Seas cover a smaller area than oceans and are usually found where land and ocean meet. Normally, the seas are partially enclosed by land. The only exception is the Sargasso Sea, which is defined by ocean currents.
We often hear that size doesn’t matter, but in the maritime sector, it does. In fact, it’s a matter of size! It is the vast surface of the ocean that slightly distinguishes it from the sea. Although the sea is also defined as a large body of saltwater, its surface area is smaller. In order to give you a reference, the largest sea (Arab) has an area of 3.6 million km², while the smallest sea (Arctic) has an area of more than 14 million km².
The difference between sea and ocean doesn’t end here, it’s also about borders! If we look at the definition of the ocean, it is written that an ocean is always surrounded by continents. The sea can be surrounded by land and/or sea. Therefore, there are several types of seas on the blue planet.
- A “shelf sea” is like an extension of the ocean. This is indeed the case with the Channel, the North Sea or the Caribbean Sea, most of which border the Atlantic.
- An “inland sea” can only be connected to one other sea like the Baltic Sea, the Black Sea or the Adriatic Sea.
- A “semi-enclosed” sea enters the ocean through a narrow passage, much like the Mediterranean Sea enters the ocean through the Strait of Gibraltar.
- A “closed” sea is not connected to any sea or ocean, such as the Caspian Sea and the Aral Sea
Water is saltier in the sea than in the ocean
The boundaries and size of the body of water are not the only differences between the ocean and the sea. In fact, the salinity of the water is also a factor to consider. Certainly one cannot distinguish the ocean from the sea by comparing the taste of the water, even if the water in the oceans is less salty than in the seas (the salinity of the oceans is 35 g/L on average).
Why are the seas saltier? The sea currents allow to regulate the salinity of the oceans thanks to the thermohaline circulation. To better understand this phenomenon, we invite you to read this article on ocean currents.
On the other hand, the seas are saltier because the evaporation of the water is more important. Since salt does not evaporate, seawater has a higher density of sodium chloride.
For example, the salinity of the Mediterranean Sea is 39 g/L and that of the Red Sea is 42 g/L. The only sea that is an exception to the rule is the Baltic Sea, which has a salinity of 7 g/L. The water can be explained by the significant inflow of fresh water and precipitation that compensates for the loss of water through evaporation.
Depth is making a difference
Another element that allows distinguishing the seas from the oceans is the depth!.
In general, the ocean is much deeper than the sea, although some seas may be almost as deep as the great oceans.
To give you some examples, the depth of the channel is 174 m, that of the North Sea is 700 m, and that of the Black Sea is 2212 m. Some seas are much deeper, like the Mediterranean at 5,267 m, the Sargasso Sea at 7,000 m or even that Coral Sea at 9,140 m.
However, the oceans can reach amazing depths, often in excess of 8,000 m, such as the Indian Ocean at 8,047 m, the Atlantic at 8,486 m, or even the Pacific Ocean with its Mariana Trench, which can reach 11,022 m, the deepest seabed in any ocean ever recorded.