Grade 6 Science Practice Test: Ocean Currents, Winds and Climate

Steady winds drag the top layer of water along and set up surface currents. Earthquakes can cause tsunamis, but not steady currents.

Near the equator sunlight hits almost straight on and is concentrated. Near the poles the same light is spread over a larger area at a low angle.

The Gulf Stream and the North Atlantic Current bring warm water from the tropics, and westerly winds carry that warmth over Western Europe.

Cold, salty water is denser, so it sinks near the poles and spreads along the ocean floor. Wind only reaches the upper layer of the ocean.

Land warms up faster than water in sunlight. Warm air over the land rises, and cooler, denser air from over the sea flows in to replace it.

Deep water is rich in nutrients. When it rises, plankton grow quickly, and many fish come to feed on them.

Because Earth spins, moving air and water are deflected, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is the Coriolis effect.

Rising air cools and its water vapor condenses into rain on the windward side. The air that comes down the other side is dry, so a rain shadow forms.

Warm air expands and becomes less dense, so cooler, denser air pushes in underneath and lifts it. This rising air is part of the global wind pattern.

Warm currents carry heat away from the equator and cold currents return cooler water. This makes the difference between tropical and polar temperatures smaller than it would be.