Oceanography Questions and Answers

Answer: C

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

• Abyssopelagic: organisms of the deep waters below about 3,000-4,000 m (a-4).
• Bathypelagic: organisms living between about 1,000 m and 3,000 m (b-3).
• Benthos: organisms living on or at the bottom of a water body (c-2).
• Euphotic zone (printed 'Uphotic'): the upper layer of a sea or lake where enough light penetrates for photosynthesis (d-1).

Option A has the first two right but swaps benthos and the euphotic zone. Options B and D misplace the two pelagic depth zones as well.

Answer: C

The transition zone between continent and ocean basin is the Continental margin.

The continental margin is the whole submerged edge of the continent, made up of the continental shelf, the continental slope and, on passive margins, the continental rise, which together lead down from the coast to the abyssal plain of the ocean basin.

The shelf and the slope are each only one part of the margin, and the abyssal floor is the deep ocean basin itself, beyond the transition.

Answer: C

Statements iii and iv are correct, so the answer is (iii) and (iv).

Hydrothermal vents form when seawater percolates down through fractures in young oceanic crust, is heated by an underlying magma chamber and leaches metals (iv). When the hot, metal-laden fluid jets back into near-freezing seawater, sulphides and other minerals precipitate, building chimneys such as black smokers (iii).

Statement i is wrong: vents cluster at mid-ocean spreading ridges and back-arc basins, where magma is shallow, not at passive continental margins. Statement ii is wrong: vents support rich chemosynthetic communities of tube worms, clams and bacteria.

Answer: C

The highest surface salinity is found between 20-40° N latitude, in the subtropics.

Salinity depends mainly on the balance of evaporation and precipitation. Under the subtropical high-pressure belts, around 20-30° in each hemisphere, descending dry air gives clear skies, strong evaporation and little rain, so surface salinity peaks there, at about 36-37 parts per thousand in the open ocean.

Near the equator (0-10°) heavy convective rainfall dilutes the surface water, so salinity is lower even though temperatures are high, and 10-20° N lies between the two regimes, below the subtropical maximum.

Answer: C

The key gives 26.7 °C as the mean annual surface temperature of seawater at the equator.

Equatorial surface waters stay warm all year, with mean temperatures in the range of about 26-28 °C, and 26.7 °C is the figure commonly quoted in oceanography textbooks. They are not the warmest in the world, because cloud cover, rain and upwelling along the equator keep temperatures slightly below those of the tropical belts on either side.

35.45 °C and 37.5 °C are far above any open-ocean annual mean (35 is closer to a salinity figure in parts per thousand), and 24.5 °C is too low for the equatorial belt.

Answer: B

The key names Salinity difference as the primary reason.

The Mediterranean loses far more water by evaporation than it gains from rain and rivers, so its water becomes saltier, about 38 parts per thousand against about 36 in the adjacent Atlantic. The salty Mediterranean water is denser and sinks, flowing out into the Atlantic at depth over the Gibraltar sill, while lighter Atlantic water flows in at the surface to replace it.

The density difference that drives the exchange is caused by the salinity difference, which is why textbooks give salinity as the primary reason. Temperature works the other way, since the Mediterranean is warmer, and the Strait of Gibraltar is the passage the current flows through, not its cause.

Answer: C

The apparent fall in sea level is called Draw down (drawdown).

When the trough of a tsunami reaches the coast before the crest, the sea retreats rapidly and exposes the seabed, sometimes by hundreds of metres. This drawdown is a natural warning sign that the crest will follow within minutes, as happened on many coasts in December 2004.

'Sea level drop', 'draw fall' and 'dip in sea level' are descriptive phrases, but drawdown is the accepted term for this phenomenon.

Answer: B

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

• A halocline is a layer of sharp salinity gradient in the water column.
• An isohyet joins places of equal rainfall over a period.
• A pycnocline is a layer of rapid density change with depth.
• An isohaline joins points of equal salinity in the ocean.

Option A swaps pycnocline and isohaline, C swaps halocline and pycnocline, and D makes isohyets a density term.

Answer: B

The sinking of the crust under ice is an isostatic change.

Under the principle of isostasy, the crust floats on the denser mantle. The weight of a thick ice sheet presses the crust down; when the ice melts, the land rises again slowly, as Scandinavia and Hudson Bay are still rising today (glacio-isostatic rebound).

Eustatic changes are worldwide changes of sea level caused by changes in the volume of ocean water, thermal expansion of seawater is one cause of them, and interglaciation is a warm period between glaciations.

Answer: B

Only pair (4) is wrongly matched, so the answer is Only (4).

The dynamical theory of tides was developed by Laplace in the late eighteenth century, treating tides as the ocean's dynamic response to the tide-generating forces. G.B. Airy is known for the canal theory of tides.

The other pairs are correct: William Whewell proposed the progressive wave theory (1833), Isaac Newton the equilibrium theory (1687), and R.A. Harris the stationary wave theory. That rules out every option including (1) or (3).