Our planet is 70% covered with water, of which more than 96% is occupied by the oceans. This means that most of the water on Earth is salty. What is the salinity of the water? How is it determined and what depends on it? Is it possible to use such water in the household? Let's try to answer these questions.
What is the salinity of the water?
Most of the water on the planet has salinity. It is usually called seawater and is found in oceans, seas and some lakes. The rest is fresh, its amount on Earth is less than 4%. Before you figure out what salinity is, you need to understand what salt is.
Salts are complex substances that consist of cations (positively charged ions) of metals and anions (negatively charged ions) of acid bases. Lomonosov defined them as "fragile bodies that can dissolve in water." Many substances are dissolved in seawater. It contains sulfates, nitrates, phosphates, cations of sodium, magnesium, rubidium, potassium, etc. Together, these substances are defined as salts.
So what is the salinity of the water? This is the content of substances dissolved in it. It is measured in thousandths - ppm, which are indicated by a special symbol -% o. Per mille determines the number of grams in one kilogram of water.
What determines the salinity of water?
In different parts of the hydrosphere and even at different times of the year, the salinity of the water varies. It changes under the influence of several factors:
- evaporation;
- ice formation;
- precipitation;
- melting ice;
- river flow;
- currents.
When water evaporates from the surface of the oceans, salts remain and do not erode. As a result, their concentration rises. The freezing process has a similar effect. Glaciers contain the largest supply of fresh water on the planet. During their formation, the salinity of the oceans increases.
Melting glaciers are characterized by the opposite effect, reducing the salt content. Besides them, the source of fresh water is precipitation and rivers flowing into the ocean. The salt level also depends on the depth and nature of the currents.
Their greatest concentration on the surface. The closer to the bottom, the less salinity. Warm currents affect the salt content in a positive direction, cold, on the contrary, reduce it.
World Ocean Salinity
What is the salinity of seawater? We already know that it is far from the same in different parts of the planet. Its indicators depend on geographical latitudes, climatic features of the area, proximity of river objects, etc.
The average salinity of the oceans is 35 ppm. A lower concentration of substances is characterized by cold areas near the Arctic and Antarctic. Although in winter, when ice is formed, the amount of salts increases.
For the same reason, the least saline ocean is the Arctic Ocean (32% o). The highest content is noted in the Indian Ocean. It covers the Red Sea and the Persian Gulf, as well as the southern tropical zone, where salinity is up to 36 ppm.
The Pacific and Atlantic oceans have approximately equal concentrations of substances. Their salinity decreases in the equatorial zone and rises in subtropical and tropical regions. Some warm and cold currents balance each other. For example, the non-salted Gulf Stream and the salted Labrador in the Atlantic Ocean.
Salinity of lakes and seas
Most of the lakes on the planet are fresh, as they are mainly fed by rainfall. This does not mean that they have no salts at all, just their content is extremely small. If the amount of dissolved substances exceeds one ppm, then the lake is considered salty or mineral. The Caspian Sea has a record value (13% o). The largest fresh lake is Baikal.
The salt concentration depends on how the water leaves the lake. Fresh water bodies are flowing, while more saline ones are closed and subject to evaporation. The determining factor is also the rocks on which the lakes formed. So, in the area of the Canadian shield, rocks are poorly soluble in water, and therefore the reservoirs there are “clean”.
The seas are connected with the oceans through the straits. Their salinity is slightly different and affects the average values of ocean waters. So, the concentration of substances in the Mediterranean Sea is 39% o and is reflected in the Atlantic. The Red Sea, with an indicator of 41%, greatly raises the average salinity of the Indian Ocean. The most saline is the Dead Sea, in it the concentration of substances is from 300 to 350% about.
Properties and value of sea water
Salt water is not suitable for business. It is not suitable for drinking or watering plants. However, many organisms have long adapted to life in it. Moreover, they are very sensitive to changes in the level of its salinity. Based on this, organisms are divided into freshwater and marine.
So, many animals and plants that live in the oceans cannot live in the fresh water of rivers and lakes. Extremely marine are edible mussels, crabs, jellyfish, dolphins, whales, sharks and other animals.
For drinking, a person uses fresh water. Salty is used for medicinal purposes. In small quantities, water with sea salt is used to restore the body. The therapeutic effect is bathing and bathing in sea water.