Which one of the following seas has highest salinity?
- (a)Red Sea
- (b)North Sea
- (c)Arabian Sea
- (d)Mediterranean Sea
Correct — A, Red Sea.
Salinity is a water budget. A basin turns saltier when evaporation removes fresh water faster than rain and rivers put it back, and saltier still when a narrow mouth stops the open ocean from flushing the excess away.
The Red Sea sits at the extreme of that freshwater balance. It runs between desert coasts, so rainfall over it is slight while evaporation is high, and it receives negligible river discharge along its whole length.
Its exchange with the ocean is restricted too, running through the narrow, shallow-silled Strait of Bab-el-Mandeb into the Gulf of Aden, which slows the mixing that would dilute it.
Surface salinity therefore settles far above the open-ocean average of about 35 ppt, commonly cited near 40 ppt.
Carry away the rule rather than the number: a marginal sea's salinity is set by its freshwater balance and by how freely it exchanges with the open ocean.
- (b)North Sea — This water is diluted, not concentrated. It lies in a cool, humid belt where evaporation is weak, and it takes in the brackish outflow of the Baltic along with discharge from the Rhine, Elbe and Thames.
Its surface salinity runs roughly 34–35 ppt, at or a little below the open-ocean average. Among the four seas listed, it is the right answer to which one is the least saline.
- (c)Arabian Sea — It does sit above the ocean average, at roughly 36 ppt, because evaporation over it is strong and its river inflow is modest. But it opens widely to the Indian Ocean, and that free exchange keeps pulling it back towards the average.
Within India's coastal geography it is the right answer to which of the two water bodies flanking peninsular India is the saltier, because the Bay of Bengal is freshened by the Ganga–Brahmaputra system and heavier rainfall.
- (d)Mediterranean Sea — This is the closest of the three. It is nearly enclosed, ringed by dry summers and strong evaporation, and its surface salinity of about 38 ppt sits clearly above the ocean average.
What holds it below the Red Sea is the fresh water it does receive — the Rhône and the Po — together with the much fresher Black Sea water entering through the Turkish straits, which brings the basin more fresh water than either of those rivers.
It is the right answer to which sea sends a warm, salty outflow through the Strait of Gibraltar to sink into the Atlantic.
Salinity is the mass of dissolved salts carried in a given mass of seawater, written in parts per thousand (ppt, or ‰) or as practical salinity units. Open-ocean water averages about 35 ppt.
The figure at any place is a balance sheet. Evaporation removes water and concentrates the salt left behind; rainfall, river discharge and melting ice dilute it.
A marginal or enclosed sea can drift furthest from the ocean average, because a narrow, shallow entrance slows the exchange that would otherwise pull it back.
Salinity and temperature together set the density of seawater, and density differences drive sinking water and the deep circulation of the oceans. Dense Mediterranean water spilling into the Atlantic at Gibraltar is one visible consequence of this.
It also lets the map of marginal seas be reasoned out instead of memorised. Desert-rimmed basins such as the Red Sea and the Persian Gulf run salty; river-fed basins such as the Baltic and the Bay of Bengal run fresh.
- Open-ocean water averages about 35 ppt of dissolved salts; Red Sea surface water is commonly cited near 40 ppt.
- The Red Sea's marine link to the Indian Ocean is the narrow, shallow-silled Strait of Bab-el-Mandeb, opening into the Gulf of Aden.
- The Red Sea lies between the deserts of north-east Africa and Arabia, so rainfall over it is slight and evaporation high.
- Mediterranean surface salinity is usually given as about 38 ppt, rising eastward towards the Levantine basin.
- Arabian Sea surface salinity is about 36 ppt, above that of the Bay of Bengal, which is diluted by large rivers and heavy rain.
- North Sea salinity is roughly 34–35 ppt; it receives Baltic outflow and the Rhine, Elbe and Thames.
- Deep brine pools in the Red Sea rift, such as the Atlantis II Deep, hold hypersaline water far saltier than the surface layer.
Evaporation set against freshwater inflow, and the width of the sea's opening, rank the four: Red Sea highest, North Sea lowest.
