Oceanic / Circulation of the Ocean – UGC NET – Solved PYQs

1. A reef separated from the mainland or inland shore by a deep lagoon is known as (SEPT 2013)

(1) Fringing reef
(2) Atoll reef
(3) Barrier reef
(4) Patch reef

Correct Answer: (3) Barrier reef

A barrier reef is a coral reef that develops parallel to a coastline but is separated from the mainland or island shore by a broad and often deep lagoon. This lagoon may vary in width from a few kilometres to several tens of kilometres and is deep enough to allow navigation in many cases. Barrier reefs are among the largest and most spectacular coral formations found in tropical and subtropical oceans. The most famous example is the Great Barrier Reef off the northeastern coast of Australia, which is the largest coral reef system in the world.

A fringing reef differs from a barrier reef because it grows directly along the coastline or is separated from the shore by only a narrow and shallow water body. It is the most common type of coral reef and is usually found attached to the landmass. An atoll reef is a ring-shaped coral reef that surrounds a central lagoon and generally develops around a subsiding volcanic island. The lagoon in an atoll occupies the area where the volcanic island once existed. A patch reef consists of isolated and irregular coral formations that occur within lagoons, continental shelves, or between larger reef systems rather than forming a continuous reef structure.

The distinction between reef types became widely known through Charles Darwin’s Theory of Coral Reef Formation, which explained the evolutionary sequence from fringing reefs to barrier reefs and finally to atolls as volcanic islands gradually subside while coral growth continues upward toward the sea surface. The presence of a deep lagoon between the reef and the mainland is the most important identifying characteristic of a barrier reef, making option (3) the correct answer.

2. Radiolarian oozes are (SEPT 2013)

(1) Terrigenous deposits
(2) Neritic deposits
(3) Pelagic deposits
(4) Littoral deposits

Correct Answer: (3) Pelagic deposits

Radiolarian oozes are a type of pelagic deposit formed from the accumulated siliceous skeletal remains of microscopic marine organisms known as radiolarians. These organisms are planktonic protozoans that inhabit the upper layers of the ocean and possess intricate skeletons made of silica. After death, their skeletal remains slowly sink to the ocean floor and accumulate over long periods, forming extensive deposits in deep ocean basins.

Pelagic deposits are sediments that accumulate in the deep-sea regions far away from continental margins. They differ from terrigenous deposits, which originate from land through processes such as weathering, river transport, wind action, and glacial activity. Pelagic sediments are primarily composed of the remains of marine organisms or chemical precipitates and cover vast areas of the ocean floor beyond the continental shelf.

Radiolarian oozes are most commonly found in regions where the productivity of radiolarians is high and where the ocean floor lies below the depth at which calcareous materials dissolve. They are particularly abundant in parts of the Pacific Ocean and equatorial regions characterized by nutrient-rich waters. Along with diatom ooze, radiolarian ooze belongs to the category of siliceous oozes, whereas globigerina ooze and pteropod ooze are examples of calcareous oozes composed mainly of calcium carbonate.

The term ooze is used when the biological component constitutes more than 30 percent of the sediment. Since radiolarian oozes are formed in the deep open ocean and represent a classic example of deep-sea biogenic sedimentation, they are classified as pelagic deposits, making option (3) the correct answer.

3. Match List-I with List-II and choose the correct answer using the codes given below (SEPT 2013)

Codes

(1) A–III, B–I, C–II, D–IV
(2) A–I, B–II, C–III, D–IV
(3) A–IV, B–I, C–III, D–II
(4) A–II, B–I, C–III, D–IV

Correct Answer: (4) A–II, B–I, C–III, D–IV

The Oyashio Current is a cold ocean current that originates in the sub-Arctic regions of the North Pacific Ocean and flows southward along the Kamchatka Peninsula and the Kuril Islands before meeting the Kuroshio Current near Japan. It carries cold, nutrient-rich waters and supports some of the world’s richest fishing grounds. Hence, A matches with II.

