Oceanography Questions and Answers

Answer: D

The current not responsible for desert formation is the Agulhas current.

Cold currents flowing along the western coasts of continents in the subtropics chill the air above them, which stabilises it and suppresses rain, helping to form coastal deserts. The Agulhas current is a warm current flowing down the south-east coast of Africa, which brings moisture rather than aridity.

The Benguela current borders the Namib Desert, the Humboldt (Peru) current the Atacama, and the West Australian current the deserts of Western Australia; all three are cold currents.

Answer: D

The correct match is a-iv, b-ii, c-i, d-iii.

1. Retrogradation: the shoreline retreats, moving landward, through erosion or rising sea level (iv).
2. Groin: a wall or embankment built at right angles to the shore to trap sand moving by longshore drift (ii).
3. Progradation: the shoreline builds out, moving oceanward, through deposition (i).
4. Backwash: the return flow of water down the beach after a wave breaks, related to the seaward undertow (iii).

Options pairing retrogradation with 'oceanward' swap it with progradation, and the option pairing the groin with oceanward movement confuses a structure with a process.

Answer: A

The warm Pacific current is the Kuroshio current.

The Kuroshio, or Japan Current, carries warm tropical water north-east along the east coast of Taiwan and Japan as the western boundary current of the North Pacific gyre, the Pacific counterpart of the Gulf Stream.

The Mozambique current (spelt 'Mozambiqe' in the paper) is warm but in the Indian Ocean. The Canaries current is a cold current of the North Atlantic, off north-west Africa. The Humboldt (Peru) current is a Pacific current but a cold one, flowing north along the coast of South America.

Answer: D

Seawater density depends on salinity, temperature and pressure.

Seawater becomes denser as salinity increases (more dissolved salt), as temperature decreases (cold water is denser), and as pressure increases with depth (water is slightly compressible). The equation of state of seawater expresses density as a function of all three; surface density is typically about 1,025 kg/m³.

Each two-factor option leaves one out. Temperature and salinity alone are often used near the surface, where they drive thermohaline circulation, but at depth pressure adds noticeably to density, so the complete answer includes all three.

Answer: C

The warm Indian Ocean current is the Agulhas current.

The Agulhas current flows south-west along the east coast of South Africa, carrying warm water from the tropical Indian Ocean as the western boundary current of the South Indian Ocean gyre. It is one of the strongest currents in the world's oceans.

The Canary current is a cold current of the North Atlantic. The Florida current is warm but in the Atlantic, feeding the Gulf Stream. The Kurile (Oyashio) current is a cold current of the North Pacific off Russia and Japan.

Answer: B

An isohaline is the line that joins the places of equal salinity.

The prefix 'halo-' refers to salt. Isohalines are drawn on maps of the oceans to show the distribution of surface or subsurface salinity, usually in practical salinity units or parts per thousand. Salinity is highest in the subtropics, where evaporation exceeds precipitation, and lower near the equator and the poles.

Lines of equal precipitation are isohyets, lines of equal temperature are isotherms, and lines of equal humidity are isohumes (or isohygrometric lines).

Answer: D

The oldest waters upwell in the North Pacific.

In the global thermohaline circulation, deep water forms by sinking in the North Atlantic and around Antarctica, then spreads slowly through the deep ocean. The North Pacific lies at the far end of this path, so its deep water has been longest out of contact with the atmosphere; radiocarbon ages there reach well over a thousand years, the oldest in the ocean.

The North Atlantic is where deep water forms, so its deep water is the youngest. The South Atlantic and Indian Oceans lie part-way along the path, and their deep waters are younger than those of the North Pacific.

Answer: D

The correct pairs are (2), (3) and (4), so the answer is (2), (3) and (4).

The Leeuwin current flows south along the west coast of Australia in the Indian Ocean (2). The Tsushima current is a branch of the warm Kuroshio flowing into the Sea of Japan in the Pacific (3). The Antilles current flows north-west past the Caribbean islands and the Bahamas in the Atlantic (4).

Pair (1) is wrong: the Irminger current is a branch of the North Atlantic Drift flowing west past Iceland towards Greenland, in the Atlantic, not the Pacific. So every option containing (1) is wrong.

Answer: B

Global mean sea level rose by 0.20 m between 1901 and 2018.

The IPCC Sixth Assessment Report states that global mean sea level increased by 0.20 m (likely range 0.15 to 0.25 m) over that period. The rate of rise has accelerated, from about 1.3 mm per year in 1901-1971 to about 3.7 mm per year in 2006-2018, driven by ocean warming and melting glaciers and ice sheets.

0.10 m is too small, and 0.30 m and 0.40 m are larger than the observed rise.

Answer: C

The answer is chloride.

Chloride is the most abundant dissolved constituent of seawater, about 55 percent by weight of the dissolved salts (about 19 g per kg of seawater). It is also highly unreactive: it is not taken up by organisms or removed into sediments to any great extent, so it stays in the ocean for a very long time, of the order of 100 million years.

Sodium is the second most abundant ion and has a somewhat shorter residence time. Lithium and aluminium are trace elements; aluminium in particular is removed very quickly onto particles.