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The ocean (also the
sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
sea
or the world ocean) is the body of
salt water Saline water (more commonly known as salt water) is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the ...
that covers approximately 70.8% of the surface of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
and contains 97% of Earth's water. Another definition is "any of the large bodies of water into which the great ocean is divided"."Ocean."
''Merriam-Webster.com Dictionary'', Merriam-Webster, https://www.merriam-webster.com/dictionary/ocean. Accessed March 14, 2021.
Separate names are used to identify five different areas of the ocean:
Pacific The Pacific Ocean is the largest and deepest of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. T ...

Pacific
(the largest),
Atlantic
Atlantic
,
Indian Indian or Indians refers to people or things related to India, or to the indigenous people of the Americas, or Aboriginal Australians until the 19th century. People South Asia * Indian people, people of Indian nationality, or people who come ...

Indian
,
Southern The name Southern may refer to: * South South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earl ...

Southern
(Antarctic), and
Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Alaska (United States), Canada, Finland, Greenland (Danish Realm, ...

Arctic
(the smallest).
Seawater Seawater, or salt water, is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of E ...

Seawater
covers approximately of the planet. The ocean is the principal component of Earth's
hydrosphere The hydrosphere (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...
, and therefore integral to
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

life
on Earth. Acting as a huge heat reservoir, the ocean influences
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena ...

climate
and
weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a p ...

weather
patterns, the
carbon cycle The carbon cycle is the biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physi ...

carbon cycle
, and the
water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, ...

water cycle
.
Oceanographers Oceanography (compound of the Greek language, Greek words ὠκεανός meaning "ocean" and γράφω meaning "Writing, write"), also known as oceanology, is the study of the physical and biological aspects of the ocean. It is an important Ea ...
divide the ocean into different vertical and horizontal zones based on physical and biological conditions. The
pelagic zone The pelagic zone consists of the water column A water column is a Concept, conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004) ...
consists of the
water column A water column is a concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind ...
from surface to ocean floor throughout the open ocean. The water column is further categorized in other zones depending on depth and on how much light is present. The
photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål ...
includes water from the surface to a depth of 1% of the surface light (about 200 m in the open ocean), where
photosynthesis Photosynthesis is a process used by plants and other organisms to into that, through , can later be released to fuel the organism's activities. Some of this chemical energy is stored in molecules, such as s and es, which are synthesized fro ...

photosynthesis
can occur. This makes the photic zone the most
biodiverse Biodiversity is the biological variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic, species In biology, a species is the basic unit of biological classification, classification and a taxonomic ...
. Photosynthesis by plants and microscopic
algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grouping that includes species from multiple distinct s. Included organisms range from , such as '','' and the s, to forms, such as the , a large whi ...

algae
(free floating
phytoplankton Phytoplankton () are the autotrophic An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compoun ...

phytoplankton
) creates organic matter using light, water, carbon dioxide, and nutrients. Ocean photosynthesis creates 50% of the oxygen in earth's atmosphere. This upper sunlit zone is the origin of the food supply which sustains most of the ocean
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

ecosystem
. Light only penetrates to a depth of a few hundred meters; the remaining ocean below is cold and dark. The
continental shelf A continental shelf is a portion of a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continen ...

continental shelf
where the ocean approaches dry land is more shallow, with a depth of a few hundred meters or less. Human activity has a greater impact on the
continental shelf A continental shelf is a portion of a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continen ...

continental shelf
.   Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. In the tropics, surface temperatures can rise to over . Near the poles where
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...

sea ice
forms, the temperature in equilibrium is about . Deep seawater temperature is between and in all parts of the ocean. Water continuously circulates in the oceans creating
ocean currents An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, wave breaking, breaking waves, cabbeling, and temperature and salinity differences. Dep ...
. These directed movements of seawater are generated by forces acting upon the water, including temperature differences,
atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies from ...

atmospheric circulation
(wind), the
Coriolis effect In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior throug ...

Coriolis effect
and differences in
salinity Salinity () is the saltiness or amount of dissolved in a body of , called (see also ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important ...

salinity
. Tidal currents originate from
tides (U.S.), low tide occurs roughly at moonrise and high tide with a high Moon, corresponding to the simple gravity model of two tidal bulges; at most places however, the Moon and tides have a phase shift. Tides are the rise and fall of sea leve ...

tides
, while surface currents are caused by wind and waves. Major ocean currents include the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current Boundary current ...
,
Kuroshio current The , also known as the Black or or the is a north-flowing, warm ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, ...
,
Agulhas current The Agulhas Current is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary current i ...
and
Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, ca ...

Antarctic Circumpolar Current
. Collectively, currents move enormous amounts of water and heat around the globe. This circulation significantly impacts global climate and the uptake and redistribution of pollutants such as
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
by moving these contaminants from the surface into the deep ocean. Ocean water contains large quantities of dissolved gases, including
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
and
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
. This
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

gas exchange
takes place at the ocean surface and solubility depends on the temperature and salinity of the water. The increasing concentration of carbon dioxide in the atmosphere due to
fossil fuel A fossil fuel is a -containing material formed underground from the remains of dead plants and animals that humans extract and to release for use. The main fossil s are , and , which humans extract through and . Fossil fuels may be burnt ...
combustion leads to higher concentrations in ocean water, resulting in
ocean acidification Ocean acidification is the ongoing decrease in the pH value of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of cont ...
. The ocean provides society with important
environmental services File:Mothugudem road near Chintoor.jpg, Social forestry in India, Social forestry in Andhra Pradesh, India, providing fuel, soil protection, shade and even well-being to travellers. Ecosystem services are the many and varied benefits to humans p ...
, including climate regulation. It also offers a means of
trade Trade involves the transfer of goods from one person or entity to another, often in exchange for money. Economists refer to a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of r ...

