Seas and Oceans: Definitions, Features and the Main Ones

Home | Category: Oceans and Sea Life


Ocean zones
Many people use the terms "ocean" and "sea" interchangeably when speaking about the ocean, but there is a difference between the two in the eyes of geographers. Seas are smaller than oceans and are usually located where the land and ocean meet. Typically, seas are found on the margins of the ocean and are partially enclosed by land. The Bering Sea, for example, is part of the Pacific Ocean. The Sargasso Sea is an exception. It is defined only by ocean currents. [Source: NOAA]

According to the “Introduction to Physical Oceanography”: There is only one ocean. It is divided into three named parts by international agreement: the Atlantic, Pacific, and Indian oceans (International Hydrographic Bureau, 1953). Seas, which are part of the ocean, are defined in several ways. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

The global ocean covers 71 percent of the Earth and is geographically divided into distinct named regions. The boundaries between these regions have evolved over time for a variety of historical, cultural, geographical, and scientific reasons. Historically, there are four named oceans: the Atlantic, Pacific, Indian, and Arctic. However, most countries — including the United States — now recognize the Southern (Antarctic) as the fifth ocean. The Pacific, Atlantic, and Indian are the most commonly known.

The Pacific Ocean is the largest and deepest of the world's ocean basin The Atlantic basin is the second largest basin, followed by the Indian Ocean basin, the Southern Ocean, and finally the Arctic Ocean basin.

Websites and Resources: National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium

Defining Oceans and Seas

Robert Stewart wrote in the “Introduction to Physical Oceanography”: The boundary between the Atlantic and Pacific is the line forming the shortest distance from Cape Horn to the South Shetland Islands. In the north, the Arctic Sea is part of the Atlantic Ocean, and the Bering Strait is the boundary between the Atlantic and Pacific. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

The Pacific Ocean extends northward from Antarctica to the Bering Strait. The boundary between the Pacific and Indian Ocean follows the line from the Malay Peninsula through Sumatra, Java, Timor, Australia at Cape Londonderry, and Tasmania. From Tasmania to Antarctica it is the meridian of South East Cape on Tasmania 147◦E. The Indian Ocean extends from Antarctica to the continent of Asia including the Red Sea and Persian Gulf.

The Southern Ocean is the 'newest' named ocean. It is recognized by the U.S. Board on Geographic Names as the body of water extending from the coast of Antarctica to the line of latitude at 60 degrees South.

Seas are mostly surrounded by land. By this definition, the Arctic and Caribbean Seas are both Mediterranean Seas, the Arctic Mediterranean and the Caribbean Mediterranean. Marginal Seas are defined by only an indentation in the coast. The Arabian Sea and South China Sea are marginal seas.

Seven Seas

Seven Seas of the Ancient World: 1) The Mediterranean Sea; 2) the Adriatic Sea; 3) the Red Sea; 4) the Black Sea; 5) the Caspian Sea; 6) the Persian Gulf; and 7) the Arabian Sea

The exact origin of the phrase 'Seven Seas' is uncertain, although there are references in ancient literature that date back thousands of years. 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. [Source: NOAA]

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. As trade picked up across the Atlantic, 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 ocean is more commonly geographically divided into the Atlantic, Pacific, Indian, Arctic, and Southern (Antarctic).

Pacific Ocean: the World’s Largest Ocean

Covering approximately 181 million square kilometers (63 million square miles) and containing more than half of the free water on Earth, the Pacific is far and away the largest of the world’s oceans. All of the world’s continents could fit into the Pacific basin. The Pacific is also 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). [Source: NOAA]

The Pacific Ocean stretches for 17,700 kilometers (11,000 miles) at the equator. It is 20 times as large as the U.S. and twice as large as the Atlantic. It encompasses half of the world's oceans and covers one third of the earth's surface. The Pacific Ocean is also deepest of the world's ocean. It contains the Marianas Trench, the deepest point in the world's ocean. Running for 2,950 kilometers (1835 miles) on the eastern side of the Marianas islands, just south of Guam, it is a deep sea canyon with a maximum depth of 11,034 meters (36,201 feet). This is more than seven miles. Mount Everest is less than six miles high. The distance between the lowest point in the Marianas Trench and the highest on the Marianas islands is the greatest elevation change on earth.

