Running marine

See also: Running

A marine running is a displacement of Eau of sea characterized by its direction, its speed and its flow. One distinguishes two types of currents. The Ground receives in an unequal way the solar energy: it is not the same one according to whether one is with the pole (because the rays arrive in a very tilted way) or with the equator. The intertropical zone receives as much energy thus than the remainder of planet. This imbalance puts moving the atmosphere and the Océan S which will rebalance the unit thermically. It generates also Vent S which are the principal factors of the current of surface . These movements are influenced by a force due to the rotation of the Earth, called Force of Coriolis. This imbalance also involves differences of Température according to the Latitude. This difference in temperature involves a difference of salinity of water and thus of Densité, creating thus the current depth .

Origin of the marine currents

The oceanic currents of surface are generally caused by the wind; it are typically directed in the direction of the needles of a watch in the northern hemisphere and the anti-clockwise direction in the southern hemisphere, because of distribution of the winds. In the currents caused by the winds, the effect of " Spiral of Ekman " results in an angular deviation compared to the winds which are in the beginning. The localization of the currents changes notably with the seasons; this phenomenon is particularly sensitive for the equatorial currents.

The deep currents are produced by the gradients of temperature and density. Circulation thermohaline, also qualified " carpet roulant" , relates to the deep currents in the oceanic basins caused by the variations of density. These currents, which run out under oceanic surface and are thus difficult to detect, are comparable to " rivers under-marines". They from now on are followed by a network of drifting underwater sensors named ARGO. Zones of ascending currents (" upwellings ") and descendants are areas where significant vertical movements are observed.

The currents of surface relate to approximately 10% of the water of the oceans. They are generally limited to the first 400 meters of the ocean. The movement of deep water is caused by forces due to the density and gravity. The difference in density is function of the temperature and salinity. The deep water is inserted in the oceanic basins located at the raised latitudes, where the temperatures are rather low so that the density increases. The leading causes of the currents are the solar radiation, the winds and gravity. Flows of the oceanic currents are measured in Sverdrup.

Currents of depths

The winds not having influence after 800m of depth, they cannot be the engines of major oceanic circulations. These currents are based on differences of temperature (the cool water is denser than warm water) and in salinity (the salt water is denser than fresh water), between the various layers of the ocean. Deepest bear the name of current thermohalin and those which go a little less in-depth bear the name of Circulation thermohaline . The warm water of surface takes care out of salt, because of evaporation what tends to make them denser. In winter, during the formation of the ice-barrier, the once formed ice expels the salt which still more weighs down the noncold water which becomes “so much” dense that it plunges towards the depths.

Not important, the currents of surface and the deep currents thus formed are inter-connected. One then introduced the picturesque expression of “travelator” (conveyer belt) to describe the transport of deep water of the Atlantique towards the Pacifique and his return on the surface. Thanks to the heat capacity of water, the ocean is an enormous reserve of heat. Its thermal inertia being much more important of that of the air, it moderates the seasonal thermal changes of the masses of air, which differently would be much more important. Thus the hot currents of the surfacings can heat the climate of an area. Contrary, the cool water which goes up on the surface moderates the temperature of water of the equatorial areas. However this circulation remains badly known because difficult to measure directly.

The ocean thus plays a crucial role for the regulation of the climate of our planet and it ensures a transport of heat of the equator towards the poles as important as the atmosphere.

Principal marine currents of surface

See too

External bonds

  • oceanic circulation
  • Ocean Surfaces Currents
  • Site of the French contribution to project ARGO

  • Vidéos on Channel IRD (Research institute for the Development - an underwater sailplane for the study of the oceanic currents

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