Answer:
Pollution of the ocean waters
Explanation:
The oceans have always been and still are the largest producers of oxygen on Earth. This is due to the enormous amount of producers that live in them. The producers have the ability to take the carbon dioxide out of the atmosphere, and release oxygen as a side product once they perform photosynthesis and respiration. The humans though use the oceans for dumping things in them, some of which are very dangerous, such as the oil spills, the plastic things, rubber, technological waste. They manage to hurt or even kill off the producers, thus reducing the intake of carbon dioxide from the atmosphere, and decrease the releasing of oxygen in it.
