Earth's oceans
(World Ocean)
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- Arctic Ocean
- Atlantic Ocean
- Indian Ocean
- Pacific Ocean
- Southern Ocean
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An ocean
(from Greek O?ea???
, Okeanos
(Oceanus)) is a major body of Seawater (salt water). The Earth's oceans cover approximately 71% of the Earth's surface, , and can be as deep as of . Scientists estimate that 230,000 marine life forms of all types are currently known, but the total could be up to 10 times that number. [1]
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OCEAN TICKETS
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Ocean or Oceans?
Though generally described as several 'separate' oceans, the earth has one global, interconnected body of salt water, often referred to as the
World Ocean or global ocean.
[2] [3] This concept of a continuous body of water with relatively free interchange among its parts is of fundamental importance to
oceanography.
[4]
The oceans are (from largest to smallest):
- Pacific Ocean which separates Asia from the Americas
- Atlantic Ocean which separates the Americas from Europe and Africa
- Indian Ocean which separates India from Africa
- Arctic Ocean which borders the northern continents and encompasses the far North including the North pole.
The Pacific and Atlantic may be further subdivided by the
equator into
northern and
southern portions. Smaller regions of the oceans are called seas,
gulfs,
bays,
straits and other names.
A
Southern ocean, surrounding
Antarctica and extending to 60°S was defined in the year 2000.
Geologically, an ocean is an area of
oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic
basalt that covers the Earth's
mantle.
Continental crust is thicker but less dense. From this perspective, the earth has three oceans: the World Ocean and the
Caspian and
Black Seas. The latter two were formed by the collision of
Cimmeria with
Laurasia. The
Mediterranean Sea is at times a discrete ocean, because
tectonic plate movement has repeatedly broken its connection to the World Ocean through the
Strait of Gibraltar. The Black Sea is connected to the Mediterranean through the
Bosporus, but the Bosporous is a natural
canal cut through continental rock some 7,000 years ago, rather than a piece of oceanic sea floor like the Strait of Gibraltar.
Despite their names, smaller landlocked bodies of saltwater that are
not
connected with the World Ocean, such as the
Aral Sea are actually
salt lakes.
Ocean and life
The ocean has a significant effect on the
biosphere. Oceanic
Evaporation, as a phase of the
water cycle, is the source of most
rainfall, and ocean temperatures determine
climate and
wind patterns that affect life on land. The border between land and ocean itself provides critical habitat for many species that require both to thrive.
Life within the ocean
evolved 3 billion years prior to life on land. Both the depth and distance from shore strongly influence the amount and kinds of
plants and
animals that live there.
[5]
Physical properties
The area of the World Ocean is ,
[6] its volume is approximately 1.3 billion cubic kilometers (310 million cu mi)
[7]. This can be thought of as a cube of water with an edge length of . Its average depth is .
Nearly half of the world's marine waters are over deep.
The vast expanses of deep ocean (anything below cover about 66% of the Earth's surface.
[8] This does not include seas not connected to the World Ocean, such as the
Caspian Sea.
The total mass of the
hydrosphere is about , which is about 0.023% of the Earth's total mass. Less than 3% is
freshwater; the rest is
saltwater, mostly in the ocean.
Color
A common misconception is that the oceans are blue primarily because the sky is blue. In fact,
water has a very slight blue color that can only be seen in large volumes. While the sky's reflection does contribute to the blue appearance of the surface, it is not the primary cause.
[9] The primary cause is the absorption by the
water molecules' nuclei of red photons from the incoming light, the only known example of color in nature resulting from vibrational, rather than electronic, dynamics.
[10]
Glow
Sailors and other mariners have reported that the ocean often emits a visible glow, or luminescence, which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow.
[11] It may be due to
bioluminescence.
[12]
[13]
[14]
Exploration
Ocean travel by boat dates back to prehistoric times, but only in modern times has extensive underwater travel become possible.
The deepest point in the ocean is the
Mariana Trench, located in the Pacific Ocean near the
Northern Mariana Islands. It has a maximum depth of
[15]. The British naval vessel, "Challenger II" surveyed the trench in 1951 and named the deepest part of the trench, the "
Challenger Deep". In 1960, the
Trieste successfully reached the bottom of the trench, manned by a crew of two men.
Much of the ocean bottom remains unexplored and unmapped. A global image of many underwater features larger than was created in 1995 based on gravitational distortions of the nearby sea surface.
