OCEANS AND SEAS COVER ABOUT 70 PERCENT of the Earth’s surface and account for about 97 percent of its total water. These oceans and seas play a crucial role in regulating temperature variations and determining climate. Their waters absorb heat from the Sun, especially in tropical regions, and the surface currents distribute it around the Earth, warming overlying air masses and neighboring land in winter and cooling them in summer. The oceans are never still. Differences in temperature and salinity drive deep current systems, while surface currents are generated by winds blowing over the oceans. All currents are deflected—to the right in the Northern Hemisphere, to the left in the Southern Hemisphere—as a result of the Earth’s rotation. This deflective factor is known as the Coriolis force. A current that begins on the surface is immediately deflected. This current in
turn generates a current in the layer of water beneath, which is also deflected. As the movement is transmitted downward, the deflections form an Ekman spiral. The waters of the oceans and seas are
also moved by the constant ebb and flow of tides. These are caused by the gravitational pull of the Moon and Sun. The highest tides (Spring tides) occur at full and new Moon; the lowest tides (neap tides) occur at first and last quarter.
