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Seawater, or salt water, is
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
from 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.
sea
or
ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large bodies of water into which the great ocean is divided".
. On average, seawater in the world's oceans has a
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
of about 3.5% (35 g/l, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately of
dissolved salts
dissolved salts
(predominantly
sodium Sodium is a with the  Na (from Latin ''natrium'') and  11. It is a soft, silvery-white, highly reactive . Sodium is an , being in of the periodic table. Its only stable is 23Na. The free metal does not occur in nature, and must be ...

sodium
() and
chloride The chloride ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical ...

chloride
()
ions An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...

ions
). Average density at the surface is 1.025 kg/l. Seawater is
denser
denser
than both
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids Total dissolved solids (TDS) is a measure of the dissolved combined content of all ...

fresh water
and pure water (density 1.0 kg/l at ) because the dissolved salts increase the mass by a larger proportion than the volume. In comparison, most human physiological saline levels are approximately one quarter of this, for example blood is 9g/l (0.9% w/v). The freezing point of seawater decreases as salt concentration increases. At typical salinity, it
freezes
freezes
at about . The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an
Antarctic The Antarctic (US English or , UK English or and or ) is a around 's , opposite the region around the . The Antarctic comprises the continent of , the and other located on the or south of the . The Antarctic region includes the , wa ...

Antarctic
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

glacier
: the measured temperature was . Seawater
pH
pH
is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units.


Geochemistry


Salinity

Although the vast majority of seawater has a salinity of between 31 g/kg and 38 g/kg, that is 3.1–3.8%, seawater is not uniformly saline throughout the world. Where mixing occurs with freshwater runoff from river mouths, near melting glaciers or vast amounts of precipitation (e.g.
Monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric ph ...

Monsoon
), seawater can be substantially less saline. The most saline open sea is 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
, where high rates of
evaporation Evaporation is a type of that occurs on the of a as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other bas ...

evaporation
, low
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...
and low river run-off, and confined circulation result in unusually salty water. The salinity in isolated bodies of water can be considerably greater still - about ten times higher in the case of the
Dead Sea The Dead Sea ( he, יָם הַמֶּלַח lit. Sea of Salt; ar, البحر الميت , lit. ''the Dead Sea'',The first article ''al-'' is unnecessary and usually not used. or Buhayrat, Bahret or Birket Lut, ''lit.'' "Lake/Sea of Lot") is a s ...

Dead Sea
. Historically, several salinity scales were used to approximate the absolute salinity of seawater. A popular scale was the "Practical Salinity Scale" where salinity was measured in "practical salinity units (PSU)". The current standard for salinity is the "Reference Salinity" scale with the salinity expressed in units of "g/kg".


Thermophysical properties of seawater

The
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
of surface seawater ranges from about 1020 to 1029 kg/m3, depending on the temperature and salinity. At a temperature of 25 °C, salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6  kg/m3. Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg/m3 or higher. The density of seawater also changes with salinity. Brines generated by seawater desalination plants can have salinities up to 120 g/kg. The density of typical seawater brine of 120 g/kg salinity at 25 °C and atmospheric pressure is 1088 kg/m3. Seawater is limited to the range 7.5 to 8.4. The
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elasticity (solid mechanics), elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends s ...
in seawater is about 1,500 m/s (whereas speed of sound is usually around 330 m/s in air at roughly 101.3kPa pressure, 1 atmosphere), and varies with water temperature, salinity, and pressure. The
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal c ...

thermal conductivity
of seawater is 0.6 W/mK at 25 °C and a salinity of 35 g/kg. The thermal conductivity decreases with increasing salinity and increases with increasing temperature.