Terence E. Hays wrote in the “Encyclopedia of World Cultures”: “If you turn a globe just so, all you can see is the Pacific Ocean, the earth's largest geographic feature. It is greater than that of all of the world's land areas combined; however, even when Australia is included, the Pacific contains only about 9 million square kilometers of dry land. The rest consists of more than half of the world's volume of free water, with an average depth of over 4,000 meters. From the Bering Strait in the north to the Antarctic Circle is a distance of more than 14,700 kilometers, and to cross the Pacific at its greatest width, between Singapore and Panama, one must travel about 19,700 kilometers. [Source:“Encyclopedia of World Cultures, Volume 2: Oceania,” edited by Terence E. Hays, 1991 |~|]

“Perhaps not surprising in the face of such immensity (especially to the modem air traveler), the most characteristic feature of the Pacific Ocean is emptiness. Although it contains more islands than are found in all other oceans combined, the overwhelming majority of the tens of thousands of islands of Oceania are in the southwestern quadrant of the Pacific. But this is still a very large area.

Discovery and Naming of the Pacific Ocean

People living along the west coast of the Americas and the east coasts of Asia and Australia have known of the Pacific Ocean for millennia. Ancient Polynesians used double-hulled sailing canoes to cover vast distances in the Pacific long before Europeans appeared on the scene. By A.D. 1300, Polynesians had settled more than 10 million square miles of the Pacific Ocean roughly between New Zealand, Hawaii and Easter Island.

Vasco Núnez de Balboa (1474-1517) was the first European recorded to have laid eyes on the the Pacific Ocean, which he named the South Sea. He hacked through dense tropical rain forests for 25 days with 190 Spaniards and several hundred Indian guides and porters to reach the Pacific in 1513. When the reached a peak with a view of the Pacific on September 25, 1513, Balboa ascended first while his men had to wait behind. "Kneeling on the ground, he raised his hands to heaven and saluted the south sea,” according to his account he gave “thanks to God and all the saints for having reserved this glory for him, an ordinary man, devoid a like of experience and authority." He then invited his men to join him and exclaimed, "Behold the much desired ocean! Behold! all ye men, who have shared such efforts behold the country of which the sons of Comogre and other natives have told us such wonders!" After four day more days walking and being carried by Indians, Balboa reached the Pacific where he waded into the surf wearing his armor and raised the banner of Castile, formally taking possession of "all that sea and the countries bordering on it" for Spain. After his return to Spain, Balboa was presented 240 perfect pearls, four pounds of lesser quality ones and 614 peso in gold. Six years after discovering the Pacific, Balboa was arrested on trumped up charges and beheaded on the orders of the jealous Spanish governor Pedro Arias Dávila. Balboa's grave lies in some unknown location in th jungle somewhere.

Portuguese navigator and explorer Ferdinand Magellan named the Pacific Ocean. In 1519, , in the employ of Spain, he 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 November 1520. He called this body of water pacific, due to the calmness of the water at the time ('pacific' means peaceful). When Magellan and his crew entered the Pacific Ocean after their long journey, they thought that the Spice Islands were close at hand. Little did they know that their destination remained thousands of kilometers away.[Source: NOAA]

Compared to what Magellan accomplished, Christopher Columbus’s journey was a ride to the park. Columbus followed sunny trade winds to the West Indies and followed the prevailing westerlies back to Europe. Magellan on the other hand traveled about ten times the distance Columbus did: through the crushing winds in the furious fifties latitudes of southern South America and icy seas of north of Antarctica, then traveled across the breadth of the Pacific (a distance about four times what Columbus traveled across the Atlantic), having absolutely no idea where land was or where he was going. Once he achieved that feat he was only halfway home. His objective was cloves and other cooking spices in the Moluccas, or Spice Islands.