The Peru Current, also known as the Humboldt Current, is a cold current that flows northward along the western coast of Latin America, particularly along the coasts of Chile and Peru. It is associated with intense coastal upwelling, which brings nutrient-rich water to the surface and creates highly productive marine ecosystems. Hence, B matches with I.

The Alaska Current is a warm ocean current that flows along the Pacific coast of North America. It influences the coastal regions of British Columbia and southern Alaska by moderating temperatures and increasing precipitation. Hence, C matches with III.

The Kuroshio Current, often referred to as the Japan Current, is a warm western boundary current of the North Pacific Ocean. It flows northward along the eastern coasts of Taiwan and Japan, transporting warm tropical waters toward higher latitudes. This current plays an important role in influencing the climate of Japan and surrounding regions. Hence, D matches with IV.

The correct matching is A–II, B–I, C–III, D–IV, which corresponds to Option (4).

4. The following question has two sets of statements, one labelled as Assertion (A) and the other labelled as Reason (R) (SEPT 2013)

Assertion (A): Western coast of Europe (UK) and Labrador (North America) are in the same latitude, but the western coast of Europe remains unfrozen and Labrador remains frozen for nine months.

Reason (R): Gulf Stream is a warm current and Labrador Current is a cold current.

Codes

(1) Both (A) and (R) are true and (R) is not the correct explanation of (A)
(2) Both (A) and (R) are true and (R) is the correct explanation of (A)
(3) (A) is true, but (R) is false
(4) (A) is false, but (R) is true

Correct Answer: (2) Both (A) and (R) are true and (R) is the correct explanation of (A)

The Assertion (A) is true. The western coast of Europe, particularly the United Kingdom, lies at latitudes comparable to those of Labrador in eastern Canada. Despite this similarity in latitude, the climatic conditions of the two regions are markedly different. The western coast of Europe experiences relatively mild winters, and its ports generally remain ice-free throughout the year. In contrast, Labrador experiences extremely cold conditions, and large areas remain frozen for much of the year.

The Reason (R) is also true. The Gulf Stream, along with its extension known as the North Atlantic Drift, is a warm ocean current that transports large quantities of heat from the tropical Atlantic toward Western Europe. This warm water heats the overlying air masses, moderating winter temperatures and creating a comparatively mild maritime climate. On the other hand, the Labrador Current is a cold ocean current that flows southward from the Arctic regions along the coast of Labrador and Newfoundland. It carries cold water and icebergs, significantly lowering temperatures along the northeastern coast of North America.

The climatic contrast between Western Europe and Labrador is primarily a result of the influence of these ocean currents. The warming effect of the Gulf Stream and North Atlantic Drift prevents extensive freezing along the western European coast, while the cooling influence of the Labrador Current contributes to prolonged freezing conditions in Labrador. Ocean currents are among the most important controls of coastal climate, often producing significant temperature differences between regions located at similar latitudes. Since the reason directly explains the climatic difference stated in the assertion, (R) is the correct explanation of (A), making Option (2) the correct answer.

5. Global change in sea level is caused by (SEPT 2013)

(1) Eustatic change
(2) Isostatic change
(3) Climatic change
(4) Diastrophism

Correct Answer: (1) Eustatic change

Eustatic change refers to a worldwide or global change in sea level that affects all ocean basins simultaneously. Such changes occur when there is an alteration in the total volume of ocean water or in the capacity of ocean basins. Major causes of eustatic sea-level change include the melting and formation of continental ice sheets, thermal expansion and contraction of seawater due to temperature variations, and long-term changes in ocean basin volume associated with tectonic processes. Since these changes influence the level of the oceans on a global scale, they are known as eustatic changes.

Isostatic change involves the vertical movement of land relative to sea level rather than a change in the volume of ocean water itself. It results from adjustments in the Earth’s crust caused by loading and unloading processes such as glaciation, sediment deposition, or erosion. In such cases, sea level may appear to rise or fall locally because the land surface is moving upward or downward.

Climatic change can influence sea level through mechanisms such as glacier melting and thermal expansion of seawater. However, climatic change is a factor contributing to eustatic sea-level variation rather than the specific term used to describe global sea-level change. The geographical concept that directly denotes worldwide fluctuations in sea level is eustasy.

