Oceanography Questions and Answers

Answer: A

Deposits between high and low water spring tide lines are littoral deposits.

The littoral (intertidal) zone lies between the highest and lowest levels reached by spring tides. Its deposits are coarse and varied (gravel, sand, shells) and are constantly reworked by waves and tides.

The other zones lie further out and deeper. Shallow water deposits cover the continental shelf below low tide, bathyal deposits the continental slope, and abyssal deposits, the fine oozes and red clay, the deep ocean floor.

Answer: C

Both statements are correct, so the answer is Both (I) and (II).

Statement (I) is the standard definition: ocean acidification describes the change in sea water chemistry caused mainly by the uptake of carbon dioxide released by burning fossil fuels.

Statement (II) gives the chemistry and the figures: dissolved CO₂ forms carbonic acid, which has lowered the average pH of surface oceans by about 0.1 units since pre-industrial times, and projections under high-emission scenarios give a further fall of 0.3 to 0.4 units by 2100. Since both hold, the options choosing only one or neither are wrong.

Answer: B

Regular deep-sea waves with rounded crests are swell.

Waves generated by wind in a storm area are short and choppy. As they travel away from where they formed, the shorter waves die out and the longer ones sort themselves into a regular train of long, low waves with rounded crests, known as swell, which can cross whole oceans.

A seiche is a standing oscillation of the water in an enclosed basin such as a lake or bay. A clapotis is a standing wave formed when waves are reflected from a vertical wall. Tidal waves are the tides, caused by the moon and sun, not regular wind waves.

Answer: A

The answer is (A) is true but (R) is false.

Assertion (A) is correct: ocean salinity varies from place to place, from under 10 parts per thousand in the Baltic to about 40 in the Red Sea, against an average of about 35.

Reason (R) is false because of the word exclusively. Surface salinity depends on several factors: evaporation (helped by temperature and wind), precipitation, inflow of fresh river water, freezing and melting of ice, and ocean currents that mix water. Temperature is only one of them, so the options calling (R) true are wrong.

Answer: D

Seamounts generally have a relief of more than 900 m above the surrounding floor.

A seamount is an isolated, usually volcanic, peak rising from the deep sea floor without reaching the surface. It is defined by its height: roughly 1,000 m or more above the surrounding floor, which falls in the last range offered.

Smaller elevations of a few hundred metres are classed as knolls or abyssal hills, which is what the three lower ranges describe. A flat-topped seamount whose summit was planed off at sea level is a guyot.

Answer: C

The correct matching is a-3, b-4, c-2, d-1.

• Continental shelf: widest off broad lowland coasts, where the land's gentle slope continues under the sea.
• Continental slope: marked by an abrupt change of gradient at the edge of the shelf.
• Ocean deeps: the trenches, the deepest parts of the ocean, the paper giving 3,000 to 5,000 fathoms.
• Deep sea plains: the abyssal plains, covering about two-thirds of the ocean floor.

The other options give the abrupt gradient change, or the two-thirds coverage, to the wrong feature.

Answer: D

Of the four factors, length of day and night is the one that does not decide how much plankton the ocean holds.

Plankton, above all the plant plankton at the base of the food chain, is limited by light and by nutrients. Depth sets how far sunlight reaches, so plankton is concentrated in the upper, lit layer of the water. Ocean currents carry nutrients and set the pattern of upwelling, which is why cold nutrient-rich waters are the richest plankton waters. Temperature and salinity control which species live in a water mass and how fast they grow.

Day length changes only with season and latitude and acts mainly by altering the light received, which depth and currents already govern, so among the options it is the weakest control and the one the key selects.

Note that day length does influence seasonal plankton blooms in high latitudes, so the item is a relative one: the key reads 'not determined by' as 'least determined by'.

Answer: D

Coral bleaching is caused mainly by excessively warm sea water temperature.

Reef-building corals live in symbiosis with algae (zooxanthellae) in their tissues, which supply food and give the corals their colour. When the water stays even 1 to 2°C above the usual summer maximum for some weeks, the stressed corals expel the algae and turn white. Mass bleaching events, such as those on the Great Barrier Reef, follow marine heat waves.

Pollution, suspended sediment and unusually cold water can also stress corals and cause local bleaching, but the major and widespread cause is high sea temperature.

Answer: B

(I) is correct but (II) is incorrect.

Statement I describes the observed pattern: surface salinity is highest (about 36 to 37) in the subtropical belts near 20 to 30 degrees of latitude, and lower near the equator and towards the poles.

Statement II gives the wrong cause. The subtropics lie under the descending air of the subtropical highs, with clear skies, strong sunshine and dry winds, so evaporation greatly exceeds precipitation, and it is this excess of evaporation that concentrates salt. An excess of precipitation is what lowers salinity at the equator, where heavy rain falls, and near the poles, where ice melts and rivers add fresh water.

Answer: C

The warm current flowing from the east coast of the U.S. towards Europe is the Gulf Stream.

The Gulf Stream starts in the Gulf of Mexico, flows north along the eastern coast of the United States and then crosses the North Atlantic, continuing as the North Atlantic Drift. It carries warm water to north-western Europe and is the reason the British Isles and Norway have mild winters for their latitude.

The Kuroshio (printed 'Kurosio') is the warm current off Japan in the Pacific. The Benguela current off south-west Africa and the Peru (Humboldt) current off South America are cold currents.