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112-438: Gyre can refer to any type of vortex in an atmosphere or a sea , even one that is human-created, but it is most commonly used in terrestrial oceanography to refer to the major ocean systems. The largest ocean gyres are wind-driven, meaning that their locations and dynamics are controlled by the prevailing global wind patterns : easterlies at the tropics and westerlies at the midlatitudes. These wind patterns result in

224-408: A Lamb–Oseen vortex . A rotational vortex – a vortex that rotates in the same way as a rigid body – cannot exist indefinitely in that state except through the application of some extra force, that is not generated by the fluid motion itself. It has non-zero vorticity everywhere outside the core. Rotational vortices are also called rigid-body vortices or forced vortices. For example, if a water bucket

336-432: A boundary layer which causes a local rotation of fluid at the wall (i.e. vorticity ) which is referred to as the wall shear rate. The thickness of this boundary layer is proportional to √ ( v t ) {\displaystyle \surd (vt)} (where v is the free stream fluid velocity and t is time). If the diameter or thickness of the vessel or fluid is less than the boundary layer thickness then

448-450: A vortex ( pl. : vortices or vortexes ) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings , whirlpools in the wake of a boat, and the winds surrounding a tropical cyclone , tornado or dust devil . Vortices are a major component of turbulent flow . The distribution of velocity, vorticity (the curl of

560-407: A convex surface. A unique example of severe geometric changes is at the trailing edge of a bluff body where the fluid flow deceleration, and therefore boundary layer and vortex formation, is located. Another form of vortex formation on a boundary is when fluid flows perpendicularly into a wall and creates a splash effect. The velocity streamlines are immediately deflected and decelerated so that

672-448: A frictional bottom boundary layer which is not necessarily physical in a stratified ocean (currents do not always extend to the bottom). Munk's solution instead relies on friction between the return flow and the sidewall of the basin. This allows for two cases: one with the return flow on the western boundary (western boundary current) and one with the return flow on the eastern boundary (eastern boundary current). A qualitative argument for

784-437: A major part of many animals' diets and can support the existence of large marine life . Indigenous Traditional Ecological Knowledge recognizes that Indigenous people, as the original caretakers, hold unique relationships with the land and waters. These relationships make TEK difficult to define, as Traditional Knowledge means something different to each person, each community, and each caretaker. The United Nations Declaration on

896-414: A nitrogen or phosphorus limited environment. This region relies on dust blowing off the state of Alaska and other landmasses nearby to supply iron. Because it is limited by iron instead of nitrogen or phosphorus, it is known as high-nutrient, low-chlorophyll region. Iron limitation in high-nutrient, low-chlorophyll regions results in water that is rich in other nutrients because they have not been removed by

1008-578: A poleward flowing, narrow, and strong western boundary current, an eastward flowing current in the midlatitudes, and an equatorward flowing, weaker, and broader eastern boundary current. The North Atlantic Gyre is located in the northern hemisphere in the Atlantic Ocean, between the Intertropical Convergence Zone (ITCZ) in the south and Iceland in the north. The North Equatorial Current brings warm waters west towards

1120-442: A single wingtip vortex , less than one wing chord downstream of that edge. This phenomenon also occurs with other active airfoils , such as propeller blades. On the other hand, two parallel vortices with opposite circulations (such as the two wingtip vortices of an airplane) tend to remain separate. Vortices contain substantial energy in the circular motion of the fluid. In an ideal fluid this energy can never be dissipated and

1232-535: A weak poleward flow over most of their area. However, there must be some return flow that goes against the Sverdrup transport in order to preserve mass balance. In this respect, the Sverdrup solution is incomplete, as it has no mechanism in which to predict this return flow. Contributions by both Henry Stommel and Walter Munk resolved this issue by showing that the return flow of gyres is done through an intensified western boundary current. Stommel's solution relies on

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1344-408: A western boundary frictional layer, as the eastern boundary frictional layer forces ∂ v / ∂ x < 0 {\displaystyle \partial v/\partial x<0} . One can make similar arguments for subtropical gyres in the southern hemisphere and for subpolar gyres in either hemisphere and see that the result remains the same: the return flow of an ocean gyre

