The ocean covers 70 percent of Earth’s surface. It contains about 1.35 billion cubic kilometers (324 million cubic miles) of water, which is about 97 percent of all the water on Earth. The ocean makes all life on Earth possible and makes the planet appear blue when viewed from space. Earth is the only planet in our solar system that is definitely known to contain liquid water.
Oceans are huge bodies of salt water. They are home to many aquatic animals like fish, dolphins, whales, squid, turtles, and octopuses.
Ocean salt primarily comes from rocks on land and openings in the seafloor. Salt in the ocean comes from two sources: runoff from the land and openings in the seafloor. Rainwater that falls on land is slightly acidic, so it erodes rocks. The eroded minerals from these rocks, including salt, are carried into the ocean by rivers and streams.
Why are oceans important?
Oceans provide food, regulate our climate, and generate most of the oxygen we breathe. They also serve as the foundation for much of the world’s economy by supporting sectors such as tourism, fisheries, and international shipping.
The ocean plays a vital role in climate and weather. The sun’s heat causes water to evaporate, adding moisture to the air. The oceans provide most of this evaporated water. The water vapor condenses to form clouds, which release their moisture as rain or other forms of precipitation. All life on Earth depends on this process, called the water cycle.
The atmosphere receives much of its heat from the ocean. As the sun warms the water, the ocean transfers heat to the atmosphere. In turn, the atmosphere distributes the heat around the globe.
Because water absorbs and loses heat more slowly than land masses, the ocean helps balance global temperatures by absorbing heat in the summer and releasing it in the winter. Without the ocean to help regulate global temperatures, Earth’s climate would be much more extreme.
Why are oceans blue?
The ocean is blue because water absorbs colors in the red part of the light spectrum. Like a filter, this leaves behind colors in the blue part of the light spectrum for us to see. The ocean may also take on green, red, or other hues as light bounces off floating sediments and particles in the water.
The Salty Sea: A Culinary Adventure from Shore to Sea
The Pacific Ocean is the largest and deepest of Earth’s five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continents of Asia and Oceania in the west and the Americas in the east.
At 165,250,000 square kilometers (63,800,000 square miles) in area (as defined with a southern Antarctic border), this largest division of the World Ocean and the hydrosphere covers about 46% of Earth’s water surface and about 32% of the planet’s total surface area, larger than its entire land area (148,000,000 km2 (57,000,000 sq mi)). The centers of both the Water Hemisphere and the Western Hemisphere, as well as the oceanic pole of inaccessibility, are in the Pacific Ocean.
Ocean circulation (caused by the Coriolis effect) subdivides it into two largely independent volumes of water that meet at the equator, the North Pacific Ocean and the South Pacific Ocean (or more loosely the South Seas). The Pacific Ocean can also be informally divided by the International Date Line into the East Pacific and the West Pacific, which allows it to be further divided into four quadrants, namely the Northeast Pacific off the coasts of North America, the Southeast Pacific off South America, Northwest Pacific off Far Eastern Asia, and the Southwest Pacific around Oceania.
The Pacific Ocean’s mean depth is 4,000 meters (13,000 feet). Challenger Deep in the Mariana Trench, located in the northwestern Pacific, is the deepest known point in the world, reaching a depth of 10,928 meters (35,853 feet). The Pacific also contains the deepest point in the Southern Hemisphere, the Horizon Deep in the Tonga Trench, at 10,823 meters (35,509 feet). The third deepest point on Earth, the Sirena Deep, is also located in the Mariana Trench.
The western Pacific has many major marginal seas, including the Philippine Sea, South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea, Gulf of Alaska, Mar de Grau, Tasman Sea, and the Coral Sea.
In the early 16th century, Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and sighted the great “Southern Sea” which he named Mar del Sur (in Spanish). Afterwards, the ocean’s current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in Spanish, Portuguese and Italian means ‘peaceful sea’.
The Atlantic Ocean is the second-largest of the world’s five oceans, with an area of about 85,133,000 km2 (32,870,000 sq mi). It covers approximately 20% of Earth’s surface and about 29% of its water surface area. It is known to separate the “Old World” of Africa, Europe, and Asia from the “New World” of the Americas in the European perception of the world.
Through its separation of Europe, Africa, and Asia from the Americas, the Atlantic Ocean has played a central role in the development of human society, globalization, and the histories of many nations. While the Norse were the first known humans to cross the Atlantic, it was the expedition of Christopher Columbus in 1492 that proved to be the most consequential. Columbus’ expedition ushered in an age of exploration and colonization of the Americas by European powers, most notably Portugal, Spain, France, and the United Kingdom. From the 16th to 19th centuries, the Atlantic Ocean was the center of both an eponymous slave trade and the Columbian exchange while occasionally hosting naval battles. Such naval battles, as well as growing trade from regional American powers like the United States and Brazil, both increased in degree during the early 20th century, and while no major military conflicts took place in the Atlantic in the present day, the ocean remains a core component of trade around the world.
The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and the Americas to the west. As one component of the interconnected World Ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south (other definitions describe the Atlantic as extending southward to Antarctica). The Atlantic Ocean is divided in two parts, by the Equatorial Counter Current, with the North(ern) Atlantic Ocean and the South(ern) Atlantic Ocean.
The Indian Ocean is the third-largest of the world’s five oceanic divisions, covering 70,560,000 km2 (27,240,000 sq mi) or ~19.8% of the water on Earth’s surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by the Southern Ocean or Antarctica depending on the definition in use. Along its core, the Indian Ocean has some large marginal or regional seas such as the Arabian Sea, Laccadive Sea, Bay of Bengal and Andaman Sea.
The Indian Ocean has been known by its present name since at least 1515 when the Latin form Oceanus Orientalis Indicus (“Indian Eastern Ocean”) is attested, named after India, which projects into it. It was earlier known as the Eastern Ocean, a term that was still in use during the mid-18th century (see map), as opposed to the Western Ocean (Atlantic) before the Pacific was surmised.
The Arctic Ocean is the smallest and shallowest of the world’s five major oceans. It spans an area of approximately 14,060,000 km2 (5,430,000 sq mi) and is known as one of the coldest of oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea. It has also been described as an estuary of the Atlantic Ocean. It is also seen as the northernmost part of the all-encompassing World Ocean.
The Arctic Ocean includes the North Pole region in the middle of the Northern Hemisphere and extends south to about 60°N. The Arctic Ocean is surrounded by Eurasia and North America, and the borders follow topographic features: the Bering Strait on the Pacific side and the Greenland Scotland Ridge on the Atlantic side. It is mostly covered by sea ice throughout the year and almost completely in winter. The Arctic Ocean’s surface temperature and salinity vary seasonally as the ice cover melts and freezes; its salinity 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. The summer shrinking of the ice has been quoted at 50%. 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, showing a continuous decline in sea ice extent. In September 2012, the Arctic ice extent reached a new record minimum. Compared to the average extent (1979–2000), the sea ice had diminished by 49%.
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of 20,327,000 km2 (7,848,000 sq mi), it is regarded as the second-smallest of the five principal oceanic divisions: 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.