Water movements in the oceans

Water Movements.

The sea is in constant motion with both regular and irregular patterns of flow.

These movements result in:

a. oxygenation of subsurface waters.

b. dispersal of metabolic wastes.

c. dispersal of nutrients.

d. dispersal of eggs, spores, larvae, and many adults.

3. Currents

a. Surface currents are driven mainly by the wind system of the earth. These wind systems are driven by the temperature differences between the tropics and the poles, modified by the rotation of the earth (Coriolis effect).

1). Since water is a much denser medium than air, the surface currents of
the oceans travel at a much slower velocity than the prevailing winds that create them. The fastest currents are found in the western part of the oceans in the northern hemisphere (Gulf Stream in North Atlantic and Kuroshio Current in North Pacific), traveling at around 2.5-4.5 mph.

2). These ocean currents do not move in exactly the same direction as theprevailing winds. They usually move at about a 45 degree angle.

b. Vertical currents are created by density differences between layers of water, which are produced by temperature and salinity concentration. This is the only mechanism whereby oxygen can be transferred from the upper layers to the subsurface waters, which is critical to all aerobic animals.

4. Waves:

a. A wave is a vertical circular motion of water that causes an undulation on the water surface. Since the motion is vertical and circular, as the wave travels across the ocean, it is the "disturbance" or "energy train" that is moving, not the water itself. The wave possesses a considerable amount of kinetic energy (energy of movement) but when it travels across the ocean, it conserves most of this energy, dissipating it only when it "breaks" upon a shoreline.

b. Waves are created primarily by wind, although there are special waves that are touched off by earthquakes or landslides.

c. When created by wind, the wind speed, duration, and fetch (area over which the wind blows) determines the size and energy of waves. In general, the faster and longer the wind blows, the larger the waves become.

d. Typically, a wave is characterized by its wave height (vertical distance from crest to trough), its wavelength (distance from crest to crest), and by its period (time it takes one wavelength to pass a certain point).

e. Since the vertical "reach" of a wave is about 1/2 its wavelength, wind-driven ocean waves rarely mix the surface waters to a depth greater than 50 meters.

f. Tsunamis: Japanese term for "harbor wave."

1). Created by tectonic events, such as underwater earthquakes, volcanic
eruptions (above or below the water), or landslides that enter the sea. A wave sequence is set in motion that travels outward from the source

2). Unlike wind driven waves, tsunamis travel extremely fast (up to 500
mph). They have very long wavelengths, with crests 100 miles or so apart, or with a period of 20-30 minutes.

3). In the open ocean, the wave height is small (often no more than a meter) so that they pass unnoticed. But, as they enter shallow water, the water may build to 75-100 feet high, causing tremendous destruction. A few minutes before the tsunami (can be only one or a series, depending on the nature of the seismic activity) reaches landfall, there is a telltale withdrawal of water from the shoreline as the tsunami trough precedes the wave.

Note: if one is located along a shoreline and there is a tsunami warning, do not venture out into the receding water area, attempting to harvest fish, lobsters, crabs, as within the next few minutes, there will be an incoming wall of water that is of sufficient force to carry an object inland for several hundred meters or longer, which would have fatal consequences to the "reaper" of the bounties of the sea.