What Is an Ocean Basin?

Karize Uy

An ocean basin is one of several structures formed by the oceanic crust. More specifically, it is a saucer-shaped depression under sea level, allowing the seawater to flow into it. It is bordered by continental margins, which extend seaward in varying degrees of inclination; this inclination determines the amount of water flowing into the basins. Ocean basins contain the earth’s oceans, which in turn hold around 97% of the earth’s supply of water. Similarly, the five major oceans of the world each have their corresponding basins similarly named.

Ocean basins are sometimes considered to be the undersea counterparts of continents.
Ocean basins are sometimes considered to be the undersea counterparts of continents.

Ocean basins are sometimes considered to be the undersea counterpart of continents, with the latter being the primary geological structure above sea level and the former being the one below it. Even features such as continental mountains, volcano chains, plains and valleys have their oceanic counterparts. Underwater mountains are called seamounts, volcanic chains are termed mid-ocean ridges, and valleys are known are oceanic trenches. The underwater counterparts, however, are usually several times larger than those above sea level. This is understandable, though, when it is taken into account that oceans cover roughly 71% of the earth’s surface, in contrast to continental landmass of only 29%.

The Sea of Japan is an example of a minor basin.
The Sea of Japan is an example of a minor basin.

Another similarity shared by a continent and an ocean basin is their tendency to change in size. There are different factors that contribute to the changing size of the earth’s basins, just as there are many factors that affect the sizes of continents. Erosion is often considered a major factor in contributing to the shrinkage of an ocean basin, along with sedimentation from ocean tributaries and tectonic plate movements. Some of the characteristics of an active basin include the presence of an elevated mid-ocean ridge, or a nearby subduction zone, or a boundary between two tectonic plates.

The Arctic and Atlantic Ocean basins, for example, are basins that are steadily growing due to the constant tectonic activity in their respective territories. The Pacific Ocean basin, on the other hand, is steadily shrinking. These, when combined with the same tectonic activity leading to continental borders shifting, are the primary factors behind what is called continental drift, or the process of different landmasses slowly moving closer or further away from each other. An ocean basin that lacks any of these factors does not change in size and is considered inactive. Several minor basins, such as those holding the Gulf of Mexico, the Sea of Japan, and the Bering Sea, have been inactive for hundreds, even thousands, of years.

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Discussion Comments


@Feryll - Don't forget that scientists have been saying for years that the state of California is going to break off from the U.S. west coast and sink into the Pacific Ocean because of tectonic activity in the area. If I remember correctly, they have predicted that a major earthquake will land the final blow that sends California into the sea. I'll believe it when I see it.

I'm not an expert, but I would guess that ocean basin topography is changing all of the time and not much really changes.


@Laotionne - I couldn't agree with you more. The landscape of the earth is constantly changing, but it happens so slowly that the average person doesn't see the major changes in a lifetime. We are living in a pretty exciting time in terms of this type of change.

Not too far in the future, if the ocean basins mentioned in this article continue to expand, there will be much less land in some areas and just think how much that will change the lives of a large number of people.


This is not something I give a lot of thought to normally, but when the last paragraph talks about how the Arctic Ocean basin and the Atlantic Ocean basin are continuing to get larger and how they are being affected by tectonic activity near them, this makes me aware of just how much the earth is changing every day.

Otherwise, I think of these types of changes as being something in the past that you study in geology or one of those other science classes. I may not live long enough to see any of the major changes, but this reminds me that the earth has not always been as it is today, and the earth will not remain forever the way it is today.

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