Chemical composition

Seawater contains more dissolved
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s than all types of freshwater. However, the ratios of solutes differ dramatically. For instance, although seawater contains about 2.8 times more
bicarbonate In inorganic chemistry#REDIRECT Inorganic chemistry features unusual bonding B: Caesium chloride Caesium chloride or cesium chloride is the inorganic compound with the formula Caesium, CsChloride, Cl. This colorless salt is an important sourc ...

bicarbonate
than river water, the
percentage In mathematics, a percentage (from Latin ''per centum'' "by a hundred") is a number or ratio expressed as a fraction (mathematics), fraction of 100. It is often Denotation, denoted using the percent sign, "%", although the abbreviations "pct.", ...

percentage
of bicarbonate in seawater as a ratio of ''all'' dissolved
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s is far lower than in river water. Bicarbonate ions constitute 48% of river water solutes but only 0.14% for seawater. Differences like these are due to the varying
residence time The residence time of a fluid parcelIn fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics ...
s of seawater solutes;
sodium Sodium is a with the  Na (from Latin ''natrium'') and  11. It is a soft, silvery-white, highly reactive . Sodium is an , being in of the periodic table. Its only stable is 23Na. The free metal does not occur in nature, and must be ...

sodium
and
chloride The chloride ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical ...

chloride
have very long residence times, while
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
(vital for
carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...

carbonate
formation) tends to precipitate much more quickly. The most abundant dissolved ions in seawater are sodium, chloride,
magnesium Magnesium is a 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 ...

magnesium
,
sulfate The sulfate or sulphate ion is a polyatomic anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having ...

sulfate
and calcium. Its
osmolarityOsmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L (pr ...
is about 1000 mOsm/l. Small amounts of other substances are found, including
amino acids Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional groups, along with a Substituent, side chain (R group) specific to each amino acid. The key Chemical element, elements of an amino ...

amino acids
at concentrations of up to 2 micrograms of nitrogen atoms per liter, which are thought to have played a key role in the
origin of life In evolutionary biology, abiogenesis, or informally the origin of life (OoL),Compare: is the natural process by which life has arisen from non-living matter, such as simple organic compounds. While the details of this process are still unkn ...
.


Microbial components

Research in 1957 by the
Scripps Institution of Oceanography The Scripps Institution of Oceanography (sometimes referred to as SIO, Scripps Oceanography, or Scripps) in San Diego, California, founded in 1903, is one of the oldest and largest centers for oceanography, ocean and Earth science research, p ...

Scripps Institution of Oceanography
sampled water in both
pelagic The pelagic zone consists of the water column A water column is a concept Concepts are defined as abstract ideas or general notions that occur in the mind, in speech, or in thought. They are understood to be the fundamental building bloc ...
and
neritic The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology Marine biology is the scientific study of the biology of marine life ...
locations in the Pacific Ocean. Direct microscopic counts and cultures were used, the direct counts in some cases showing up to 10 000 times that obtained from cultures. These differences were attributed to the occurrence of bacteria in aggregates, selective effects of the culture media, and the presence of inactive cells. A marked reduction in bacterial culture numbers was noted below the
thermocline A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colo ...

thermocline
, but not by direct microscopic observation. Large numbers of spirilli-like forms were seen by microscope but not under cultivation. The disparity in numbers obtained by the two methods is well known in this and other fields. In the 1990s, improved techniques of detection and identification of microbes by probing just small snippets of
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
, enabled researchers taking part in the
Census of Marine Life The Census of Marine Life was a 10-year, US $650 million scientific initiative, involving a global network of researchers in more than 80 nations, engaged to assess and explain the Biodiversity, diversity, distribution, and abundance of Marine lif ...
to identify thousands of previously unknown microbes usually present only in small numbers. This revealed a far greater diversity than previously suspected, so that a litre of seawater may hold more than 20,000 species. Mitchell Sogin from the
Marine Biological Laboratory The Marine Biological Laboratory (MBL) is an international center for research and education in biological and environmental science. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution affiliated with the Univ ...
feels that "the number of different kinds of bacteria in the oceans could eclipse five to 10 million." Bacteria are found at all depths in 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 ...
, as well as in the sediments, some being aerobic, others anaerobic. Most are free-swimming, but some exist as
symbionts Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, ...
within other organisms – examples of these being bioluminescent bacteria.
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a of that obtain energy via . The name ''cyanobacteria'' refers to their color (), giving them their other name, "blue-green algae", though modern botanists restrict the term ' to s and do not ...

