Movements of Ocean Water (Waves, Tides, Currents) — Practice

Question 1

Distinguish between spring tides and neap tides with reference to the positions of the Moon and Sun.

Accepted Answer

Spring Tide: occurs when the Sun, Moon, and Earth are aligned in a straight line (syzygy) — at new moon and full moon. The gravitational pulls of the Sun and Moon combine, creating the MAXIMUM tidal range (highest high tides, lowest low tides). Neap Tide: occurs when the Sun and Moon are at right angles to the Earth (quadrature) — at first and last quarter moon. The pulls partially cancel each other, creating MINIMUM tidal range. Both occur twice monthly, regardless of the calendar season.

Question 2

Explain how ocean currents influence the climate of coastal regions, using the Gulf Stream and the Peru Current as examples.

Accepted Answer

Ocean currents transport heat from the tropics toward the poles (warm currents) and cold water toward the equator (cold currents), moderating coastal climates. Gulf Stream (warm): originates in the Gulf of Mexico, flows northeast across the Atlantic to Western Europe. It carries warm tropical water northward, keeping the UK, Ireland, France, and Norway 5-10°C warmer than their latitudes would suggest — London (51°N) has a mild, wet climate while Winnipeg (same latitude) has brutal winters. Peru/Humboldt Current (cold): flows northward along South America's west coast. Cold upwelling water cools the overlying air; when this cold air moves over warm land it cannot hold moisture → no rain → the Atacama Desert (world's driest) forms despite being on a coast. Cold currents create deserts; warm currents prevent them.

Question 3

Describe the general circulation of ocean water and explain the role of ocean currents in creating the world's major fishing grounds.

Accepted Answer

Ocean surface circulation forms GYRES — large circular current loops driven primarily by prevailing winds. In the Northern Hemisphere, gyres rotate clockwise (Coriolis deflects water right); in the Southern Hemisphere, anticlockwise. Warm currents flow along the western sides of ocean basins (Gulf Stream-Atlantic west, Kuroshio-Pacific west) while cold currents flow along eastern sides (California, Peru, Canary, Benguela). This arrangement creates contrasting coastal climates — mild western coastlines of continents in mid-latitudes (Western Europe, Japan) vs cold, dry eastern coasts. Fisheries: Cold currents create UPWELLING — winds drive surface water away from coasts, drawing cold, nutrient-rich deep water upward. This nutrient supply fuels massive phytoplankton blooms → zooplankton → fish. The Peru/Humboldt Current supports one of the world's most productive fisheries (anchovy, tuna). Convergence zones where warm and cold currents meet create mixing of nutrients and temperatures: Grand Banks (North Atlantic — Gulf Stream meets cold Labrador Current) and Japan Banks (Kuroshio meets cold Oyashio) are among the world's richest fishing grounds. These zones have historically supported major fishing industries for nations like Canada, Iceland, and Japan.

Practice — Movements of Ocean Water (Waves, Tides, Currents)

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