What is the difference between a sea and an ocean?

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The majority of the Earth’s water is stored in its oceans, seas, and bays which make up 96.5%  of the 1.36 billion tons of water.  While some use the terms ocean and sea interchangeably, there is a difference in the geographic definitions of those two terms.

An ocean represents a far larger body of open water than a sea.  By definition, a sea is a smaller part of an ocean and is typically partially contained by an area of land.  Therefore, all seas are found in areas where the ocean and land meet.

In this example below, the Indian Ocean is shown as the open body of water.  The two areas of water that are partially enclosed by land are named the Red Sea and the Oman Sea.

Map showing the Indian Ocean, Oman Sea, and the Red Sea. Map: Epmistes, MediaWiki Commons.

Map showing the Indian Ocean, the Oman Sea, and the Red Sea. Map: Epmistes, MediaWiki Commons.

What are the Seven Seas?

The Sevens Seas is a historic term naming the dominant trade routes and regional bodies of waters.  The definition of what those Seven Seas are has changed over time.  The term is believed to have first appeared in 2,300 BCE Hymn 8 of the Sumerian Enheduanna to the goddess Inanna (Meador, 2001).  The ancient Greeks named the seven seas as Aegean, Adriatic, Mediterranean, Black, Red, and Caspian seas, and the Persian Gulf.

While no longer a common phrase, the modern day Seven Seas are the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and Southern Oceans.

References

Meador, Betty De Shong, ed. (2001). Inanna, Lady of Largest Heart: Poems of the Sumerian High. Translated by Betty De Shong Meador. University of Texas. ISBN 0-292-75242-3.

What are the seven seas? NOAA

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