1456-573: A wind stress curl that drives Ekman pumping in the subtropics (resulting in downwelling) and Ekman suction in subpolar regions (resulting in upwelling). Ekman pumping results in an increased sea surface height at the center of the gyre and anticyclonic geostrophic currents in subtropical gyres. Ekman suction results in a depressed sea surface height and cyclonic geostrophic currents in subpolar gyres. Wind-driven ocean gyres are asymmetrical, with stronger flows on their western boundary and weaker flows throughout their interior. The weak interior flow that

1568-511: Is a region where large amounts of heat transported northward by the ocean are released into the atmosphere, thereby modifying the climate of northwest Europe. The North Atlantic Subpolar Gyre has a complex topography with a series of basins in which the large-scale circulation is characterized by cyclonic boundary currents and interior recirculation. The North Atlantic Current develops out of the Gulf Stream extension and turns eastward, crossing

1680-474: Is always in the form of a western boundary current. The western boundary current must transport on the same order of water as the interior Sverdrup transport in a much smaller area. This means western boundary currents are much stronger than interior currents, a phenomenon called "western intensification". There are five major subtropical gyres across the world's oceans: the North Atlantic Gyre,

1792-552: Is an important time for photosynthesis as the light limitation imposed during winter is lifted and there are high levels of nutrients available. However, in the North Atlantic Subpolar Gyre, spring productivity is low in comparison to expected levels. It is hypothesized that this low productivity is because phytoplankton are less efficiently using light than they do in the summer months. Ocean gyres typically contain 5–6 trophic levels . The limiting factor for

1904-402: Is called a vortex tube . In general, vortex tubes are nested around the axis of rotation. The axis itself is one of the vortex lines, a limiting case of a vortex tube with zero diameter. According to Helmholtz's theorems , a vortex line cannot start or end in the fluid – except momentarily, in non-steady flow, while the vortex is forming or dissipating. In general, vortex lines (in particular,

2016-635: Is cyclonic, counterclockwise in the northern hemisphere and clockwise in the southern hemisphere, around a low-pressure area , such as the persistent Aleutian Low and the Icelandic Low . The wind stress curl in this region drives the Ekman suction, which creates an upwelling of nutrient-rich water from the lower depths. Subpolar circulation in the southern hemisphere is dominated by the Antarctic Circumpolar Current , due to

2128-471: Is demonstrated by smoke rings and exploited in vortex ring toys and guns . Two or more vortices that are approximately parallel and circulating in the same direction will attract and eventually merge to form a single vortex, whose circulation will equal the sum of the circulations of the constituent vortices. For example, an airplane wing that is developing lift will create a sheet of small vortices at its trailing edge. These small vortices merge to form

2240-548: Is driven by the convergence of warm, salty waters from the south and cold, fresher waters from the north. As these waters meet, the warm, dense water sinks beneath the lighter, colder water, initiating a complex circulation pattern. The North Atlantic Subpolar Gyre has significant implications for climate regulation, as it helps redistribute heat and nutrients throughout the North Atlantic, influencing weather patterns and supporting diverse marine life. Additionally, changes in

2352-640: Is located nearby two of the most prominent research stations in the world for Antarctic study, the Ross Gyre remains one of the least sampled gyres in the world. The Weddell Gyre is located in the Southern Ocean surrounding Antarctica, just outside of the Weddell Sea. It is characterized by a clockwise rotation of surface waters, influenced by the combined effects of winds, the Earth's rotation, and

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2464-406: Is negative (south, equatorward) in the northern hemisphere ( f > 0 {\displaystyle f>0} ). Conversely, for a positive Ekman velocity (e.g., Ekman suction in subpolar gyres), Sverdrup transport is positive (north, poleward) in the northern hemisphere. As the Sverdrup balance argues, subtropical ocean gyres have a weak equatorward flow and subpolar ocean gyres have

