Upwelling

Buoyancy ( also English upwelling ) refers to the rising of water in oceans, marginal seas and lakes from deeper layers to the near-surface, light-filled layer. The water in the deeper layers is usually colder and richer in nutrients than the water in the surface layer. Therefore buoyancy generally leads to a cooling and nutrient enrichment of surface water.

Associated with the buoyant vertical velocities are in the order of 10 m / day. They are thus smaller than the measurement error of currently available flow meter. The rise of movements to take more than one period of the inertial oscillation.

Causes

Cause the buoyancy of the water is low in most cases, the divergence of the wind-driven Ekman transport in the covering layer of turbulent sea surface. Ekman divergent transport is excited in the top layer of the open ocean, when the field of the wind shear stress divided by the sea surface by the Coriolis having a positive rotation. In addition, a fluttering above the equator, spatially constant east wind generated equatorial upwelling. On the shores of the sea buoyancy is stimulated when hemispherical a spatially constant wind blowing parallel to the coast on the north ( south), so that looking in the direction of the wind vector, the coast of left (right ) hand is.

Effects of buoyancy

Abiotic effects

If the surface is warmer than the deeper layers of a marine, buoyancy leads to a regional cooling of the sea surface temperature. This is usually equatorward of the oceanic polar front of the case. The overlying atmosphere is influenced in different ways. The atmospheric boundary layer over a colder surface water is stabilized, thereby reducing the turbulence in the boundary layer. As a result, the momentum of the Gradientwindes in the higher atmospheric layers can not be strongly applied to the marine boundary layer, and thus the wind speed over cold water is lower than the warm surface water. Effect, the influence of the surface temperature of the wind velocity on the sea surface, that the rotation of the wind vector is amplified by a temperature gradient transverse to the wind direction, by a temperature gradient parallel to the wind direction, however, the divergence of the wind field ( Risien Chelton & 2008). The cool surface temperature in upwelling regions is the dew point of the air above it layers down, so that is often fog over the upwelling region. The sea breeze during the day forms the fog advected from coastal upwelling area up to some 10 km inland, where it contributes especially in deserts to supply water to the plant and animal world.

Biotic effects

An important effect of the ocean and its life world have the nutrients in the deep water. This is largely to nutrient salts such as nitrates and phosphates, which in the decomposition of sinking from the surface layer of organic material, detritus or marine snow called, go back in the water the deeper layers in solution. The swelling with the buoyancy in the euphotic zone nutrients cause there a proliferation of phytoplankton, this often takes on the proportions of an algae bloom that can be seen even from space. This high primary production is the basis of the oceanic food chain. Therefore, the population density higher species of the marine ecosystem is comparatively large in permanent upwelling. This upwelling areas with extremely high rate of biomass production have great economic importance especially as they are often located off the coast of less productive regions.

Occurrence of buoyancy

Due to the characteristics of the planetary circulation there are only certain areas of the world where permanent or seasonal buoyancy can be excited. In the open ocean is a long-lasting boost, especially in the subpolar regions where moving the cores of low-pressure areas, and along the equatorial ocean, to the blowing of the south-east trade, observed ( Sverdrup & Fleming 1942, Tomczak & Godfrey 1994).

Coastal upwelling areas are preferably located on the western coasts of continents in the sphere of influence of the trade winds ( Sverdrup & Fleming 1942, Tomczak & Godfrey 1994). The most important upwelling areas are found along the western coast of South America (Peru, Chile) and North America (California, Oregon ) and the west coasts of North Africa (Morocco, Mauritania and Senegal) and the Southern Africa (Namibia, South Africa). All these areas were rich fishing grounds, which are an important economic factor of the neighboring countries. In addition, the permanent coastal upwelling areas in the trade areas reinforce the desert climate of adjacent land by the interaction of cold surface water at the coast with the atmosphere.

In between annual periods the otherwise very stable buoyancy phenomena change in the trade areas through action at a distance from the western parts of the equatorial Pacific and the Atlantic. A temporary weakening of trade winds in the western equatorial ocean triggers the propagation of an equatorial Kelvin wave along the equator, which crosses the whole ocean and eventually propagates poleward as coastal Kelvin wave on the eastern shores of the oceans. The Kelvin wave leads the warm surface water from the western equatorial ocean with and lowers the thermal thermocline from along its propagation path. This process prevents the lift nutrient-rich, cold water in the surface layer. It then comes to a collapse of the fish population and to increase the surface temperature alters the interaction with the atmosphere in such a way that it comes in the otherwise arid coastal areas with heavy rainfall. This phenomenon is called the Pacific El Niño and occurs on average every 5 years. In the Atlantic, it is called Benguela Niño and occurs here but only at a distance of about 10 years.

The southwest monsoon causes buoyancy during the northern summer in the Arabian Sea, on the Somali coast, the south coast of the Arabian Peninsula ( Tomczak & Godfrey 1994), as well as on the coast of Vietnam.

Short-term buoyancy can form on all coasts, when the wind blows parallel to the coast, so that the coast on the northern (southern ) hemisphere to the left (right ) looking lies in the direction of the wind vector and it lasts longer than an inertial period.

Pictures of Upwelling

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