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Subsurface Currents
A subsurface ocean current is an oceanic current that runs beneath surface currents. Examples include the Equatorial Undercurrents of the Pacific, Atlantic, and Indian Oceans, the California Undercurrent, and the Agulhas Undercurrent, the deep thermohaline circulation in the Atlantic, and bottom gravity currents near Antarctica. The forcing mechanisms vary for these different types of subsurface currents. Density current The most common of these is the density current, epitomized by the Thermohaline current. The density current works on a basic principle: the denser water sinks to the bottom, separating from the less dense water, and causing an opposite reaction from it. There are numerous factors controlling density. Salinity One is the salinity of water, a prime example of this being the Mediterranean/Atlantic exchange. The saltier waters of the Mediterranean sink to the bottom and flow along there, until they reach the ledge between the two bodies of water. At this point, they ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ocean Current
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents are primarily horizontal water movements. An ocean current flows for great distances and together they create the global conveyor belt, which plays a dominant role in determining the climate of many of Earth’s regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate for its high latitude compared to other areas at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equatorial Undercurrent
The Cromwell Current (also called Pacific Equatorial Undercurrent or just Equatorial Undercurrent) is an eastward-flowing subsurface current that extends the length of the equator in the Pacific Ocean. The Cromwell Current was discovered in 1952 by Townsend Cromwell, a researcher with the Honolulu Laboratory of the Fish and Wildlife Service (later the United States Fish and Wildlife Service). It is wide and flows to the east. It is hidden under the surface of the Pacific Ocean at the equator and is relatively shallow compared to other ocean currents being only from top to base. It is a powerful current with top velocities of up to 1.5 m/s (2.9 knots; 3.4 mph). The current's core coincides with the thermocline and its distance from the parallel Equatorial Counter Current is approximately . It has 1,000 times the volume of the Mississippi River and its length is . Discovery In 1951 researchers on board a Fish and Fish and Wildlife Service fisheries research vessel were engaged in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity Current
In fluid dynamics, a gravity current or density current is a primarily horizontal flow in a gravitational field that is driven by a density difference in a fluid or fluids and is constrained to flow horizontally by, for instance, a ceiling. Typically, the density difference is small enough for the Boussinesq approximation to be valid. Gravity currents can be thought of as either finite in volume, such as the pyroclastic flow from a volcano eruption, or continuously supplied from a source, such as warm air leaving the open doorway of a house in winter. Other examples include dust storms, turbidity currents, avalanches, discharge from wastewater or industrial processes into rivers, or river discharge into the ocean. Gravity currents are typically much longer than they are tall. Flows that are primarily vertical are known as plumes. As a result, it can be shown (using dimensional analysis) that vertical velocities are generally much smaller than horizontal velocities in the curre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water. A contour line of constant salinity is called an ''isohaline'', or sometimes ''isohale''. Definitions Salinity in rivers, lakes, and the ocean is conceptually simple, but technically challenging to define and measure precisely. Conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like sodium chloride, magnesium sulfate, potassium nitrate, and sodium bicarbonate which dissolve into ions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mediterranean Sea (oceanography)
A mediterranean sea () is, in oceanography, a mostly enclosed sea that has limited exchange of water with outer oceans and with water circulation dominated by salinity and temperature differences rather than winds or tides. The eponymous Mediterranean Sea, for example, is almost completely enclosed by Europe, Asia, and Africa. List of mediterranean seas The Mediterranean seas of the Atlantic Ocean * The namesake Mediterranean Seas, including the Black Sea, the Sea of Azov, the Aegean Sea (including the so called Thracian Sea and Sea of Crete), the Adriatic Sea, the Alboran Sea, the Ligurian Sea, the Balearic Sea, the Tyrrhenian Sea, the Ionian Sea, and the Sea of Marmara. * The Arctic Ocean (or ''Arctic Mediterranean Sea'', which many regard as an ocean) * The American Mediterranean Sea: the combination of the Gulf of Mexico and the Caribbean Sea. * The Baltic Sea * Baffin Bay The Mediterranean seas of the Indian Ocean * The Persian Gulf * The Red Sea * The Australasian Me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe and Asia from the "New World" of the Americas in the European perception of the World. The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and North and South America to the west. As one component of the interconnected World Ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south (other definitions describe the Atlantic as extending southward to Antarctica). The Atlantic Ocean is divided in two parts, by the Equatorial Counter Current, with the North(ern) Atlantic Ocean and the South(ern) Atlantic Ocean split at about 8°N. Scientific explorations of the A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation; if buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification. Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments. Classification Sediment can be classified based on its grain size, grain shape, and c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ekman Spiral
