It's also a matter of aerobic verses anaerobic waters. Waters at depth contain less free oxygen, therefore contribute less to the oxidation of materials. But yes TB, as you said, when the waters are stirred up, say by ships, boats, and submersibles, it greatly affects the oxygen content in the water, or rather the free oxygen as pressure changes can cause the gasses in or out of solution.
There is your science lesson for today. For homework, review chapters 33 and 34, and remember there is a test on Friday. Class dismissed.