Why is ocean circulation important

This will probably frustrate those who prefer their science to send a clear signal. But then, science is rarely so obliging. Can the effects of climate change and natural variability on the AMOC be disentangled? And if the ocean circulation is sensitive to climate change, as is highly likely, will the currents respond abruptly and perhaps violently at some point, or will the transition be smooth?

These are among the most pressing questions in climate science. The slow progress on answering them should offer a stark reminder that the oceans are the most under-sampled component of the Earth system.

The AMOC is just one part of a world-spanning circulation system, the physics — and influence on chemical cycling — of which is only poorly understood.

Numerical models are an indispensable tool for studying ocean circulation and climate. But despite ever-increasing computer power, models fall short when it comes to reconstructing something as nuanced and variable as ocean circulation. Long-term, serial measurements of circulation strength are what is needed. It is crucial, therefore, that existing ocean monitoring systems —including the Overturning in the Subpolar North Atlantic Program and the South Atlantic Meridional Overturning Circulation programme — are maintained over decades to come.

Data from these arrays of monitoring instruments are just beginning to shed light on the complex water flows in key ocean regions. Yet securing funding for lengthy studies is an ongoing fight. There is more to be done. Ocean currents act much like a conveyor belt, transporting warm water and precipitation from the equator toward the poles and cold water from the poles back to the tropics. Home Ocean Exploration Facts How does the ocean affect climate and weather on land?

How does the ocean affect climate and weather on land? The density of surface water increases when frigid air blows during winter across the ocean at high latitudes. The water density increases further by evaporation and by salt expulsion when sea ice is formed. From these regions, a cold deep water layer spreads over the entire ocean basins. The thermohaline circulation moves water masses around between the different ocean basins [9] [10].

The conveyor belt is fed in the northern North Atlantic with high-salinity water due to evaporation supplied by the Gulf Stream , which sinks to great depth after cooling down in the Arctic region, forming the North Atlantic Deep Water NADW.

The replacement of this dense sinking water generates a continuous surface flow feeding the conveyor belt. This current compensates for the net northward surface flow in the Atlantic Ocean. The cold dense water from the Antarctic zone fills the deep water layer in these oceans and then gradually rises and mixes with the surface waters of the Indian and Pacific oceans. The mixing of deep ocean water is promoted by strong surface winds, by tides, by upwelling and by abyssal circulation [12] [8].

The circulation is finally completed by a warm surface return current to the Atlantic Ocean that passes south of Africa and America, see figure 5. The whole trip takes more than 1, years to complete. To maintain the large-scale thermohaline circulation of the ocean, it has been estimated that about 2.

It has long been recognized that winds and tides are two important sources of mechanical energy to drive the ocean interior mixing.

Although most of the tidal energy from Moon and Sun on the global ocean is dissipated in the shallow seas, perhaps 1. The breaking of internal waves is believed to be a principal contributor to pelagic turbulence.

They are thought to play an important role in diapycnal mixing to sustain the global system of thermohaline circulation. However, recent calculations on the basis of observations suggest that the wind power is only 0.

In recent decades, biogenic mixing is thought to be another significant contributor to ocean mixing Katija and Dabiri, [17]. From small zooplankton to large mammals, swimming animals are capable of carrying bottom water with them as they migrate upward, and that movement indeed creates an inversion that results in ocean mixing. The global power input from this process is estimated in the order of a TW of energy, comparable with levels caused by winds and tides.

After all, each day, billions of tiny krill and some jellyfish migrate hundreds of meters from the deep ocean toward the surface where they feed. The deep ocean is a huge storehouse of heat, carbon, oxygen and nutrients. Deep ocean circulation regulates uptake, distribution and release of these elements. The low overturning rate stabilizes our global climate.

By carrying oxygen into the deeper layers it supports the largest habitat on earth. Present theories for explaining the deep ocean circulation predict that global warming will have a negative impact on the deep ocean circulation. 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.

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. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.