Seawater

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Seawater

Seawater is water

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
from a sea

SEA

See also: Sea and seasThe three-letter acronym SEA may refer to:People/organizations/businesses*Scientists and Engineers for America, a pro-science political advocacy group....
or ocean

Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
. On average, seawater in the world's oceans has a salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. Salinity in Australian English and North American English may also refer to the salt in soil ....
of about 3.5%, or 35 parts per thousand (also expressed 35‰ or 35 ppt). This means that every 1 kg of seawater has approximately 35 grams of dissolved salts

Sea salt

Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
: Na⁺, Cl^-).

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Salinity

Seawater composition (by mass) (salinity = 35)
Element	Percent	Element	Percent
Oxygen Oxygen Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...	85.84	Sulfur Sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....	0.091
Hydrogen Hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....	10.82	Calcium Calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....	0.04
Chlorine Chlorine Chlorine...	1.94	Potassium Potassium Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....	0.04
Sodium Sodium Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....	1.08	Bromine Bromine Bromine , , meaning "stench " ), is a chemical element with the symbol Br and atomic number 35. A halogen element, bromine is a reddish-brown Volatility liquid at Standard conditions for temperature and pressure that is intermediate in reactivity between chlorine and iodine....	0.0067
Magnesium Magnesium Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....	0.1292	Carbon Carbon Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....	0.0028

Although the vast majority of seawater has a salinity of between 3.1% and 3.8%, seawater is not uniformly saline throughout the world. Where mixing occurs with fresh water runoff from river mouths or near melting glaciers, seawater can be substantially less saline. The most saline open sea is the Red Sea

Red Sea

The Red Sea is a salt water inlet of the Indian Ocean between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb sound and the Gulf of Aden....
, where high rates of evaporation

Evaporation

Precipitation (meteorology)

File:MeanMonthlyP.gifIn meteorology, precipitation is any product of the condensation of Atmosphere water vapor that is deposited on the earth's surface....
and river inflow, and confined circulation result in the formation of unusually salty seawater. The salinity in isolated bodies of water (for example, the Dead Sea

Dead Sea

For the Brian Keene book of the same name, see Dead Sea The Dead Sea is a salt lake between Israel and the West Bank to the west, and Jordan to the east....
) can be considerably greater.

The density

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
of surface seawater ranges from about 1020 to 1029 kg·m^-3, depending on the temperature and salinity. Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg·m^-3 or higher. Seawater pH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
is limited to the range 7.5 to 8.4. The speed of sound

Speed of sound

Sound is a vibration that travels through an elasticity medium as a wave. The speed of sound describes how much distance such a wave travels in a certain amount of time....
in seawater is about 1500 m·s^-1, and varies with water temperature and pressure.

Compositional differences from fresh water

Seawater is more enriched in dissolved ions of all types than fresh water. However, the ratios of various solutes differ dramatically. For instance, although seawater is about 2.8 times more enriched with bicarbonate

Bicarbonate

In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. Its chemical formula is HCO3−....
than river water based on molarity, the percentage

Percentage

In mathematics, a percentage is a way of expressing a number as a fraction of 100 . It is often denoted using the percent sign, "%". For example, 45% is equal to 45 / 100, or 0.45....
of bicarbonate in seawater as a ratio of all dissolved ions is far lower than in river water; bicarbonate ions constitute 48% of river water solutes, but only 0.41% of all seawater ions. Differences like these are due to the varying residence time

Residence time

Residence time is a broadly useful concept that expresses how fast something moves through a system in equilibrium. It is the average time a substance spends within a specified region of space, such as a reservoir....
s of seawater solutes; sodium and chlorine have very long residence times, while calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
(vital for carbonate

Carbonate

In chemistry, a carbonate is a salt or ester of carbonic acid....
formation) tends to precipitate out much more quickly.

