The ocean zones are layers of water stacked by depth: sunlight, twilight, midnight, abyss and trenches. Each has its own light level and its own kind of life.
Key takeaways
- Sunlight sets the top layers: the epipelagic zone is the only one with enough light for photosynthesis.
- The zones are usually given as about 200 m, 1,000 m, 4,000 m and 6,000 m.
- The ocean averages 4,085 m deep in our grid, so most of the water is in the dark zones.
- Our map has no zone layer. It colours the seabed by depth, so you read the zones from the colour ramp.
How the ocean zones work
Scientists split the open water into layers, mostly because light fades with depth. The names used by most textbooks are these [1].
| Zone | Common name | Depth (approx.) | Light |
|---|---|---|---|
| Epipelagic | Sunlight zone | Surface to 200 m | Enough for photosynthesis |
| Mesopelagic | Twilight zone | 200 m to 1,000 m | A trace of sunlight |
| Bathypelagic | Midnight zone | 1,000 m to 4,000 m | None |
| Abyssopelagic | Abyssal zone | 4,000 m to just above the floor | None |
| Hadopelagic | Hadal zone | Below 6,000 m, mostly in trenches | None |
These limits are conventions. Sources differ by a few hundred metres, and the water changes gradually from one layer to the next. The zones describe the water. The seabed has its own names, such as shelf, slope and plain, which describe the ground.
The two sets of terms line up loosely. The continental shelf sits mostly within the epipelagic zone, because shelves are shallow. The slope runs down through the twilight and midnight zones. The abyssal plains lie in the abyssal zone, and the trenches reach into the hadal zone.
Our map does not draw ocean zones. The seabed is shaded relief coloured by depth, so you read the zone from the colour ramp or from the depth in the card when you tap. How the colours work is explained in how to read the colours.
An example from our data
The ocean is deep enough that most of it is in the dark. The five oceans average 4,085 m by area, and the Pacific Ocean averages 4,315 m. In the Pacific, only 0.7% of the area is shallower than 200 m, which is roughly the bottom of the sunlit zone. By contrast, 93.6% of the North Sea is shallower than 200 m, so nearly all of its seabed is in the top zone.
At the other end, 1.8% of the Pacific is deeper than 6,000 m, in the hadal zone. The deepest point of all is 10,927 m, at Challenger Deep.
The slider steps at 200 m and 6,000 m happen to match the top and bottom edges of this scheme. They are a convenient way to see how little of the seabed is in the sunlight zone, and how little is in the hadal zone, with the vast middle in between. The slider is a bathtub model, so it shows depth, not light.
The thing people get wrong
People often assume that the ocean is dark below a few metres. It is not. The sunlight zone reaches to about 200 m, and a trace of light reaches 1,000 m [1]. But because the average depth is so much greater, most of the water is in the dark layers.
Another common mistake is to treat the zone depths as fixed, exact lines. They are conventions, and sources differ by a few hundred metres on where each layer starts [1].
Frequently asked questions
How many ocean zones are there?
Five are usually named by depth: epipelagic, mesopelagic, bathypelagic, abyssopelagic and hadopelagic.
Which ocean zone has sunlight?
Only the top one, the epipelagic zone, has enough light for photosynthesis. The mesopelagic zone gets a trace, and the zones below it get none.
Sources
- Pelagic zone, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).