What causes ocean currents, but also what actually are ocean currents and why do they flow in certain patterns or shift? These are good questions and not as difficult to answer as most think. An ocean current is a large mass of water that moves in one direction are approximately the same speed. This is best seen by the Gulf Stream as it moves from the Gulf of Mexico across the Atlantic and near the coast of Britain. It is a strong surface current that is frequently used by ships to decrease fuel consumption and time. But what causes ocean currents?
There are two main causes of ocean currents, the Earth’s rotation and temperature differences. Obviously, as an object rotates, the mass shifts and starts to move. If you do this with a solid, it all seems to move together, if you do it with a liquid the movement becomes more random and patterns form. The oceans are fluid and the Earth is rotating or moving, that is why we have day and night on a 24 hour cycle! This mean that in the Northern Hemisphere most major currents flow clockwise and in the Southern Hemisphere it is counterclockwise.
The currents can then be further complicated by density gradients, and there are differences in density in the oceans. The differences are caused basically by temperature. As warm warms above 4 degrees Celsius, it starts to rise, as it drops it condenses. The poles are cold and the equator is warm. Water are the poles tends to sink and flows down to the equator and the water in the tropics heads north, thus you have the Gulf Stream running north!
To “muddy the waters” even more, there are small currents found in the oceans that change and shift, but are again due to temperature changes as well as gravitational effects. What causes them and are they really ocean currents? They can be caused by a number of factors, a major river such as the Amazon emptying into the Atlantic. The pull of the moon creates tidal currents. Underwater volcanic vents change the temperatures and gradients, creating minor currents that can last for centuries! Maybe not important on a global scale, but they can effect ships and small islands!
What cause a current to shift or change, geography! The surface of the floor of the sea changes the way water flows. It can be changed by natural means, silting up of an area or plate shifting that result in tsunamis or even by man-made structures, though that is generally more localized!
What causes ocean currents, temperature changes and the rotation of the Earth. It is as basic as that!