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In this article, you will learn about the meaning of seawater, origin, composition, and impacts, etc. Seawater, or saltwater, is sea or ocean water. On average, seawater in the oceans of the world has a salinity of about 3.5 percent. This means that every kg of seawater contains approximately 35 grams of dissolved salt. The average surface density is 1,025 kg/l. Seawater is denser than fresh water and pure water because dissolved salts raise the mass by a larger proportion than the volume. The seawater freezing point lowers down as the concentration of salt increases.

Seawater is a rich source of numerous commercially important chemical elements. Most of the world's magnesium is obtained from seawater, but so are large amounts of bromine. In some parts of the world, sodium chloride (table salt) is still produced by the evaporation of seawater. In addition, when desalinated, water from the sea can provide an unlimited supply of drinking water. Several large desalination plants are designed in dry areas along the coastlines of the Middle East and elsewhere to ease freshwater shortages. 

Seawater Meaning

Seawater Meaning: Seawater is a mixture of 96.5 percent water, 2.5 percent salts, and smaller amounts of other substances, including inorganic and organic dissolved solids, particulate matter, and few other atmospheric gases.


Scientific findings on the roots of sea salt began with Sir Edmond Halley in 1715, who proposed that the salt and other minerals would be transported to the sea by rivers after the rain had washed it out of the ground. Upon reaching the ocean, these salts were concentrated as more salt arrived over time. Halley concluded that most of the lakes that do not have ocean outlets have a high salt content. Halley referred to this process as "continental weathering" Halley's theory was partially correct. In addition, when the ocean formed, sodium leached out of the ocean floor. The presence of other dominant ions of salt, chloride, tends to result from the outgassing of chloride with other gasses from the Earth's interior mostly through volcanoes and hydrothermal vents. Consequently, sodium and chloride ions were the most abundant components of sea salt. Ocean salinity has been steady for billions of years, most possibly as a result of a chemical/tectonic system that removes as much salt as it deposits; for example, sodium and chloride sinks include evaporite deposits, pore-water burials, and marine basalt reactions.


Seawater comprises more dissolved ions than any kind of freshwater. Nevertheless, the ratios of the solutes vary dramatically. For example, although seawater comprises about 2.8 times more bicarbonate than river water, the percentage of bicarbonate in seawater as a ratio of all dissolved ions is much lower than in river water. Bicarbonate ions account for 48 percent of river water solutions, but only 0.14 percent for seawater. Differences such as these are mainly owing to the varying residence times of seawater solutes; sodium and chloride have quite long residence periods, while calcium tends to precipitate much faster. Sodium, chloride, magnesium, sulfate, and calcium are the most abundant dissolved ions in seawater.

Due to their common chemical and physical properties, several of the features of seawater correspond to those of water in general. For instance, the molecular structure of seawater, like that of freshwater, favours the creation of bonds between molecules. Some of the distinct features of seawater are directly related to its salt content. For instance, the viscosity of seawater is higher than that of freshwater due to its higher salinity. Seawater density is also higher for the same reason. The freezing point of seawater is lower than that of pure water, and its boiling point is higher.

Human Impacts

Changing climate, increasing atmospheric carbon dioxide, heavy metals, and pollution in many ways are distorting global ocean geochemistry. The rate of change for some aspects is significantly higher than in the historical and recent geological record. Primary issues include increased acidity, reduced subsurface oxygen in waters, increased level of coastal nitrogen, and widespread increase in mercury and persistent organic pollutants. Most of these abnormalities are either directly or indirectly linked to human burning of fossil fuels, fertilizer, and industrial activity.

Even though oceans are an enormous reservoir, human activities have begun to affect their chemistry on a local and global scale. The accumulation of nutrients to coastal waters results in increased phytoplankton growth, high concentrations of dissolved and particulate organic materials, reduced penetration of light through seawater, and variations of the community structure of sub-dwelling organisms. Through industrial and automotive emissions, the concentration of lead on the surface of the ocean has increased dramatically on a global scale compared to pre-industrial levels.

Did You Know?

  • Saltwater functions as a conveyor belt to transport heat around the planet. 

  • Even though humans cannot remain healthy drinking saltwater, many creatures in the oceans and seas depend on saltwater for their very existence. 

  • Fish living in saltwater will end up dying in freshwater, and vice versa.

FAQ (Frequently Asked Questions)

1. Can Humans Survive on Saltwater in the Oceans Instead of Freshwater?

Ans. Accidental consumption of small amounts 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 counter-productive as more water must be excreted to eliminate salt through urine than the amount of water obtained from seawater itself. In normal circumstances, it would be considered unwise to drink large amounts of unfiltered seawater.

Although many ocean-going vessels desalinate drinking water from seawater by means of vacuum distillation or multi-stage flash distillation in an evaporator or, more recently, reverse osmosis. These energy-intensive systems were not generally available during the Age of Sail. Larger sailing warships with huge crews, such as Nelson's HMS Victory, were equipped with distilling equipment in their galleys. Animals such as fish, whales, sea turtles, and seabirds, such as penguins and albatrosses, have adjusted to survive in a high saline habitat.

2. Describe the Physical Features of Seawater.

Ans. The physical properties of seawater include both 'thermodynamic properties' such as density and freezing point, as well as transport properties such as electrical conductivity and viscosity. Density is, in general, a significant feature in ocean science, since small spatial alterations in density result in spatial variations in pressure at a given depth, which, in turn, drive ocean circulation. Physical properties can be measured directly. Nevertheless, direct measurements can be difficult to perform, especially in the field, which in many situations it is more convenient to measure a few important 'state variables' on which the properties depend, and then look obtain the desired property as a function of the measured state in a table, or calculate this using a mathematical formula.