Properties of Water

In general, currents in the deeper ocean are caused by the mixing of bodies of water at different temperatures, salinity levels, pressures, and densities, although this may not be the direct cause.

Salinity

Salinity is the scientific term for the amount of saltiness in water. All water has some dissolved salts in it, but the ocean has much more salt than fresh water.

Ocean water is always evaporating into the atmosphere, but the salt remains in the ocean. Thus, the ocean remains salty even though fresh water is continually being added by rainfall and by rivers and runoff from land.

Temperature

Temperature can vary a lot in the ocean. Shallow tropical waters can reach close to 90°F (31° C), while water at the poles will be close to freezing (28.4°F, -2° C). Seawater freezes at a lower temperature than fresh water (32° F, 0° C) because of its salt content.

The warmest water in any area is at the surface, and the coldest water is at the bottom. This is partly because the sun warms surface water. However, cold water is heavier (denser) than warm water, so cold water naturally moves toward the bottom and warm toward the top.

Pressure

Pressure is a measure of the weight of the water and atmosphere pushing downward at any given point. There is 15 pounds per square inch of pressure at sea level. In the deepest parts of the ocean, pressure is around 15,000 pounds per square inch, an increase of 1,000 times.

Density

Density is the scientific term for the weight of water. Salt water weighs more than fresh water, so it is heavier. The more salt the water contain, the denser it is. Because it weighs more, saltier water sinks. Density is a measure of weight, technically the weight of a liquid divided by how much space it talkes up. Salinity, temperature, and pressure work together to create density.

Movement happens when two opposing forces are not in balance. When one part of the ocean is denser than the surrounding area, water movement will take place. This creates currents. Because of the many factors involved, the flow of currents is very complex.