Oceanography Questions and Answers

Answer: C

The subsidence theory of coral reef formation was put forward by Charles Darwin after his voyage on the Beagle. He held that fringing reefs grow upward as the volcanic island sinks slowly, turning into barrier reefs and finally into an atoll. Daly proposed the glacial control theory, in which sea level changes during the ice age were the cause. Agassiz held that reefs grow on submarine platforms, and Davis supported Darwin but is not the author of the theory.

Answer: B

A tide at a place is followed by the next high tide after an interval of about 12 hours 26 minutes, since the moon's orbital motion makes the tidal day about 24 hours 52 minutes. A tide at 6 p.m. is therefore followed by the next one at about 6.26 a.m. of the next day. The timings 00.13 a.m., 12.39 p.m. and 06.52 p.m. correspond to an interval of 6 hours 13 minutes, 18 hours 39 minutes and 24 hours 52 minutes, which are not the gap between two successive high tides.

Answer: C

A tide is the periodic rise and fall of water (iii). A tsunami is a rise of sea water in wave form caused by seismic activity such as an undersea earthquake (iv). The Gulf Stream is a warm and comparatively fast moving ocean current (i). The Labrador current is a cold ocean current (ii). The correct matching is a-iii, b-iv, c-i, d-ii, which is code C. Codes A and B make the tide a current, and code D puts the tsunami against the tide.

Answer: A

The Falkland current is a cold current (ii). The Norwegian current is in the Atlantic Ocean (iii), where it carries warm water north. The Florida current is a warm current (i). The Okhotsk (printed Okholsk) current is the cold current off the Kamchatka Peninsula (iv). The matching is a-ii, b-iii, c-i, d-iv, which is code A. Codes B, C and D place a cold current with a warm one or with the wrong location. The Norwegian current is a branch of the North Atlantic Drift, and the Okhotsk current flows south along the coast of Kamchatka and Sakhalin.

Answer: C

Surface ocean currents get their energy from the wind. Steady winds such as the trades and the westerlies drag the surface water by friction, and the Coriolis effect and the shape of the coasts then give the currents their pattern, such as the gyres.

Salinity differences help drive the deeper thermohaline circulation, not the surface currents. Tectonics shapes the ocean basins but supplies no energy for the flow. Tsunamis are waves caused by earthquakes and similar events and are not a continuous source of current energy.

Answer: A

The unusually high and low tides near new moon and full moon are called spring tides. At those times the sun, moon and earth lie roughly in one line, and the gravitational pulls of sun and moon add together to give the highest high tides and the lowest low tides.

Neap tides occur near the first and last quarter, when the sun and moon pull at right angles and the tidal range is smallest. Super tide and fall tide are not standard terms in tidal theory and describe no accepted type.

Answer: B

Darwin's subsidence theory is related to coral reefs. Darwin proposed that a fringing reef round a volcanic island becomes a barrier reef and then an atoll as the island slowly sinks while the coral grows upward to stay near the surface where light is available. The theory explains why coral structures are found in deep water around many Pacific islands. It has nothing to do with marine terraces, which are raised wave-cut platforms, with the cycle of erosion, or with tides. Option B is correct.

Answer: C

Tsunamis are produced by sub-marine earthquakes. A sudden movement of the sea floor at a fault displaces a great volume of water, and the waves travel across the ocean at high speed, rising when they reach shallow water. Tides are due to the pull of the moon and sun, cyclones make storm surges, which are a different kind of wave, and the shrinking of the earth's crust is a theory of mountain building. Option C is correct.

Answer: A

Terrigenous deposits cover the largest percentage of the ocean floor, in the key. These are sediments derived from land, such as sand, silt and clay brought by rivers, winds and glaciers. They cover the continental shelves and slopes and spread far into the ocean basins. Biogenous oozes made of the remains of organisms, hydrogenous deposits formed by chemical precipitation, and cosmogenous deposits from space cover smaller areas. Option A is the keyed answer.