The Importance of Salinity in the Ocean

Salinity is a crucial parameter that affects various aspects of the ocean. It refers to the measure of the amount of dissolved salts in water, typically expressed in grams per liter or parts per thousand (‰). Understanding salinity is essential for studying the physical and chemical properties of water, as well as its impact on marine organisms. In this article, we will explore the distribution of salinity, its controlling factors, and the reasons why high salinity does not drown humans in the sea.

Source of Oceanic Salinity

The primary source of oceanic salinity is the land. Rivers bring dissolved salts from continental areas to the oceans. Additionally, volcanic ashes contribute to the salinity of the oceans.

Controlling Factors of Salinity

Several factors influence the amount of salinity in different oceans and seas:

• Evaporation: There is a direct positive relationship between the rate of evaporation and salinity. Greater evaporation leads to higher salinity in the water and vice versa. High temperatures and low humidity create ideal conditions for evaporation, resulting in increased salt concentration.
• Precipitation: Salinity is inversely proportional to rainfall. Regions with high rainfall, such as the equatorial region, tend to have lower salinity. Conversely, areas with low rainfall, like subtropical high-pressure belts, experience higher salinity.
• Influx of River Water: Rivers carry salts from the land to the oceans. However, large rivers pour considerable amounts of freshwater at their mouths, reducing the overall salinity at those points.
• Atmospheric Pressure and Wind Direction: Anticyclonic conditions with stable air and high temperatures increase the salinity of surface water. Prevailing winds also redistribute salt, driving away saline water to less saline areas.
• Ocean Currents: Oceanic currents play a role in mixing seawater and influencing the spatial distribution of salinity. Warm equatorial currents drive salts away from western coastal areas and accumulate them along eastern coasts. Oceanic currents have less impact on enclosed and marginal seas.

Composition of Seawater

Seawater contains a composite solution of various mineral substances in a dilute form. The major salts in seawater include sodium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, potassium sulfate, calcium carbonate, and magnesium bromide.

Distribution of Salinity

The spatial distribution of salinity in the ocean can be studied from a horizontal and vertical perspective.

Horizontal Distribution

Salinity levels vary from enclosed seas to open seas. On average, salinity decreases from the equator towards the poles. However, the equator itself accounts for a relatively low salinity level. The highest salinity is typically recorded at latitudes between 20 and 40 degrees north, while the average salinity at 10-30 degrees south is around 35 ‰. Marginal areas of oceans often have lower salinity due to the influx of fresh water from rivers.

Vertical Distribution

Vertical distribution refers to the variation in salinity with depth. It is influenced by factors such as temperature, density, and currents. Typically, salinity decreases with depth, as freshwater and melting ice dilute the surface water. However, there can be variations depending on specific oceanic conditions and geographic locations.

Significance of Salinity

Salinity is crucial for studying the ocean’s overall health. It affects various physical and chemical properties of water, including density, heat capacity, conductivity, and freezing point. Salinity also impacts the types of organisms that can survive in different aquatic environments. By understanding salinity patterns, scientists can gain insights into ocean circulation, climate models, and marine ecosystems.

Fun Fact

Did you know that the Dead Sea, located between Israel and Jordan, has one of the highest levels of salinity in the world? Its salinity reaches about 34.2%, which is almost ten times saltier than the average ocean water.

In conclusion, salinity is a crucial parameter that affects various aspects of the ocean. It is influenced by factors such as evaporation, precipitation, river inflow, atmospheric pressure, wind direction, and ocean currents. Understanding salinity patterns helps scientists study the ocean’s physical and chemical properties, as well as its impact on marine life.

Mutiple Choice Questions

1. What is salinity?
a) The measure of the amount of dissolved salts in water
b) The weight ratio of dissolved materials to sample sea water
c) The density of water
d) The freezing point of water

Explanation: Salinity is the measure of the amount of dissolved salts in water. It is usually expressed in grams of salt per liter or kilogram of water, or in parts per thousand (‰).

