Salinity distribution MCQ Quiz - Objective Question with Answer for Salinity distribution - Download Free PDF

The correct answer is Both 1 and 2.

Key Points

• Highest salinity is observed in the regions between 20º-40º North latitude. This is primarily due to higher evaporation rates and limited freshwater input in these zones.
• Regions within this latitude experience high temperatures, leading to significant evaporation. This process concentrates the salt content in the water, increasing salinity.
• Humidity remains relatively low in these areas as a result of dry air masses, which further accelerates the evaporation process.
• These high-salinity zones are typically found in subtropical areas, such as the Atlantic Ocean near the Tropic of Cancer.
• Both statements are correct as they reflect scientific observations about the relationship between evaporation, temperature, and salinity patterns.

Additional Information

• Salinity: The concentration of dissolved salts in water, usually measured in parts per thousand (ppt). Average ocean salinity is about 35 ppt.
• Evaporation: A process where water is converted into vapor due to heat. Higher evaporation rates increase salinity as water vapor leaves behind dissolved salts.
• Subtropical High-Pressure Zones: These regions, located around 20º-40º latitude, are characterized by descending air currents that limit precipitation and contribute to arid conditions.
• Impact of Salinity: High salinity influences water density, circulation patterns, and marine ecosystems. It plays a critical role in global thermohaline circulation.
• Low Humidity and Salinity Relationship: In areas with low humidity, the atmosphere absorbs more moisture, increasing evaporation rates and subsequently raising salinity levels in water bodies.

The correct answer is option 1.

Key Points

• Statement 1 – Incorrect – While evaporation is high at the equator, heavy rainfall reduces salinity. Maximum salinity is found in subtropical regions (20°–30° latitudes), where evaporation is high, but precipitation is low.
• Statement 2 – Incorrect – An increase in salinity generally increases density, but if temperature rises, density may decrease despite high salinity (due to thermal expansion).
• Statement 3 – Correct – Deep ocean water has higher density due to lower temperatures and higher salinity, making it heavier and more stable.
• Statement 4 – Incorrect – Freshwater inflow from rivers reduces salinity, as it dilutes ocean water.

The correct answer is Both 1 and 2.

Key Points

• Water with high salinity is indeed denser than water with low salinity. This is because the dissolved salts in the water increase its mass without significantly increasing its volume, leading to greater density.
• Cold water is denser than warm water. As water cools, its molecules move closer together, increasing its density. This is why cold water sinks below warm water in bodies of water.

 Additional Information

• Salinity is the concentration of dissolved salts in water. It is typically measured in parts per thousand (ppt).
• In oceans, salinity averages about 35 ppt, but it can be higher in areas with high evaporation rates and lower in areas with freshwater input.
• Water density is a crucial factor in ocean circulation, influencing the formation of currents and the mixing of ocean layers.
• Thermohaline circulation is the large-scale ocean circulation driven by global density gradients created by surface heat and freshwater fluxes.

Key Points

• Salinity is typically measured as the amount of salt in grams per kilogram of water, not per liter. It is usually expressed in parts per thousand . Hence Statement 1 is incorrect: 
• The average ocean salinity is about 35 parts per thousand (‰), meaning there are 35 grams of dissolved salts per 1,000 grams of seawater. Hence Statement 2 is correct. 
• High salinity does increase the density of water, making it easier for objects to float due to the greater buoyancy in denser water. Hence Statement 3 is correct. 
• Hence, option 2 is correct.

The correct answer is option 2, i.e Increasing salinity of seawater causes its density to increase.

Key Points

• Salinity is the term used to define the total content of dissolved salts in seawater.
• It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.
• It is usually expressed as parts per thousand or ppt.
• The relation between salinity of seawater with depth and its density is as follows:

• Salinity changes with depth, but the way it changes depends upon the location of the sea. Hence, Option 1 is NOT correct.
• Salinity at the surface varies as it increases by the loss of water to ice or evaporation, or decreased by the input of freshwaters, such as from the rivers.
• Salinity at depth is very much fixed, because there is no way that water is ‘lost’, or the salt is ‘added.’ Hence, Option 3 is NOT correct.
• The lower salinity water rests above the higher salinity dense water.
• Salinity in general increases with depth and there is a distinct zone called the halocline where salinity increases sharply.
• Other factors being constant, increasing salinity of seawater causes its density to increase. Hence, Option 2 is correct.

The correct answer is option 3, i.e. Dead Sea.

Key PointsThe Dead Sea:

• The Dead Sea, located between Jordan and Israel, is renowned for its extremely high salinity levels.
• The salinity of the Dead Sea is approximately 33.7%, which is about 9.6 times saltier than the ocean.
• This high salinity is due to the high rate of evaporation and the lack of an outlet, which causes minerals to accumulate in the water.
• The Dead Sea is a Lake. It is also called the Salt Sea.
• The Dead Sea is the world's saltiest water body with 33.7% salinity.  Hence option 3 is correct.
• Due to high salt concentration (natural buoyancy), people can easily float in the Dead Sea.
• Dead sea bordering Jordan to the east, and Palestine and Israel to the west.
• It is Earth’s lowest elevation on land.