Cyanobacteria
played an important role in the evolution of ocean processes, enabling the development of
stromatolites Stromatolites () or stromatoliths () are layered sedimentary formation of rocks, formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing microorganism, sulfate-reducing bacteria ...

stromatolites
and oxygen in the atmosphere. Some bacteria interact with
diatoms Diatoms (''diá-tom-os'' 'cut in half', from ''diá'', 'through' or 'apart', and the root of ''tém-n-ō'', 'I cut') are a major group of algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic ...

diatoms
, and form a critical link in the cycling of silicon in the ocean. One anaerobic species, ''
Thiomargarita namibiensis ''Thiomargarita namibiensis'' is a Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized by their cell env ...
'', plays an important part in the breakdown of
hydrogen sulfide Hydrogen sulfide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...

hydrogen sulfide
eruptions from diatomaceous sediments off the Namibian coast, and generated by high rates of
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
growth in the
Benguela Current The Benguela Current is the broad, northward flowing ocean current that forms the eastern portion of the South Atlantic Ocean gyre. The current extends from roughly Cape Point in the south, to the position of the Angola-Benguela front in the n ...
upwelling zone, eventually falling to the seafloor. Bacteria-like
Archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

Archaea
surprised marine microbiologists by their survival and thriving in extreme environments, such as the
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 ...
on the ocean floor. Alkalotolerant
marine bacteria Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in Marine habitat, marine environments, that is, in the saline water, saltwater of seas or oceans or the brackish water of coast ...
such as ''
Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 validly described species. The members of the genus demonstrate a great deal of Metabolism, metabolic diversity and conse ...

Pseudomonas
'' and ''
Vibrio ''Vibrio'' is a genus of Gram-negative bacteria, possessing a curved-rod (comma) shape, several species of which can cause foodborne illness, foodborne infection, usually associated with eating undercooked seafood. Typically found in Seawater, s ...
'' spp. survive in a range of 7.3 to 10.6, while some species will grow only at pH 10 to 10.6. Archaea also exist in pelagic waters and may constitute as much as half the ocean's
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...
, clearly playing an important part in oceanic processes. In 2000 sediments from the ocean floor revealed a species of Archaea that breaks down
methane Methane (, ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Earth ...
, an important
greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plant Plants are predominantly photosynthetic Photo ...

greenhouse
gas and a major contributor to atmospheric warming. Some bacteria break down the rocks of the sea floor, influencing seawater chemistry. Oil spills, and runoff containing human sewage and chemical pollutants have a marked effect on microbial life in the vicinity, as well as harbouring pathogens and toxins affecting all forms of
marine life Marine life, sea life, or ocean life is the plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, thr ...

marine life
. The protist
dinoflagellates The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, ...

dinoflagellates
may at certain times undergo population explosions called blooms or
red tide A red tide is a phenomenon of discoloration of sea surface. It is a common name for Harmful algal bloom, harmful algal blooms occurring along coastal regions, which result from large concentrations of aquatic microorganisms, such as protozoans a ...

red tide
s, often after human-caused pollution. The process may produce
metabolites In biochemistry, a metabolite is an intermediate or end product of metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabo ...

metabolites
known as biotoxins, which move along the ocean food chain, tainting higher-order animal consumers. ''
Pandoravirus salinus ''Pandoravirus salinus'' is a large virus of genus ''Pandoravirus'', found in coastal sediments in Chile, and is one of the largest viruses identified, along with ''Pandoravirus dulcis''. It is 2.5 million nucleobases long, encodes for about 2,50 ...
'', a species of very large virus, with a genome much larger than that of any other virus species, was discovered in 2013. Like the other very large viruses ''
Mimivirus ''Mimivirus'' is a genus of giant viruses, in the family ''Mimiviridae''. Amoeba serve as their natural hosts. This genus contains a single identified species named ''Acanthamoeba polyphaga mimivirus'' (APMV), which serves as its type species. I ...

Mimivirus
'' and ''
Megavirus Megavirus is a viral genus containing a single identified species named ''Megavirus chilensis'', phylogenetically related to Acanthamoeba polyphaga Mimivirus (APMV). In colloquial speech, Megavirus chilensis is more commonly referred to as just ...

