Salinity of the Ocean

1. Arabian Sea records higher salinity than the Bay of Bengal because

Arabian Sea records higher salinity than the Bay of Bengal because

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Arabian Sea exhibits high rate of evaporation and low influx of fresh-water
Arabian Sea has shallow water
Arabian Sea has more enclosed land
Arabian Sea receives more rainfall
This question was previously asked in
UPSC CAPF – 2018
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The correct answer is A) Arabian Sea exhibits high rate of evaporation and low influx of fresh-water.
Salinity in oceans is primarily affected by evaporation, precipitation, freshwater influx from rivers, and freezing/melting of ice. The Arabian Sea experiences a higher rate of evaporation due to clearer skies and higher temperatures in parts influenced by dry winds. Crucially, the Bay of Bengal receives enormous volumes of freshwater from large rivers like the Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, and Cauvery, which significantly dilutes its water and lowers its salinity compared to the Arabian Sea, which receives fewer major rivers.
Average salinity of the Arabian Sea is around 36 parts per thousand (ppt), while the average salinity of the Bay of Bengal is lower, around 30-33 ppt, particularly lower near the river mouths.

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2. Consider the following statements relating to Sea Salinity : 1. The

Consider the following statements relating to Sea Salinity :

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  • 1. The ocean salinity depends on evaporation and precipitation
  • 2. Any change in the temperature or density influences the salinity
  • 3. Major source of sea salinity is terrestrial discharge by rivers

Which of the statements given above are correct?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
This question was previously asked in
UPSC CAPF – 2016
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All three statements relating to sea salinity are correct.
1. The ocean salinity depends on evaporation and precipitation: High evaporation increases salinity by removing water. High precipitation decreases salinity by adding fresh water. This statement is correct.
2. Any change in the temperature or density influences the salinity: Temperature affects the rate of evaporation and ice formation (brine rejection), thus influencing salinity. Density is determined by temperature and salinity. Changes in density (e.g., due to temperature changes) can cause water masses to move, influencing the distribution of salinity through mixing and circulation. This statement is correct.
3. Major source of sea salinity is terrestrial discharge by rivers: Rivers carry dissolved salts and minerals from the land, derived from the weathering of rocks, into the oceans. This continuous input over geological time is the primary reason for the ocean’s saltiness. This statement is correct.
Other contributions to sea salinity include volcanic outgassing, dissolution of seafloor rocks, and hydrothermal vents, but riverine input is the most significant source of dissolved solids.

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3. Which one of the following is known as a zone of sharp salinity change

Which one of the following is known as a zone of sharp salinity change in the vertical section of ocean?

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Thermocline
Halocline
Photic zone
Pycnocline
This question was previously asked in
UPSC NDA-2 – 2018
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A halocline is a layer of water in which the salinity changes significantly with depth. This zone represents a strong vertical salinity gradient.
This question tests specific oceanographic terminology used to describe vertical gradients of physical properties in the ocean.
A thermocline is a layer where temperature changes rapidly with depth. A pycnocline is a layer where density changes rapidly with depth (density is influenced by both temperature and salinity). The photic zone (or euphotic zone) is the upper layer of a body of water where sunlight penetrates and photosynthesis occurs; it is defined by light penetration, not by a gradient of a physical property.

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4. Directions : The following 05 (Five) items consist of two statements,

Directions : The following 05 (Five) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the answers to these items using the code given below :
Code :

  • Both the Statements are individually true and Statement II is the correct explanation of Statement I.
  • Both the Statements are individually true but Statement II is not the correct explanation of Statement I.
  • Statement I is true but Statement II is false.
  • Statement I is false but Statement II is true.

52.
Statement I: There is high salinity in Red Sea.
Statement II: Rate of evaporation is high in Red Sea.

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Both the Statements are individually true and Statement II is the correct explanation of Statement I.
Both the Statements are individually true but Statement II is not the correct explanation of Statement I.
Statement I is true but Statement II is false.
Statement I is false but Statement II is true.
This question was previously asked in
UPSC NDA-1 – 2016
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The correct answer is A) Both the Statements are individually true and Statement II is the correct explanation of Statement I.
Statement I is true. The Red Sea has one of the highest salinities among the world’s seas, typically ranging between 36 to 41 parts per thousand (ppt), significantly higher than the average ocean salinity of around 35 ppt.
Statement II is true. The Red Sea is located in a hot and arid region with high temperatures, low humidity, and strong winds, leading to very high rates of evaporation. It also receives very little freshwater input from rivers or significant rainfall. High evaporation removes pure water, leaving the salts behind, which directly increases the concentration of salt in the remaining water body. Therefore, high evaporation is the primary reason for the high salinity of the Red Sea.
Other factors contributing to the Red Sea’s high salinity include limited exchange of water with the open ocean (Mediterranean Sea and Arabian Sea through narrow straits) and its location over a rift valley system which might involve subsurface brine inputs in some areas, although evaporation is the dominant factor for the overall high salinity.

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5. The salt in sea water comes from:

The salt in sea water comes from:

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rain.
chemical exchange between sea water and its substratum as well as hydrothermal emissions.
evaporation of water and concentration of dissolved salts.
mixing of different density waters during natural warm and cold current movements.
This question was previously asked in
UPSC Geoscientist – 2020
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The salt in sea water primarily originates from the weathering and erosion of rocks on land, with rivers carrying dissolved minerals and salts to the ocean. Additionally, significant contributions come from chemical reactions between seawater and the ocean floor (rock-water interactions) and from hydrothermal emissions at mid-ocean ridges and other volcanic activity, which release dissolved minerals into the water.
The salinity of the ocean is a result of geological processes involving the dissolution of minerals from rocks on land and the seabed, transported by rivers and released through volcanic and hydrothermal activity.
While evaporation concentrates the existing salts, it is not the *source* of the salts themselves. Rain contains very little dissolved salt. Mixing of water masses influences temperature and currents but doesn’t create the salts. Therefore, chemical exchange with the substratum and hydrothermal vents are key processes, alongside riverine input, that contribute to the ocean’s salt content.

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6. Isohalines are lines joining equal :

Isohalines are lines joining equal :

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temperature
pressure
rainfall
salinity
This question was previously asked in
UPSC CDS-1 – 2022
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Isohalines are lines joining equal salinity.
Iso- lines (or isolines) are lines on a map that connect points of equal value for a specific quantity. The term isohaline is specifically used in oceanography and limnology to connect points of equal salt concentration (salinity) in water bodies.
Other common isolines include:
– Isotherms: Lines joining points of equal temperature.
– Isobars: Lines joining points of equal atmospheric pressure.
– Isohyets: Lines joining points of equal rainfall.
– Isobat: Line connecting points of equal depth in a water body.
– Contour lines: Lines joining points of equal elevation above a reference level.

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