how deep is the ocean The ocean is divided into several zones based on depth and temperature, including: Epipelagic zone The upper open ocean, from the surface to 650 feet deep. This is the zone humans know best because it's the easiest to reach. Mesopelagic zone Also known as the twilight zone or midwater zone, this zone extends from 650 to 3,300 feet deep. It contains the thermocline, where water temperature decreases rapidly with depth. Bathypelagic zone Also known as the midnight zone, this