Megavirus
'', ''Pandoravirus'' infects amoebas, but its genome, containing 1.9 to 2.5 megabases of DNA, is twice as large as that of ''Megavirus'', and it differs greatly from the other large viruses in appearance and in genome structure. In 2013 researchers from
Aberdeen University , mottoeng = The fear of the Lord is the beginning of wisdom , established = , type = Public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the t ...
announced that they were starting a hunt for undiscovered chemicals in organisms that have evolved in deep sea trenches, hoping to find "the next generation" of antibiotics, anticipating an "antibiotic apocalypse" with a dearth of new infection-fighting drugs. The EU-funded research will start in the Atacama Trench and then move on to search trenches off New Zealand and Antarctica. The ocean has a long history of human waste disposal on the assumption that its vast size makes it capable of absorbing and diluting all noxious material. While this may be true on a small scale, the large amounts of sewage routinely dumped has damaged many coastal ecosystems, and rendered them life-threatening. Pathogenic viruses and bacteria occur in such waters, such as ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative bacteria, Gram-negative, Facultative anaerobic organism, facultative anaer ...

Escherichia coli
'', ''
Vibrio cholerae ''Vibrio cholerae'' is a species of Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain o ...

Vibrio cholerae
'' the cause of
cholera Cholera is an infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of tissues to the infectious agents and the s they produce. An infectious disease, also known as a transmissible disea ...

cholera
,
hepatitis A Hepatitis A is an infectious disease of the liver The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces biochemicals necessary for digestion and growth. In humans, it is l ...
,
hepatitis E Hepatitis E is inflammation of the liver caused by infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissu ...
and
polio Poliomyelitis, commonly shortened to polio, is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology) ...

polio
, along with protozoans causing
giardiasis Giardiasis is a parasitic disease caused by ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''). About 10% of those infected have no symptoms. Individuals who experience symptoms may have diarrhea, abdominal pain ...
and
cryptosporidiosis Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease A parasitic disease, also known as parasitosis, is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, ...
. These pathogens are routinely present in the ballast water of large vessels, and are widely spread when the ballast is discharged.


Origin and history

The water in the sea was thought to come from the Earth's
volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

volcano
es, starting 4 billion years ago, released by degassing from molten rock. More recent work suggests much of the Earth's water may come from
comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...

comet
s.
Scientific theories A scientific theory is an explanation of an aspect of the natural science, natural world and universe that can be reproducibility, repeatedly tested and verified in accordance with the scientific method, using accepted protocol (science), protocol ...
behind the origins of sea salt started with Sir
Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such ...

Edmond Halley
in 1715, who proposed that salt and other minerals were carried into the sea by rivers after rainfall washed it out of the ground. Upon reaching the ocean, these salts concentrated as more salt arrived over time (see
Hydrologic 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, ...

Hydrologic cycle
). Halley noted that most lakes that don't have ocean outlets (such as the
Dead Sea The Dead Sea ( he, יָם הַמֶּלַח lit. Sea of Salt; ar, البحر الميت , lit. ''the Dead Sea'',The first article ''al-'' is unnecessary and usually not used. or Buhayrat, Bahret or Birket Lut, ''lit.'' "Lake/Sea of Lot") is a s ...

Dead Sea
and 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
, see
endorheic basin An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...
), have high salt content. Halley termed this process "continental weathering". Halley's theory was partly correct. In addition, sodium leached out of the ocean floor when the ocean formed. The presence of salt's other dominant ion, chloride, results from
outgassingOutgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

outgassing
of chloride (as
hydrochloric acid Hydrochloric acid +(aq) Cl−(aq) or H3O+ Cl− also known as muriatic acid, is an aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a salin ...

hydrochloric acid
) with other gases from Earth's interior via
volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

volcano
s and
hydrothermal vent A hydrothermal vent is a fissure A fissure is a long, narrow crack opening along the surface of the Earth. It is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in the Earth's crust, on ice sheets and glaciers, and ...
s. The sodium and chloride ions subsequently became the most abundant constituents of sea salt. Ocean salinity has been stable for billions of years, most likely as a consequence of a chemical/
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building A mountain is an elevated portion of the Earth's crust, gene ...
system which removes as much salt as is deposited; for instance, sodium and chloride sinks include
evaporite An evaporite () is a water-soluble Solubility is the property of a solid, liquid or gaseous chemical substance called ''solution, solute'' to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depend ...
deposits, pore-water burial, and reactions with seafloor
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extrusi ...

basalt
s.


