True
The major sources of oxygen in the upper zones of ocean water are as follows-
a) Atmosphere
b) Photosynthesis of plant in water
In the deeper zones of ocean, the survival of plants is not possible as there is no sunlight. In the absence of plant the oxygen contributed through photosynthesis remains lacking at greater ocean depths. Also there is no oxygen contributed by atmosphere as well. Thus there is more oxygen in the upper zones of ocean