trade
and transport and access to food and other
resources A resource is a source or supply from which a benefit is produced and that has some utility. Resources can broadly be classified upon their availability — they are classified into renewable and non-renewable resources. They can also be classif ...

resources
. Known to be the
habitat Ibex in an alpine habitat In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. ...

habitat
of over 230,000
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
, it may contain far more – perhaps over two million species. However, the ocean is subject to numerous
environmental A biophysical environment is a life, biotic and Abiotic component, abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environ ...
threats, including
marine pollution Marine pollution occurs when substances used or spread by humans, such as industrial waste, industrial, agricultural pollution, agricultural and municipal solid waste, residential waste, particle (ecology), particles, noise, excess carbon dioxi ...
,
overfishing Overfishing is the removal of a species of fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, an ...
,
ocean acidification Ocean acidification is the ongoing decrease in the pH value of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of cont ...
and other effects of climate change. The continental shelf and
coastal waters The term territorial waters is sometimes used informally to refer to any area of water over which a state has jurisdiction Jurisdiction (from Latin ''Wikt:ius#Latin, juris'' 'law' + ''Wikt:dictio, dictio'' 'declaration') is the practical auth ...

coastal waters
that are most influenced by human activity are especially vulnerable.


Terminology


Ocean and sea

The terms "the ocean" or "the sea" used without specification refer to the interconnected body of salt water covering the majority of the Earth's surface. It includes the ,
Pacific The Pacific Ocean is the largest and deepest of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. T ...

Pacific
,
Indian Indian or Indians refers to people or things related to India, or to the indigenous people of the Americas, or Aboriginal Australians until the 19th century. People South Asia * Indian people, people of Indian nationality, or people who come ...

Indian
,
Southern The name Southern may refer to: * South South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earl ...

Southern
and
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic Ocean
s. As a general term, "the ocean" is mostly interchangeable with "the sea" in
American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English is the most influential form of ...
, but not in
British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and usage and is employed by a populatio ...
. Strictly speaking, a "sea''"'' is a body of water (generally a division of the world ocean) partly or fully enclosed by land. The word "sea" can also be used for many specific, much smaller bodies of seawater, such as the
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
or the
Red Sea The Red Sea ( ar, البحر الأحمر, translit=al-Baḥr al-ʾAḥmar; or ; Coptic Coptic may refer to: Afro-Asia * Copts, an ethnoreligious group mainly in the area of modern Egypt but also in Sudan and Libya * Coptic language, a Northe ...

Red Sea
. There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as
marginal sea This is a list of seas of the World Ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's w ...
s) or wholly (as inland seas) bordered by land.


World ocean

The contemporary concept of the ''World Ocean'' was coined in the early 20th century by the
Russian Russian refers to anything related to Russia, including: *Russians (русские, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (россияне), Russian language term ...
oceanographer
Yuly Shokalsky Yuly Mikhailovich Shokalsky (russian: Юлий Михайлович Шокальский; October 17, 1856 in Saint Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, ...
to refer to the continuous ocean that covers and encircles most of Earth. The global, interconnected body of salt water is sometimes referred to as the world ocean or global ocean." The concept of a continuous body of water with relatively free interchange among its parts is of fundamental importance to
oceanography Oceanography (from the Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period ...
.


Etymology

The word ''ocean'' comes from the figure in
classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history History (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ...
,
Oceanus In Greek mythology, Oceanus (; grc-gre, , also Ὠγενός, Ὤγενος, or Ὠγήν) was a Titans (mythology), Titan son of Uranus (mythology), Uranus and Gaia, the husband of his sister the Titan Tethys (mythology), Tethys, and the fath ...

Oceanus
(; grc-gre, ''Ōkeanós'', ), the elder of the
Titans In Greek mythology, the Titans (Ancient Greek, Greek: , ''Titânes'', , ''Titán'') were the pre-Olympian gods. According to the ''Theogony'' of Hesiod, they were the twelve children of the primordial parents Uranus (mythology), Uranus (Sky) and ...
in classical
Greek mythology Greek mythology is the body of myth Myth is a folklore genre Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief A belief is an Attitude (psyc ...
. Oceanus was believed by the
ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era was ...
and
Romans Roman or Romans usually refers to: *Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, ...
to be the divine personification of an enormous
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river
encircling the world. The concept of Ōkeanós has an
Indo-European The Indo-European languages are a language family native to western and southern Eurasia. It comprises most of the languages of Europe together with those of the northern Indian subcontinent and the Iranian Plateau. Some European languages of ...
connection. Greek Ōkeanós has been compared to the
Vedic FIle:Atharva-Veda samhita page 471 illustration.png, upright=1.2, The Vedas are ancient Sanskrit texts of Hinduism. Above: A page from the ''Atharvaveda''. The Vedas (, , ) are a large body of religious texts originating in ancient India. Com ...

Vedic
epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases.


Geography


Oceanic divisions

The major oceanic divisions – listed below in descending order of area and volume – are so named based on nearest
continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of th ...

continent
s, various
archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as ...

archipelago
s, and other criteria. Oceans are fringed with coastlines that run for 360,000 kilometres in total distance. They are also connected to smaller, adjoining bodies of water such as,
seas This is a list of seas of the World Ocean, including marginal seas, areas of water, various gulfs, bights, bays, and straits. Terminology * Ocean – the four to seven largest named bodies of water in the World Ocean, all of which have "Ocean" ...
,
gulfs A gulf is a large inlet from the ocean into the landmass, typically with a narrower opening than a bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean The ocean ...
,
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface ...

bay
s, bights, and
strait A strait is a naturally formed, narrowing, typically navigable waterway that connects two larger bodies of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly it ...

strait
s.
Seawater Seawater, or salt water, is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of E ...

