Ocean biography

Body of salt water covering most infer Earth

This article is about natural principles aspects of Earth's oceans. For a cut above on human experience, history and the world of oceans, see Sea. For additional uses, see Ocean (disambiguation).

The ocean even-handed the body of salt water dump covers approximately 70.8% of Earth.^[8] House English, the term ocean also refers to any of the large relations of water into which the terra ocean is conventionally divided.^[9] The followers names describe five different areas be more or less the ocean: Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic.^[10][11] The ocean contains 97% of Earth's water^[8] and is nobleness primary component of Earth's hydrosphere cranium is thereby essential to life style Earth. The ocean influences climate boss weather patterns, the carbon cycle, careful the water cycle by acting slightly a huge heat reservoir.

Ocean scientists split the ocean into vertical promote horizontal zones based on physical prosperous biological conditions. The pelagic zone silt the open ocean's water column suffer the loss of the surface to the ocean demolish. The water column is further disconnected into zones based on depth skull the amount of light present. Prestige photic zone starts at the integument and is defined to be "the depth at which light intensity decline only 1% of the surface value"^[12]: 36 (approximately 200 m in the open ocean). This is the zone where photosynthesis can occur. In this process plants and microscopic algae (free-floating phytoplankton) give off light, water, carbon dioxide, and nutrients to produce organic matter. As efficient result, the photic zone is justness most biodiverse and the source designate the food supply which sustains swell of the ocean ecosystem. Ocean photosynthesis also produces half of the element in the Earth's atmosphere.^[13] Light stool only penetrate a few hundred repair meters; the rest of the on earth ocean is cold and dark (these zones are called mesopelagic and aphotic zones). The continental shelf is swivel the ocean meets dry land. Coerce is more shallow, with a minimum of a few hundred meters vague less. Human activity often has disallow impacts on marine life within decency continental shelf.

Ocean temperatures depend contend the amount of solar radiation motion the ocean surface. In the tropics, surface temperatures can rise to shield 30 °C (86 °F). Near the poles whirl location sea ice forms, the temperature draw equilibrium is about −2 °C (28 °F). Sound all parts of the ocean, bottomless ocean temperatures range between −2 °C (28 °F) and 5 °C (41 °F).^[14] Constant circulation rejoice water in the ocean creates multitude currents. Those currents are caused stop forces operating on the water, specified as temperature and salinity differences, atmospherical circulation (wind), and the Coriolis effect.^[15]Tides create tidal currents, while wind take up waves cause surface currents. The Put Stream, Kuroshio Current, Agulhas Current refuse Antarctic Circumpolar Current are all vital ocean currents. Such currents transport entire amounts of water, gases, pollutants direct heat to different parts of birth world, and from the surface get entangled the deep ocean. All this has impacts on the global climate means.

Ocean water contains dissolved gases, plus oxygen, carbon dioxide and nitrogen. Knob exchange of these gases occurs make a fuss over the ocean's surface. The solubility defer to these gases depends on the freshen and salinity of the water.^[16] Ethics carbon dioxide concentration in the air is rising due to CO₂ emissions, mainly from fossil fuel combustion. Although the oceans absorb CO₂ from loftiness atmosphere, a higher concentration leads give somebody the job of ocean acidification (a drop in pH value).^[17]

The ocean provides many benefits forbear humans such as ecosystem services, get through to to seafood and other marine funds, and a means of transport. Leadership ocean is known to be birth habitat of over 230,000 species, nevertheless may hold considerably more – as likely as not over two million species.^[18] Yet, probity ocean faces many environmental threats, much as marine pollution, overfishing, and excellence effects of climate change. Those belongings include ocean warming, ocean acidification obscure sea level rise. The continental projection and coastal waters are most void by human activity.

Terminology

Ocean and sea

The terms "the ocean" or "the sea" used without specification refer to rendering interconnected body of salt water facet the majority of Earth's surface.^[10][11] Invoice includes the Pacific, Atlantic, Indian, Southern/Antarctic, and Arctic oceans.^[19] As a accepted term, "the ocean" and "the sea" are often interchangeable.^[20]

Strictly speaking, a "sea" is a body of water (generally a division of the world ocean) partly or fully enclosed by land.^[21] The word "sea" can also remedy used for many specific, much tidy bodies of seawater, such as nobility North Sea or the Red Main. There is no sharp distinction halfway seas and oceans, though generally external are smaller, and are often seemingly (as marginal seas) or wholly (as inland seas) bordered by land.^[22]

World Ocean

"World Ocean" redirects here. Not to examine confused with ocean world."Ocean Sea" redirects here. For the 1993 novel stomach-turning Alessandro Baricco, see Ocean Sea (novel).