Pacific Basin Elevations

Magellan was blessed with unusually good weather across the Pacific, thus the name. During the three months and 20 days at sea, his ships didn't encounter a single storm. "In truth," Magellan write, the sea "is very pacific, for during that time we did not suffer any storm." Even so he had a rough time because it gross miscalculated the distance he had to travel and didn’t bring enough and supplies for his crew. Neither Magellan or his crew had any idea what lay ahead and Magellan thought at most the journey would take a couple of weeks. No European had ever been in this part of the world before and no one knew how wide the Pacific was for a system of longitude had not yet been devised. "We issued forth from the said strait and entered the Pacific Sea," wrote Magellan’s chronicler Pigafatta, "where we remained for three months and twenty days without taking on board provisions or any other provisions or any other refreshment."

Atlantic Ocean

The Atlantic Ocean is the world’s second largest ocean. Covering an area of approximately 106,460,000 square kilometers (41,105,000 square miles), it borders the east coast of the Americas and the west coast of Europe and Africa and separate sthe "Old World" of Africa, Europe and Asia from the "New World" of the Americas form European perception of the World. Up north, the Atlantic connects to the Arctic Ocean and to the Southern Ocean to the south. [Source: NOAA]

Covering approximately 20 percent of the Earth’s surface and containing 29 percent of its surface water area, the Atlantic Ocean is larger than the Indian Ocean but is only slightly larger than half the size of the Pacific Ocean. From the Atlantic Ocean, the Pacific Ocean can be reached through the Straights of Magellan at the tip of South America. The Indian Ocean can be reached from the Atlantic by rounding the Cape of Good Hope at the southern tip of Africa.

Scientists often divide the Atlantic into two basins: the North Atlantic and the South Atlantic. The North Atlantic, where waters sink after being chilled by arctic temperatures, is the start of the “global ocean conveyor,” a circulation pattern that helps regulate Earth’s climate.

The Atlantic Ocean derives its name from the Greek god, Atlas. Atlantic means "Sea of Darkness" in Arabic. The 12th-century Arab geographer Al-Idrisi wrote: "No one knows what is in that sea, because of many obstacles to navigation — profound darkness, high waves, frequent storms, innumerable monsters which people it, and violent winds. No sailor dares to penetrate it; they limit themselves to sailing along the coast without losing sight of land." [Source: "Search for Columbus" by Eugene Lyon, January 1992]

Atlantic bathymetry

The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and North and South America to the west. The Atlantic has irregular coasts indented by numerous bays, gulfs and seas. These include the Baltic Sea, Black Sea, Caribbean Sea, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea and Norwegian Sea.The 16,000-kilometer-long (10,000-mile-long) Mid-Atlantic Ridge (MAR) divides the Atlantic longitudinally into two halves. The longest mountain range in the world, the MAR rises two to three kilometers (1.2–1.9 miles) above the surrounding ocean floor. It s rift valley is the divergent boundary between the North American and Eurasian tectonic plates in the North Atlantic and the South American and African plates in the South Atlantic. The MAR produces basaltic volcanoes such as Eyjafjallajökull, Iceland, and produces pillow lava on the ocean floor. [Source: Wikipedia]

Indian Ocean

The Indian Ocean is the third-largest of the world's five oceanic divisions. Covering 70,560,000 square kilometers (27,240,000 square miles) and accounts for 19.8 percent of the water on Earth's surface, it is bordered by Africa to the west, Asia to the north, Australia to the east and the Southern Ocean or Antarctica to the south. Large marginal seas that branch off the Indian Ocean include the Red Sea, Arabian Sea, the Persian Gulf, Bay of Bengal, and Andaman Sea. [Source: Wikipedia]

The Indian Ocean has been known by its present name since at least 1515. It was named after India, which projects into it. It was earlier known as the Eastern Ocean when it was navigated primarily by people form east Africa and the Middle East. Chinese explorers in the 15th century called it the Western Oceans. The Indian Ocean region was known to the ancient Greeks a the Erythraean Sea.

The ocean-floor of the Indian Ocean is divided by spreading ridges and crisscrossed by aseismic structures The borders of the Indian Ocean used to extends to Antarctica but in 2000 the International Hydrographic Organization recognized the Southern Ocean separately and removed waters south of 60°S from the Indian Ocean. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf.

