Ocean current
As ocean currents is called the horizontal and vertical transport of water masses in the oceans. Ocean currents are mainly affected by the wind and the tides. Also significant is the thermohaline circulation which depends on salinity and water temperature, which change the water density.
Definition
Ocean currents are mass flows of sea water. There are both regional and changing in short periods as the tidal currents and continuous movement of water on a global scale, such as the Gulf. This large-scale ocean currents are collectively referred to as global conveyor belt.
Numerous drive effects and influences determine the transport of water masses in the oceans. The movements in the near-surface layers are often long been known that. In the deeper layers object recent research Normally, these are related to thermohalin currents. These are quite reliable in general and particularly in the larger flow patterns of the global conveyor belt in their appearance, but may also vary due to meteorological and ozeanologische factors. Most of these variance follows a rhythm that adapts to the seasons, and thus depends on the variability of the solar radiation.
Formation
The flows are mainly caused by temperature differences and different salinities of sea water (depending salty the water is, the greater its density is ) generated resulting from the warming of water masses by the sun and cooled off. However, the wind friction on the surface of the sea ( Ekman spiral, upwelling ) provides a significant contribution. The differences in water density effect in vertical currents as driving.
The local history of ocean currents is affected except by the flow generating forces, acting through the secondary distribution of the land masses, the topography (relief) of the seabed, the Coriolis force, the centrifugal force during rotation movements, and the friction force. The most important elements are associated with the water temperature ( sea surface temperature), salinity, and from this result, the density of water.
Types of flow
Ocean currents are distinguished by various features:
- Constant currents
- Periodic currents
- Occasional currents
- Tidal stream (see tide )
- Surf return current (see surf)
- Gravity flows ( see gravitation)
- Compensation flows or compensation flows
- Friktionsströmungen or drift currents which are based on friction at the interface of water / air
- Corkscrew flow, caused by the wind in combination with the Coriolis force
- Warm currents
- Cold currents
- Salty currents
- Low-sodium currents
- Surface currents
- Deep currents
- Bottom currents
- Coastal currents
The boundaries of this classification are partially redundant and usually have real flows a combination of different influences on.
Large-scale ocean currents
(w = warm, k = cold)
Water vortex
In the peripheral area of ocean currents it comes to turbulence, which with the cooperation of the Coriolis force eddy (English: eddy ) with a diameter between 20 km and 200 km arise. You can a few weeks to several months have stock and thereby to cover distances of several hundred kilometers. With the vertebrae sea water is trapped in the formation region and thus for example warm Gulf Stream water and salty, heavy Mediterranean water flowing over the Gibraltar sill in the Atlantic, are distributed in the area. Such salt- rich water vortex from the Mediterranean ( a Meddy - Mediterranean eddy ) is typically located 600 m below the sea surface and has a diameter of 100 km.
Cold and warm water vortex can be observed by satellites as they manifest themselves as changes in sea level. It was also observed that water vortex, where cold, nutrient-rich water from the deep sea is promoted to the sea surface, seem like a briefly existing upwelling. This multiplies there explosively phytoplankton, which can also be observed by satellites.
Importance of ocean currents
Climate
On the climate ocean currents can have a major impact. The IPCC AR5 report notes with high probability, the recorded 90 % of the additional energy accumulation by global warming from 1971 to 2010 from the ocean. This observation is based on La Niña years when passing through changing wind circulation increasingly warmer water masses about ocean currents into deeper ocean layers, which influences the heat content of the oceans. This is explored by climatologists in the context of anthropogenic climate change.
Depending on the ocean currents grow eg on the southwest coast of England palms. In winter, the temperature here usually above freezing, and thus significantly higher than in other areas on similar latitudes. The warm Gulf Stream transports large amounts of energy and heats notably had flooded coastal regions of Europe. The warm sea water tends to evaporation, the moist air is raining the water vapor content over land from cold again or when it is lifted to the mountains and thereby cooled. About evaporative cooling and condensation heat there is a transfer of heat energy as far as the moist air inland drives, causing it to precipitate.
The west coast of Norway is largely ice-free in winter, while lying on the same latitudes east coast of Greenland ( which is hardly hit by the Gulf Stream ) spread icebergs and glaciers has. Also due to the Gulf Stream is the relatively mild climate of Iceland. Compared to the cold and snowy climate of northern Russia becomes clear how large can be caused by warm ocean currents climatic differences.
By cold ocean currents can also form significantly rougher areas on the other hand. For example, the Atacama Desert is caused by the Humboldt Current and the Namib by the Benguela Current. This is based on the generally Arctic or Antarctic water, the low surface temperature. This usually causes premature condensation of the humidity and limits the convection, which is why in the adjacent coastal regions there is less rainfall. In part, it may lead to decades of drought. On the other hand, there are very often fog, which take advantage of some of the livestock in these regions specifically to meet their water needs.
Transport
- Energy transport (heat from the equator to the poles)
- Ablation: removal of sediments by ocean currents
- Landing: from sediment - together with wave action and wind (eg Bunge country; sandbank, Watts, Spit )
- Distribution contained in the water, floating substances ( oxygen, nutrients, phytoplankton, radioactive materials, but, for example, oil, plastic waste, pollen )
- Simplification of navigation and shipping
- Ice drift
- Attenuation of the Earth's rotation about the Coriolis force and friction