Oceanography

Where a warm and a cold current converge, the mixing brings nutrient rich deep water into the sunlit surface layer, which supports a bloom of phytoplankton, which supports zooplankton, which supports commercially valuable fish in very large concentrations. The classic grounds are all of this type: the Grand Banks off Newfoundland where the Labrador current meets the Gulf Stream, the north west Pacific grounds off Japan where the Oyashio meets the Kuroshio, and the north east Atlantic grounds where the North Atlantic Drift meets cold Arctic water.

• Option (c) states this and is correct.
• Option (a) is the deliberate trap and differs from the answer by a single word: atmospheric currents are winds, and while wind drives the upwelling that produces the other great fishery type off Peru and north west Africa, the convergence being described here is oceanic.
• Option (b) is incorrect as a general proposition; river discharge does deliver nutrients and estuaries are highly productive, but large freshwater input lowers salinity and the world's principal fishing grounds are not defined by it.
• Option (d) is incorrect because an undulating shelf floor is not itself a control on productivity, although a broad and shallow shelf is a real advantage; the operative factor is nutrient supply to the photic zone, not bottom topography. The elimination route is to read options (a) and (c) against each other and notice that only one word separates them.

The equatorial counter-current flows eastward in a narrow band between the westward flowing North and South Equatorial Currents. The key takes option (b). The mechanism is that the trade driven equatorial currents converge water and drive it west, piling it against the western margin of the ocean basin and raising sea level there by tens of centimetres; the resulting east-west pressure gradient forces a return flow, which surfaces as the counter-current in the zone between the two westward drifts.

• Option (a) is wrong because the Earth's rotation deflects moving water rather than driving it eastward, and it deflects in opposite senses in the two hemispheres.
• Option (c) is wrong because salinity contrasts drive the deep thermohaline circulation on a timescale of centuries, not a surface current of this speed.
• Option (d) is the serious competitor: the doldrums belt of calms is where the counter-current is found, because there the weak trades cannot oppose the return flow, but calm is the permissive condition that allows the current to surface rather than the force that generates it.

• Statement 2 is correct and is the substance of the research the question draws on. Ocean Mean Temperature integrates heat through the upper ocean layer rather than sampling only the skin, so it captures the heat content actually available to drive convection, and the January to March value in the south western Indian Ocean has been shown to predict whether the following monsoon will be above or below the long period average with greater accuracy than sea surface temperature.
• Statement 1 is treated as incorrect by the official key. The keyed answer is therefore 2 only, giving (b), with (a) and (d) rejected outright and (c) rejected only on the treatment of statement 1.

• Statement 1 is incorrect and is the decisive statement: licensing of exploration and exploitation in the Area, meaning the seabed beyond national jurisdiction, is the exclusive function of the International Seabed Authority established under the United Nations Convention on the Law of the Sea. The Global Ocean Commission was a time bound independent advocacy initiative that produced recommendations on ocean governance and had no licensing power at all.
• Statement 2 is correct: India holds ISA contracts for polymetallic nodules in the Central Indian Ocean Basin and for polymetallic sulphides in the Indian Ocean ridges, and is designated a pioneer investor.
• Statement 3 is correct: rare earth elements occur in deep sea muds and in ferromanganese crusts on the ocean floor. Hence 2 and 3, giving (b). The general rule worth teaching is that bodies named Commission or Panel in ocean governance advise, while the Authority created by treaty licenses.

Both statements follow from the same mechanism, wind driven surface circulation.

• Statement 1 is correct: the trade winds blow from east to west across the tropics, piling warm surface water against the western margins of ocean basins and producing the western boundary currents such as the Gulf Stream and Kuroshio, while the eastern margins experience compensating upwelling of cold water, as off Peru and Namibia. This is why the western tropical Pacific warm pool exists and why El Nino, which relaxes the trades, is so consequential.
• Statement 2 is correct: in the temperate belt the westerlies drive warm water eastward, so the North Atlantic Drift warms the eastern Atlantic and north western Europe, leaving the western sections at comparable latitudes colder, which is why Labrador is far colder than Britain. Hence (c). Teaching the gyre as a single closed circulation makes both statements fall out of one diagram.

Both statements are correct and together explain why the Red Sea is among the most saline open seas in the world, with salinity around 40 parts per thousand.

• Statement 1 holds because the Red Sea lies within the subtropical high pressure belt, flanked by the Sahara and the Arabian deserts, and receives negligible rainfall, of the order of a few centimetres a year.
• Statement 2 holds because no perennial river drains into the Red Sea. Its catchment is desert, and such wadis as exist flow only briefly after rare storms. With high evaporation under intense insolation, no riverine inflow and almost no precipitation, the water balance is maintained chiefly by inflow from the Gulf of Aden through the Bab el Mandeb, and the deficit drives the high salinity.

Hence (c), and options (a), (b) and (d) each reject a correct statement.