The Indian Ocean has an average depth of 3,741 meters (12,274 feet) and a maximum depth of 7,906 meters (25,938 feet) in the Java Trench off Indonesia. All of the Indian Ocean is in the Eastern Hemisphere and the centre of the Eastern Hemisphere, the 90th meridian east, passes through the Ninety East Ridge. In contrast to the Atlantic and Pacific, the Indian Ocean is enclosed by major landmasses and an archipelago on three sides and does not stretch from pole to pole. Centered on the Indian Peninsula and surounded by South and Southeast Asia, Western Asia, Northeast, East and Southern Africa and Australia, it has a maximum length of 9,600 kilometers (6,000 miles) (Antarctica to Bay of Bengal) and a maximum width of 7,600 kilometers (4,700 miles) (Africa to Australia). Its shore length is 66,526 kilometers (41,337 miles).

Indian Ocean

Arctic Ocean

The Arctic Ocean (also known as the Northern Ocean) is located in the Northern Hemisphere and mostly in the Arctic north polar region. the smallest and shallowest of the world's five major oceanic divisions, it is recognized by the International Hydrographic Organization (IHO) as an ocean, although some oceanographers regard it as an estuary of the Atlantic Ocean or a water body like the Mediterranean Sea. The salinity of the Arctic Ocean is the lowest on average of the five major oceans, due to low evaporation, heavy fresh water inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities. [Source: Wikipedia]

The Arctic Ocean is the smallest of the world's five ocean basins. With an area of about 15.8 million square kilometers (6.1 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 1,205 meters (3,953 feet) and it is 5,567 meters (18,264 feet) deep at its deepest point. [Source: NOAA]

In some places in the Arctic Ocean the water is highly stratified with relatively fresh water supplied by river water on top and more saline water in the lower depths. In some basins the water has remained undisturbed and isolated for more than 500 years. Rivers supply about a third of the fresh water that enters the Arctic Ocean. Scientist can track down the source of these water by the unique chemical signature of the water. The movements of ice, surface water and near surface water are driven by the clockwise Beaufort Gyre. Below this is a contraclockwise current that moves water primarily of Atlantic origin to the east along the continental margin.

Almost completely surrounded by Eurasia and North America, the Arctic Ocean is partly covered by sea ice throughout the year (and almost completely in the winter). The Arctic Ocean's surface temperature and salinity vary seasonally as the ice cover melts and freezes. The summer shrinking of the ice has been quoted at 50 percent. The US National Snow and Ice Data Center (NSIDC) uses satellite data to provide a daily record of Arctic sea ice cover and the rate of melting compared to an average period and specific past years. [Source: Wikipedia]

The Arctic Ocean’s 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.

Southern Ocean

The Southern Ocean is the 'newest' named ocean. It is recognized by the U.S. Board on Geographic Names as the body of water extending from the coast of Antarctica to the line of latitude at 60 degrees South. The boundaries of this ocean were proposed to the International Hydrographic Organization (IHO) in 2000. However, not all countries agree on the proposed boundaries, so this has yet to be ratified by members of the IHO. The U.S. is a member of the IHO. [Source: NOAA]

Also known as the Antarctic Ocean, the Southern Ocean is comprised the southernmost waters of the world ocean, generally taken to be south of 60° S latitude and encircling Antarctica. Covering of 20,327,000 square kilometers (7,848,000 squar miles), it is considered the second-smallest of the five principal oceans — smaller than the Pacific, Atlantic, and Indian oceans but larger than the Arctic Ocean. Since the 1980s, the Southern Ocean has been subject to rapid climate change, which has led to changes in the marine ecosystem. [Source: Wikipedia]

Sarah Gibbens wrote in National Geographic: Those familiar with the Southern Ocean know it’s unlike any other. “Anyone who has been there will struggle to explain what's so mesmerizing about it, but they'll all agree that the glaciers are bluer, the air colder, the mountains more intimidating, and the landscapes more captivating than anywhere else you can go,” says Seth Sykora-Bodie, a marine scientist at the National Oceanic and Atmospheric Administration (NOAA) and a National Geographic Explorer. [Source: Sarah Gibbens, National Geographic, June 8, 2021]

“The Southern Ocean has long been recognized by scientists, but because there was never agreement internationally, we never officially recognized it,” National Geographic Society Geographer Alex Tait said. Geographers debated whether the waters around Antarctica had enough unique characteristics to deserve their own name, or whether they were simply cold, southern extensions of the Pacific, Atlantic, and Indian Oceans. “It’s sort of geographic nerdiness in some ways,” Tait said.

