"Ocean layers" refers to the different levels or sections within the ocean that have distinct characteristics such as temperature, density, and salinity.
The differences in recent trends among the different ocean layers are profound. (judithcurry.com)
But as our atmosphere warms under global warming, our oceans also are heating up, pushing cooler ocean layers deeper. (science.howstuffworks.com)
Now I will agree that it is generally accepted wisdom that the deep ocean currents turn over in the period of centuries, the upper ocean layers decades. (illconsidered.blogspot.ru)