Diastrophism refers to large-scale crustal deformation caused by tectonic forces, including folding, faulting, uplift, and subsidence. These processes modify landforms and regional coastal configurations but do not specifically represent global sea-level changes.

In geomorphology and oceanography, worldwide rises and falls in sea level are collectively described as eustatic sea-level changes, a concept widely used in the study of marine transgressions, regressions, coastal evolution, and Quaternary environmental change. Hence, Option (1) Eustatic change is the correct answer.

6. Which among the following has postulated the Subsidence Theory related to coral reef? (DEC 2013)

(1) Daly
(2) Agassiz
(3) Darwin
(4) Davis

Correct Answer: (3) Darwin

The Subsidence Theory of Coral Reef Formation was proposed by Charles Darwin in 1842 during his studies of coral reefs and volcanic islands. This theory is regarded as one of the most influential explanations for the origin and development of coral reefs. Darwin developed the theory after observations made during his voyage on HMS Beagle and sought to explain the formation of fringing reefs, barrier reefs, and atolls through a single evolutionary process.

According to Darwin, coral reefs initially develop as fringing reefs around volcanic islands situated in warm tropical seas. Over geological time, the volcanic island gradually begins to sink or subside due to crustal movements. As subsidence occurs, the coral organisms continue to grow upward toward the sea surface because reef-building corals require sunlight and shallow water conditions. The continued growth of corals keeps pace with the sinking landmass.

As the island sinks further, a lagoon develops between the reef and the land, transforming the fringing reef into a barrier reef. Continued subsidence eventually causes the volcanic island to disappear beneath the sea surface, leaving behind a ring-shaped reef enclosing a central lagoon. This final stage results in the formation of an atoll. Darwin used this sequence to explain the gradual transition from fringing reefs to barrier reefs and finally to atolls.

Other scholars proposed alternative theories. Reginald Daly advanced the Glacial Control Theory, suggesting that coral reefs developed on wave-cut platforms formed during periods of lower sea level associated with glaciation. Alexander Agassiz emphasized the role of submarine erosion and marine processes in reef development. William Morris Davis later modified and supported aspects of Darwin’s ideas through geomorphological interpretations. Among these theories, the classic Subsidence Theory is specifically associated with Charles Darwin, making Option (3) the correct answer.

7. Match List-I with List-II and select the correct answer using the codes given below (DEC 2013)

Codes

(1) A–II, B–I, C–III, D–IV
(2) A–I, B–II, C–III, D–IV
(3) A–III, B–IV, C–I, D–II
(4) A–IV, B–III, C–II, D–I

Correct Answer: (3) A–III, B–IV, C–I, D–II

A tide refers to the periodic rise and fall of ocean water caused primarily by the gravitational attraction of the Moon and, to a lesser extent, the Sun. This regular movement of seawater produces high tides and low tides at predictable intervals. Hence, A matches with III.

A tsunami is a series of large sea waves generated by sudden disturbances on the ocean floor, most commonly undersea earthquakes, volcanic eruptions, or submarine landslides. These waves travel rapidly across ocean basins and increase greatly in height near coastlines. Thus, a tsunami represents the rise of sea water in wave form due to seismic activity. Hence, B matches with IV.

The Gulf Stream is a warm and relatively fast-moving ocean current in the North Atlantic Ocean. It originates in the Gulf of Mexico and flows northeastward toward Europe, transferring large amounts of heat and significantly influencing the climate of Western Europe. Hence, C matches with I.

The Labrador Current is a cold ocean current that flows southward from the Arctic Ocean along the coasts of Labrador and Newfoundland. It carries cold water and icebergs into the North Atlantic and contributes to the colder climatic conditions of northeastern North America. Hence, D matches with II.

The correct matching is A–III, B–IV, C–I, D–II, which corresponds to Option (3).

