CDS (I) 2020 General Knowledge · Question 66 of 120

Correct — B, North Atlantic Drift and Brazil Current. Both are warm. The North Atlantic Drift is the Gulf Stream's continuation across the ocean, carried east by the westerlies towards north-west Europe, and it is the reason ports on the Norwegian coast stay ice-free at latitudes where the Canadian side is frozen. The Brazil Current is a western boundary current of the South Atlantic, flowing polewards down the Brazilian coast until it meets the cold Falkland (Malvinas) Current. The general rule does all the work here: western boundary currents run along the eastern coasts of continents, carry warm water polewards, and are narrow, deep and fast; eastern boundary currents run along the western coasts, carry cold water equatorwards, and are broad, shallow and slow, with upwelling and a coastal desert behind them. Every current in the other three options fails that test in at least one member.

• (a)Kuroshio and California Current — A mixed pair. The Kuroshio is warm — the North Pacific's western boundary current, the Gulf Stream's counterpart off Japan — but the California Current is a cold eastern boundary current flowing south along the western coast of North America.
• (c)Canaries and Benguela Current — Both are cold. The Canary Current cools the coast off north-west Africa and the Benguela does the same off Namibia; each is an eastern boundary current with strong upwelling, and each has a coastal desert behind it — the Sahara's Atlantic margin and the Namib.
• (d)West Wind Drift and Falkland Current — Both are cold. The West Wind Drift is the Antarctic Circumpolar Current, the coldest large current in the ocean, and the Falkland (Malvinas) Current is its offshoot running north along Argentina, where it collides with the warm Brazil Current.

Surface ocean currents are driven mainly by the prevailing winds and deflected by the Coriolis force into great gyres — clockwise in the northern hemisphere, anticlockwise in the southern. On the western side of each gyre, water piles up against the continent and runs polewards as a narrow, fast, warm western boundary current; on the eastern side it returns equatorwards as a broad, slow, cold current with upwelling along the coast.

Rather than memorise a list, place each current on the gyre. Warm currents flow away from the equator along the east coasts of continents: Gulf Stream and its North Atlantic Drift, Kuroshio, Brazil, Agulhas, East Australian. Cold ones flow towards the equator along west coasts: Canary, Benguela, California, Humboldt (Peru), West Australian. Two names sit outside the scheme and are worth learning separately — the West Wind Drift, which circles Antarctica and is cold, and the Falkland Current, which peels north off it. The paper's option (a) is the classic half-right trap: the Kuroshio is genuinely warm, and a candidate who stops reading after the first name loses the mark.

• The North Atlantic Drift is the eastward continuation of the Gulf Stream and keeps north-west European ports ice-free in winter.
• The Brazil Current is the warm western boundary current of the South Atlantic and meets the cold Falkland Current off Argentina.
• Western boundary currents (east coasts of continents) are warm, narrow, deep and fast; eastern boundary currents (west coasts) are cold, broad, shallow and slow.
• The Canary and Benguela Currents are cold, and the Sahara's Atlantic margin and the Namib Desert lie behind them.
• The West Wind Drift is the Antarctic Circumpolar Current — cold, and the only current that circles the globe unobstructed.

• Judging a pair by its first name only — the Kuroshio is warm, but the California Current beside it is not.
• Assuming a current is warm because it flows in the tropics; the Canary and Benguela both do and both are cold.
• Confusing the Falkland Current with the Brazil Current because they meet in the same waters.

As a warm-or-cold sorting question, sometimes inverted to 'which is NOT a cold current', and occasionally through the coastal desert a cold current supports.

• practice — not a real PYQ

  Which one of the following pairs consists of two cold ocean currents?

  • (a)Gulf Stream and Kuroshio
  • (b)Humboldt and Benguela
  • (c)Agulhas and Brazil
  • (d)East Australian and North Atlantic Drift

  Answer(b) Humboldt and Benguela — both are eastern boundary currents flowing equatorwards along west coasts, with upwelling and a coastal desert behind each.

• practice — not a real PYQ

  The comparatively ice-free winter ports of north-western Europe are best explained by

  • (a)the Labrador Current
  • (b)the North Atlantic Drift
  • (c)the Canary Current
  • (d)the West Wind Drift

  Answer(b) the North Atlantic Drift — the warm eastward continuation of the Gulf Stream, pushed towards Europe by the westerlies.