More than 70% of the Earth's surface is occupied by the World Ocean. This is the name of the single and continuous water shell of our planet, which consists of oceans and seas. There are four oceans in total: the Pacific, Atlantic, Indian and Arctic. For many years, there have been disputes about the existence of a fifth, Southern Ocean, but not all countries want to recognize its existence. There are 100 seas in the world, which are divided into marginal, internal and interisland. It is very easy to distinguish an ocean from a sea – oceans are much larger and deeper than seas. But what other differences are there between them? Perhaps you did not even suspect some of the features of seas and oceans.
There are no clear boundaries between seas and oceans, but there are differences between them. Photo source: priroda.club
How to distinguish a sea from an ocean
According to the scientific publication IFL Science, there are no strict rules for defining oceans and seas. For example, there is the Sargasso Sea in the world, which is not surrounded by land like all the others, but is still officially considered a sea. Another example is the Southern Ocean – in some countries it is called the fifth ocean, while in other parts of the world they do not want to recognize it as such.
The Sargasso Sea does not have a single shore, because it is surrounded by ocean currents. Image source: proartspb.ru
Ocean boundaries on the world map. Image source: familii.ru
In short, oceans and seas differ from each other in size, depth, geographic location, water salinity level and other characteristics. We will talk about all this now.
What is an ocean
When we think of the oceans, we think of an unimaginably large body of water that covers a huge part of the Earth's surface. The largest ocean in terms of area and depth is the Pacific Ocean, covering 178 million square kilometers. The Pacific Ocean's greatest depth is estimated at 10,994 meters. Scientists have yet to explore the bottom of any of the four oceans because the great depths put a lot of pressure on people and equipment.
At the bottom of the oceans, where sunlight doesn't reach, live real monsters. Image source: poknok.art
The boundaries of each ocean are defined by the continents that surround them. But the Southern Ocean, which was recognized by the National Geographic Society in 2021, is not surrounded by land. It is surrounded by an invisible ring of the Antarctic Circumpolar Current (the West Wind Current), which goes around Antarctica. Due to the lack of continents around it, some countries refuse to consider it an ocean, so it is generally accepted that there are still only four oceans.
Here are the main features of the oceans that distinguish them from the seas:
- oceans are larger than seas and occupy 71% of the Earth's surface;
- oceans are deeper than seas and their depth is more than 11,000 meters;
- oceans do not have clear boundaries;
- oceans consist of salt water with a uniform composition;
- oceans are home to a huge number of animals due to their large size.
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What is a sea?
Seas are much smaller in area and depth than oceans. The Sargasso Sea mentioned above is the largest in the world, its area is estimated at about 8.5 million square kilometers, which is comparable to the size of Brazil. It is also the only sea that has no shores – it is limited by ocean currents.
By location, seas are divided into several categories. Image source: dzen.ru
All other seas on Earth are at least partially surrounded by land, and some are located inside continents. Seas surrounded on all sides are called intercontinental, and these include the Mediterranean, Red and Caribbean Seas.
Here are the main differences between seas and oceans:
- mine are much smaller than oceans, and are also partially or completely surrounded by land (except for the Sargasso Sea);
- seas are shallower than oceans;
- seas have varying degrees of salinity, in some places the water in them is completely fresh;
- the seas have less biodiversity, which depends on the level of salinity, water temperature and geographic location.
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At the end of the article, it is worth noting that the oceans are much more dangerous than the seas. If you go on an ocean voyage, you can't count on quick help – if a person gets lost in the ocean on a boat or a small raft, the chances of rescue will be close to zero. But some people still manage to escape. In 2023, we told you about refugees who sailed across the ocean on a ship's rudder on the back of the ship. Their journey lasted two weeks, and needless to say, they miraculously survived? You can read about this amazing story in our article “Men without food and water swam across the ocean in two weeks – how did they do it?”