![]() ![]() The placement of the Earth’s landmasses and the rotation of the planet cause the boundary currents to be narrowest and deepest on the western edge of the subtropical gyres. The subtropical gyres are surrounded by four linked currents: two boundary currents oriented roughly north-south at their eastern and western edges and two east-west currents at the northern and southern extent of the gyre. Another subpolar gyre, the only one centered on a landmass, circles Antarctica driven by the near-constant westerly winds that blow over the Southern Ocean, unimpeded by land. Smaller counterclockwise gyres centered at around 60 degrees north latitude are created by the prevailing winds around permanent sub-Arctic low-pressure systems. The force of gravity pulling on this large mass of water creates a pressure gradient similar to that in an atmospheric high pressure system which in turn leads to a stable, rotating mass of water.įive permanent subtropical gyres can be found in the major ocean basins-two each in the Atlantic and Pacific Oceans and one in the Indian Ocean-turning clockwise in the Northern Hemisphere and counterclockwise in the Southern. The net wind-driven movement of water, known as Ekman transport, creates a bulge in each ocean basin that is as much as three feet (one meter) higher than mean global sea level. This forms a phenomenon called an Ekman spiral that was first described by Swedish mathematician Vagn Walfrid Ekman in 1905, but it was not until the late 1980s that a team from WHOI first observed it in the open ocean. ![]() In addition, each successive layer of water is slightly deflected from the motion of the one above, like a deck of cards fanned out. Earth's rotation causes an apparent force known as the Coriolis effect to deflect straight-line movement across the surface about 45 degrees to the right in the Northern Hemisphere and 45 degrees to the left in the Southern Hemisphere. The resulting motion is not in line with the wind, however. As this topmost layer of water moves, it pulls on the water directly beneath it, which in turn pulls on the layer of water beneath that to create the beginnings of an ocean current. Friction between the air and the water sets the sea surface in motion. Persistent subtropical high pressure systems centered at about 30 degrees north and south latitude create patterns of strong winds known as the trades and the westerlies. Wind is the primary force that creates and moves surface currents Earth's rotation plays an important role in steering the water's motion. Gyres are spiraling circulations thousands of miles in diameter and rimmed by large, permanent ocean currents.Įddies are smaller, temporary loops of swirling water that can travel long distances before dissipating. They are formed primarily by wind blowing across the surface of the ocean and by differences in the temperature, density and pressure of water and are steered by Earth's rotation as well as the location of the continents and topography of the ocean bottom. Their effects can also extend down for miles, in some places reaching the ocean bottom.Ĭurrents are coherent streams of water moving through the ocean and include both long, permanent features such as the Gulf Stream, as well as smaller, episodic flows in both coastal waters and the open ocean. These features are important components of Earth's global ocean circulation that move water mainly horizontally. ![]() At the surface and beneath, currents, gyres and eddies play a crucial role in physically shaping the coasts and ocean bottom in transporting and mixing energy, chemicals and other materials within and among ocean basins and in sustaining countless plants and animals that rely on the oceans for life-including humans. Other Expeditions Highlighting WHOI ResearchĮven on the calmest days, Earth's oceans are constantly on the move.Expedition to Stellwagen Bank National Marine Sanctuary.How do polynyas help feed emperor penguins?.Why is pressure different in the ocean?.What’s the difference between climate and weather?. ![]()
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