The correct answer is salinity.

Key Points

• Isohalines
  • It is used on maps to show the salinity of different places. Hence, Option 4 is correct.
  • The average salinity of the ocean is 3.5% or 35 parts of salt in 1000 parts of water.
  • The salinity of the Great Salt Lake, (Utah, USA), the Dead Sea, and the Lake Van in Turkey are 220, 240, and 330 respectively.
  • The oceans and salt lakes are becoming saltier as time goes on because the rivers dump more salt into them, while freshwater is lost due to evaporation.
• The more frequently drawn isopleths include:
  • Isotherm (equal temperature)
  • Isobar (equal pressure)
  • Isohyets (equal rainfall)
  • Isonephs (equal cloudiness)
  • Isohels (equal sunshine)
  • contours (equal heights)
  • Isobaths (equal depths)

The correct answer is 1000.

Key Points

• Salinity is the term used to define the total content of dissolved salts in seawater.
• It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.
• The average salinity of the oceans is 35 parts per thousand. 
• The salinity of the dead sea is around 340 grams per litre of water.

• The Dead Sea is a sea that is the saltiest of all oceans and seas.

Additional Information

• Factors affecting ocean salinity are mentioned below:
  • The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
  • Surface salinity is greatly influenced in coastal regions by the freshwater flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
  • Wind also influences the salinity of an area by transferring water to other areas. 
  • The ocean currents contribute to the salinity variations.
  • Salinity, temperature, and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of water in an area.

The correct answer is Atlantic Ocean.

Key Points

• In the Atlantic Ocean high salinity is not recorded at the Equator rather it is observed between 50-20 Degree latitudes.
• The average salinity of the Atlantic Ocean is 36 grams per liter. In the South Atlantic Ocean between 10-30 degrees salinity is higher along the western margin than the eastern margin.
• The average salinity of overall oceans is 35 Grams per liter.
• Pacific Ocean average Salinity - 35 Grams per liter
• Indian Ocean average Salinity - 34 Grams per liter
• Arctic Ocean average Salinity - 33 Grams per liter

Additional Information

• The Atlantic Ocean consists of 4 major, upper water masses with distinct salinity and temperature.
• The North Atlantic's wide range of salinities is caused by the asymmetry of the northern subtropical gyre and a large number of contributions from a wide range of sources.
• The second-largest of the world's oceans is the Atlantic Ocean.
• The ocean covers almost 20 percent of Earth's surface and about 29 % of its water surface area.
• The Atlantic Ocean is known to separate the 'Old World' from the 'New World' in the European perception of the World.

Important Points

• The area of the Atlantic ocean is about 106460000 square km.

• Major Ocean are the following
  • Atlantic ocean
  • Pacific ocean
  • Indian ocean
  • Arctic ocean
  • Southern ocean

The correct answer is Rivers.

Key Points

Oceanic salinity

• Salt in the ocean comes from two sources: runoff from the land (i.e. Rivers) and openings in the seafloor.
• Rocks on land are the major source of salts dissolved in seawater.
• Rainwater that falls on land is slightly acidic, so it erodes rocks. Hence, option 1 is correct.
• This releases ions that are carried away to streams and rivers that eventually feed into the ocean.
• Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not removed, so their concentrations increase over time.
• Another source of salts in the ocean is hydrothermal fluids, which come from vents in the seafloor.
• Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up around 85% of all dissolved ions in the ocean.
• The concentration of salt in seawater (salinity) varies with temperature, evaporation, and precipitation.

The correct answer is option 1 i.e Arabian Sea exhibits high rate of evaporation and low influx of fresh water

Explanation:

• Low salinity trend is observed in the Bay of Bengal due to influx of river water by the river Ganga.
• Arabian Sea exhibits high rate of evaporation and low influx of fresh water

Factors affecting Ocean Salinity:

• The salinity of water in the surface layer of oceans depend mainly on evaporation and precipitation.
• Surface salinity is greatly influenced in coastal regions by the fresh water flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
• Wind, also influences salinity of an area by transferring water to other areas.
• The ocean currents contribute to the salinity variations.
• Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of an area.

Arabian Sea:

• It is a region of the northern Indian Ocean.
• It is bounded by Pakistan and Iran, on the west by the Gulf of Aden, Guardafui Channel and the Arabian Peninsula, on the southeast by the Laccadive Sea, on the southeast by Somali Sea and on the east by India.

Bay of Bengal:

• It is the northeastern part of the Indian Ocean.
• It is bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar islands of India. Its southern limit is a line between Sangaman Kanda, Sri Lanka and the north westernmost point of Sumatra(Indonesia).

The correct answer is 4) Only II.

Key PointsLatitudinal Distribution of Salinity in the Oceans

• Equatorial Regions
  • The equatorial regions experience high temperatures, which promote high rates of evaporation.
  • However, these regions also receive substantial rainfall, which dilutes the ocean water, lowering salinity levels.
  • As a result, the highest salinity is not found in the equatorial regions. Hence Statement I is incorrect.
• Mid-Latitude Regions
  • Mid-latitude regions, particularly between 20° to 30° North and South, tend to have the highest salinity levels.
  • This is due to high evaporation rates and lower precipitation rates compared to equatorial regions.
• Northern Hemisphere
  • The Northern Hemisphere, especially the North Atlantic Ocean, usually has higher salinity levels compared to the Southern Hemisphere.
  • This is due to greater evaporation, fewer large freshwater inputs, and the enclosed nature of seas (like the Mediterranean Sea) contributing to higher salinity. Hence Statement II is correct.