Seawater
covers approximately and is customarily divided into five principal oceans, as below:


Ocean ridges and ocean basins

Every
ocean basin 400px, Diagrammatic cross-section of an ocean basin, showing the various geographic features In hydrology Hydrology (from Greek: wikt:ὕδωρ, ὕδωρ, "hýdōr" meaning "water" and wikt:λόγος, λόγος, "lógos" meaning "study") ...

ocean basin
has a
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
, which creates a long mountain range beneath the ocean. Together they form the global mid-oceanic ridge system that features the longest
mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arisen from the same cause, us ...

mountain range
in the world. The longest continuous mountain range is . This underwater mountain range is several times longer than the longest continental mountain range—the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sou ...

Andes
.
Oceanographers Oceanography (compound of the Greek language, Greek words ὠκεανός meaning "ocean" and γράφω meaning "Writing, write"), also known as oceanology, is the study of the physical and biological aspects of the ocean. It is an important Ea ...
state that less than 20% of the oceans have been mapped.


Formation

The origin of Earth's oceans is unknown. Oceans are thought to have formed in the
Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the International Commission on Stratigraphy The International Commissio ...

Hadean
eon and may have been the cause for the emergence of life. Scientists believe that a sizable quantity of
water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , even though it provide ...

water
would have been in the material that formed the Earth. Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. This is called
atmospheric escape Atmospheric escape is the loss of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive ...
.
Plate tectonics upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written L ...
, post-glacial rebound, and
sea level rise Tide gauge measurements show that the current global sea level rise began at the start of the 20th century. Between 1900 and 2017, the globally averaged sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloqui ...

sea level rise
continually change the
coastline The coast, also known as the coastline or seashore, is defined as the area where land meets the sea or ocean, or as a line that forms the boundary between the land and the ocean The ocean (also the sea or the world ocean) is the body ...

coastline
and structure of the world ocean. A global ocean has existed in one form or another on Earth for eons.


Physical properties


Volumes

The volume of water in all the oceans together is approximately 1.335 billion cubic kilometers (320.3 million cubic miles).


Depth

The average depth of the oceans is about 4 km. More precisely the average depth is . Nearly half of the world's marine waters are over deep. "Deep ocean," which is anything below 200 meters (660 ft.), covers about 66% of Earth's surface. This figure does not include seas not connected to the World Ocean, such as the
Caspian Sea The Caspian Sea (also known as Mazandaran Sea, Hyrcanian Ocean, or Khazar Sea), tk, Hazar deňzi, az, Xəzər Dənizi, russian: Каспийское море, script=Latn, fa, دریای مازندران، دریای خزر, script=Latn, tly, ...

Caspian Sea
. The deepest point in the ocean is the
Mariana Trench The Mariana Trench or Marianas Trench is located in the western Pacific Ocean 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, de ...
, located in the Pacific Ocean near the
Northern Mariana Islands The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands (CNMI; ch, Sankattan Siha Na Islas Mariånas; cal, Commonwealth Téél Falúw kka Efáng llól Marianas), is an unincorporated territories of the Unit ...

Northern Mariana Islands
. Its maximum depth has been estimated to be . The British naval vessel ''Challenger II'' surveyed the trench in 1951 and named the deepest part of the trench the "
Challenger Deep The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere (the oceans), with a depth of by direct measurement from deep-diving submersible A submersible is a small watercraft designed to operate underwater. The t ...
". In 1960, the
Trieste Trieste ( , ; sl, Trst ; german: Triest ) is a city and in northeastern . It is the capital city, and largest city, of the of , one of two autonomous regions which are not subdivided into . Trieste is located at the head of the , on a narrow ...

Trieste
successfully reached the bottom of the trench, manned by a crew of two men.


Color


Oceanic zones

Oceanographers Oceanography (compound of the Greek language, Greek words ὠκεανός meaning "ocean" and γράφω meaning "Writing, write"), also known as oceanology, is the study of the physical and biological aspects of the ocean. It is an important Ea ...
divide the ocean into different vertical and horizontal zones defined by physical and biological conditions. The
pelagic zone The pelagic zone consists of the water column A water column is a Concept, conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004) ...
consists of the
water column A water column is a concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind ...
of the open ocean, and can be divided into further regions categorized by light abundance and by depth.


Grouped by light penetration

* The
photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål ...
includes the oceans from the surface to a depth of 200 m; it is the region where
photosynthesis Photosynthesis is a process used by plants and other organisms to into that, through , can later be released to fuel the organism's activities. Some of this chemical energy is stored in molecules, such as s and es, which are synthesized fro ...

photosynthesis
can occur and is, therefore, the most
biodiverse Biodiversity is the biological variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic, species In biology, a species is the basic unit of biological classification, classification and a taxonomic ...
. Photosynthesis by plants and microscopic
algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grouping that includes species from multiple distinct s. Included organisms range from , such as '','' and the s, to forms, such as the , a large whi ...

algae
(free floating
phytoplankton Phytoplankton () are the autotrophic An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compoun ...

phytoplankton
) allows the creation of organic matter from chemical precursors including water and carbon dioxide. This organic matter can then be consumed by other creatures. Much of the organic matter created in the photic zone is consumed there but some sinks into deeper waters. * Below the photic zone is the mesopelagic or twilight zone where there is a very small amount of light. Below that is the aphotic deep ocean to which no surface sunlight at all penetrates. Life that exists deeper than the photic zone must either rely on material sinking from above (see
marine snow In the deep ocean, marine snow is a continuous shower of mostly organic detritus In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical process ...

marine snow
) or find another energy source.
Hydrothermal vents A hydrothermal vent is a on the seafloor from which heated water discharges. Hydrothermal vents are commonly found near active places, areas where s are moving apart at s, ocean basins, and . are rocks and mineral ore deposits formed by the a ...
are a source of energy in what is known as the aphotic zone (depths exceeding 200 m). The pelagic part of the photic zone is known as the epipelagic.