Human impacts

Climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
, rising levels of
carbon dioxide in Earth's atmosphere Carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occu ...
, excess nutrients, and pollution in many forms are altering global oceanic
geochemistry Geochemistry is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanatio ...
. Rates of change for some aspects greatly exceed those in the historical and recent geological record. Major trends include an increasing
acidity An acid is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms ...
, reduced subsurface oxygen in both near-shore and pelagic waters, rising coastal nitrogen levels, and widespread increases in
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

mercury
and persistent organic pollutants. Most of these perturbations are tied either directly or indirectly to human fossil fuel combustion, fertilizer, and industrial activity. Concentrations are projected to grow in coming decades, with negative impacts on ocean biota and other marine resources. One of the most striking features of this is
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 ...
, resulting from increased CO2 uptake of the oceans related to higher atmospheric concentration of CO2 and higher temperatures, because it severely affects
coral reef A coral reef is an underwater 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 c ...

coral reef
s,
mollusk Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s,
echinoderm An echinoderm () is any member of the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of ...
s and
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda, amphipods and mantis shrimp. The ...
s (see
coral bleaching Coral bleaching occurs when coral polyp (zoology), polyps expel algae that live inside their tissues. Normally, coral polyps live in an Endosymbiont, endosymbiotic relationship with these algae, which are crucial for the health of the coral and the ...

coral bleaching
).


Human consumption

Accidentally consuming small quantities of clean seawater is not harmful, especially if the seawater is taken along with a larger quantity of fresh water. However, drinking seawater to maintain hydration is counterproductive; more water must be excreted to eliminate the salt (via
urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be cons ...

urine
) than the amount of water obtained from the seawater itself. In normal circumstances, it would be considered ill-advised to consume large amounts of unfiltered seawater. The actively regulates the levels of sodium and chloride in the blood within a very narrow range around 9 g/L (0.9% by weight). In most open waters concentrations vary somewhat around typical values of about 3.5%, far higher than the body can tolerate and most beyond what the kidney can process. A point frequently overlooked in claims that the kidney can excrete NaCl in Baltic concentrations of 2% (in arguments to the contrary) is that the gut cannot absorb water at such concentrations, so that there is no benefit in drinking such water. Drinking seawater temporarily increases blood's NaCl concentration. This signals the
kidney The kidneys are two reddish-brown bean-shaped organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized ...

kidney
to excrete sodium, but seawater's sodium concentration is above the kidney's maximum concentrating ability. Eventually the blood's sodium concentration rises to toxic levels, removing water from cells and interfering with
nerve A nerve is an enclosed, cable-like bundle of fibers (called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, ...

nerve
conduction, ultimately producing fatal
seizure An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temp ...
and
cardiac arrhythmia Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the heartbeat is irregular, too fast, or too slow. The heart rate that is too fast – above 100 beats per minute in adults – is called tach ...
.
Survival manual Survival skills are techniques that a person may use in order to sustain life in any type of natural environment or built environment. These techniques are meant to provide basic human needs, basic necessities for human life which include water ...
s consistently advise against drinking seawater. A summary of 163
life raft 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 d ...
voyages estimated the risk of death at 39% for those who drank seawater, compared to 3% for those who did not. The effect of seawater intake on rats confirmed the negative effects of drinking seawater when dehydrated. The temptation to drink seawater was greatest for sailors who had expended their supply of fresh water, and were unable to capture enough rainwater for drinking. This frustration was described famously by a line from
Samuel Taylor Coleridge Samuel Taylor Coleridge (; 21 October 177225 July 1834) was an , , and who, with his friend , was a founder of the in England and a member of the . He also shared volumes and collaborated with , , and . He wrote the poems ' and ', as well ...