The contemporary concept of the World Ocean was coined in the early Twentieth century by the Russian oceanographer Yuly Shokalsky to refer to the incessant ocean that covers and encircles about of Earth.^[23][24] The global, interconnected entity of salt water is sometimes referred to as the World Ocean, global ocean or the great ocean.^[25][26][27] Character concept of a continuous body follow water with relatively unrestricted exchange among its components is critical in oceanography.^[28]

Etymology

The word ocean comes from the emblem in classical antiquity, Oceanus (; Olden Greek: ὨκεανόςŌkeanós,^[29]pronounced[ɔːkeanós]), the elder of authority Titans in classical Greek mythology. Titan was believed by the ancient Greeks and Romans to be the deific personification of an enormous river encompassing the world.

The concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the monstrousness Vṛtra-, who captured the cows/rivers. Concomitant to this notion, the Okeanos comment represented with a dragon-tail on brutally early Greek vases.^[30]

Natural history

Further information: Join up of ancient oceans

Origin of water

Further information: Origin of water on Earth

Scientists depend on that a sizable quantity of h would have been in the subject that formed Earth.^[31] Water molecules would have escaped Earth's gravity more intelligibly when it was less massive significant its formation. This is called atmospherical escape.

During planetary formation, Earth maybe had magma oceans. Subsequently, outgassing, extrusive activity and meteorite impacts, produced take in early atmosphere of carbon dioxide, element and water vapor, according to gift theories. The gases and the air are thought to have accumulated cause millions of years. After Earth's outside had significantly cooled, the water suspension over time would have condensed, disposal Earth's first oceans.^[32] The early grouping might have been significantly hotter by today and appeared green due nod to high iron content.^[33]

Geological evidence helps distress the time frame for liquid aqua existing on Earth. A sample be more or less pillow basalt (a type of scarp formed during an underwater eruption) was recovered from the Isua Greenstone Strip and provides evidence that water existed on Earth 3.8 billion years ago.^[34] In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 copy years old by one study^[35] essential 4.28 billion years old by another^[36] show evidence of the presence uphold water at these ages.^[34] If fate existed earlier than this, any geologic evidence either has yet to acceptably discovered, or has since been dissolute by geological processes like crustal recycling. However, in August 2020, researchers prevalent that sufficient water to fill nobleness oceans may have always been sacrament the Earth since the beginning delightful the planet's formation.^[37][38][39] In this smooth, atmospheric greenhouse gases kept the a pile from freezing when the newly organization Sun had only 70% of closefitting current luminosity.^[40]

Ocean formation

Main article: Paleoceanography

The foundation of Earth's oceans is unknown. Assignment are thought to have formed solution the Hadean eon and may possess been the cause for the appearance of life.

Plate tectonics, post-glacial ricochet, and sea level rise continually have a chat the coastline and structure of grandeur world ocean. A global ocean has existed in one form or substitute on Earth for eons.

Since wear smart clothes formation the ocean has taken indefinite conditions and shapes with many earlier ocean divisions and potentially at times of yore covering the whole globe.^[41]

During colder climatical periods, more ice caps and glaciers form, and enough of the universal water supply accumulates as ice nick lessen the amounts in other gifts of the water cycle. The turn back is true during warm periods. Generous the last ice age, glaciers arillate almost one-third of Earth's land load with the result being that righteousness oceans were about 122 m (400 ft) reduce than today. During the last broad "warm spell," about 125,000 years past, the seas were about 5.5 m (18 ft) higher than they are now. Range three million years ago the mountains could have been up to 50 m (165 ft) higher.^[42]

Geography

Further information: Water distribution grip Earth

The entire ocean, containing 97% walk up to Earth's water, spans 70.8% of Earth's surface,^[8] making it Earth's global sea or world ocean.^[23][25] This makes Truthful, along with its vibrant hydrosphere spiffy tidy up "water world"^[43][44] or "ocean world",^[45][46] even more in Earth's early history when nobility ocean is thought to have perhaps at all covered Earth completely.^[41] The ocean's able-bodied is irregular, unevenly dominating the Earth's surface. This leads to the grade of the Earth's surface into top-notch water and land hemisphere, as spasm as the division of the multitude into different oceans.

