What are the seas?

We explain everything about the sea, what types exist and their depth. In addition, differences with the ocean and examples of seas of the world.

1. What are the seas?

The surface of our planet is covered in three quarters by water , forming the huge bodies of salt water we know as oceans , and those of smaller size, known as seas.

In other words, a sea is a mass of salt water of local or regional importance , much smaller in perspective than the ocean in which it is inserted. Its dimensions, shape and portion surrounded by land can be extremely varied.

Some bodies of salt water, instead of being called seas, are called gulfs, bays or other forms. In principle, this is due to historical considerations, since human populations have chosen since ancient times to always settle by the sea, given the transport , food and benign climate facilities that their coasts usually offer.

For a long time there was talk of “the seven seas” to refer to the different known maritime regions, but in reality their number amounts to more than fifty , endowed with a gigantic diversity in terms of shapes, sizes and ecosystems . Even endorheic lakes, that is, salt water lakes fully encapsulated on the mainland, are often referred to as seas.

The seas have been the inspiration of humanity since very early, motivating artistic works , incredible stories and summoning the adventurer to travel. They are often attributed a female presence, when not maternal, since life began in its waters. They are often supposed to be the scene of underwater kingdoms or submerged mythical civilizations, such as Atlantis.

2. Difference between sea and ocean

Stated as simply as possible, the difference between the seas and the oceans is in size . Almost all seas, in fact, are part of some specific ocean, so it could be said that the oceans are a major or superior maritime unit.

There are, therefore, five oceans in the world: Atlantic, Pacific, Indian, Arctic and Antarctic; but more than fifty seas spread across the globe.

3. Sea depth

Both the oceans and the seas have an average depth of 4.26 kilometers , distributed very unevenly. In some locations the sea may be flatter, while in other regions it goes deep into ocean trenches and continental trenches.

For example, the Mariana Trench, located in the western Pacific Ocean, has a maximum depth recorded in the Challenger Abyss, 10,994 meters deep.

4. Types of seas

The seas are classified into three types, depending on their geographical location and their characteristics:

• Coastal or coastal seas . These are very wide gulfs of the oceanic coast, which do not have any type of underwater separation from the open ocean, but have wider tides, lower depth and higher temperatures .
• Continental seas . Its name comes from the fact of being located within a specific continent , but maintaining a communication with the ocean to which they belong by means of a strait of some kind, generally of little depth. This causes substantial differences between the continental sea and the ocean, especially in terms of salinity and temperature. The tides of this type of seas are so low that they usually go completely unnoticed.
• Seas closed . They are also called endorheic lakes, as they are lakes of more or less salty water, large areas, located within a continental shelf and with little or no direct water exchange with the oceans. This causes that the properties of its waters are always very particular.

5. Examples of seas

Here are some examples of each type of sea listed above:

Coastal or coastal seas:

• The Beaufort Sea , located in the North Atlantic Ocean, between Alaska and the Canadian Yukon.
• The Norwegian Sea , part of the North Atlantic Ocean, located northwest of Norway and between the North and Greenland seas.
• The Oman Sea , also called the Gulf of Oman, is part of the enormous Arabian Sea, in the Indian Ocean, and communicates with the Persian Gulf through the Strait of Hormuz.
• The Arabian Sea , the largest on the planet, is part of the Indian Ocean and is located in the southwestern region of Asia, between Hindustan and the Arabian Peninsula. It has 3,862 square kilometers of surface.
• The Coral Sea , located in the western Pacific Ocean, off the coast of Australia, where the Great Barrier Reef is located, the largest coral reef on the planet.

Continental seas:

• The North Sea , belonging to the North Atlantic Ocean, is located between the coasts of Norway and Denmark, Germany, the Netherlands, Belgium, France and the British Isles. It connects through the English Channel to the rest of the Atlantic, to the Baltic Sea through the Kiel Canal and to the Norwegian Sea through the north.
• The Mediterranean Sea , located between southern western Europe and northern Africa, gets its name from the fact that the classical cultures that emerged in its surroundings thought it to be the center of the Earth. It is connected to the Atlantic Ocean through the Strait of Gibraltar.
• The sea of ​​Japan , which receives its name by being between the coasts of that country and those of its neighbors China, Korea and Russia, connects with five other regional seas through shallow straits.
• The Baltic Sea , located in northern Europe, is an inland sea of ​​brackish water open to the North Sea and also connected to the Atlantic Ocean through the Kattegat and Skagerrak Straits. It has two gulfs: Finland and Botnia, and is the largest amber deposit in the world.

Closed seas:

• The dead sea , located in a depression 435 meters below sea level, between Israel, Palestine and Jordan, has waters of a radically different composition from the ocean, full of calcium, magnesium, potassium and bromine, which make them so dense that sinking into them is almost impossible. Nor is there any aquatic life in the Dead Sea, which justifies its name.
• The Caspian Sea , between Europe and Asia, is the largest lake on the planet, located in an endorheic basin of the Earth 28 meters below sea level. It is fed by the Volga River, the Emba, the Ural and the Kurá.
• The Aral Sea , located in Central Asia, between Kazakhstan and Uzbekistan, is a sea highly contaminated by agricultural fertilizers commonly used in the region during the 20th century. Its surface was once 68,000 square kilometers, which made it one of the largest lakes in the world, but now it has been reduced to only 10% of its surface, in one of the largest environmental disasters in recent history.