Oxygen tends to be abundant in the surface layer and deep layer bottom, but lowest in the pycnocline. Slide 4 of 17 Oxygen tends to be abundant in the surface layer and deep layer bottom, but lowest in the pycnocline.
Surface layer is rich in oxygen because of photosynthesis and contact with the atmosphere.
Oxygen minimum layer occurs at about 150 to 1500m below the surface and coincides with the pycnocline. Sinking food particles settle into this layer and become suspended in place because of the greater density of the water below. The food draws large numbers of organisms which respire, consuming oxygen. Decay of uneaten material consumes additional oxygen. Density difference prevents mixing downward of oxygen-rich water from the surface or upwards from the deep layer.