It has been in the news lately about what the difference is between a college and a university. In the U.S. my understanding is that, if it offers up to a bachelor's degree or below it is a college, if it offers up to a master's degree or a PhD it is a university.
But what is the difference between a sea and an ocean? The definitions of the two go back to ancient times and the definitions are relatively simple. An ocean is one of the few main bodies of water in the world. A sea is a branch off an ocean, partially separated from the main body of the ocean by land.
A sea is sometimes called a "gulf". I really don't see any definable difference between a sea and a gulf. Why is the Caribbean Sea a sea but the Gulf of Mexico is a gulf? Why is the Red Sea a sea but the Persian Gulf is a gulf?
Maybe if it's partially separated from the sea by islands it's a sea, but if it's partially enclosed by the mainland it's a gulf, as with the Gulfs of Thailand or Tonkin. But then shouldn't the Bay of Bengal be a gulf? But if it is a gulf then why is the Arabian Sea a sea?
Since the seas and oceans were named many centuries ago a lot has been learned about geology and how the earth operates. A body of water was named as either a sea or an ocean by it's scale and position. An ocean was one of the few large bodies of water that separated the continents and a sea was a branch of the ocean, partially separated by the main body of the ocean by islands or the shape of the mainland.
But these definitions are just about the role of the body of water in the surface of the earth. Seas and oceans are also structured differently. Seas are typically relatively shallow branches of oceans while the oceans are the deep wide bodies of water that separate continents.
Regarding the difference between a sea and an ocean the most important rule does not seem to be depth. Seas are usually shallow because they enclose part of a continental shelf but some seas can be deep if they go beyond the continental shelf.
The most important rule in differentiating a sea from an ocean is continents. An ocean separates continents while a sea is adjacent to a continent.
The seas and oceans were named long before this was understood. I cannot see that there is any process for reclassification of seas and oceans. Maybe it's time that there was because the Mediterranean is really an ocean, and not a sea.
Unlike seas the Mediterranean separates continents. It separates Europe and Africa. In geological terms Europe and Asia are often considered as one continent, Eurasia. But if we consider Europe and Asia as separate continents then the Mediterranean actually separates three continents.
Seas are branches of the ocean, partially separated from it by islands. Seas are not usually branches of other seas, although this is not a strict rule. The Yellow Sea branches off the East China Sea and the Baltic Sea branches off the North Sea. But the Mediterranean has no less than four of the world's major seas branching off it, the Black Sea, the Aegean Sea, the Adriatic Sea, and the Tyrrhenian Sea. No other sea has anything like this.
Like an ocean the Mediterranean has a deep center, with shallow continental shelves on either side. Dark blue is deeper than light blue. Image from Google Earth.
There are two things that the Mediterranean doesn't have to be an ocean. The first is the scale, in terms of surface area it is much more like a sea than an ocean. The second is that the other oceans are all joined together but the Mediterranean is connected to the Atlantic Ocean only by the narrow Straight of Gibraltar.
If we were to consider the Mediterranean as an ocean there is something that has to be taken into account. The Mediterranean would be the only ocean with it's long axis being aligned latitudinally, or east-west. Since the general movement of the continents has been northward, this means that the Mediterranean has been "squeezed" in ways that the other oceans haven't.
Each ocean has what we could call a defining geological factor. The Pacific Ocean is defined by the Pacific Plate, which is by far the largest of the earth's tectonic plates. The Hawaiian Islands are where magma from below manages to break through the plate. The Atlantic Ocean is defined by the Mid-Atlantic Ridge, which is pushing the two sides of the ocean apart. The Atlas Mountains of Morocco was once part of the Appalachians. Iceland, with it's volcanic activity, is where the Mid-Atlantic Ridge pokes above the surface of the water. The Indian Ocean is defined by being in the south while the general movement of the continents, driven by the spin of the earth, is northward. The Arctic Ocean is defined as the remaining water space in the far north remaining after the movement of the continents northward.
The defining geological factor of the Mediterranean is that it is aligned perpendicular, rather than parallel, to the general movement of the continents northward. This caused it to be compressed or "squeezed", by the northward movement of Africa, as well as the Arabian Peninsula, but, other than that, it has the characteristics of an ocean, rather than a sea. The Red Sea is sometimes described as the beginning of an ocean. The Mediterranean could likewise be described as the closing of an ocean.
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