How fast do currents move

Ocean currents are also critically important to sea life. They carry nutrients and food to organisms that live permanently attached in one place, and carry reproductive cells and ocean life to new places.

Rivers flow because of gravity. What makes ocean currents flow? Tides contribute to coastal currents that travel short distances. Major surface ocean currents in the open ocean, however, are set in motion by the wind, which drags on the surface of the water as it blows.

The water starts flowing in the same direction as the wind. But currents do not simply track the wind. Other things, including the shape of the coastline and the seafloor, and most importantly the rotation of the Earth, influence the path of surface currents.

In the Northern Hemisphere, for example, predictable winds called trade winds blow from east to west just above the equator. The winds pull surface water with them, creating currents. As these currents flow westward, the Coriolis effect —a force that results from the rotation of the Earth—deflects them.

The currents then bend to the right, heading north. 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.

Models generally suggest that a weak AMOC could cause a substantial cooling effect in Western Europe, as less and less heat is transported north from the equator.

The new research is another example of the often competing effects of climate change. In this case, warming drives stronger winds, which result in faster ocean circulation across much of the globe. Both can be true at once, Hu noted. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. All over the world, the oceans are changing in profound ways.

The reason is accelerating winds. Get smart. Sign up for our email newsletter. Let's say that every day, during a certain season, a strong wind started to blow from the north to the south along the shores of a continent. Think of the force of this wind like a hand gently pushing water. The displaced water is turned oceanward by the Earth's rotation. Why doesn't this phenomenon, also known as the Coriolis Effect, cause the ocean to recede like it does at low tide?

Is it because the wind only moves the top layer of water? No — underneath that surface current, cold, nutrient-rich water rushes in to take the place of the surface water. Though the wind moves surface water first, eventually, deep ocean water is affected by surface weather as well. Currents in the deep ocean are caused mostly by a phenomenon called thermohaline circulation. Thermohaline circulation starts in the North Atlantic Ocean where the water is really cold much colder than the ocean off the coast of Cape Cod or Maine, where brutal winters freeze freshwater lakes, ponds and even rivers, but not the oceans.

In the North Atlantic, however, it can get so cold that even the ocean water will freeze. When salt water freezes, it leaves behind a lot of extra salt, making for really dense water. Think of that dense water as heavy. That heavy water sinks rapidly in areas where polar ice has formed. This cold, dense, sinking water is the foundation for a system of currents that covers the whole globe.

As this cold water travels away from the ice to sunnier latitudes, it starts to warm.