The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary

The Sargasso Sea is a vast patch of ocean is named for a genus of free-floating seaweed called Sargassum. While there are many different
types of algae found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagic' — this means that the algae not only freely floats
around the ocean, but it reproduces vegetatively on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.

Sargassum provides a home to an amazing variety of marine species. Turtles use sargassum mats as nurseries where hatchlings have food and shelter. Sargassum also provides essential habitat for marine species,such as shrimp, crab, and fish, that have adapted specifically to this floating algae. The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Commercial fish, such as tuna, and birds also migrate through the Sargasso Sea and depend on it for food.

While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined only by ocean currents. It lies within the Northern Atlantic Subtropical Gyre. The Gulf Stream establishes the Sargasso Sea's western boundary, while the Sea is further defined to the north by the North Atlantic Current, to the east by the Canary Current, and to the south by the North Atlantic Equatorial Current. Since this area is defined by boundary currents, it's borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.

For more information:
What's the difference between an ocean and a sea? (Ocean Fact)

Sargassum: A Complex 'Island' Community at Sea (NOAA's Ocean Explorer)

Sampling the Sargassum Community: Dip Nets and Green-Light Lures (NOAA's Ocean Explorer)

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Ferdinand Magellan named the Pacific Ocean. In 1519, Portuguese explorer Ferdinand Magellan, in the employ of Spain, began a journey across the Atlantic Ocean to seek a western route to the Spice Islands via South America.

After braving perilous seas and navigating through what are now known as the Straits of Magellan, his small fleet entered an unfamiliar ocean in Nov. 1520. ...

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With an area of about 5.4 million square miles, the Arctic Ocean is about 1.5 times as big as the United States. It is bordered by Greenland, Canada, Norway, Alaska, and Russia. The average depth of the Arctic Ocean is 12,000 feet and it is 17,850 feet at its deepest point.

The Arctic Ocean is almost completely covered with ice for the majority of the year and its average temperature seldom rises above freezing. However, this ocean is anything but barren.

Tunnels within sea ice called brine channels house bacteria and algae that feed flatworms and other tunnel-dwelling creatures. Melting ice also forms ponds on top of the ice that develop into biological communities.

When the ice melts, organisms and nutrients are released into the water. This promotes algae growth below the ice. These algae provide food for small organisms called zooplankton, which are a food source for fish, squid, seals, and whales. Some of these larger creatures, in turn, are preyed upon by polar bears that live on the ice.

When the creatures below the ice die, they sink to the bottom of the ocean and provide nutrients for sponges, sea anemones, and other bottom dwelling creatures. When these communities grow, they provide food once again for larger creatures such as seals, fish, and whales.

 

For more information:
What is the largest ocean basin on Earth?
How many oceans are there?
Russian-U.S. Arctic Census – NOAA Ocean Explorer
Frequently Asked Questions about the Arctic – NOAA Arctic Theme Page

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Covering approximately 155 million square kilometers (59 million square miles) and containing more than half of the free water on Earth, the Pacific is by far the largest of the world’s ocean basins. All of the world’s continents could fit into the Pacific basin.

The Pacific is the oldest of the existing ocean basins. Its oldest rocks have been dated at about 200 million years. The Pacific basin is referred to as the “Ring of Fire” due to intense earthquake and volcanic activity occurring near areas of tectonic plate subduction (where one tectonic plate is forced under another).

The Atlantic basin is the second largest basin, followed by the Indian Ocean basin, the Southern Ocean, and finally the Arctic Ocean basin.

For more information:
New Zealand American Submarine Ring of Fire 2007, NOAA Ocean Explorer
Submarine Ring of Fire 2006, NOAA Ocean Explorer

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The origins of the phrase 'Seven Seas' can be traced to ancient times.

In various cultures at different times in history, the Seven Seas has referred to bodies of water along trade routes, regional bodies of water, or exotic and far-away bodies of water.

In Greek literature (which is where the phrase entered Western literature), the Seven Seas were the Aegean, Adriatic, Mediterranean, Black, Red, and Caspian seas, with the Persian Gulf thrown in as a "sea."

In Medieval European literature, the phrase referred to the North Sea, Baltic, Atlantic, Mediterranean, Black, Red, and Arabian seas.

After Europeans 'discovered' North America, the concept of the Seven Seas changed again. Mariners then referred to the Seven Seas as the Arctic, the Atlantic, the Indian, the Pacific, the Mediterranean, the Caribbean, and the Gulf of Mexico.

Not many people use this phrase today, but you could say that the modern Seven Seas include the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and Southern Oceans.

However, our oceans are more commonly geographically divided into the Atlantic, Pacific, Indian, Arctic, and Southern (Antarctic) Oceans.

For more information:
How many oceans are there?
NOAA Nautical Charts
A History of Charting America's Waters, NOAA 200th Anniversary Web Site

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Most scientists agree that the atmosphere and the oceans accumulated gradually over millions and millions of years with the continual ‘degassing’ of the Earth’s interior.

According to this theory, the ocean formed from the escape of water vapor and other gases from the molten rocks of the Earth to the atmosphere surrounding the cooling planet.  

After the Earth's surface had cooled to a temperature below the boiling point of water, rain began to fall—and continued to fall for centuries. As the water drained into the great hollows in the Earth's surface, the primeval ocean came into existence. The forces of gravity prevented the water from leaving the planet.

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While there is only one global ocean, the seas are geographically divided into the Atlantic, Pacific, Indian, Arctic, and Southern (Antarctic) Oceans.

These five oceans are not separate bodies of water; they form one continuous oceanic mass. The boundaries between these five oceans arose over time for a variety of historical, cultural, geographical, and scientific reasons.

The Pacific, the Atlantic and the Indian Oceans are known as the three major oceans.

The Southern Ocean is the 'newest' ocean. The boundaries of this ocean were set in 2000 by the International Hydrographic Organization. The U.S. is a member of this organization, represented by the NOS Office of Coast Survey.

For more information:
Office of Coast Survey
A History of Charting America's Waters, NOAA 200th Anniversary Web Site

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