An ocean basin is a large depression in the Earth's surface that is filled with seawater. It is floored by oceanic crust and includes the deep plains, ridges and trenches of the ocean floor.
Key takeaways
- An ocean basin is the bowl; the ocean is the water that fills it.
- Its floor is oceanic crust, which is thinner and denser than the crust under the continents.
- Basins open and close over millions of years as plates move: the Atlantic is growing, while the Pacific is shrinking.
- Our map names 110 ocean basins, including the Angola Basin.
How ocean basins work
An ocean basin is a large basin lying below sea level and filled with seawater. The word is used in two ways [1]. In the wide sense, it means any part of the Earth covered by seawater, so the whole of the Atlantic, the Pacific and so on are each a basin. In the narrower sense used on our map, it names a particular deep depression on the seabed, bounded by ridges, plateaus or continental margins, like the Angola Basin.
The floor of a basin is oceanic crust, which is thinner and denser than continental crust [1]. It is made at mid-ocean ridges, where plates pull apart and magma rises to fill the gap [2]. As the crust moves away from the ridge it cools, and the seabed gets deeper with distance from the ridge [1]. At the far side it may plunge back into the Earth at a trench, where one plate sinks beneath another [2].
Because the plates keep moving, basins are not permanent. The Atlantic Ocean basin began to form about 180 million years ago as continents split from the supercontinent Pangaea, and it is still growing. The Pacific is active but shrinking [1]. A basin collects sediment eroded from the continents, which is why its floor includes smooth abyssal plains [1].
A basin typically holds several of the features this site names: abyssal plains, abyssal hills, ridges and seamounts. Our map does not draw basins as a layer. It shows the shape of the seabed through its depth colours, and the basin names are labels on the map.
An example from our data
Our grid names 110 ocean basins. Three examples show the range of depths. The Angola Basin in the South Atlantic has a deepest cell of 5,546 m, 902 km from Angola. The Argentine Basin is 5,156 m at its deepest, and the Canada Basin in the Arctic is 3,796 m.
They sit in different oceans. The Atlantic Ocean has a mean depth of 3,883 m, while the Arctic Ocean averages 2,306 m. The basin depths are grid values for the deepest cell near each feature, so they can differ from published figures.
The thing people get wrong
Many people think an ocean basin is a smooth, bowl-shaped dip, deepest in the middle. In fact a basin with a mid-ocean ridge, like the Atlantic, is shallowest along the ridge, which is a mountain range. The seabed gets deeper away from the ridge as the crust cools [1].
It is also easy to treat "ocean" and "ocean basin" as the same. The ocean is the water, and the basin is the shape of the ground that holds it. On our map the oceans and seas have their own pages, such as the Pacific Ocean, while basins are named seabed features.
Frequently asked questions
What is the difference between an ocean and an ocean basin?
The ocean is the water. The basin is the large hollow in the Earth's crust that holds it.
How are ocean basins formed?
By plate tectonics. Continents split apart and new oceanic crust forms between them at a ridge, and the crust cools and sinks to form a basin that fills with water.
Sources
- Oceanic basin, Wikipedia.
- Understanding plate motions, USGS (This Dynamic Earth).
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).