Geochemical explanations

**Total Molar Composition of Seawater (Salinity = 35)**
Component	Concentration (mol/kg)
H₂O Water (molecule) File:Blue-water-pool.jpgWater is the most abundant molecule on Earth's surface, constituting about 70% of the Earth's surface in liquid, solid, and gaseous states....	53.6
Cl^- Chloride The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....	0.546
Na⁺ Sodium Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....	0.469
Mg²⁺ Magnesium Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....	0.0528
SO₄^2- Sulfate In inorganic chemistry, a sulfate is a salt of sulfuric acid....	0.0282
Ca²⁺ Calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....	0.0103
K⁺ Potassium Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....	0.0102
C_T Total inorganic carbon The total inorganic carbon or dissolved inorganic carbon is the sum of inorganic carbon species in a solution. The inorganic carbon species include carbon dioxide, carbonic acid, bicarbonate anion, and carbonate anion....	0.00206
Br^- Bromide A bromide ion is a bromine atom with electric charge of -1.Compounds with bromine in formal oxidation state -1 are called bromides, and each individual chemical in this class can be called a bromide, as well....	0.000844
B_T Total boron The total boron is the sum of boron species in a solution. In the environment these species usually include boric acid and borate, for example:...	0.000416
Sr²⁺ Strontium Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically....	0.000091
F^- Fluoride Fluoride is the Redox form of fluorine. Both organic compounds and inorganic compounds containing the chemical element fluorine are considered fluorides....	0.000068

Scientific theories behind the origins of sea salt started with Sir Edmond Halley in 1715, who proposed that salt and other minerals were carried into the sea by rivers, having been leached out of the ground by rainfall runoff. Upon reaching the ocean, these salts would be retained and concentrated as the process of evaporation

Evaporation

Evaporation is the slow vaporization of a liquid and the reverse of condensation. A type of phase transition, it is the process by which molecules in a liquid State of matter spontaneously become gaseous ....
(see Hydrologic cycle) removed the water. Halley noted that of the small number of lakes in the world without ocean outlets (such as the Dead Sea

Dead Sea

For the Brian Keene book of the same name, see Dead Sea The Dead Sea is a salt lake between Israel and the West Bank to the west, and Jordan to the east....
and the Caspian Sea

Caspian Sea

The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the List of lakes by area or a full-fledged sea. It has a surface area of 371,000 square kilometers and a volume of 78,200 cubic kilometers ....
, see endorheic basin

Endorheic

An endorheic basin is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans. Normally the water accruing in drainage basins flows out through surface rivers or by underground diffusion through Permeability rock to the oceans....
), most have high salt content. Halley termed this process "continental weathering".

Halley's theory is partly correct. In addition, sodium

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
was leached out of the ocean floor when the oceans first formed. The presence of the other dominant ion

Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
of salt, chloride

Chloride

The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....
, results from "outgassing" of chloride

Chloride

The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....
(as hydrochloric acid

Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
) with other gases from Earth's interior via volcano

Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
s and hydrothermal vent

Hydrothermal vent

A hydrothermal vent is a fissure vent in a planet's surface from which Geothermal heated water issues. Hydrothermal vents are commonly found near volcano active places, areas where tectonic plates are moving apart, ocean basins, and hotspot ....
s. The sodium and chloride ions subsequently became the most abundant constituents of sea salt

Sea salt

Sea salt, obtained by the evaporation of seawater, is used in cooking and cosmetics. Historically called bay salt, its mineral content gives it a different taste from table salt, which is pure sodium chloride, usually refined from mined rock salt or from sea salt....
.

Ocean salinity has been stable for billions of years, most likely as a consequence of a chemical/tectonic system which removes as much salt as is deposited; for instance, sodium and chloride sinks include evaporite

Evaporite

Evaporites are water-soluble mineral sedimentary rock that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks....
deposits, pore water burial, and reactions with seafloor basalts. Since the ocean's formation, sodium is no longer leached out of the ocean floor, but instead is captured in sedimentary layers covering the bed of the ocean. One theory is that plate tectonics result in salt being forced under the continental land masses, where it is again slowly leached to the surface.

Human consumption of seawater

Accidentally consuming small quantities of clean seawater is not harmful, especially if the seawater is consumed along with a larger quantity of fresh water. However, consuming seawater to maintain hydration is counterproductive; in the long run, more water must be expended to eliminate the seawater's salt (through excretion

Excretion

Excretion is the process of eliminating waste products of metabolism and other non-useful materials. It is an essential process in all forms of life....
in urine

Urine

Urine is a liquid waste product of the body secreted by the kidneys by a process of filtration from blood called urination and excreted through the urethra....
) than the amount of water that is gained from drinking the seawater itself.