Southern Ocean: Defined by its Current?

Sarah Gibbens wrote in National Geographic: While the other oceans are defined by the continents that fence them in, the Southern Ocean is defined by a current. Scientists estimate that the Antarctic Circumpolar Current (ACC) was established roughly 34 million years ago, when Antarctica separated from South America. That allowed for the unimpeded flow of water around the bottom of the Earth. [Source: Sarah Gibbens, National Geographic, June 8, 2021]

Thermohaline circulation
click the image once and click it again in Wikicommons

“The ACC flows from west to east around Antarctica, in a broad fluctuating band roughly centered around a latitude of 60 degrees south—the line that is now defined as the northern boundary of the Southern Ocean. Inside the ACC, the waters are colder and slightly less salty than ocean waters to the north.

“Extending from the surface to the ocean floor, the ACC transports more water than any other ocean current. It pulls in waters from the Atlantic, Pacific, and Indian Oceans, helping drive a global circulation system known as the conveyor belt, which transports heat around the planet. Cold, dense water that sinks to the ocean floor off Antarctica also helps store carbon in the deep ocean. In both those ways, the Southern Ocean has a crucial impact on Earth’s climate.

“Scientists are currently studying how human-driven climate change is altering the Southern Ocean. Ocean water moving through the ACC is warming, scientists have learned, but it’s unclear how much this is impacting Antarctica. Some of the most rapid melting of the continents ice sheets and shelves have been where the ACC is closest to land.”

Black Sea

Black Sea is a huge inland sea, covering 507,900 square kilometers (196,100 square miles) with an average depth of 3,906 feet. Twice the size of Michigan, it is surrounded by Bulgaria, Romania, Russia, the Ukraine, Georgia and Turkey and is connected to the Mediterranean Sea by the half-mile-wide Bosporus at Istanbul, the Sea of Marmara and the Dardanelles. Because it has few outlets it has virtually no tides. The water is warm enough for swimming in the summer, and can generate some surprisingly large waves in some places when the wind kicks up.

The Black Sea gets it name from storms that frequently darken the skies over the sea and the sea itself. Black Sea generates a lot its own moisture and winds that blow in from the northwest bring even more. The coastal areas of the Black Sea receive quite a bit of rainfall (mostly in the winter) and are quite lush and green. There summertime temperatures are generally significantly cooler than the Mediterranean Sea but still plenty warm enough for topless sunbathing.

Mediterranean Sea

Mediterranean Sea means "Sea in the Middle of the Earth." Covering 2,500,000 square kilometers (970,000 square miles), it stretches 3,700 kilometers (2,300 miles) from the Atlantic Ocean in east to Israel in the west, and is 1,100 kilometers (700 miles) at its broadest point (between Croatia to Libya). They Tyrrrhenian Sea, Adriatic Sea and Aegean Sea are all branches of the Mediterranean, which at one time was a lake.

The Mediterranean became a sea several million years ago when the Atlantic ocean broke through a limestone formation that stretched from Iberia (Spain and Portugal) into Africa, releasing a 1,500-meter-high (5,000-foot-high) series of cascades that transformed southern Europe and filled in the Spain basin over a period of about a 100 years. Today the Mediterranean lies in a very geologically-active earthquake-prone area region, as the people from Turkey and Italy will tell you, made up of the colliding African and Eurasian tectonic plates.

Mediterranean Sea and Black Sea

The surface currents of the Mediterranean move at about 5 kph (three miles per hour) from west east. About 75 meters (250 feet) below the surface is a current that rushes in the opposite direction towards the Atlantic. Relatively few river flow into the Mediterranean and the hot climate of the region produces a high rate of evaporation which means the sea is getting saltier. Without the movement of water between the Mediterranean and the Atlantic, the Mediterranean would be little more than a lake.

