As ocean currents (engl. Current , current ) refers to the systemic horizontal and vertical transport of water masses in the world's oceans and seas : they are u. A. influenced or caused by the earth's rotation , tides , different water densities due to different salinity and water temperatures as well as winds (" drift current "). The " Thermohaline circulation " is of great importance .
(Smaller-scale) water vortex (Engl. Eddy ), members or effects of ocean currents, while in turn part of the "large oceanic eddy" are (Engl. Gyre ).
Ocean currents are mass flows of sea water . There are regional and in short periods changing like the tidal currents , as well as continuous water movements of global proportions like the Gulf Stream . These large-scale ocean currents are collectively referred to as the global conveyor belt .
Numerous driving effects and influencing factors determine the transport of water masses in the oceans: The movements in the near-surface layers have often been known for a long time, while those in the deeper layers are the subject of more recent research. Normally, these are thermohalin- induced currents . As a rule, and especially with the larger flow patterns of the global conveyor belt, these are quite reliable in their occurrence, but can also vary due to meteorological and oceanological influencing factors. Usually this variance follows a rhythm that adapts to the seasons and thus depends on the variability of solar radiation .
The currents are mainly caused by temperature differences and different salinity of the sea water (the more salty the water is, the greater its density), which result from the warming of water masses, by solar radiation and their cooling. However, wind friction on the surface of the sea ( Ekman spiral , upwelling ) also makes a decisive contribution. The differences in water density act as a driving force in vertical currents.
The local course of the ocean currents is influenced, besides by the current-generating forces, by the secondary distribution of the land masses, the topography (relief) of the seabed , the Coriolis force , the centrifugal force during rotational movements and the frictional force . The most important parameters are the water temperature ( sea surface temperature ), the salinity and the resulting density of the water.
Types of flow
Ocean currents are differentiated based on various characteristics:
- Temporal duration
- constantly, periodically, temporarily
- Origin and cause
- Temperature and salinity
- warm / cold or salty / low in salt
- Location or occurrence
The boundaries of this classification partially overlap: as a rule, the major ocean currents are a combination of various influences.
Large-scale ocean currents
The "great oceanic eddies" (English gyre , from gyrate , rotate, gyrate, swirl , " ocean eddies ") are:
- Indian Ocean Gyre : " Agulhas Current "
- North Atlantic Gyre
- North Pacific Gyre ( North Pacific Gyre )
- South Atlantic Gyre
- South Pacific Gyre
(w = warm; k = cold)
|Agulhas current||Indian Ocean (Southeast African coast)||w|
|Antarctic Circumpolar Current||Atlantic , Pacific and Indian Oceans||k|
|Equatorial countercurrent||in the Pacific and Indian Ocean respectively||w|
|Azores Current||Atlantic (Azores threshold)||w|
|Benguela Current||Atlantic (South West African coast)||k|
|Brazil current||Atlantic Ocean (East Brazilian Coast)||w|
|Chinese coastal current||Pacific ( East China Sea , South China Sea )||w|
|Falkland Current||Atlantic ( Falkland Islands )||k|
|Florida Current||Atlantic Ocean ( Gulf of Mexico , Florida Strait )||w|
|Gulf Stream||Atlantic (American East Coast, North Atlantic)||w|
|Guinea Current||Atlantic ( Gulf of Guinea )||w|
|Humboldt Current / Peru Current||Pacific (South American West Coast)||k|
|Irmingerstrom||Atlantic (Northern European Sea)||w|
|California Stream||Pacific (American West Coast)||k|
|Canary Current||Atlantic (Western European and West African coast)||k|
|Cape Horn Stream||Pacific, Atlantic (southern tip of South America)||k|
|Caribbean current||Atlantic Ocean ( Caribbean Sea , Gulf of Mexico)||w|
|Kuroshio||Pacific (Western Pacific, Sea of Japan )||w|
|Labrador Stream||Atlantic (Atlantic, Newfoundland Basin)||k|
|Mozambique stream||Indian Ocean ( Strait of Mozambique )||w|
|North Equatorial Current||each in the Atlantic, Pacific and Indian Oceans||w|
|North Atlantic Current||Atlantic||w|
|North Pacific Vortex||Pacific||w|
|Norwegian current||Atlantic (North Sea, European North Sea)||w|
|Eastern Australian Current||Pacific ( Tasman Sea )||w|
|East and West Greenland currents||Atlantic (Atlantic, European Arctic Ocean)||k|
|Oyashio stream||Pacific ( Bering Sea )||k|
|Portugal current||Atlantic (Portuguese coast)||w|
|Somali flow||Indian Ocean (Northeast African coast)||w|
|South Equatorial Current||each in the Atlantic, Pacific and Indian Oceans||w|
|Western australian current||Indian Ocean ( Western Australian coast)||k|
At the edge of the ocean currents there is turbulence , with the help of the Coriolis force eddy ( eddy ) with a diameter between 20 and 200 km: They can exist for a few weeks to several months and cover distances of many hundreds of kilometers. With the eddies, sea water from the area of origin is enclosed; For example, warm Gulf Stream water and salty , heavy Mediterranean water, which flows over the Gibraltar threshold into the Atlantic, can be distributed over the area. Such a salty water eddy from the Mediterranean Sea (a Meddy - Mediterranean eddy ) is typically about 600 m below the sea surface and has a diameter of about 100 km.