8. Match List-I with List-II and select the correct answer using the codes given below (DEC 2013)

Codes

(1) A–II, B–III, C–I, D–IV
(2) A–I, B–II, C–IV, D–III
(3) A–III, B–I, C–II, D–IV
(4) A–IV, B–III, C–I, D–II

Correct Answer: (1) A–II, B–III, C–I, D–IV

The Falkland Current, also known as the Malvinas Current, is a cold ocean current that flows northward along the eastern coast of South America. It originates from the Antarctic region and carries cold subpolar waters toward lower latitudes. Hence, A matches with II (Cold current).

The Norwegian Current is associated with the Atlantic Ocean and represents a continuation of the warm North Atlantic Drift flowing along the coast of Norway. It transports relatively warm waters into high northern latitudes and plays a major role in maintaining the comparatively mild climate of Scandinavia. Hence, B matches with III (Atlantic Ocean).

The Florida Current is a warm current that flows through the Florida Strait between Florida and Cuba. It forms an important component of the Gulf Stream system and transports warm tropical waters into the North Atlantic Ocean. Hence, C matches with I (Warm current).

The Okhotsk Current (spelled Okholsk in the question) is associated with the region around the Kamchatka Peninsula and the Sea of Okhotsk in the northwestern Pacific Ocean. It carries cold waters and significantly influences the climatic and oceanographic conditions of the surrounding area. Hence, D matches with IV (Kamchatka Peninsula).

The correct matching is A–II, B–III, C–I, D–IV, which corresponds to Option (1).

9. Cold dry wind experienced particularly in winter along the eastern coast of the Atlantic Ocean and in northern Italy is called (DEC 2013)

(1) Cyclone
(2) Bora
(3) Tornado
(4) Hurricane

Correct Answer: (2) Bora

The Bora is a cold, dry, and often very strong local wind that blows during winter, particularly along the eastern coast of the Adriatic Sea and parts of northern Italy. It originates when cold, dense continental air accumulates over the elevated inland plateaus and mountain regions of southeastern Europe and then descends rapidly toward the comparatively warmer coastal areas. As the air rushes downhill through mountain passes and valleys, it gains speed and produces powerful gusts that can significantly lower temperatures.

The Bora is classified as a katabatic wind, meaning it is driven by gravity as cold, dense air flows downslope from higher elevations to lower areas. Its effects are most pronounced along the coasts of Croatia, Slovenia, and northeastern Italy, where it can disrupt transportation, navigation, and daily activities due to its intensity. The wind is generally associated with clear skies, low humidity, and sharp drops in temperature.

The other options refer to different atmospheric phenomena. A cyclone is a large-scale low-pressure system characterized by inward spiraling winds. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. A hurricane is a powerful tropical cyclone that develops over warm ocean waters in tropical regions. None of these terms describe the cold, dry winter wind characteristic of the Adriatic and northern Italian region.

The Bora is one of the most well-known local winds of Europe and serves as an important example of how topography and pressure differences influence regional climatic conditions and wind systems.

11. Salinity in water bodies increases with (DEC 2013)

(1) Increase in evaporation and decrease in admixture of fresh water
(2) Decrease in evaporation and increase in admixture of fresh water
(3) Decrease in evaporation and no change in admixture of fresh water
(4) Increase in evaporation and increase in admixture of fresh water

Correct Answer: (1) Increase in evaporation and decrease in admixture of fresh water

Salinity refers to the concentration of dissolved salts in water, usually expressed in parts per thousand (‰) or practical salinity units (PSU). The salinity of oceans, seas, lakes, and other water bodies is controlled by a balance between processes that remove water and those that add freshwater. Among these processes, evaporation and freshwater input are particularly important.

When evaporation increases, water changes into water vapour and leaves the water body, but the dissolved salts remain behind. This results in a higher concentration of salts in the remaining water, leading to an increase in salinity. Regions with high temperatures, dry climates, and strong evaporation rates often exhibit higher salinity levels. Examples include the Red Sea, Persian Gulf, and subtropical oceanic regions.

A decrease in the admixture of fresh water also raises salinity because less freshwater is available to dilute the dissolved salts. Freshwater enters oceans and seas through rainfall, river discharge, melting snow, and glacial melt. When these sources are reduced, the concentration of salts becomes relatively higher. Conversely, heavy rainfall, large river inflows, and glacier melt lower salinity by adding freshwater to the system.