The Mediterranean is over 4,875 meters (16,000 feet) deep in a trench east of Crete but has virtually no tides. Water levels are often determined less by tides than winds such as the “Vendaval” (astrong westerly that blows through the Straits of Gibraltar), the “La Tramontana” (the strong wind off the Spanish coast), the “le Mistral” (the cold dry wind northwest wind of the Riviera), the “Khamsin”, the “Sirroco”, the “Gregale” (a northeast wind that blows through Malta) and the Levanter (an eastern wind that brings humidity).

In the 6th century B.C., the Mediterranean was 60 centimeters (two feet) lower than it is today. Over the centuries the Mediterranean has been controlled by Phoenicians, Greeks, Romans, Vandals, Byzantines, Moors, Muslims, Normans, French, Spanish, Turks and English. The English writer Dr. Samuel Johnson once said, "The grand object of traveling is to see the shores of the Mediterranean. On these shores were the great Empires of the world: the Assyrian, the Persian, the Grecian, and the Roman. All our religion, almost all our law, almost all our arts, almost all that sets us above savages, has come to us from the shores of the Mediterranean."

The Mediterranean is surrounded by 27 nations with a total population of almost a billion people and over a hundred different ethnic groups who speak more than 50 languages. The largest islands are Sicily Sardinia, Corsica, Cyprus, Crete and Majorca.

The Mediterranean coast boasts well-preserved ancient cities, beach resorts, huge cliffs, spectacular mountains, pebble beaches, sand beaches, translucent waters that vary from purple to green. Along the windy roads that hug the coast you can find pine forests, olive grove, pistachio trees, orange orchards and even a few banana plantations. The most accessible and beautiful parts of the region are in the west near the Aegean Sea.

The Mediterranean is arguable the world’s biggest tourist draw. Possibly more people enjoy vacationing on its shores than either the Atlantic or the Pacific. The main thing that has drawn tourist over the years is the excellent climate. The swimming season extends from April to November and the air temperatures are mild the remaining months of the year.

Some 13,000 plant species are unique to the Mediterranean, which is regarded as a biodiversity hot spot. In the waters are stripped dolphins, monk seals loggerhead turtles and even sperm whales and few great white sharks. Each year there is great migration of bluefin tuna through the Straits of Gibraltar from the Atlantic to the Mediterranean. With the exception of the tuna, the fisheries in the Mediterranean yield much less fish than the an equivalent area of the Atlantic.

South China Sea

South China Sea

The South China Sea lies south of China’s Guangdong Province and Hong Kong. By some reckonings it is the world's largest sea, covering 3,500,000 square kilometers (1,400,000 square miles). A marginal sea that is part of the Pacific Ocean, the South China Sea stretches from the Karimata and Malacca straits to the Strait of Taiwan and carries tremendous strategic importance.

In the last 2,500 years mariners for Malaysia, China and Indonesia navigated the South China Sea to trade sandalwood, silk, tea and spices. Today it carries roughly a third of the world's shipping and accounts for a tenth of the world's fish catch. China, Vietnam, Taiwan, Malaysia, Indonesia, Brunei and the Philippines all have 200-mile coastal economic zones in the South China Sea. All of these countries also claim the Spratly Islands which are in the middle of the sea

About $5.3 trillion of global trade passes through the South China Sea each year, $1.2 trillion of which passes through U.S. ports. Below the South China Sea is an estimated $3 trillion worth of oil, gas and minerals. Fisheries in the South China Sea have been decimated by overfishing and polluting chemicals from shrimp farms and factories. By some estimates there is enough oil under the South China Sea to last China for 60 years.

The South China Sea is south of China; east of Vietnam; west of the Philippines; east of the Malay Peninsula and Sumatra, up to the Strait of Singapore in the western, and north of the Bangka Belitung Islands and Borneo. In recent years, China’s claim that the entire sea is it exclusive possession has been a hot international issue and a point of outrage with China.

Sargasso Sea

The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary. 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, its borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.

The Sargasso Sea is a vast patch of ocean 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.

healthy sargassum ecosystem

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 shrimp, crab, fish, and other marine species 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.

Image Sources: Wikimedia Commons; YouTube, NOAA

Text Sources: National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

This site contains copyrighted material the use of which has not always been authorized by the copyright owner. Such material is made available in an effort to advance understanding of country or topic discussed in the article. This constitutes 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. If you are the copyright owner and would like this content removed from, please contact me.