SDI Open Water Scuba Diver Practice Exam

What primarily causes permanent ocean currents?

1. Tides

2. Wind patterns only

3. The sun warming water near the equator and the earth's rotation

4. Seasonal variations in temperature

The correct answer is: The sun warming water near the equator and the earth's rotation

The primary cause of permanent ocean currents is the sun warming water near the equator combined with the Earth's rotation. The sun heats the surface of the ocean unevenly, primarily due to the curvature of the Earth and its axial tilt, leading to temperature gradients. Warmer water near the equator becomes less dense and rises, while cooler water in higher latitudes is denser and sinks. This differential heating sets up a pattern of movement in the water, aided by the Coriolis effect, which is a result of the Earth’s rotation. This effect causes moving water to turn and twist rather than flow in a straight line, influencing the direction of currents. Together, these factors establish the great ocean currents like the Gulf Stream and the North Atlantic Drift, which are consistent and long-lasting, unlike those influenced by tides or seasonal variations that change with time and conditions. Consequently, understanding these processes is crucial for grasping why permanent ocean currents have the characteristics they do, such as their predictable paths and their role in regulating global climate and marine ecosystems.