What makes current in the ocean

Oceanic currents are driven by three main factors:. The rise and fall of the tides. Tides create a current in the oceans, which are strongest near the shore, and in bays and estuaries along the coast. These are called "tidal currents. In some locations, strong tidal currents can travel at speeds of eight knots or more.

Occasional events such as huge storms and underwater earthquakes can also trigger serious ocean currents, moving masses of water inland when they reach shallow water and coastlines. Earthquakes may also trigger rapid downslope movement of water-saturated sediments, creating strong turbidity currents.

Finally, when a current that is moving over a broad area is forced into a confined space, it may become very strong. On the ocean floor, water masses forced through narrow openings in a ridge system or flowing around a seamount may create currents that are far greater than in the surrounding water, affecting the distribution and abundance of organisms as well as the scientists and their equipment seeking to study these organisms.

Currents on the surface are determined by three major factors: the major overall global wind patterns, the rotation of the Earth, and the shape of ocean basins.

The ripples in the cup are tiny waves, just like the waves that wind forms on the ocean surface. The movement of hot chocolate throughout the cup forms a stream or current, just as oceanic water moves when wind blows across it. But what makes the wind start to blow? When sunshine heats up air, the air expands, which means the density of the air decreases and it becomes lighter. Like a balloon, the light warm air floats upward, leaving a slight vacuum below, which pulls in cooler, denser air from the sides.

The cooler air coming into the space left by the warm air is wind. This hotter air rises up at the equator and as colder air moves in to take its place, winds begin to blow and push the ocean into waves and currents.

Wind is not the only factor that affects ocean currents. The Earth is a sphere that spins on its axis in a counterclockwise direction when seen from the North Pole. The further towards one of the poles you move from the equator, the shorter the distance around the Earth. This means that objects on the equator move faster than objects further from the equator. While wind or an ocean current moves, the Earth is spinning underneath it.

As a result, an object moving north or south along the Earth will appear to move in a curve, instead of in a straight line. Wind or water that travels toward the poles from the equator is deflected to the east, while wind or water that travels toward the equator from the poles gets bent to the west. The Coriolis Effect bends the direction of surface currents. The third major factor that determines the direction of surface currents is the shape of ocean basins Figure At about 30 degrees north latitude, a different set of winds, the westerlies, push the currents back to the east, producing a closed clockwise loop.

The same thing happens below the equator, in the Southern Hemisphere, except that here the Coriolis effect bends surface currents to the left, producing a counter-clockwise loop. Large rotating currents that start near the equator are called subtropical gyres. These surface currents play an important role in moderating climate by transferring heat from the equator towards the poles.

Subtropical gyres are also responsible for concentrating plastic trash in certain areas of the ocean. In contrast to wind-driven surface currents, deep-ocean currents are caused by differences in water density. It all starts with surface currents carrying warm water north from the equator.

The water cools as it moves into higher northern latitudes, and the more it cools, the denser it becomes. In the North Atlantic Ocean, near Iceland, the water becomes so cold that sea ice starts to form. The salt naturally present in seawater does not become part of the ice, however.

It is left behind in the ocean water that lies just under the ice, making that water extra salty and dense. The denser water sinks, and as it does, more ocean water moves in to fill the space it once occupied. This water also cools and sinks, keeping a deep current in motion. These currents circulate around the globe in a thousand-year cycle. The Coriolis effect makes storms swirl clockwise in the Southern hemisphere and counterclockwise in the Northern Hemisphere.

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