The oceanic, wind driven Ekman spiral is the result of a force balance created by a shear stress force, Coriolis force and the water drag. This force balance gives a resulting current of the water different from the winds. In the ocean, there are two places where the Ekman spiral can be observed. At the surface of the ocean, the shear stress force corresponds with the wind stress force. At the bottom of the ocean, the shear stress force is created by friction with the ocean floor. This phenomenon was first observed at the surface by the Norwegian oceanographer Fridtjof Nansen during his Fram expedition. He noticed that icebergs did not drift in the same direction as the wind. His student, the Swedish oceanographer Vagn Walfrid Ekman, was the first person to physically explain this process. Bottom Ekman Spiral In order to derive the properties of an Ekman spiral a look is taken at a uniform, horizontal geostrophic interior flow in a homogeneous fluid. This flow will by denoted by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vagn Walfrid Ekman
Vagn Walfrid Ekman (3 May 1874 – 9 March 1954) was a Swedish oceanographer. Born in Stockholm to Fredrik Laurentz Ekman, himself an oceanographer, he became committed to oceanography while studying physics at the University of Uppsala and, in particular, on hearing Vilhelm Bjerknes lecture on fluid dynamics. During the expedition of the ''Fram'', Fridtjof Nansen had observed that icebergs tend to drift not in the direction of the prevailing wind but at an angle of 20°-40° to the right. Bjerknes invited Ekman, still a student, to investigate the problem. Later, in 1905, Ekman published his theory of the Ekman spiral which explains the phenomenon in terms of the balance between frictional effects in the ocean and the Coriolis force, which arises from moving objects in a rotating environment, like planetary rotation. On completing his doctorate in Uppsala in 1902, Ekman joined the International Laboratory for Oceanographic Research, Oslo where he worked for seven years, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coriolis Effect
In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the left of the motion of the object. In one with anticlockwise (or counterclockwise) rotation, the force acts to the right. Deflection of an object due to the Coriolis force is called the Coriolis effect. Though recognized previously by others, the mathematical expression for the Coriolis force appeared in an 1835 paper by French scientist Gaspard-Gustave de Coriolis, in connection with the theory of water wheels. Early in the 20th century, the term ''Coriolis force'' began to be used in connection with meteorology. Newton's laws of motion describe the motion of an object in an inertial (non-accelerating) frame of reference. When Newton's laws are transformed to a rotating frame of reference, the Coriolis and centrifugal accelerations appe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope movement. Processes that lead to subsidence include dissolution of underlying carbonate rock by groundwater; gradual compaction of sediments; withdrawal of fluid lava from beneath a solidified crust of rock; mining; pumping of subsurface fluids, such as groundwater or petroleum; or warping of the Earth's crust by tectonic forces. Subsidence resulting from tectonic deformation of the crust is known as tectonic subsidence and can create accommodation for sediments to accumulate and eventually lithify into sedimentary rock. Ground subsidence is of global concern to geologists, geotechnical engineers, surveyors, engineers, urban planners, landowners, and the public in general.National Research Council, 1991. ''Mitigating losses from land subsi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maelstrom (whirlpool)
A whirlpool is a body of rotating water produced by opposing currents or a current running into an obstacle. Small whirlpools form when a bath or a sink is draining. More powerful ones formed in seas or oceans may be called maelstroms ( ). ''Vortex'' is the proper term for a whirlpool that has a downdraft. In narrow ocean straits with fast flowing water, whirlpools are often caused by tides. Many stories tell of ships being sucked into a maelstrom, although only smaller craft are actually in danger. Smaller whirlpools appear at river rapids and can be observed downstream of artificial structures such as weirs and dams. Large cataracts, such as Niagara Falls, produce strong whirlpools. Notable whirlpools Saltstraumen Saltstraumen is a narrow strait located close to the Arctic Circle, south-east of the city of Bodø, Norway. It has one of the strongest tidal currents in the world. Whirlpools up to in diameter and in depth are formed when the current is at its strongest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