Regions
Oceanographers divide the ocean into regions depending on physical and biological conditions of these areas. The
pelagic zone includes all open ocean regions, and can be divided into further regions categorized by depth and light abundance. The
photic zone covers the oceans from surface level to 200 meters down. This is the region where photosynthesis can occur and therefore is the most biodiverse. Since plants require photosynthesis, life found deeper than this must either rely on material sinking from above (see
marine snow) or find another energy source;
hydrothermal vents are the primary option in what is known as the
aphotic zone (depths exceeding 2000m). The pelagic part of the photic zone is known as the
epipelagic. The pelagic part of the aphotic zone can be further divided into regions that succeed each other vertically according to temperature.
The
mesopelagic is the uppermost region. Its lowermost boundary is at a
thermocline of , which, in the tropics generally lies at . Next is the
bathypelagic lying between , typically between and Lying along the top of the abyssal plain is the
abyssalpelagic, whose lower boundary lies at about . The final zone includes the deep trenches, and is known as the
hadalpelagic. This lies between and is the deepest oceanic zone.
Along with pelagic aphotic zones there are also
benthic aphotic zones. These correspond to the three deepest zones. The
bathyal zone covers the continental slope down to about . The
abyssal zone covers the abyssal plains between 4,000 and 6,000 m. Lastly, the
hadal zone corresponds to the hadalpelagic zone which is found in the oceanic trenches.
The pelagic zone can also be split into two subregions, the
neritic zone and the
oceanic zone. The neritic encompasses the water mass directly above the
continental shelves, while the oceanic zone includes all the completely open water.
In contrast, the
littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions. It is also known as the
intertidal zone because it is the area where tide level affects the conditions of the region.
Geology
The ocean floor spreads from
mid-ocean ridges where two
plates adjoin. Where two plates move towards each other, one plate
subducts under another plate (oceanic or contintential) leading to an
oceanic trench.
Climate effects
Ocean currents greatly affect the Earth's
climate by transferring heat from the tropics to the polar regions, and transferring warm or cold air and precipitation to coastal regions, where winds may carry them inland. Surface heat and freshwater
fluxes creates global
density gradients that drive the
thermohaline circulation part of large-scale ocean circulation. It plays an important role in supplying heat to the polar regions, and thus in sea ice regulation. Changes in the thermohaline circulation are thought to have significant impacts on the earth's radiation budget. Insofar as the thermohaline circulation governs the rate at which deep waters reach the surface, it may also significantly influence atmospheric carbon dioxide concentrations.
For a discussion of the possibilities of changes to the thermohaline circulation under
global warming, see
shutdown of thermohaline circulation.
It is often stated that the thermohaline circulation is the primary reason that the climate Western Europe is so temperate. An alternate hypothesis claims that this is largely incorrect, and that Europe is warm mostly because it lies downwind of an ocean basin, and because
atmospheric waves bring warm air north from the
subtropics.
[16] [17]
The
Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans.
One of the most dramatic forms of
weather occurs over the oceans:
tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms).
Biology
Lifeforms native to oceans include:
- Radiata
- Fish
- Cetacea such as whales, dolphins and porpoises,
- Cephalopods such as octopus and squid
- Crustaceans such as lobsters, clams, shrimp and krill
- Marine worms
- Plankton
- Echinoderms such as brittle stars, starfish, sea cucumbers and sand dollars
Economy
The oceans are essential to transportation: most of the world's goods move by
ship between the world's
seaports.
Oceans are also the major supply source for the
fishing industry. Some of these are
shrimp,
fish,
crabs and
lobster. Oceanic fisheries employ xxx people directly and indirectly.
[18]
Ancient oceans
Continental drift continually reconfigures the oceans, joining and splitting bodies of water. Ancient oceans include:
- Bridge River Ocean, the ocean between the ancient Insular Islands and North America.
- Iapetus Ocean, the southern hemisphere ocean between Baltica and Avalonia.
- Panthalassa, the vast world ocean that surrounded the Pangaea supercontinent.
- Rheic Ocean
- Slide Mountain Ocean, the ocean between the ancient Intermontane Islands and North America.
- Tethys Ocean, the ocean between the ancient continents of Gondwana and Laurasia.
- Khanty Ocean, the ocean between Baltica and Siberia.
- Mirovia, the ocean that surrounded the Rodinia supercontinent.
- Paleo-Tethys Ocean, the ocean between Gondwana and the Hunic terranes.
- Proto-Tethys Ocean,
- Pan-African Ocean, the ocean that surrounded the Pannotia supercontinent.
- Superocean, the ocean that surrounds a global supercontinent.
- Ural Ocean, the ocean between Siberia and Baltica.
Extraterrestrial oceans
See also Extraterrestrial liquid water
Earth is the only known
planet with liquid water on its surface and is certainly the only one in our own
solar system. However, liquid water is thought to be present under the surface of the
Galilean moons
Europa and, with less certainty,
Callisto and
Ganymede.