Grouped by depth and temperature

The pelagic part of the aphotic zone can be further divided into vertical regions according to depth and temperature: * The mesopelagic is the uppermost region. Its lowermost boundary is at a thermocline of which generally lies at in the tropics. Next is the bathypelagic lying between , typically between and . Lying along the top of the abyssal plain is the abyssal zone, abyssopelagic, whose lower boundary lies at about . The last and deepest zone is the hadal zone, hadalpelagic which includes the oceanic trench and lies between . * The benthic zones are aphotic and correspond to the three deepest zones of the deep-sea. 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 oceanic trenches. Distinct boundaries between ocean surface waters and deep waters can be drawn based on the properties of the water. These boundaries are called Thermocline, thermoclines (temperature), Halocline, haloclines (salinity), Chemocline, chemoclines (chemistry), and Pycnocline, pycnoclines (density). If a zone undergoes dramatic changes in temperature with depth, it contains a thermocline, a distinct boundary between warmer surface water and colder deep water. The tropical thermocline is typically deeper than the thermocline at higher latitudes. Polar regions of Earth, Polar waters, which receive relatively little solar energy, are not stratified by temperature and generally lack a thermocline because surface water at polar latitudes are nearly as cold as water at greater depths. Below the thermocline, water everywhere in the ocean is very cold, ranging from −1°C to 3°C. Because this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9°C. If a zone undergoes dramatic changes in salinity with depth, it contains a halocline. If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline. Temperature and salinity control the density of ocean water, with colder and saltier water being more dense, and this density in turn regulates the global water circulation within the ocean. The halocline often coincides with the thermocline, and the combination produces a pronounced pycnocline, a boundary between less dense surface water and dense deep water.


Grouped by distance from land

The pelagic zone can be further subdivided into two sub regions based on distance from land: the neritic zone and the oceanic zone. The neritic zone encompasses the water mass directly above the continental shelves and hence includes
coastal waters The term territorial waters is sometimes used informally to refer to any area of water over which a state has jurisdiction Jurisdiction (from Latin ''Wikt:ius#Latin, juris'' 'law' + ''Wikt:dictio, dictio'' 'declaration') is the practical auth ...

coastal waters
, whereas the oceanic zone includes all the completely open water. 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.


Temperature

Ocean temperatures depends on the amount of solar radiation falling on its surface. In the tropics, with the Sun nearly overhead, the temperature of the surface layers can rise to over while near the poles the temperature in equilibrium with the
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...

sea ice
is about . There is a continuous circulation of water in the oceans. Warm surface currents cool as they move away from the tropics, and the water becomes denser and sinks. The cold water moves back towards the equator as a deep sea current, driven by changes in the temperature and density of the water, before eventually welling up again towards the surface. Deep seawater has a temperature between and in all parts of the globe. Seawater with a typical salinity of 35‰ has a freezing point of about −1.8°C (28.8°F). When its temperature becomes low enough, ice crystals form on the surface. These break into small pieces and coalesce into flat discs that form a thick suspension known as frazil. In calm conditions this freezes into a thin flat sheet known as nilas, which thickens as new ice forms on its underside. In more turbulent seas, frazil crystals join into flat discs known as pancakes. These slide under each other and coalesce to form Drift ice, floes. In the process of freezing, salt water and air are trapped between the ice crystals. Nilas may have a salinity of 12–15‰, but by the time the sea ice is one year old, this falls to 4–6‰. Ocean heat content, Ocean warming accounts for over 90% of Earth's energy accumulation from Earth's Energy Imbalance, global warming between 1971 and 2020. About one third of that extra heat has been estimated to propagate to depths below 700 meters.


Ocean currents and global climate


Types of ocean currents

An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the
Coriolis effect In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior throug ...

Coriolis effect
, temperature and
salinity Salinity () is the saltiness or amount of dissolved in a body of , called (see also ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important ...

salinity
differences. Ocean currents are primarily horizontal water movements. They have different origins, such as tides for tidal currents, or wind and waves for surface currents. Tidal currents are in phase with the tide, hence are Quasiperiodicity, quasiperiodic; associated with the influence of the moon and sun pull on the ocean water. Tidal currents may form various complex patterns in certain places, most notably around Cape (geography), headlands. Non-periodic or non-tidal currents are created by the action of winds and changes in density of water. In littoral zones, breaking waves are so intense and the depth measurement so low, that maritime currents reach often 1 to 2 Knot (unit), knots. The wind and waves create surface currents (designated as "drift currents"). These currents can decompose in one quasi-permanent current (which varies within the hourly scale) and one movement of Stokes drift under the effect of rapid waves movement (which vary on timescales of a couple of seconds). The quasi-permanent current is accelerated by the breaking of waves, and in a lesser governing effect, by the friction of the wind on the surface. This acceleration of the current takes place in the direction of waves and dominant wind. Accordingly, when the ocean depth increases, the Earth's rotation, rotation of the earth changes the direction of currents in proportion with the increase of depth, while friction lowers their speed. At a certain ocean depth, the current changes direction and is seen inverted in the opposite direction with current speed becoming null: known as the Ekman spiral. The influence of these currents is mainly experienced at the mixed layer of the ocean surface, often from 400 to 800 meters of maximum depth. These currents can considerably change and are dependent on the yearly Season, seasons. If the mixed layer is less thick (10 to 20 meters), the quasi-permanent current at the surface can adopt quite a different direction in relation to the direction of the wind. In this case, the water column becomes virtually homogeneous above the thermocline. The wind blowing on the ocean surface will set the water in motion. The global pattern of winds (also called
atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies from ...

atmospheric circulation
) creates a global pattern of ocean currents. These are not only driven by the wind but also by the effect of the circulation of the earth (coriolis force). Theses major ocean currents include the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current Boundary current ...
,
Kuroshio current The , also known as the Black or or the is a north-flowing, warm ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, ...
,
Agulhas current The Agulhas Current is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary current i ...
and
Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, ca ...

