American Oceans

What’s the Difference Between the Ocean and the Sea?

Chances are, you’ve used the term “sea” or “ocean” a few times in your life. But, did you know there is a difference between the two?

large bodies of water showing difference ocean and sea

Technically speaking, the term “sea” is used to describe smaller bodies of water, while the term “oceans” is used to describe larger bodies of water.

This isn’t the only difference when comparing seas vs oceans. Keep reading to learn what defines an ocean, and what defines a sea.

What Boundaries Define an Ocean?

There are five main oceans in the world. These are the Pacific, Indian, Arctic, Atlantic, and (more recently recognized as an ocean) the Southern (or Antarctic). But what defines these bodies of water as ‘oceans’? 

boundaries between waters define different ocean areas

In general, the water which covers the Earth is often referred to as the World Ocean, as the ocean makes up one global, interconnected body of saltwater.

A fundamental part of oceanography is the concept of one continuous body of salt water (which covers 70% of the Earth’s surface).

However, the World Ocean has been subdivided into five major oceans. The oceans are largely defined by the continents that frame them. 

boundaries under the world five major ocean

Pacific: This is the largest of the oceans that span between Australia, Asia, and the West Americas. It meets the Atlantic Ocean at Cape Horn in South America. 

Atlantic: The second largest of the oceans surrounds the Americas, West Africa, and Europe. At Cape Agulhas in the south of Africa, the Atlantic Ocean meets the Indian Ocean.

Indian: This is the third largest of the oceans which surround India, the Arabain Peninsula, and Southeast Asia.

It also spans between East Africa and Western Australia, where it meets the Pacific Ocean near Australia. 

Arctic: This is the smaller of the five, extends northward of the Atlantic ocean at Greenland and Iceland. It also joins the Pacific at the Bering Strait.

The Arctic Ocean surrounds the North Pole and touches North America, Siberia and Scandinavia. Depending on the season, the Arctic can partially be covered by ice. 

Southern (Antarctic): This is a newly recognized ocean subdivision that surrounds Antarctica, and is the second smallest of the oceans. Like the Arctic Ocean, it is partially covered in ice depending on the time of year. 

What Makes a Sea, a Sea?

Often people confuse the terms ‘ocean’ and ‘sea’ when talking about the ocean. Typically seas are considered smaller bodies of water and are partially covered by land – often noted as to where the ocean meets the land.

Although the ocean generally refers to the enormous body of salt water that covers most of the Earth.

Seas are defined as a “division of these waters, more or less definitely marked off by land boundaries.”

It also usually refers to the water surrounding smaller landmasses, as opposed to entire continents (which defines what the oceans are). 

Some of the larger and well-known seas that you’ve probably heard of are the Mediterranean Sea, the Red Sea, the Arabian Sea, and the Caribbean Sea. 

Not all seas can be categorized by surrounding landmasses. There’s a large portion of the Atlantic Ocean which is named the Sargasso Sea. It is not bound by any land and is instead defined by where it sits between ocean currents. 

It also gets a little more confusing, as not all bodies of water that are considered ‘seas’ have ‘sea’ in their name. They’re also referred to as gulfs and bays – like the Gulf of Mexico and the Bay of Bengal.

The Hudson Bay is considered an inland sea too. Just to add further confusion, not every body of water that has ‘sea’ in its name is actually a sea.

The Dead Sea and the Caspian Sea are actually saltwater lakes. Although there are more than 50 seas in the world, we usually hear about the ‘seven seas’.

These refer to the seven divisions of the ocean, which are practically the same as the five oceans stated above except the Pacific Ocean is divided into north and south, and so is the Atlantic. 

Although this can be difficult to understand, a ‘sea’ commonly refers to the body of water that connects land to the ocean. 

Are Seas Deeper than the Ocean?

Just like they are smaller in size, seas are generally much shallower than oceans. On average, the depth of the ocean is around 3,700 meters (only 10% of the Earth’s ocean floor has been mapped out so this is an estimated figure), but parts of it go much deeper.

For example, the Mariana Trench in the Pacific Ocean is the deepest known location on Earth at 11,034 meters.

To put that depth into perspective, if you took Mount Everest (the tallest mountain on Earth) and placed it at the bottom of the Mariana Trench it would be completely submerged. 

Oceans may generally be considered deeper, however, there are some seas that reach some pretty great depths.

The Caribbean Sea is considered the deepest sea in the world, and has a depth of 7,686 meters – significantly higher than the average depth of the ocean. 

Final Thoughts

Hopefully this article has helped clarify the difference between the terms “sea” vs “ocean”. It’s simple to remember that when talking about smaller bodies of water, you should use “sea” and when discussing larger bodies of water, use “ocean”.

Do you have any fun ways to help people remember these terms? Sound off in the comments below!