Geysers have been found on
Enceladus, though these may not involve bodies of liquid water. Other icy moons may have once had internal oceans that have now frozen, such as
Triton. The planets
Uranus and
Neptune may also possess large oceans of liquid water under their thick atmospheres, though their internal structure is not well understood.
There is currently much debate over whether
Mars once had an ocean in its northern hemisphere, and over what happened to it; recent findings by the
Mars Exploration Rover mission indicate Mars had long-term standing water in at least one location, but its extent is not known.
Astronomers believe that
Venus had liquid water and perhaps oceans in its very early history. If they existed, all later vanished via
resurfacing.
Liquid hydrocarbons are thought to be present on the surface of
Titan, though
lakes
may be a more accurate term. The
Cassini-Huygens space mission initially discovered only what appeared to be dry lakebeds and empty river channels, suggesting that Titan had lost what surface liquids it might have had. Cassini's more recent fly-by of Titan offers radar images that strongly suggest hydrocarbon lakes near the colder polar regions. Titan is thought to have a subterranean water ocean under the ice and hydrocarbon mix that forms its outer crust.
Beyond the solar system, the planet
Gliese 581 c is at the right distance from its sun to support liquid surface water. However, its
greenhouse effect would make it too hot for oceans to exist on the surface. On
Gliese 581 d the greenhouse effect may bring temperatures suitable for surface oceans. Astronomers dispute whether
HD 209458 b has water vapour in its atmosphere.
Gliese 436 b is believed to have "hot ice." Neither of these planets are cool enough for liquid water—but if water molecules exist there, they are also likely to be found on planets at a suitable temperature.
[19]
Culture
The original concept of "ocean" goes back to notions of
Mesopotamian and
Indo-European mythology, imagining the world to be encircled by a great river.
Okeanos
, "O?ea???" in
Greek, reflects the ancient Greek observation that a strong current flowed off
Gibraltar and their subsequent assumption that it was a great river. (Compare also
Samudra
from
Hindu mythology and
Jörmungandr from
Norse mythology.) The world was imagined to be enclosed by a
celestial ocean above the heavens, and an ocean of the underworld below (compare
Ras?,
Varuna).
Artworks which depict maritime themes are known as
marine art, a term which particularly applies to common styles of European painting of the 17th to 19th centuries.
See also
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- Earthdive
- International Maritime Organization
- Law of the Sea
- Marginal sea
- Marine biology
- Marine debris
- Marine pollution
- Mediterranean sea
- Ocean acidification
- Oceanography
- Pelagic zone
- Polar seas
- Sea
- Sea level and sea level rise
- Sea salt
- Sea state
- Seven Seas
- Seawater
- Water
- World Ocean Atlas
- World Ocean Day
References
- Census of Marine Life maps an ocean of species
- "Ocean". ''The Columbia Encyclopedia.'' 2002. New York: Columbia University Press
- "Distribution of land and water on the planet". ''UN Atlas of the Oceans
- Maps of the whole world ocean
- ''Biology: Concepts & Connections.'' Chapter 34: The Biosphere: An Introduction to Earth's Diverse Environment. (sec 34.7)
- The World's Oceans and Seas
- Volume of Earth's Oceans
- Deep-Sea Fishes
- BAD PHYSICS: Misconceptions spread by K-6 Grade School Textbooks
- Why is water blue?
- Mystery Ocean Glow Confirmed in Satellite Photos
- 11/21/2005, Usa today: A glowing sea, courtesy of algae Quote: "...The water glowed green in the direction of the movement...A: Little microscopic creatures (called ''Lingulodinium polyedrum'') that glow in the dark caused the alluring strange display that night..."
- 05 October 2005, New Scientist: Sea's eerie glow seen from space Quote: "...The ancient mariners were right. Tales of "milky seas" that glow bluish-white at night and extend as far as the horizon have been spun by sailors for centuries. Now this eerie glow has been spotted from space....The glowing area spanned {{convert|15400|km2|mi2}}, an area the size of Connecticut (Image: Steven D Miller, US Naval Research Laboratory)..."
- NASA, DAAC Study: The Incredible Glowing Algae Quote: "...Each year, the North Atlantic Ocean announces springtime by producing “blooms” large enough to be seen from space. These explosive increases in microscopic marine algae, called phytoplankton, appear as sudden bright blossoms in satellite imagery..."
- Ocean Studies - RAIN
- The Source of Europe's Mild Climate]
- Is the Oceanic Heat Transport in the North Atlantic Irrelevant to the Climate in Europe?
- {{cite web
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- ''Hot "ice" may cover recently discovered planet''