Antarctic Circumpolar Current
. The Antarctic Circumpolar Current encircles Antarctica and influences the area's climate as well as connecting currents in several oceans.


Relationship of currents and climate

Collectively, currents move enormous amounts of water and heat around the globe influencing
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena ...

climate
. These wind driven currents are largely confined to the top hundreds of meters of the ocean. At greater depth the drivers of water motion are the thermohaline circulation. This is driven by the cooling of surface waters at northern and southern polar latitudes creating dense water which sinks to the bottom of the ocean. This cold and dense water moves slowly away from the Geographical pole, poles which is why the waters in the deepest layers of the world ocean are so cold. This deep ocean water circulation is relatively slow and water at the bottom of the ocean can be isolated from the ocean surface and atmosphere for hundreds or even a few thousand years. This circulation has important impacts on global climate and the uptake and redistribution of pollutants such as
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
by moving these contaminants from the surface into the deep ocean.       Ocean current, Ocean currents greatly affect Earth's climate by transferring heat from the tropics to the polar regions and thereby also affecting air temperature and precipitation in coastal regions and further inland. Surface heat and freshwater Flux, fluxes create global Density gradient, 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 Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...

sea ice
regulation. Oceans moderate the climate of locations where prevailing winds blow in from the ocean. At similar latitudes, a place on Earth with more influence from the ocean will have a more moderate climate than a place with more influence from land. For example, the cities San Francisco (37.8 N) and New York (40.7 N) have different climates because San Francisco has more influence from the ocean. San Francisco, on the west coast of North America, gets Westerlies, winds from the west over the Pacific Ocean, and the influence of the ocean water yields a more moderate climate with a warmer winter and a longer, cooler summer, with the warmest temperatures happening later in the year. New York, on the east coast of North America gets Westerlies, winds from the west over land, so New York has colder winters and hotter, earlier summers than San Francisco. Warmer ocean currents yield warmer climates in the long term, even at high latitudes. At similar latitudes, a place influenced by warm ocean currents will have a warmer climate overall than a place influenced by cold ocean currents. French Riviera (43.5 N) and Rockland, Maine (44.1 N) have same latitude, but the French Riviera is influenced by warm waters transported by the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current Boundary current ...
into the Mediterranean Sea and has a warmer climate overall. Maine is influenced by cold waters transported south by the Labrador Current giving it a colder climate overall. Changes in the thermohaline circulation are thought to have significant impacts on Earth's energy budget. Since the thermohaline circulation governs the rate at which deep waters reach the surface, it may also significantly influence Carbon dioxide in Earth's atmosphere, atmospheric carbon dioxide concentrations. However, climate change might result in the shutdown of thermohaline circulation in the future. This would in turn trigger cooling in the North Atlantic, Europe, and North America.


Waves and swell

The motions of the ocean surface, known as undulations or wind waves, are the partial and alternate rising and falling of the ocean surface. The series of mechanical waves that propagate along the interface between water and air is called Swell (ocean), swell – a term used in sailing, surfing and navigation. These motions profoundly affect ships on the surface of the ocean and the well-being of people on those ships who might suffer from Motion sickness, sea sickness. Wind blowing over the surface of a body of water forms Wind wave, waves that are perpendicular to the direction of the wind. The friction between air and water caused by a gentle breeze on a pond causes Capillary wave, ripples to form. A strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in the Southern Hemisphere in the Roaring Forties, long, organized masses of water called Swell (ocean), swell roll across the ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the Fetch (geography), fetch, the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between the two can produce broken, irregular seas. Constructive interference can cause individual (unexpected) rogue waves much higher than normal.Garrison, Tom (2012)
''Essentials of Oceanography''
6th ed. pp. 204 ff. Brooks/Cole, Belmont, California, Belmont. .
Most waves are less than high and it is not unusual for strong storms to double or triple that height. Rogue waves, however, have been documented at heights above . The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is pushed across the surface of the ocean by the wind, but this represents a transfer of energy and not a horizontal movement of water. As waves approach land and Waves and shallow water, move into shallow water, they change their behavior. If approaching at an angle, waves may bend (refraction) or wrap around rocks and headlands (diffraction). When the wave reaches a point where its deepest oscillations of the water contact the Seabed, ocean floor, they begin to slow down. This pulls the crests closer together and increases the Wave height, waves' height, which is called wave shoaling. When the ratio of the wave's height to the water depth increases above a certain limit, it "Wave breaking, breaks", toppling over in a mass of foaming water. This rushes in a sheet up the beach before retreating into the ocean under the influence of gravity. Earthquakes, Types of volcanic eruptions, volcanic eruptions or other major geological disturbances can set off waves that can lead to tsunamis in coastal areas which can be very dangerous.