2576-460: Is never removed, it would consist of circular motion forever. A key concept in the dynamics of vortices is the vorticity , a vector that describes the local rotary motion at a point in the fluid, as would be perceived by an observer that moves along with it. Conceptually, the vorticity could be observed by placing a tiny rough ball at the point in question, free to move with the fluid, and observing how it rotates about its center. The direction of

2688-408: Is one of the largest ecosystems on Earth with an area that accounts for around 10% of the global ocean surface area. Within this massive area is Point Nemo , the location on Earth that is farthest away from all continental landmass (2,688 km away from the closest land). The remoteness of this gyre complicates sampling, causing this gyre to be historically under sampled in oceanographic datasets. At

2800-444: Is spun at constant angular speed w about its vertical axis, the water will eventually rotate in rigid-body fashion. The particles will then move along circles, with velocity u equal to wr . In that case, the free surface of the water will assume a parabolic shape. In this situation, the rigid rotating enclosure provides an extra force, namely an extra pressure gradient in the water, directed inwards, that prevents transition of

2912-399: Is started, a vortex usually forms ahead of each propeller , or the turbofan of each jet engine . One end of the vortex line is attached to the engine, while the other end usually stretches out and bends until it reaches the ground. When vortices are made visible by smoke or ink trails, they may seem to have spiral pathlines or streamlines. However, this appearance is often an illusion and

3024-461: Is the Rossby parameter , ρ {\displaystyle \rho } is the water density, and w E {\displaystyle w_{E}} is the vertical Ekman velocity due to wind stress curl (positive up). It can be clearly seen in this equation that for a negative Ekman velocity (e.g., Ekman pumping in subtropical gyres), meridional mass transport (Sverdrup transport)

3136-610: Is the case in tornadoes and in drain whirlpools. A vortex with helical streamlines is said to be solenoidal . As long as the effects of viscosity and diffusion are negligible, the fluid in a moving vortex is carried along with it. In particular, the fluid in the core (and matter trapped by it) tends to remain in the core as the vortex moves about. This is a consequence of Helmholtz's second theorem . Thus vortices (unlike surface waves and pressure waves ) can transport mass, energy and momentum over considerable distances compared to their size, with surprisingly little dispersion. This effect

3248-442: Is typical over most of the gyre is a result of the conservation of potential vorticity . In the shallow water equations (applicable for basin-scale flow as the horizontal length scale is much greater than the vertical length scale), potential vorticity is a function of relative (local) vorticity ζ {\displaystyle \zeta } (zeta), planetary vorticity f {\displaystyle f} , and

3360-533: Is very likely to push the large-scale ocean gyres towards higher latitudes. A garbage patch is a gyre of marine debris particles caused by the effects of ocean currents and increasing plastic pollution by human populations. These human-caused collections of plastic and other debris are responsible for ecosystem and environmental problems that affect marine life, contaminate oceans with toxic chemicals, and contribute to greenhouse gas emissions . Once waterborne, marine debris becomes mobile. Flotsam can be blown by

3472-669: The Maud from 1918 to 1925. His measurements of bottom depths, tidal currents, and tidal elevations on the vast shelf areas off the East Siberian Sea correctly described the propagation of tides as Poincare waves . Upon his return from this long expedition exploring the shelf seas to the north of Siberia, he became the chair in meteorology at the University of Bergen . He was made director of California's Scripps Institution of Oceanography in 1936, initially for three years but

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3584-678: The Antarctic Circumpolar Current and the Antarctic Continental Shelf . The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. The WG is situated in the Atlantic sector of the Southern Ocean, south of 55–60°S and roughly between 60°W and 30°E (Deacon, 1979). It stretches over

3696-520: The Beaufort Sea . This gyre functions as a critical mechanism for the transport of heat, nutrients, and sea ice within the Arctic region, thus influencing the physical and biological characteristics of the marine environment. Negative wind stress curl over the region, mediated by the sea ice pack, leads to Ekman pumping, downwelling of isopycnal surfaces, and storage of ~20,000 km3 of freshwater in