Samuel Taylor Coleridge
's ''
The Rime of the Ancient Mariner ''The Rime of the Ancient Mariner'' (originally ''The Rime of the Ancyent Marinere'') is the longest major poem by the English poet Samuel Taylor Coleridge, written in 1797–98 and published in 1798 in the first edition of ''Lyrical Ballads'' ...
'': ::: ''"Water, water, everywhere,
And all the boards did shrink;
Water, water, everywhere,
Nor any drop to drink."'' Although humans cannot survive on seawater, some people claim that up to two cups a day, mixed with fresh water in a 2:3 ratio, produces no ill effect. The French physician
Alain Bombard Alain Bombard (; Paris, 27 October 1924 – Paris, 19 July 2005) was a France, French biologist, physician and politician famous for sailing in a small boat across the Atlantic Ocean without provision. He theorized that a human being could very we ...
survived an ocean crossing in a small Zodiak rubber boat using mainly raw fish meat, which contains about 40 percent water (like most living tissues), as well as small amounts of seawater and other provisions harvested from the ocean. His findings were challenged, but an alternative explanation was not given. In his 1948 book, ''
Kon-Tiki The ''Kon-Tiki'' expedition was a 1947 journey by raft across the Pacific Ocean from South America to the Polynesian islands, led by Norwegian explorer and writer Thor Heyerdahl. The raft was named ''Kon-Tiki'' after the Inca god Viracocha, for ...
'',
Thor Heyerdahl Thor Heyerdahl (; 6 October 1914 – 18 April 2002) was a Norway, Norwegian adventurer and Ethnography, ethnographer with a background in zoology, botany and geography. Heyerdahl is notable for his Kon-Tiki expedition, ''Kon-Tiki'' expedition i ...

Thor Heyerdahl
reported drinking seawater mixed with fresh in a 2:3 ratio during the 1947 expedition. A few years later, another adventurer, William Willis, claimed to have drunk two cups of seawater and one cup of fresh per day for 70 days without ill effect when he lost part of his water supply. During the 18th century, Richard Russell (doctor), Richard Russell advocated the medical use of this practice in the UK, and René Quinton expanded the advocation of this practice to other countries, notably France, in the 20th century. Currently, it is widely practiced in Nicaragua and other countries, supposedly taking advantage of the latest medical discoveries. Most oceangoing vessels desalination, desalinate Drinking water, potable water from seawater using processes such as vacuum distillation or multi-stage flash distillation in an evaporator (marine), evaporator, or, more recently, reverse osmosis. These energy-intensive processes were not usually available during the Age of Sail. Larger sailing warships with large crews, such as Horatio Nelson, 1st Viscount Nelson, Nelson's , were fitted with distilling apparatus in their galley (kitchen), galleys. Animals such as fish, whales, sea turtles, and seabirds, such as penguins and albatrosses have adapted to living in a high saline habitat. For example, sea turtles and saltwater crocodiles remove excess salt from their bodies through their tear ducts.


Mineral extraction

Minerals have been extracted from seawater since ancient times. Currently the four most concentrated metals – Sodium, Na, Mg, Calcium, Ca and Potassium, K – are commercially extracted from seawater. During 2015 in the US 63% of
magnesium Magnesium is a 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 ...

magnesium
production came from seawater and brines. Bromine is also produced from seawater in China and Japan. Lithium extraction from seawater was tried in the 1970s, but the tests were soon abandoned. The idea of extracting uranium from seawater has been considered at least from the 1960s, but only a few grams of uranium were extracted in Japan in the late 1990s.


Standard

ASTM International has an international standard for artificial seawater: ASTM D1141-98 (Original Standard ASTM D1141-52). It is used in many research testing labs as a reproducible solution for seawater such as tests on corrosion, oil contamination, and detergency evaluation.


See also

* * * * * * * * * * * * global ocean salinity


References


External links


Technical Papers in Marine Science 44, Algorithms for computation of fundamental properties of seawater, ioc-unesco.org, UNESCO 1983
Tables
Tables and software for thermophysical properties of seawater
MIT * {{Authority control Aquatic ecology Chemical oceanography Liquid water Physical oceanography Oceanographical terminology