Tides

Tides are the regular rise and fall in water level experienced by oceans in response to the Gravity, gravitational influences of the moon and the sun, and the effects of the Earth's rotation. During each tidal cycle, at any given place the water rises to a maximum height known as "high tide" before ebbing away again to the minimum "low tide" level. As the water recedes, it uncovers more and more of the foreshore, also known as the intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. In the open ocean tidal ranges are less than 1 meter, but in coastal areas these tidal ranges increase to more than 10 meters in some areas. Some of the largest tidal ranges in the world occur in the Bay of Fundy and Ungava Bay in Canada, reaching up to 16 meters. Other locations with record high tidal ranges include the Bristol Channel between England and Wales, Cook Inlet in Alaska, and the Río Gallegos, Santa Cruz, Río Gallegos in Argentina. Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes. This is half the 24 hours and 50 minute period that it takes for the Earth to make a complete revolution and return the moon to its previous position relative to an observer. Tidal force or tide-raising force decreases rapidly with distance, so the moon has more than twice as great an effect on tides as the Sun. When the sun, moon and Earth are all aligned (full moon and new moon), the combined effect results in the high "spring tides". A storm surge can occur when high winds pile water up against the coast in a shallow area and this, coupled with a low pressure system, can raise the surface of the ocean at high tide dramatically.


Water cycle, weather and rainfall

Ocean water represents the largest body of water within the global
water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, ...

water cycle
(oceans contain 97% of Earth's water). Evaporation from the ocean moves water into the atmosphere to later rain back down onto land and the ocean. Oceans have a significant effect on the biosphere. The ocean as a whole is thought to cover approximately 90% of the Earth's biosphere. Oceanic evaporation, as a phase of the water cycle, is the source of most rainfall (about 90%). Ocean temperatures affect
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena ...

climate
and wind patterns that affect life on land. One of the most dramatic forms of
weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a p ...

weather
occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms). As the world's ocean is the principal component of Earth's
hydrosphere The hydrosphere (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...
, it is integral to
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

life
on Earth, forms part of the
carbon cycle The carbon cycle is the biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physi ...

carbon cycle
and
water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, ...

water cycle
, and – as a huge heat reservoir – influences climate and weather patterns.


Chemical composition of seawater


Salinity

Salinity is a measure of the total amounts of dissolved salts in seawater. It was originally measured via measurement of the amount of chloride in seawater and hence termed chlorinity. It is now routinely measured by measuring Electrical resistivity and conductivity, electrical conductivity of the water sample. Salinity can be calculated using the chlorinity, which is a measure of the total mass of halogen ions (includes fluorine, chlorine, bromine, and iodine) in seawater. By international agreement, the following formula is used to determine salinity: Salinity (in ‰) = 1.80655 × Chlorinity (in ‰) The average ocean water chlorinity is about 19.2‰, and, thus, the average salinity is around 34.7‰. Salinity has a major influence on the density of seawater. A zone of rapid salinity increase with depth is called a halocline. The temperature of maximum density of Salinity#Seawater, seawater decreases as its salt content increases. Freezing temperature of water decreases with salinity, and boiling temperature of water increases with salinity. Typical seawater freezes at around −2 °C at atmospheric pressure. If precipitation exceeds evaporation, as is the case in Polar regions of Earth, polar and Temperate climate, temperate regions, salinity will be lower. If evaporation exceeds precipitation, as is sometimes the case in Tropics, tropical regions, salinity will be higher. Thus, oceanic waters in polar regions have lower salinity content than oceanic waters in temperate and tropical regions. However, the formation of
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...

sea ice
at high latitudes excludes salt from the ice and thereby increases salinity in the residual seawater in some polar regions.


General characteristics of ocean surface waters

The waters in different regions of the ocean have quite different temperature and salinity characteristics. This is due to differences in the local water balance (precipitation vs evaporation) and the "sea to air" temperature gradients. These characteristics can vary a lot within ocean regions but the table below provides an illustration of the sort of values usually encountered.


Oxygen, carbon dioxide, other gases and the carbon cycle

Ocean water contains large quantities of dissolved gases, including
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
and
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
. These dissolve into ocean water via
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

gas exchange
at the ocean surface, with the solubility of these gases depending on the temperature and salinity of the water. The increasing Carbon dioxide in Earth's atmosphere, carbon dioxide concentrations in the atmosphere due to
fossil fuel A fossil fuel is a -containing material formed underground from the remains of dead plants and animals that humans extract and to release for use. The main fossil s are , and , which humans extract through and . Fossil fuels may be burnt ...
combustion lead to higher concentrations in the ocean waters and
ocean acidification Ocean acidification is the ongoing decrease in the pH value of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of cont ...
.IUCN (2017
THE OCEAN AND CLIMATE CHANGE
IUCN (International Union for Conservation of Nature) Issues Brief.
The dissolving atmospheric carbon dioxide then reacts with bicarbonate and carbonate ions in seawater. The process of
photosynthesis Photosynthesis is a process used by plants and other organisms to into that, through , can later be released to fuel the organism's activities. Some of this chemical energy is stored in molecules, such as s and es, which are synthesized fro ...

photosynthesis
in the surface ocean also consumes some carbon dioxide and releases oxygen which may then return to the atmosphere. This photosynthesis in the ocean is dominated by microscopic phytoplankton, a type of free floating algae. The subsequent bacterial decomposition of organic matter formed by photosynthesis in the ocean consumes oxygen and releases carbon dioxide. The sinking and bacterial decomposition of some organic matter in deep ocean water, at depths where the waters are out of contact with the atmosphere, leads to a reduction in oxygen concentrations and increase in carbon dioxide, carbonate and bicarbonate. This Oceanic carbon cycle, cycling of carbon dioxide in oceans is an important part of the global
carbon cycle The carbon cycle is the biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physi ...

carbon cycle
. The oceans represent a major sink for carbon dioxide taken up from the atmosphere by photosynthesis and by dissolution. There is also increasing attention focused on carbon dioxide uptake in coastal marine habitats such as Mangrove, mangroves and Salt marsh, saltmarshes, a process sometimes referred to as “Blue carbon”. The attention on these habitats is because these are strong carbon sinks and also habitats under considerable threat from human activities and environmental degradation. This decrease in oxygen concentration increases with the amount of sinking organic matter and the time the water is out of contact with the atmosphere. Most of the deep waters of the ocean still contain relatively high concentrations of oxygen sufficient for most animals to survive. However, there are some ocean areas with water with very low oxygen due to long periods of isolation from the atmosphere, and this oxygen deficiency could be made worse by climate change.


