Geography Quiz: Oceans and Ocean Currents

It is a warm current of the Indian Ocean that flows southward along the eastern coast of southern Africa, carrying tropical water towards the Cape before most of it turns back into the Indian Ocean.

El Nino, Spanish for the child, is the warm surface water that appears off the coast of Peru and Ecuador around Christmas in some years, replacing the normally cold Peru or Humboldt current.

The Ring of Fire is a horseshoe-shaped belt running around the rim of the Pacific Ocean, from the Andes up the west coast of the Americas, across the Aleutians and down through Japan, the Philippines and Indonesia to New Zealand.

Textbooks describing the distribution of water on earth give about 97.2 per cent as ocean water, roughly 2 per cent locked in ice caps and glaciers, and well under 1 per cent as groundwater, lakes, rivers, soil moisture and water vapour together.

Spring tides occur at new moon and at full moon, when the sun, the earth and the moon lie in a straight line, a position called syzygy.

The bay narrows and shallows inland, so the incoming tidal wave is funnelled into a smaller and smaller cross-section and its height is greatly magnified, giving the greatest difference between high and low water anywhere on earth.

It flows northward along the western coast of southern Africa, carrying cool water from the Southern Ocean towards the equator, and the upwelling along it makes the Namibian coast a rich fishing zone while helping to keep the Namib desert dry.

The warm Gulf Stream moving north-east meets the cold Labrador current coming south past Newfoundland. Nutrients carried by the cold water mix with the warmer surface layer, plankton multiplies, and huge shoals of cod once gathered there.

Sodium chloride makes up most of it, with magnesium, calcium and potassium salts making up the rest. Salinity varies with evaporation, rainfall, river inflow and the melting or freezing of ice, so the figure is an average rather than a fixed value.

Its southern end holds the Challenger Deep, the deepest surveyed point on earth at roughly eleven kilometres below sea level, deep enough to swallow Mount Everest with water to spare.

The continental shelf is the gently sloping submerged edge of a continent, usually taken down to about two hundred metres.