Waves, Tides, & Currents

Motion of the Ocean The ocean never rests. Currents, waves, and tides all move and mix the ocean waters.

Surface Circulation Both currents and waves are driven by wind which in turn is by heat from the sun. Winds and currents are strongly influenced by the Coriolis Effect.

Coriolis Effect Because the earth is rotating, anything that moves on its surface tends to turn a little to one side rather than moving in a straight line.

Coriolis Effect It is too slight to notice if you are walking or driving, but for things like winds and ocean currents that move over large distances.

In the North Hemisphere the Coriolis Effect always deflects things to the right. In the Southern Hemisphere things are deflected to the left.

Winds Winds are driven by the heat from the sun. Most solar energy is absorbed at the equator. Warm air rises causing cooler adjacent air is sucked in to replace the rising air, creating wind.

Winds do not move in a straight line, but are bent by the Coriolis Effect. These winds are called trade winds and approach the equator at about 45°

Currents Major wind fields of the atmosphere push the sea surface, creating currents. All of the major currents of the oceans are driven by winds.

When pushed by the winds, the currents do not move the same direction as the wind, but due to the Coriolis Effect, move off at a 45° angle.

Gyres Under the influence of the Coriolis Effect, the wind-driven surface currents combine into huge, more or less circular systems called gyres.

California Current Kuroshio North Equatorial Current

South Equatorial Current Peru Current

Canary Current North Equatorial Current

South Equatorial Current Benguela Current

Waves Waves are the most probably the most familiar ocean phenomena.

Wave Anatomy The highest point of a wave is called the crest and the lowest part the trough. The distance of an ocean wave is expressed as the wavelength.

Water movement Under a wave crest the water moves up and forward; under the troughs it moves down and backwards. On the whole the water particles don’t go anywhere at all; they just move in circles.

Waves As waves approach the shore they touch the bottom and begin to slow down. They almost never approach the shore straight on due to the coriolis effect. As a result one end reaches the shallow water before the other.

Bending This means that one end travels faster than the other and results in a bending of the wave, called refraction. The result of life is that there is a tremendous variation in intensity of wave impact, or wave shock.

Tides The sea surface has been rising and falling in rhythmic patterns known as tides for billions of years.

Tides Tides are extremely influential on the life of near shore organisms. They alternately expose and submerge organisms on shorelines, drive circulations of bays, trigger spawning, etc.

Tides The tides are caused by the gravitational pull of the moon, the sun, and rotations of the earth, moon, and sun.

Centrifugal force Strictly speaking the moon does not rotate about the earth. It and the earth rotate about a common point, their combined center of mass.

On the side where the moon pulls strongly on earth, it pulls of the surface water as well. On the opposite side centrifugal force pushed water away from the earth.

Add the Sun Although the sun is much larger it is 400 times farther away and results in a pull half that of the moon.

Spring Tides When the sun and moon are in line with each other, which happens at full and new moons, their effects add together. Called spring tides, the difference between high and low tide is large.

Spring Tide

Neap tide When the sun and moon are at right angles with each other, which happens at first quarter and third quarter, their effects diminish together. Called neap tides, the difference between high and low tide is small.

Neap Tide

Moon Phases