Residence times of chemical elements and ions

The ocean waters contain all of the chemical elements as dissolved ions, but the concentration in which they occur range from some with very high concentrations of several grammes per liter, such as sodium and chloride, to others, such as iron, with tiny concentration of a few ng (10−9) g/l. The concentration of any element depends on its rate of supply to the ocean from rivers, the atmosphere and hydrothermal vents, and the rate of its removal. Hence very abundant elements in ocean water like sodium, have quite high rates of input, reflecting high abundance in rocks and relatively rapid weathering, coupled to very slow removal from the ocean because sodium ions are rather unreactive and very soluble. By contrast some other elements such as iron and aluminium are abundant in rocks but very insoluble, meaning that inputs to the ocean are low and removal is rapid. Oceanographers consider the balance of input and removal by estimating the residence time of an element as the average time the element would spend dissolved in the ocean before it is removed. This removal is usually to the sediments, but in the case of water and some gases to the atmosphere. These cycles represent part of the major global cycle of elements that has gone on since the Earth first formed. The residence times of the very abundant elements like sodium in the ocean are estimated to be millions of years, while for highly reactive and insoluble elements, residence times are only hundreds of years.


Nutrients

A few elements such as
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
, phosphorus and potassium are essential for life, are major components of biological material, and are commonly called “nutrients”. Nitrate and phosphate have ocean Residence time, residence times of 10,000 and 69,000 years, respectively, while potassium is a much more abundant ion in the ocean with a residence time of 12 million years. The biological cycling of these elements means that this represents a continuous removal process from the ocean's water column as degrading organic material sinks to the ocean floor as sediment. Phosphate from Intensive farming, intensive agriculture and Sewage treatment, untreated sewage is transported via runoff to rivers and coastal zones to the ocean where it is metabolized. Eventually, it sinks to the ocean floor and is no longer available to humans as a commercial resource. Production of Phosphorite, rock phosphate, an essential ingredient in inorganic fertilizer is a slow geological process occurring in some of the world's ocean sediments thus making minable sedimentary apatite (phosphate) in effect a non-renewable resource (see peak phosphorus). This continuous net deposition loss of non-renewable phosphate from human activities may become a resource problem in the future for fertilizer production and food security.


Marine life

Life within the ocean evolution, evolved 3 billion years prior to life on land. Both the depth and the distance from shore strongly influence the biodiversity of the plants and animals present in each region. The diversity of life in the ocean is immense, including: * Animals: most animal phylum, phyla have species that inhabit the ocean, including many that are only found in marine environments such as Porifera, sponges, Cnidaria (such as corals and jellyfish), Ctenophora, comb jellies, Brachiopods, and Echinoderms (such as sea urchins and sea stars). Many other familiar animal groups primarily live in the ocean, including cephalopods (includes octopus and squid), crustaceans (includes lobsters, crabs, and shrimp), fish, sharks, cetaceans (includes whales, dolphins, and porpoises). In addition, many land animals have adapted to living a major part of their life on the oceans. For instance, seabirds are a diverse group of birds that have adapted to a life mainly on the oceans. They feed on marine animals and spend most of their lifetime on water, many only going on land for breeding. Other birds that have adapted to oceans as their living space are penguins, Gull, seagulls and Pelecaniformes, pelicans. Seven species of turtles, the sea turtles, also spend most of their time in the oceans. *Plants: including seagrass, sea grasses, or mangroves *Algae: algae is a "catch-all" term to include many photosynthesis, photosynthetic, protist, single-celled eukaryotes, such as green algae, diatoms, and dinoflagellates, but also multicellular algae, such as some red algae (including organisms like Pyropia, which is the source of the edible nori seaweed), and brown algae (including organisms like kelp). *Bacteria: ubiquitous single-celled prokaryotes found throughout the world * Archaea: prokaryotes distinct from bacteria, that inhabit many environments of the ocean, as well as many extremophile, extreme environments * Fungi: many marine fungi with diverse roles are found in oceanic environments


Human uses of the oceans

The ocean has been linked to human activity throughout history. These activities serve a wide variety of purposes, including History of navigation, navigation and exploration, naval warfare, travel, Freight transport, shipping and
trade Trade involves the transfer of goods from one person or entity to another, often in exchange for money. Economists refer to a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of r ...

