principle.
Of course, biology is never so simple. You can have most life killed by lack of oxygen even while being submerged in a soup of oxygen producers because anoxia is a relative term. Life also breathes. And, unlike photosynthesis, breathing is done also at night. At the end of the night life can experience troubles to survive.
And there is the chemistry also. Stuff reacts chemically with the salts or organic matter suspended in the sea. This can release oxygen as by-product, remove oxygen and store it in some molecule, or remain neutral about it.
Chemistry can also affect oxygen producers. Too much fertilizer and your plant will die by thirst. In the sea the problem is reduced because your flower pot can decide to swim away or sink away.