2. What is the primary source of oceanic salinity?
a) Rivers bringing salts from continental areas
b) Volcanic ashes
c) Evaporation
d) Precipitation

Explanation: The primary source of oceanic salinity is land. Rivers bring salts in solution form from the continental areas and volcanic ashes are also a major source of oceanic salinity.

3. Which factor affects salinity by having a direct positive relationship with it?
a) Evaporation
b) Precipitation
c) Influx of river water
d) Prevailing winds

Explanation: Evaporation has a direct positive relationship with salinity. Greater the rate of evaporation, higher the salinity and vice versa. Evaporation causes more concentration of salt, leading to higher salinity.

4. In which region does salinity decrease due to high rainfall?
a) Subtropical high-pressure belts
b) Equatorial region
c) Trade winds belts
d) Sub-polar and polar zones

Explanation: The region with high rainfall, such as the equatorial region, records low salinity. Precipitation is inversely proportional to salinity, so higher rainfall leads to lower salinity.

5. How does the influx of river water affect salinity?
a) Salinity is reduced at the mouth of rivers
b) Salinity increases at the mouth of rivers
c) Salinity remains unchanged
d) Salinity decreases in rainy seasons

Explanation: The influx of river water reduces salinity at the mouth of rivers. The big and voluminous rivers pour down immense water at the mouth of the ocean, causing a decrease in salinity.

6. How do anti-cyclonic conditions affect salinity?
a) Increase salinity of surface water of oceans
b) Decrease salinity of surface water of oceans
c) Have no effect on salinity
d) Cause high precipitation

Explanation: Anti-cyclonic conditions with stable air and high temperature increase the salinity of the surface water of the oceans. Subtropical high-pressure belts represent such conditions, leading to high salinity.

7. How do oceanic currents affect the spatial distribution of salinity?
a) They mix seawaters and influence salinity
b) They have no influence on salinity
c) They increase salinity along the western coasts
d) They increase salinity along the eastern coasts

Explanation: Oceanic currents affect the spatial distribution of salinity by mixing seawaters. Equatorial warm currents drive away salts from the western coastal areas and accumulate them along eastern coastal areas, influencing salinity.

8. What is the composition of seawater in terms of salts?
a) A composite solution of mineral substances in dilute form
b) Pure water
c) No salts are present in seawater
d) A mixture of acids and bases

Explanation: Seawater contains a composite solution of a huge amount of mineral substances in dilute form, making it an active solvent. It consists of various salts such as sodium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and more.

9. How does salinity vary with latitude?
a) Salinity decreases from the equator towards the poles on average
b) Salinity increases from the equator towards the poles on average
c) Salinity remains constant throughout all latitudes
d) Salinity is highest near the equator

Explanation: Salinity decreases from the equator towards the poles on average. However, it is important to note that higher salinity is seldom recorded near the equator. The highest salinity is typically found at 20-40 degrees north latitude.

10. Which sea has salinity below normal?
a) Baltic Sea
b) Red Sea
c) Persian Gulf
d) Mediterranean Sea

Explanation: The Baltic Sea has salinity below normal, recording a salinity of 3-15‰. The Red Sea, Persian Gulf, and Mediterranean Sea have salinity above the normal.

Brief Summary | UPSC – IAS

Salinity is the measure of the amount of dissolved salts in water and affects various properties and organisms in aquatic environments. The primary source of oceanic salinity is land, with rivers bringing salts in solution form. Factors such as evaporation, precipitation, influx of river water, prevailing winds, ocean currents, and sea waves all influence the amount of salinity in different oceans and seas. Evaporation has a direct positive relationship with salinity, while precipitation is inversely proportional to salinity. Other factors such as atmospheric pressure, wind direction, and circulation of oceanic water also play a role. Salinity varies horizontally and vertically across different latitudes and regions.