Oceanography Questions and Answers

Answer: C

Organic deposits made by living or dead organisms that form a rock elevation like a ridge are known as reefs. Coral polyps build up calcareous skeletons that form ridges, close to the ocean surface.

Corals are the organisms themselves, not the ridge. 'Conyons' is not a landform of this kind, and guyots are flat-topped submerged volcanic seamounts, not organic ridges.

Reefs are built over a long time by coral polyps and algae, which deposit calcium carbonate. Fringing reefs, barrier reefs and atolls are the main types, and they grow in warm clear shallow water of the tropics, usually where the temperature stays above about 20 degrees Celsius.

Answer: C

The cold current along the coast of Chile and Peru is the Humboldt current (also called the Peru current).

It carries cold water north from the southern ocean along the west coast of South America and supports a rich fishery. The Agulhas is a warm current off south-east Africa, the Canary is a cold current off north-west Africa, and El Nino is a warm episode off Peru that disturbs the Humboldt current, not the cold current itself.

Answer: C

The average difference in water level between high tide and low tide at a place is the tidal range.

The range is the vertical difference between consecutive high and low water and is largest at spring tides. A tidal bore is a wave moving up a river or estuary on the incoming tide, the tidal period is the time between successive tides, and a tidal wave is a loose name for a very large wave such as a tsunami or a tidal bore, so options A, B and D are wrong. The range depends on the shape of the coast and the phase of the moon: it is large in funnel-shaped inlets such as the Bay of Fundy and small in open oceans.

Answer: C

Flat-topped sea mounts are known as guyots.

A guyot is an undersea mountain, usually volcanic, whose summit was planed flat by wave action when it stood at sea level and then sank below the surface. Shoals and banks are shallow elevations of the sea bed, often sandy, that may be a hazard to navigation, and reefs are ridges of rock or coral near the surface. None of these is a drowned flat-topped volcano.

Answer: A

The statement that is not correct is that salinity is directly related to precipitation: heavy rainfall dilutes the sea surface, so salinity is inversely related to precipitation. The other statements are correct, since higher evaporation raises salinity, rivers bring fresh water and lower the salinity near their mouths, and salinity is highest in the tropics and lower near the equator and towards the poles. The answer is A.

Answer: D

The origin of ocean currents is related to all of these: gravitational force of the sun and moon, which causes tides and modifies currents, winds, which drive the surface currents, and differences in salinity and density, which set up currents between waters of different density. Since each factor contributes, the answer is 'All of the above', option D. Winds are the main driver of surface currents, density differences cause vertical movement and the pull of the sun and moon adds to tidal currents, so all three act, as the key states.

Answer: A

Salinity increases with increase in evaporation and decrease in the admixture of fresh water. Evaporation removes water but leaves the salts behind, so the concentration rises, and with little river or rain input there is no fresh water to dilute it.

The other options either reduce evaporation or add fresh water, both of which lower salinity, or leave one factor unchanged. Increased evaporation together with increased admixture of fresh water pulls in opposite directions, so it cannot be said to raise salinity.

Answer: C

The Assertion is wrong and the Reason is right. The Dead Sea is among the saltiest water bodies on earth, with salinity around 30 per cent or more, not very low. The Reason is a true statement: it lies in a hot dry region with high evaporation, low precipitation and internal drainage, and these are exactly why its salinity is so high.

The options saying (A) is right, or both are right, fail because the Dead Sea's salinity is very high. The option saying both are wrong fails because the Reason is a correct description of the setting.

Answer: D

Reef-building corals need warm water, and they thrive where the mean annual temperature is above about 20 degrees C (best at 23 to 25 degrees). This is why coral reefs are limited to the tropical seas between about 30 degrees north and south, mainly on the west side of oceans. Water cooler than 20 degrees C, as in the options below 10, 10 to 15 and 15 to 20 degrees C, does not allow the living reef to develop. So more than 20 degrees C is the answer.

Answer: D

A coral reef is an organic ocean deposit built by coral polyps (i). A shoal is a detached elevation of the sea floor with shallow depth (iv). An abyssal plain is the deep flat surface of the ocean floor (ii). The continental slope is the steep descent from the shelf bed (iii). The right matching is a-i, b-iv, c-ii, d-iii, which is code D. The other codes confuse the flat abyssal plain with the steep slope or the shoal with the deposit.