trade
, food production (e.g. fishing, whaling, seaweed farming, aquaculture), leisure (Cruising (maritime), cruising, sailing, recreational boat fishing, scuba diving), power generation (see marine energy and offshore wind power), extractive industries (offshore drilling and deep sea mining), Fresh water, freshwater production via desalination. Many of the world's goods are moved by ship between the world's seaports. Large quantities of goods are transported across the ocean, especially across the Atlantic and around the Pacific Rim. A lot of cargo, such as manufactured goods, is usually transported within Shipping container, standard sized, lockable containers, loaded on purpose-built container ships at Container port, dedicated terminals. Containerization greatly increased the efficiency and decreased the cost of moving goods by sea, and was a major factor leading to the rise of globalization and exponential increases in international trade in the mid-to-late 20th century. Oceans are also the major supply source for the fishing industry. Some of the major harvests are shrimp, fish, crabs, and lobster. The biggest commercial fishery globally is for Anchovy, anchovies, Alaska pollock and tuna. A report by Food and Agriculture Organization, FAO in 2020 stated that "in 2017, 34 percent of the fish stocks of the world’s marine fisheries were classified as Overfishing, overfished". Fish and other fishery products from both wild fisheries and aquaculture are among the most widely consumed sources of protein and other essential nutrients. Data in 2017 showed that "fish consumption accounted for 17 percent of the global population’s intake of animal proteins". In order to fulfill this need, coastal countries have exploited marine resources in their exclusive economic zone, although fishing vessels are increasingly venturing further afield to exploit stocks in international waters. The ocean offers a very large supply of energy carried by ocean waves, tides,
salinity Salinity () is the saltiness or amount of dissolved in a body of , called (see also ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important ...

salinity
differences, and Ocean thermal energy, ocean temperature differences which can be harnessed to Electricity generation, generate electricity. Forms of Sustainable energy, sustainable marine energy include tidal power, Ocean thermal energy conversion, ocean thermal energy and wave power. Offshore wind power is captured by wind turbines placed out on the ocean; it has the advantage that wind speeds are higher than on land, though wind farms are more costly to construct offshore. There are large deposits of petroleum, as oil and natural gas, in rocks beneath the ocean floor. Oil platform, Offshore platforms and drilling rigs Offshore drilling, extract the oil or gas and store it for transport to land. "Freedom of the seas" is a principle in international law dating from the seventeenth century. It stresses freedom to navigate the oceans and disapproves of war fought in international waters. Today, this concept is enshrined in the United Nations Convention on the Law of the Sea (UNCLOS). There are two major international legal organizations that are involved in ocean governance on a global scale, namely the International Maritime Organization and the United Nations. The International Maritime Organization (IMO), which was ratified in 1958 is responsible mainly for maritime safety, liability and compensation and they have held some conventions on marine pollution related to shipping incidents. Ocean governance is the conduct of the policy, actions and affairs regarding the world's oceans.


Threats

Human activities affect marine life and marine habitats through many negative influences, such as marine pollution (including marine debris and microplastics) overfishing,
ocean acidification Ocean acidification is the ongoing decrease in the pH value of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of cont ...
and other effects of climate change on oceans.


Marine pollution


Plastic pollution


Overfishing


Climate change


Ocean acidification


Protection

Protecting Earth's oceans ecosystem/s against its recognized #Threats, threats is a major component of environmental protection and is closely related to sustainable development. One of its main techniques is the creation and enforcement of marine protected areas (MPAs). Other techniques may include standardization, standardized product certifications, supply chain transparency requirements policies, policies to prevent marine pollution, eco-tariffs, research and development, ecosystem-assistance (e.g. Coral bleaching#Artificial assistance, for coral reefs), support for sustainable seafood (e.g. Sustainable fishery#Remediation, sustainable fishing practices and types of aquaculture), banning and systematically obstructing (e.g. via higher costs policies) unsustainable ocean use and associated industries (e.g. Cruise ship#Environmental impact, cruise ship travel, Environmental effects of shipping, certain shipping practices), Environmental monitoring, monitoring, revising waste management of plastics and Environmental impact of fashion, fashion industry pollutants, protection of marine resources and components whose extraction or disturbance would cause substantial harm, engagement of broader publics and impacted communities, novel decision-making mechanisms, and the development of ocean clean-up projects. Ocean protection serves to i.a. protect human health and to safeguard stable conditions of this natural ecosystem upon which humans depend. It may be necessary to consider marine protection within a national, regional and international context. Marine protection could also have synergistic effects – for instance, according to a study, a global network of MPAs designed to improve fisheries productivity could substantially increase future catch. In 2021, 43 expert scientists published the first scientific framework version that – via integration, scientific review, review, clarifications and standardization – enables the evaluation of levels of protection of marine protected areas and can serve as a guide for any subsequent efforts to improve, plan and monitor marine protection-quality and -extents such as in efforts towards the 30%-protection-goal of the "Global Deal For Nature" and Sustainable Development Goal 14, the UN's SDG 14.


Extraterrestrial oceans

Extraterrestrial oceans may be composed of water or other Chemical element, elements and Chemical compound, compounds. The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for oceans' existence elsewhere in the Solar System. Although Earth is the only known planet with large stable bodies of liquid water on its surface and the only one in the Solar System, other celestial bodies are thought to have large oceans. In June 2020, NASA, NASA scientists reported that it is likely that exoplanets with oceans may be ''common'' in the Milky Way, Milky Way galaxy, based on Mathematical model, mathematical modeling studies.


Supercritical fluid on gas giants

The inner structure of gas giants remain poorly understood. Scientists suspect that under extreme pressure, hydrogen would act as a supercritical fluid. Hence the likelihood of "oceans" of liquid hydrogen deep in the interior of gas giants like Jupiter. The possibility of oceans of liquid carbon have been hypothesized to occur on ice giants, notably Neptune and Uranus.


See also

* European Atlas of the Seas * Land and water hemispheres * List of seas * Marine heatwave * World Ocean Atlas * World Oceans Day


References


External links


FAO (Food and Agriculture Organization of the United Nations) Fisheries Division

NOAA – National Oceanic and Atmospheric Administration (United States)

United Nations Decade of Ocean Science for Sustainable Development (2021–2030)
{{Authority control Oceans, Oceanography, Oceans Coastal and oceanic landforms Bodies of water