Oceanography - 2 - Free MCQ Practice Test with solutions, UPSC Geography

Only one

Statement 1 is incorrect - the Aleutian Islands form an island arc in the North Pacific Ocean, extending from the Alaska Peninsula toward the Kamchatka Peninsula and separating parts of the Bering Sea from the open Pacific.

Statement 2 is incorrect - the Canary Islands lie off northwest Africa in the North Atlantic Ocean, not the Pacific.

Statement 3 is correct - Nancowry belongs to the Nicobar group situated in the eastern part of the Indian Ocean.

Statement 4 is incorrect - the Azores are a Portuguese archipelago in the North Atlantic Ocean, not the Arctic.

Therefore, exactly 1 statement is correct.

1 and 2 only

Statement 1 is correct. Continental shelves form through a combination of processes: long-term sea-level fluctuations (eustatic changes), river (fluvial) deposition when shelves were exposed during low stands, marine erosion and reworking during high stands, and local tectonic subsidence or uplift. These combined processes produce the broad, gently sloping margins that we recognize as continental shelves.

Statement 2 is correct. Continental shelves host thick accumulations of sedimentary deposits that are important repositories of mineral and energy resources - notably hydrocarbons (oil and natural gas) - and also contain economically valuable sands, gravels and phosphorite deposits; they are also highly productive fisheries.

Statement 3 is incorrect. The widest continental shelf in the world is the Siberian shelf off northern Russia in the Arctic Ocean, extending up to about 1,200 km, not in the Pacific Ocean.

Thus, only the first two statements are correct.

Only three

Southern Ocean is generally defined as the ocean surrounding Antarctica, most commonly taken as the waters south of 60°S. Several marginal seas bordering Antarctica are therefore included in it, such as the Weddell Sea, Ross Sea, Bellingshausen Sea and the Amundsen Sea.

Independent verification of the four named bodies: Weddell Sea - part of the Southern Ocean (True); Ross Sea - part of the Southern Ocean (True); Bellingshausen Sea - part of the Southern Ocean (True); Tyrrhenian Sea - a basin of the Mediterranean Sea in the northern hemisphere, not part of the Southern Ocean (False). Hence, exactly three of them belong to the Southern Ocean.

Only one pair

Oceanic trenches are long, narrow, steep-sided depressions formed at convergent plate boundaries by subduction, where one oceanic plate is forced beneath another; they commonly extend about 3-4 km below the surrounding abyssal plain.

Pair 1 is correct: the Puerto Rico Trench lies in the western part of the Atlantic Ocean (North Atlantic), and is the deepest point in the Atlantic basin.

Pair 2 is correct: the Sunda (Java) Trench is located in the eastern Indian Ocean south of the islands of Sumatra and Java.

Pair 3 is incorrect: the South Sandwich Trench lies in the southern Atlantic Ocean near the South Sandwich Islands, not in the Pacific.

Hence, only one of the given pairings is incorrectly matched. Standard school references commonly list about 26 oceanic trenches worldwide: roughly 22 in the Pacific, 3 in the Atlantic and 1 in the Indian Ocean.

Abyssal Plain

Abyssal plains are the broad, very flat regions of the deep-ocean floor that are covered by thick accumulations of fine sediment; they constitute the single largest physiographic division of the ocean basins, occupying over 50% of the seafloor.

By contrast, the continental shelf is a relatively shallow, gently sloping zone (average gradient ≈1° or less) and occupies only about 7% of the seafloor, while the continental slope is a much steeper transition zone seaward of the shelf and accounts for roughly 9%. The continental rise is the depositional apron at the base of the slope and is much smaller in area than the abyssal plains.

The dominance of the abyssal plains in areal extent is due to widespread deposition of fine sediments (clay and biogenic oozes) that bury underlying relief and create extremely flat expanses between continental margins and mid-ocean ridges.

A: 1 only

Statement 1 is correct. A fjord is a drowned glacial valley: glaciers carve deep, U-shaped valleys with steep sides, and subsequent sea-level rise or subsidence floods these valleys to form deep, steep-sided inlets (classic examples are the Norwegian fjords).

Statement 2 is incorrect. A ria is a drowned river valley produced when rising sea level floods a fluvial valley, not a "raised" river valley.

Statement 3 is incorrect. A Dalmatian coastline forms by the submergence of a landscape of parallel ridges and valleys so that the ridges remain as long, narrow islands running parallel to the shore; it is not created by deposition by river sediments.

B: 2 only

Salinity is conventionally expressed as grams of dissolved salts per 1000 g of seawater, i.e., parts per thousand (ppt). The global ocean's average salinity is about 35 ppt.

Statement 1 is incorrect. The largest continuous source of the ocean's dissolved salts is chemical weathering of continental rocks, with salts and ions delivered to the ocean primarily by river runoff. Additional, smaller sources include hydrothermal vents, submarine volcanism, seafloor dissolution, and atmospheric deposition, but these do not constitute the primary global input.

Statement 2 is correct. Surface salinity is strongly affected by inputs and removals of freshwater: evaporation increases salinity, while precipitation, river runoff, and ice melt decrease it. Regional differences (e.g., high salinity in semi-enclosed, arid basins vs. low salinity near large river mouths) and surface mixing by wind and currents make freshwater inputs a major control on surface salinity patterns.

Only two. The cold currents among the list are the Benguela Current and the Labrador Current.

Gulf Stream: a warm current originating in the Gulf of Mexico and flowing northward along the eastern coast of North America, transporting heat into the North Atlantic.

Benguela Current: a cold current flowing northward along the southwest coast of Africa (off Namibia and Angola), associated with coastal upwelling and cooler, arid coastal climates.

North Atlantic Drift: the northeastward extension of the Gulf Stream; it is a warm current that helps moderate the climate of Western Europe.

Labrador Current: a cold current flowing southward from the Arctic along the Labrador and Newfoundland coasts, often meeting the warm Gulf Stream and creating fog and ice hazards.

Therefore, two of the listed currents are cold.

Both 1 and 2

Ekman transport results from wind stress on the ocean surface combined with the Coriolis effect, producing a net surface-water transport at roughly 90° to the wind (to the right in the Northern Hemisphere, to the left in the Southern Hemisphere).

In subtropical basins, the prevailing trade winds and westerlies drive surface waters toward the basin interior via convergent Ekman transport, creating a slight mound of water (Ekman pumping). The pressure gradient from that mound is balanced by a circular geostrophic flow, forming the characteristic subtropical gyre with intensified western boundary currents. Thus Ekman transport is a primary wind-driven mechanism that helps produce subtropical gyres.

Under La Niña, strengthened trade winds push warm surface water westward across the tropical Pacific, which enhances coastal upwelling of cold, nutrient-rich water along the South American coast. The increased nutrient supply boosts primary productivity and often leads to higher fish abundance (historically benefitting fisheries for small pelagics such as anchovies), so fishing activity frequently increases during La Niña events.

Both 1 and 2

Tides are produced by the differential gravitational pull of the Moon and the Sun on different parts of Earth; the observed tidal amplitude depends on how the lunar and solar tidal forces combine.

Spring tides occur at the new moon and full moon phases, when the Sun, Moon and Earth are approximately aligned. In this configuration the solar and lunar tidal forces add, producing the maximum tidal range (the highest high tides and the lowest low tides).

Neap tides occur at the first and third (last) quarter moon phases, when the Sun and Moon are at right angles as seen from Earth. Their tidal effects partially cancel, producing the minimum tidal range (smaller difference between high and low tides).