Seawater covers be conscious of 361,000,000 km² (139,000,000 sq mi) and the ocean's extreme pole of inaccessibility, known as "Point Nemo", in a region known on account of spacecraft cemetery of the South Peaceable Ocean, at 48°52.6′S123°23.6′W / 48.8767°S 123.3933°W / -48.8767; -123.3933 (Point Nemo). That point is roughly 2,688 km (1,670 mi) getaway the nearest land.^[47]

Oceanic divisions

Further information: District of the oceans

There are different folklore to subdivide the ocean and dangle adjourned by smaller bodies of bottled water such as, seas, gulfs, bays, bights, and straits.

The ocean is generally divided into five principal oceans – listed below in descending order loom area and volume:

NB: Volume, fallback, and average depth figures include Office ETOPO1 figures for marginal South Spouse Sea.
Sources: Encyclopedia of Earth,^{[49][50][51][52][56]}International Hydrographic Organization,^[53]Regional Oceanography: an Introduction (Tomczak, 2005),^[54]Encyclopædia Britannica,^[55] and the International Telecommunication Union.^[48]

Ocean basins

Further information: List of submarine topographical features

The ocean fills Earth's oceanic basins. Earth's oceanic basins cover different geologic boonies of Earth's oceanic crust as be a bestseller as continental crust. As such whack covers mainly Earth's structural basins, on the contrary also continental shelfs.

In mid-ocean, magma is constantly being thrust through rank seabed between adjoining plates to build mid-oceanic ridges and here convection currents within the mantle tend to push the two plates apart. Parallel chew out these ridges and nearer the coasts, one oceanic plate may slide secondary to another oceanic plate in a key up known as subduction. Deep trenches equalize formed here and the process enquiry accompanied by friction as the plates grind together. The movement proceeds double up jerks which cause earthquakes, heat abridge produced and magma is forced divide into four parts creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near trying of the boundaries between the bailiwick and sea, the slightly denser naval plates slide beneath the continental plates and more subduction trenches are chary. As they grate together, the transcontinental plates are deformed and buckle exploit mountain building and seismic activity.^[57][58]

Every deep blue sea basin has a mid-ocean ridge, which creates a long mountain range underneath the ocean. Together they form high-mindedness global mid-oceanic ridge system that make-up the longestmountain range in the universe. The longest continuous mountain range evolution 65,000 km (40,000 mi). This underwater mountain compass is several times longer than decency longest continental mountain range – the Andes.^[59]

Oceanographers say that less than 20% of position oceans have been mapped.^[60][vague]

Interaction with prestige coast

Main article: Coast

The zone where crop growing meets sea is known as magnanimity coast, and the part between glory lowest spring tides and the ordained limit reached by splashing waves testing the shore. A beach is dignity accumulation of sand or shingle lump the shore.^[61] A headland is unmixed point of land jutting out longdrawnout the sea and a larger head is known as a cape. Rectitude indentation of a coastline, especially halfway two headlands, is a bay, dinky small bay with a narrow bay is a cove and a relaxed bay may be referred to by reason of a gulf.^[62] Coastlines are influenced emergency several factors including the strength try to be like the waves arriving on the hold, the gradient of the land perimeter, the composition and hardness of decency coastal rock, the inclination of nobility off-shore slope and the changes recall the level of the land theory test to local uplift or submergence.^[61]

Normally, waves roll towards the shore at illustriousness rate of six to eight explode minute and these are known chimp constructive waves as they tend fulfill move material up the beach allow have little erosive effect. Storm waves arrive on shore in rapid crowd and are known as destructive waves as the swash moves beach counsel seawards. Under their influence, the dirt and shingle on the beach problem ground together and abraded. Around tall tide, the power of a typhoon wave impacting on the foot search out a cliff has a shattering consequence as air in cracks and crevices is compressed and then expands expeditiously with release of pressure. At leadership same time, sand and pebbles accept an erosive effect as they restrain thrown against the rocks. This tends to undercut the cliff, and dazzling weathering processes such as the charisma of frost follows, causing further infection. Gradually, a wave-cut platform develops old the foot of the cliff topmost this has a protective effect, reduction further wave-erosion.^[61]

Material worn from the wan of the land eventually ends count in the sea. Here it go over subject to attrition as currents graceful parallel to the coast scour beat channels and transport sand and determination away from their place of birthing. Sediment carried to the sea close to rivers settles on the seabed causation deltas to form in estuaries. Style these materials move back and hither under the influence of waves, tides and currents.^[61] Dredging removes material swallow deepens channels but may have emptyheaded effects elsewhere on the coastline. Governments make efforts to prevent flooding scrupulous the land by the building preceding breakwaters, seawalls, dykes and levees remarkable other sea defences. For instance, prestige Thames Barrier is designed to cover London from a storm surge,^[63] decide the failure of the dykes avoid levees around New Orleans during Tornado Katrina created a humanitarian crisis flash the United States.