Additional Information

• Southern Hemisphere
  • The Southern Hemisphere generally has lower salinity levels due to larger oceanic areas and significant freshwater inputs from large river systems such as the Amazon.
  • Additionally, the Southern Ocean has lower salinity levels due to the melting of polar ice caps and extensive mixing with less saline waters.
• Polar Regions
  • Polar regions tend to have much lower salinity levels.
  • This is due to the melting of ice which adds fresh water to the oceans and the low rate of evaporation in these cold regions.

The correct answer is A is true but R is false.

Key Points

• Generally, salinity decreases from the equator towards the pole but the highest salinity is seldom recorded near the equator because near the equator, there is heavy rainfall, high relative humidity, cloudiness, and calm air of the doldrums.
• The polar areas experience very little evaporation and receive large amounts of freshwater from the melting of ice. This leads to low levels of salinity, ranging between 20ppt and 32ppt.
• The maximum oceanic salinity (37ppt) is observed between 20° N and 30° N and 20° W - 60° W. It gradually decreases towards the north.

Confusion Points

• One needs to understand here that statement first is correct.
• As on an average, salinity decreases from equator towards the poles.
• However, it is important to note that the highest salinity is seldom recorded near the equator though this zone records high temperature and evaporation but high rainfall reduces the relative proportion of salt. Thus, the equator accounts for only 35‰ salinity.
• If we talk about the statement of Reason- it is incorrect because Salinity further decreases in the polar zones because of influx of Glacial melt-water. 

The Correct Answer is 35%o.

Key Points

• Sea water salinity is expressed as a ratio of salt (in grams) to liter of water.
• In sea water there is typically close to 35 grams of dissolved salts in each liter.
• It is written as 35‰ The normal range of ocean salinity ranges between 33-37 grams per liter (33‰ - 37‰). 
• Salinity means the total content of dissolved salts in Sea or Ocean.
  Salinity is calculated as the amount of salt dissolved in 1,000 gm of seawater.
• It is generally expressed as ‘parts per thousand’ (ppt).
  A salinity of 24.7 % has been regarded as the upper limit to fix ‘brackish water’.
• It is a significant factor in deciding several characteristics of the chemistry of natural waters and biological processes.

Additional Information

• Factors affecting ocean salinity
  • Salinity, temperature, and density of water are interconnected. The salinity of water in the surface layer of oceans is influenced by:
    • Evaporation
    • Precipitation
  • In the coastal regions, the surface salinity is influenced by the freshwater flow from rivers.
  • In the Polar region, the surface salinity is influenced by the processes of freezing and melting of ice.
  • The wind also influences the salinity of an area by moving water to other areas.
  • The ocean currents contribute to the salinity variations.
  • The change in the density or temperature influences the salinity of water in an area.
• Share of different salts
  • Sodium chloride — 77.7%
  • Magnesium chloride—10.9%
  • Magnesium sulphate —.4.7%
  • Calcium sulphate — 3.6%
  • Potassium sulphate — 2.5%

 Key Points

Important Points

Gulf of Karabugas:

• The most remarkable natural evaporite basin in the world is the Kara-bogaz Gulf (Karabogazgöl, in the Turkmen language; or Zaliv, “gulf” in Russian), situated in an isolated embayment off the eastern shore of the Caspian Sea, in the Turkmen Republic of the USSR (41°N, 53°E).
• Kara-bogaz means “black throat” and is used to refer simply to the entrance channel; in older literature, the gulf is referred to as the Adji-Darya (or “salt water”).
• Evaporation is always so high that the gulf is 4.5 meters below the level of the Caspian

Additional Information

The Great Salt Lake:

• The Great Salt Lake is located in  Utah state of USA.
• It is about 75 miles long and 35 miles wide.
• The Lake is a remnant of a massive Ice age lake- Lake Bonneville.
• It has an average salinity of  (50 - 270o/_oo).
• The high salinity of the lake is due to salts brought in by water flowing into the lake but with no outlet.

The Dead Sea:

• The Dead Sea is also called the Salt Sea. It is bordered by Jordan in the east and Palestine and Israel to the west. 
• It has an average salinity of 238(o/_oo).
• It is the place having the lowest elevation on the Earth's surface, 435m below sea level. 
• No form of life exists in the Dead sea.

• Lake Van is the largest lake in Turkey.
• It lies in the far east of Turkey, in the provinces of Van and Bitlis. It receives water from many small streams that descend from the surrounding mountains.
• It is one of the world's few endorheic lakes (a lake having no outlet) of size greater than 3,000 square kilometers.
•  It is situated at a height of 1,640 m.
• It has an average salinity of (330o/_oo)
• Despite the high altitude and winter, high salinity mainly prevents it from freezing at such times.​