Cold and warm water eddies can be observed with satellites, as they are noticeable by changes in the sea level. It was also observed that water vortex in which cold, nutrient-rich sea water is pumped from the depths of the ocean as a briefly existing upwelling effect: This multiplies there explosively phytoplankton , which can also be observed by satellites.
Until recently unknown, spontaneously occurring and rapidly rotating, temporary ocean eddies with a radius of a few kilometers in the Baltic Sea have been investigated since summer 2016 as part of an extensive research project at the Helmholtz-Zentrum Geesthacht (" Expedition Clockwork Ocean ").
Importance of ocean currents
Ocean currents can have a major impact on the climate. The IPCC AR5 report states that there is a high probability that 90% of the additional energy accumulation from global warming from 1971 to 2010 was absorbed by the ocean. This observation is based on La Niña years when, due to changing wind circulation, warmer water masses increasingly reach deeper ocean layers via ocean currents, which influences the heat content of the oceans . This is researched by climatologists in the context of anthropogenic climate change .
Depending on the ocean currents, z. B. on the south west coast of England palm trees. In winter, the temperature here is usually above freezing point, and thus significantly higher than in other areas at similar latitudes: The warm Gulf Stream transports large amounts of energy and particularly heats up the coastal regions of Europe. The warm sea water tends to evaporate , the humid air rains down the water vapor content over the colder land mass again or when it climbs up mountains and cools down in the process. Thermal energy is transferred via evaporation cold and condensation heat, provided that the moist air drifts inland and causes precipitation there.
The west coast of Norway is also largely ice-free in winter, while the east coast of Greenland , which is at the same latitude (which is hardly hit by the Gulf Stream), has widespread icebergs and glaciers. The relatively mild climate of Iceland is also due to the Gulf Stream . In comparison to the cold and snowy climate of northern Russia, it becomes clear how great the climatic differences caused by warm ocean currents can be.
On the other hand, cold ocean currents can also form significantly rougher areas. B. the Atacama desert caused by the Humboldt Current and the Namib by the Benguela Current. The basis for this is the low surface temperature of the usually Arctic or Antarctic water. This usually causes premature condensation of the air humidity and restricts convection, which is why little precipitation falls in the adjacent coastal regions. Sometimes it can lead to dry periods lasting for decades. On the other hand, there is very often fog, which some living beings in these regions use specifically to cover their water needs (see fog condensation ).
The ancient Greek term Ὠκεανός Okeanos ("ocean") denotes the world current flowing around the earth's disk and is personified in ancient Greece as the god Okeanos : Homer (approx. 800 BC ) is both the origin of the world and the Current that flows around the world and is distinguished from the sea. At the same time it is the origin of the gods and of all rivers, seas, springs and wells, of which only Eurynomials and Perses are named. His wife is the sea goddess Tethys .
- Energy transport (heat from the equator to the poles)
- Ablation: the removal of sediments by ocean currents
- Landing: of sediment - together with wave movement and wind (e.g. bungeland ; sandbank , mud flats , spit )
- Distribution of substances contained in the water, including floating substances (oxygen, nutrients, phytoplankton, radioactive substances, but also e.g. oil, plastic waste, pollen)
- Simplification of navigation and shipping
- Ice drift
- Damping of the earth's rotation via Coriolis force and friction
Due to the increasing ice melt on the polar ice caps associated with global warming, the salt content of the seawater changes with the additional fresh water input . This also changes the thermohaline dynamics there: the formation of the Antarctic soil - like the North Atlantic deep water, are "engines" of the thermohaline circulation .
- 5gyres.org: The 5 Gyres Institute: More Ocean. Less plastic.
- Bildungswiki Klimawandel , bildungsserver.de: Ocean currents (and climate)
- Geo Data Zone , geodz.com: The ecological balance of the ocean currents List of all ocean currents, scientific literature, color overview
- University of South Carolina , geol.sc.edu: What are eddies?
- NASA , nasasearch.nasa.gov: ocean currents video
- University of Miami , oceancurrents.rsmas.miami.edu: Ocean Surface Currents
- scinexx.de: Ocean currents - the key to the climate of the future
- From: Albert L. Arey, Frank L. Bryant, William W. Clendenin, William T. Morrey: Physiography for High Schools .
- Army Specialized Training Division. Army Service Forces Manual M-101 .
- nationalgeographic.org: ocean gyre (July 13, 2016).
- Stefan Rahmstorf: The Thermohaline Ocean Circulation . 2006 ( online PDF ).
- Scientists Use Satellites To Detect Deep-ocean Whirlpools .
- deutschlandfunk.de , Wissenschaft im Brennpunkt , July 9, 2016, Frank Grotelüschen : Eddy in the Baltic Sea. A measurement campaign takes up the chase. (July 9, 2016).
- Intergovernmental Panel on Climate Change; IPCC: Summary for Policymakers . In: IPCC Fifth Assessment Report (AR5) . 2013 ( PDF - WG1).
- Gerald A. Meehl, Julie M. Arblaster, John T. Fasullo, Aixue Hu & Kevin E. Trenberth : Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods . In: Nature Climate Change . 1, 2011, pp. 360-364. doi : 10.1038 / nclimate1229 .
- Friedrich Kluge : Etymological dictionary of the German language . 24th edition. Berlin 2002.
- Homer Iliad 14, 201.
- Homer Iliad 21, 195-197
- Homer Iliad 18:398
- Homer Odyssey 10, 139.
- deutschlandfunk.de , Forschung aktuell , August 31, 2016, Dagmar Röhrlich : Antarctica: The drive for global ocean circulation is weak (September 3, 2016).