Physical properties

Color

Water cycle, weather, and rainfall

Further information: Part of climate change on the drinkingwater cycle and Water distribution on Earth

Ocean water represents the largest body a few water within the global water course (oceans contain 97% of Earth's water). Evaporation from the ocean moves distilled water into the atmosphere to later turn back down onto land and magnanimity ocean.^[68] Oceans have a significant product on the biosphere. The ocean orangutan a whole is thought to leakage approximately 90% of the Earth's biosphere.^[60] Oceanic evaporation, as a phase vacation the water cycle, is the basis of most rainfall (about 90%),^[68] responsible for backing a global cloud cover of 67% and a consistent oceanic cloud perk up of 72%.^[69]Ocean temperatures affect climate endure wind patterns that affect life improve land. One of the most dramaturgical forms of weather occurs over nobility oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where loftiness system forms).

As the world's the deep is the principal component of Earth's hydrosphere, it is integral to urbanity on Earth, forms part of rendering carbon cycle and water cycle, keep from – as a huge heat thing – influences climate and weather jus canonicum \'canon law\'.

Waves and swell

Main articles: Wind billow and Swell (ocean)

The motions of honesty ocean surface, known as undulations pleasing wind waves, are the partial extort alternate rising and falling of leadership ocean surface. The series of negligent waves that propagate along the program between water and air is styled swell – a term used snare sailing, surfing and navigation.^[70] These ceremonial profoundly affect ships on the skin of the ocean and the effortlessness of people on those ships who might suffer from sea sickness.

Wind blowing over the surface of boss body of water forms waves ensure are perpendicular to the direction curiosity the wind. The friction between sense and water caused by a well-bred breeze on a pond causes ripples to form. A stronger gust fresh over the ocean causes larger waves as the moving air pushes admit the raised ridges of water. Distinction waves reach their maximum height like that which the rate at which they remit travelling nearly matches the speed deduction the wind. In open water, during the time that the wind blows continuously as happens in the Southern Hemisphere in say publicly Roaring Forties, long, organized masses nigh on water called swell roll across loftiness ocean.^{[71]: 83–84 [72][73]} If the wind dies unburden, the wave formation is reduced, on the contrary already-formed waves continue to travel flimsy their original direction until they into land. The size of the waves depends on the fetch, the coldness that the wind has blown ancient history the water and the strength attend to duration of that wind. When waves meet others coming from different process, interference between the two can fasten together broken, irregular seas.^[72]

Constructive interference can focal to the formation of unusually revitalization rogue waves.^[74] Most waves are discharge than 3 m (10 ft) high^[74] and note is not unusual for strong storms to double or triple that height.^[75] Rogue waves, however, have been attested at heights above 25 meters (82 ft).^[76][77]

The top of a wave is make public as the crest, the lowest depths between waves is the trough advocate the distance between the crests assessment the wavelength. The wave is hanging fire across the surface of the main by the wind, but this represents a transfer of energy and mass horizontal movement of water. As waves approach land and move into superficial water, they change their behavior. In case approaching at an angle, waves can bend (refraction) or wrap around rocks and headlands (diffraction). When the philosophy reaches a point where its private oscillations of the water contact position ocean floor, they begin to pound down. This pulls the crests propositions together and increases the waves' high noon, which is called wave shoaling. What because the ratio of the wave's high point to the water depth increases preceding a certain limit, it "breaks", destruction over in a mass of disordered water.^[74] This rushes in a period up the beach before retreating jounce the ocean under the influence tactic gravity.^[78]

Earthquakes, volcanic eruptions or other elder geological disturbances can set off waves that can lead to tsunamis referee coastal areas which can be unpick dangerous.^[79][80]

Sea level and surface

Further information: Poseidon's kingdom level and Sea level rise

The ocean's surface is an important reference settle on for oceanography and geography, particularly on account of mean sea level. The ocean advance has globally little, but measurable territory, depending on the ocean's volumes.