This occurs because the amount of sodium chloride

Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
in human blood is actively regulated within a very narrow range of 9 g/L (0.9% by weight) by the kidney. Drinking seawater (which contains about 3.5% ions of dissolved sodium chloride) temporarily increases the concentration of sodium chloride in the blood. This in turn promotes sodium excretion by the kidney, but the sodium concentration of seawater is above the maximum concentrating ability of the human kidney. Eventually with further seawater intake the blood concentration of sodium will rise to toxic levels, removing water from all cells and interfering with nerve conduction ultimately giving seizures and heart arrhythmias which become fatal.

Of note, various animals adapt to harsh living conditions. For example, the desert rat is able to concentrate sodium far more efficiently than the human kidney, and therefore would be able to survive by drinking seawater.

Survival manuals consistently advise against drinking seawater. For example, the book "Medical Aspects of Harsh Environments" (Chapter 29 - Shipboard Medicine) presents a summary of 163 life raft

Lifeboat (shipboard)

A lifeboat is a small watercraft carried on a ship to provide a means of emergency evacuation in the event of a disaster aboard the ship. Lifeboats may be rigid or inflatable vessels; the inflatable type are sometimes referred to as raft....
voyages. The risk of death was 39% for those who drank seawater, compared to only 3% for those who did not drink seawater. The effect of seawater intake has also been studied in laboratory setting in rats. (Etzion and Yagil; Metabolic effects in rats drinking increasing concentrations of seawater. Comp Biochem Physiol A. 1987;86(1):49-55.) . This study confirmed the negative effects of drinking seawater when dehydrated.

The temptation to drink seawater has always been greatest for sailors who have expended their supply of fresh water, and are unable to capture enough rainwater for drinking. This frustration is described famously by a line from Samuel Taylor Coleridge

Samuel Taylor Coleridge

Samuel Taylor Coleridge was an England poet, critic and Philosophy who was, along with his friend William Wordsworth, one of the founders of the Romanticism in England and one of the Lake Poets....
's The Rime of the Ancient Mariner
The Rime of the Ancient Mariner

The Rime of the Ancient Mariner is the longest major poem by the England poet Samuel Taylor Coleridge written in 1797?98 and published in the first edition of Lyrical Ballads ....
:

"Water, water, every where,

Nor any drop to drink."

Although it is clear that a human cannot survive on seawater alone, some people claim that one can drink up to two cups a day, mixed with fresh water in a 2:3 ratio, without ill effect. The French physician Alain Bombard

Alain Bombard

Alain Bombard was a France biologist, physician and politician famous for sailing across the Atlantic Ocean in a small boat.Alain Bombard was born in Paris....
claimed to have survived an ocean crossing in a small raft using only seawater and other provisions harvested from the ocean, but the veracity of his findings was challenged. In Kon-Tiki

Kon-Tiki

Kon-Tiki is the raft used by Norway explorer and writer Thor Heyerdahl in his 1947 expedition across the Pacific Ocean from South America to the Polynesia....
, Thor Heyerdahl

Thor Heyerdahl

Thor Heyerdahl was a Norway ethnographer and adventurer with a scientific background in zoology and geography. Heyerdahl became famous for his Kon-Tiki expedition, in which he sailed 4,300 miles by raft from South America to the Tuamotu Islands....
reported drinking seawater mixed with fresh in a 40/60% ratio. A few years later another adventurer named William Willis

William Willis (traveller)

William Willis was an American sailor and rafter who is famous due to his solo expeditions across oceans. Willis became a sailor when just a teenager, leaving his home in Hamburg to sail around Cape Horn....
claimed to have drunk two cups of seawater and one cup of fresh per day for 70 days without ill effect when he lost his part of his water supply.

Most modern ocean-going vessels create drinkable (potable) water from seawater using desalination

Desalination

Desalination, desalinization, or desalinisation refers to any of several processes that remove excess sodium chloride and other minerals from water....
processes such as vacuum distillation

Vacuum distillation

Vacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure causing evaporation of the most volatile liquid ....
, multi-stage flash distillation, or by the use of reverse osmosis

Reverse osmosis

Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
. However these processes are energy intensive, and most were not available or practical during the age of sail

Age of Sail

The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century....
.