A common pelagic scheme uses epipelagic (0–200 m), mesopelagic (200–1,000 m), bathypelagic (1,000–4,000 m), abyssopelagic (4,000–6,000 m) and hadal depths below about 6,000 m. Boundaries are useful approximations, not walls.
Three things to know
- Sunlit zone
- 0–200 m
- Enough light for photosynthesis in much of the layer.
- Deep ocean
- >200 m
- NOAA commonly defines the deep ocean below the reach of strong sunlight.
- Hadal zone
- >6,000 m
- Mostly ocean trenches, representing a small fraction of seafloor area.
Light fades first
The epipelagic receives sunlight and supports nearly all marine photosynthesis. In the mesopelagic, light becomes too weak for meaningful photosynthesis even though animals can still see some wavelengths. Below about 1,000 meters, sunlight is effectively absent and most visible light is made by organisms.
Depth changes more than darkness
Pressure rises, temperature generally falls and food supply becomes more episodic. Oxygen can also reach a minimum at mid-depths before increasing in some deeper water masses. Species are adapted to combinations of these conditions, not to a depth label alone.
Two ways to divide the sea
Pelagic zones describe open water. Benthic terms describe the seafloor at comparable depths. A swimming lanternfish and a sea cucumber directly beneath it occupy different ecological settings even when a depth gauge reads the same number.
What people usually ask
Where does the midnight zone begin?
The bathypelagic, often called the midnight zone, begins at about 1,000 meters in the common scheme.
Is the hadal zone the deepest ocean?
Yes. It covers trench environments deeper than roughly 6,000 meters, down to nearly 11,000 meters.
Here’s where the answer came from
Open the original government science or research-institution source behind this page.