Introduction
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.
Origin
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.
Composition
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.
FAQs on Seawater
1. What exactly is seawater and what does it contain?
Seawater is the water found in oceans and seas. It is not pure water but a complex mixture containing approximately 96.5% water and 3.5% dissolved substances. These substances are primarily salts, with sodium chloride being the most abundant, along with smaller amounts of other dissolved minerals, gases, and organic materials.
2. What are the key physical properties of seawater?
The primary physical properties of seawater that influence ocean behaviour are:
- Temperature: This varies with depth and latitude and is a major factor in determining water density.
- Salinity: The concentration of dissolved salts, which also heavily influences density.
- Density: A crucial property that drives ocean currents, as denser water sinks below less dense water.
- Freezing Point: Due to its salt content, seawater freezes at a lower temperature than fresh water, typically around -1.9°C.
3. Why is seawater considered a mixture and not a compound?
Seawater is classified as a mixture because its components (water and salts) are physically combined, not chemically bonded. This means:
- The proportions of salt to water can vary from place to place.
- The individual components retain their own chemical properties.
- The salts can be separated from the water through physical processes like evaporation or desalination. A compound, by contrast, has a fixed chemical formula and can only be separated by chemical reactions.
4. What is the average salinity of seawater and what causes it to change?
The average salinity of the world's oceans is about 35 parts per thousand (ppt). However, this value can vary significantly based on location. The main factors that alter salinity are:
- Evaporation: In warm, dry climates, high evaporation rates remove fresh water and leave salts behind, increasing salinity.
- Precipitation and River Runoff: High rainfall or the inflow of fresh water from rivers dilutes the seawater, lowering its salinity.
- Formation and Melting of Sea Ice: When seawater freezes, most of the salt is excluded from the ice, making the surrounding water saltier. When ice melts, it releases fresh water, decreasing salinity.
5. How do temperature and salinity affect the density of seawater?
Temperature and salinity are the two main drivers of seawater density. The relationship is straightforward:
- As temperature decreases, seawater becomes denser.
- As salinity increases, seawater becomes denser.
6. Why is it dangerous for humans to drink seawater for hydration?
Humans cannot survive by drinking seawater because it leads to severe dehydration. Our kidneys are only able to produce urine that is less salty than seawater. To get rid of the excess salt ingested from the ocean, the body must use up more of its existing fresh water than was gained by drinking the seawater in the first place, resulting in a net water loss.
7. What are the most important uses of seawater for the planet and humanity?
Seawater is a critical resource with several important functions and applications:
- Climate Regulation: Oceans absorb and transport enormous amounts of heat and absorb carbon dioxide, helping to stabilise the Earth's climate.
- Desalination: It serves as a source of fresh water for drinking and agriculture in arid regions through the process of desalination.
- Transportation: It is the foundation of global trade, allowing for the shipping of goods worldwide.
- Mineral Resource: Important minerals and elements like salt, magnesium, and bromine are extracted from seawater.
- Ecosystem Support: It provides the habitat for a vast array of marine life, which is a key part of the global food web.