3808-646: The Scripps Institution of Oceanography and the Norwegian Polar Institute . He was born at Sogndal in Sogn og Fjordane , Norway. He was the son of Lutheran theologian Edvard Sverdrup (1861–1923) and Maria Vollan (1865–1891). His sister Mimi Sverdrup Lunden (1894–1955) was an educator and author. His brother Leif Sverdrup (1898–1976) was a General with the U.S. Army Corps of Engineers . His brother Einar Sverdrup (1895–1942)

3920-509: The Sverdrup balance . This balance describes wind-driven ocean gyres away from continental margins at western boundaries. After leaving Scripps, he became director of the Norwegian Polar Institute in Oslo and continued to contribute to oceanography, ocean biology, and polar research. In biological oceanography, his critical depth hypothesis (published in 1953) was a significant milestone in

4032-414: The vector analysis formula ∇ × u → {\displaystyle \nabla \times {\vec {\mathit {u}}}} , where ∇ {\displaystyle \nabla } is the nabla operator and u → {\displaystyle {\vec {\mathit {u}}}} is the local flow velocity. The local rotation measured by

4144-933: The Arctic Ocean. Their influence on the distribution of freshwater has broad impacts for global sea level rise and climate dynamics. Depending on their location around the world, gyres can be regions of high biological productivity or low productivity. Each gyre has a unique ecological profile but can be grouped by region due to dominating characteristics. Generally, productivity is greater for cyclonic gyres (e.g., subpolar gyres) that drive upwelling through Ekman suction and lesser for anticyclonic gyres (e.g., subtropical gyres) that drive downwelling through Ekman pumping, but this can differ between seasons and regions. Subtropical gyres are sometimes described as "ocean deserts" or "biological deserts", in reference to arid land deserts where little life exists. Due to their oligotrophic characteristics, warm subtropical gyres have some of

4256-502: The Atlantic Ocean, with potentially important effects for global thermohaline circulation . The gyre circulation is completed by the north flowing West Australian Current , which forms the eastern boundary of the gyre. The North Pacific Gyre , one of the largest ecosystems on Earth, is bordered to the south by the Intertropical Convergence Zone and extending north to roughly 50°N. At the southern boundary of

4368-781: The Atlantic in a wide band between about 45°N and 55°N creating the southern border of the North Atlantic Subpolar Gyre. There are several branches of the North Atlantic Current, and they flow into an eastern intergyral region in the Bay of Biscay , the Rockall Trough , the Iceland Basin, and the Irminger Sea . Part of the North Atlantic Current flows into the Norwegian Sea, and some recirculate within

4480-643: The Caribbean and defines the southern edge of the North Atlantic Gyre. Once these waters reach the Caribbean they join the warm waters in the Gulf of Mexico and form the Gulf Stream , a western boundary current. This current then heads north and east towards Europe, forming the North Atlantic Current . The Canary Current flows south along the western coast of Europe and north Africa, completing

4592-617: The Igliniit project, and the Wales Inupiaq Sea Ice Directory have made strides in the inclusion and documentation of indigenous people's thoughts on global climate, oceanographic, and social trends. One example involves ancient Polynesians and how they discovered and then travelled throughout the Pacific Ocean from modern day Polynesia to Hawaii and New Zealand. Known as wayfinding , navigators would use

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4704-454: The Māori and other indigenous communities. Ocean circulation re-distributes the heat and water-resources, therefore determines the regional climate. For example, the western branches of the subtropical gyres flow from the lower latitudes towards higher latitudes, bringing relatively warm and moist air to the adjacent land, contributing to a mild and wet climate (e.g., East China, Japan). In contrast,

4816-423: The North Atlantic have a "bloom and crash" pattern following seasonal and storm patterns. The highest productivity in the North Atlantic occurs in boreal spring when there are long days and high levels of nutrients. This is different to the subpolar North Pacific, where almost no phytoplankton bloom occurs and patterns of respiration are more consistent through time than in the North Atlantic. Primary production in