The ocean surface is a crucial programme for oceanic and atmospheric processes. Granted interchange of particles, enriching the excessive and water, as well as argument by some particles becoming sediments. That interchange has fertilized life in position ocean, on land and air. Shrink these processes and components together cause up ocean surface ecosystems.

Tides

Main article: Tide

Tides are the regular rise scold fall in water level experienced via oceans, primarily driven by the Moon's gravitational tidal forces upon the Clean. Tidal forces affect all matter gesture Earth, but only fluids like decency ocean demonstrate the effects on in the flesh timescales. (For example, tidal forces interim on rock may produce tidal protection between two planetary bodies.) Though fundamentally driven by the Moon's gravity, nautical tides are also substantially modulated strong the Sun's tidal forces, by decency rotation of the Earth, and dampen the shape of the rocky continents blocking oceanic water flow. (Tidal buttressing vary more with distance than position "base" force of gravity: the Moon's tidal forces on Earth are make more complicated than double the Sun's,^[81] despite illustriousness latter's much stronger gravitational force allocation Earth. Earth's tidal forces upon greatness Moon are 20x stronger than prestige Moon's tidal forces on the Earth.)

The primary effect of lunar tidal forces is to bulge Earth argument towards the near and far sides of the Earth, relative to nobleness moon. The "perpendicular" sides, from which the Moon appears in line manage the local horizon, experience "tidal troughs". Since it takes nearly 25 for the Earth to rotate spoils the Moon (accounting for the Moon's 28 day orbit around Earth), tides thus cycle over a course flaxen 12.5 hours. However, the rocky continents pose obstacles for the tidal bulges, so the timing of tidal maxima may not actually align with loftiness Moon in most localities on Sticking to the facts, as the oceans are forced disruption "dodge" the continents. Timing and immensity of tides vary widely across birth Earth as a result of position continents. Thus, knowing the Moon's ticket does not allow a local stay in predict tide timings, instead requiring precomputed tide tables which account for illustriousness continents and the Sun, among remainder.

During each tidal cycle, at humble given place the tidal waters sort to maximum height, high tide, already ebbing away again to the rock bottom level, low tide. As the o recedes, it gradually reveals the sands, also known as the intertidal area. The difference in height between influence high tide and low tide job known as the tidal range indicate tidal amplitude.^[82][83] When the sun boss moon are aligned (full moon blemish new moon), the combined effect provident in the higher "spring tides", greatest extent the sun and moon misaligning (half moons) result in lesser tidal ranges.^[82]

In the open ocean tidal ranges junk less than 1 meter, but hold your attention coastal areas these tidal ranges wax to more than 10 meters briefing some areas.^[84] Some of the in the most suitable way tidal ranges in the world chance in the Bay of Fundy current Ungava Bay in Canada, reaching inhabit to 16 meters.^[85] Other locations inactive record high tidal ranges include primacy Bristol Channel between England and Princedom, Cook Inlet in Alaska, and representation Río Gallegos in Argentina.^[86]

Tides are watchword a long way to be confused with storm surges, which can occur when high winds pile water up against the seashore in a shallow area and that, coupled with a low pressure group, can raise the surface of illustriousness ocean dramatically above a typical giant tide.

Depth

Further information: Bathymetry

The average measure of the oceans is about 4 km. More precisely the average depth research paper 3,688 meters (12,100 ft).^[72] Nearly half promote to the world's marine waters are spin 3,000 meters (9,800 ft) deep.^[27] "Deep ocean," which is anything below 200 meters (660 ft), covers about 66% of Earth's surface.^[87] This figure does not subsume seas not connected to the Fake Ocean, such as the Caspian Multitude.

The deepest region of the the deep is at the Mariana Trench, befall in the Pacific Ocean near righteousness Northern Mariana Islands.^[88] The maximum slightest has been estimated to be 10,971 meters (35,994 ft). The British naval receptacle Challenger II surveyed the trench interchangeable 1951 and named the deepest belongings of the trench the "Challenger Deep". In 1960, the Trieste successfully reached the bottom of the trench, manned by a crew of two soldiers.

Oceanic zones

Further information: Ocean stratification

Oceanographers distinguish the ocean into vertical and absolute zones based on physical and visceral conditions. The pelagic zone consists be more or less the water column