- Enclosure by itself does not make a sea salty. The Baltic is nearly landlocked yet among the least saline seas, because river inflow and a cool, humid climate outweigh evaporation there.
- The Mediterranean also evaporates hard and is nearly enclosed, so it reads like a defensible pick; what keeps it below the Red Sea is the Rhône and Po discharge plus the fresher Black Sea inflow through the Turkish straits.
- The Dead Sea and the Great Salt Lake are hypersaline lakes rather than seas open to an ocean; reaching for a saltier 'sea' by name pulls the reasoning away from the options actually listed.
- Warmth is not the test. The Bay of Bengal is tropical and dilute because rivers and rain freshen it, while salinity tracks the freshwater budget rather than the temperature.
Here the idea is put as a straight superlative — four named seas, pick the saltiest. The options fix the comparison: the work is to rank those four against one another, not against every basin on Earth.
That ranking follows from the freshwater balance and the width of each sea's opening, so it can be reasoned out from the geography of the four rather than recalled from a table of figures.
UPSC_1995_GS1_Q151995The same shape of item: one physical-geography superlative to be picked out of four named entities, settled by reasoning about the factor that controls the quantity rather than by recalling a ranked list. What differs is the whole subject. That question turns on relief, where the thickness of the ice sheet lifts Antarctica's mean elevation above the other continents; this one turns on a sea's freshwater balance and how freely it exchanges with the open ocean.
- practice — not a real PYQ
The surface salinity of the Red Sea stands well above the open-ocean average chiefly because
- (a)it lies between arid coasts with high evaporation, receives very little river water, and exchanges with the ocean through a narrow strait
- (b)heavy monsoon rain falls over its basin through most of the year
- (c)large glacier-fed rivers empty into it from the north
- (d)cold polar water sinks into it and displaces the surface layer
Answera — Evaporation is high over desert-rimmed water, freshwater input is slight, and the narrow, shallow-silled Bab-el-Mandeb slows the exchange that would dilute the basin. Those three together push surface salinity towards roughly 40 ppt.Option b inverts the mechanism, since rainfall dilutes rather than concentrates, and the Red Sea basin is arid.
Option c fails because the sea's northern arms, the Gulfs of Suez and Aqaba, are bordered by desert, and its freshwater inflow is negligible.
Option d describes water of high latitudes; Red Sea deep water is warm, and an inflow of ordinary ocean water would in any case lower this basin's salinity rather than raise it.
- practice — not a real PYQ
Compared with the Bay of Bengal, the Arabian Sea has higher surface salinity mainly because
- (a)it receives far less river discharge and loses more water to evaporation
- (b)it is much shallower and therefore warms faster
- (c)it receives greater rainfall than the Bay of Bengal
- (d)it lies outside the influence of the monsoon system
Answera — The Bay of Bengal takes the Ganga–Brahmaputra, Mahanadi, Godavari and Krishna discharge along with heavier rainfall over the water surface, so it is diluted to around 33 ppt, while the Arabian Sea, with a modest river inflow and stronger evaporation, holds about 36 ppt.Option b names a property that does not control surface salinity, and warming alone does not add salt.
Option c reverses the rainfall comparison and would in any case lower salinity, not raise it.
Option d is wrong because the south-west monsoon is centred on the Arabian Sea.
- practice — not a real PYQ
Which one of the following seas would be expected to have the lowest surface salinity?
- (a)Baltic Sea
- (b)Red Sea
- (c)Mediterranean Sea
- (d)Persian Gulf
Answera — The Baltic is a cool, nearly enclosed basin fed by a large number of rivers, and its exchange with the North Sea runs through the narrow, shallow Danish straits. Evaporation there is weak against that inflow, so the water is brackish, commonly under 10 ppt across much of the basin.The other three lie in dry, strongly evaporating settings and run above the open-ocean average of about 35 ppt: the Red Sea near 40 ppt, the Mediterranean about 38 ppt, and the Persian Gulf, ringed by desert, higher still than the ocean average.
Note what the pair Baltic–Red Sea teaches: a restricted opening does not raise salinity by itself, it preserves whatever the local water balance produces.