Options involving decreased evaporation or increased freshwater input are associated with lower salinity levels because they either reduce salt concentration or increase dilution. The combined effect of high evaporation and limited freshwater inflow creates the most favourable conditions for salinity to rise. This relationship explains the high salinity found in enclosed and semi-enclosed seas located in arid regions where evaporation greatly exceeds precipitation and river discharge. For this reason, Option (1) Increase in evaporation and decrease in admixture of fresh water is the correct answer.

12. Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R) (DEC 2013)

Assertion (A): The salinity in the Dead Sea is very low.

Reason (R): Dead Sea is located in a tropical dry climatic region where evaporation is high, precipitation is low and drainage is internal.

Codes

(1) Both (A) and (R) are true
(2) Both (A) and (R) are false
(3) (A) is false, but (R) is true
(4) (A) is true, but (R) is false

Correct Answer: (3) (A) is false, but (R) is true

The Assertion (A) is false because the Dead Sea is one of the saltiest water bodies in the world. Its salinity is exceptionally high, reaching nearly ten times that of average ocean water. The high concentration of dissolved salts makes the water extremely dense, allowing people to float easily on its surface. Due to this extreme salinity, very few organisms can survive in the Dead Sea, which is why it is called the “Dead” Sea.

The Reason (R) is true. The Dead Sea is located in an arid region of Southwest Asia between Jordan and Israel. The area experiences a hot and dry climate, characterized by very high evaporation rates and very low annual precipitation. In addition, the Dead Sea is an endorheic basin or internally drained basin, meaning that water entering the sea has no outlet to the ocean. Rivers such as the Jordan River bring dissolved minerals into the basin, but the water can leave only through evaporation.

As water evaporates, the dissolved salts remain behind and accumulate over time. The combination of intense evaporation, limited rainfall, and internal drainage continuously increases the concentration of salts in the water. These environmental conditions are precisely responsible for the extraordinarily high salinity of the Dead Sea. Since the assertion incorrectly states that salinity is very low, while the reason correctly describes the climatic and hydrological conditions of the region, the correct answer is Option (3) (A) is false, but (R) is true.

13. Which one of the following primary greenhouse gases is not associated with global warming? (DEC 2013)

(1) Water vapour
(2) Carbon dioxide
(3) Methane
(4) Hydrogen

Correct Answer: (4) Hydrogen

Greenhouse gases are atmospheric gases that absorb and re-radiate outgoing longwave or infrared radiation, trapping heat within the Earth’s atmosphere and producing the greenhouse effect. This natural process helps maintain temperatures suitable for life, but increasing concentrations of greenhouse gases have intensified the phenomenon, leading to global warming and climate change.

Water vapour is the most abundant greenhouse gas in the atmosphere and plays a major role in regulating Earth’s energy balance. It acts as a feedback mechanism because warmer temperatures increase evaporation, which in turn raises atmospheric water vapour content and enhances warming. Carbon dioxide (CO₂) is the most important anthropogenic greenhouse gas and is released through the burning of fossil fuels, deforestation, and various industrial activities. It is a major contributor to the enhanced greenhouse effect. Methane (CH₄) is another significant greenhouse gas with a much greater heat-trapping capacity per molecule than carbon dioxide over shorter time periods. It is emitted from wetlands, livestock farming, rice cultivation, landfills, and fossil fuel extraction.

Hydrogen (H₂) is not classified as a primary greenhouse gas because it does not significantly absorb infrared radiation in the manner required to produce the greenhouse effect. Although hydrogen may indirectly influence atmospheric chemistry under certain conditions, it is not recognized as a major greenhouse gas responsible for global warming. Standard lists of greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, ozone, and certain synthetic gases such as chlorofluorocarbons and hydrofluorocarbons.

The greenhouse effect and global warming are primarily associated with gases that possess the molecular structure necessary to absorb terrestrial infrared radiation. Since hydrogen lacks this characteristic and is not considered a primary greenhouse gas, Option (4) Hydrogen is the correct answer.