4928-630: The North Pacific Gyre, the North Equatorial Current flows west along the equator towards southeast Asia. The Kuroshio Current is the western boundary current of the North Pacific Gyre, flowing northeast along the coast of Japan. At roughly 50°N, the flow turns east and becomes the North Pacific Current . The North Pacific Current flows east, eventually bifurcating near the west coast of North America into

5040-462: The Rights of Indigenous Peoples begins by reminding readers that “respect for Indigenous knowledge, cultures and traditional practices contributes to sustainable and equitable development and proper management of the environment” Attempts to collect and store this knowledge have been made over the past twenty years. Conglomerates such as The Indigenous Knowledge Social Network (SIKU) https://siku.org/ ,

5152-563: The Ross Sea continental shelf, where they may drive ice shelf melting and increase sea level. The deepening of sea level pressures over the Southeast Pacific/Amundsen-Bellingshausen Seas generates a cyclonic circulation cell that reduces sea surface heights north of the Ross Gyre via Ekman suction. The relative reduction of sea surface heights to the north facilitates a northeastward expansion of

5264-452: The Sea (ICES). His many publications include his magnum opus The Oceans: Their Physics, Chemistry and General Biology by Sverdrup, Martin W. Johnson and Richard H. Fleming (1942, new edition 1970) which formed the basic curriculum of oceanography for the next 40 years around the world. In 1928, he married Gudrun (Vaumund) Bronn (1893–1983) and adopted her daughter Anna Margrethe. He

5376-663: The South Atlantic Gyre, the Indian Ocean Gyre, the North Pacific Gyre, and the South Pacific Gyre. All subtropical gyres are anticyclonic, meaning that in the northern hemisphere they rotate clockwise, while the gyres in the southern hemisphere rotate counterclockwise. This is due to the Coriolis force . Subtropical gyres typically consist of four currents: a westward flowing equatorial current,

5488-765: The South Pacific Gyre circulation. Like the North Pacific Gyre, the South Pacific Gyre has an elevated concentration of plastic waste near the center, termed the South Pacific garbage patch . Unlike the North Pacific garbage patch which was first described in 1988, the South Pacific garbage patch was discovered much more recently in 2016 (a testament to the extreme remoteness of the South Pacific Gyre). Subpolar gyres form at high latitudes (around 60° ). Circulation of surface wind and ocean water

5600-400: The Southern Ocean, affecting the distribution of sea ice and influencing regional climate patterns. The Ross Sea , Antarctica , is a region where the mixing of distinct water masses and complex interactions with the cryosphere lead to the production and export of dense water, with global-scale impacts. which controls the proximity of the warm waters of the Antarctic Circumpolar Current to

5712-690: The Weddell abyssal plain, where the Weddell Sea is situated, and extends east into the Enderby abyssal plain. The anti-cyclonic Beaufort Gyre is the dominant circulation of the Canada Basin and the largest freshwater reservoir in the Arctic Ocean's western and northern sectors. The Gyre is characterized by a large-scale, quasi-permanent, counterclockwise rotation of surface waters within

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5824-417: The axis line) are either closed loops or end at the boundary of the fluid. A whirlpool is an example of the latter, namely a vortex in a body of water whose axis ends at the free surface. A vortex tube whose vortex lines are all closed will be a closed torus -like surface. A newly created vortex will promptly extend and bend so as to eliminate any open-ended vortex lines. For example, when an airplane engine

5936-406: The axis line, with depth inversely proportional to r . The shape formed by the free surface is called a hyperboloid , or " Gabriel's Horn " (by Evangelista Torricelli ). The core of a vortex in air is sometimes visible because water vapor condenses as the low pressure of the core causes adiabatic cooling ; the funnel of a tornado is an example. When a vortex line ends at a boundary surface,

6048-416: The axis, and increases as one moves away from it, in accordance with Bernoulli's principle . One can say that it is the gradient of this pressure that forces the fluid to follow a curved path around the axis. In a rigid-body vortex flow of a fluid with constant density , the dynamic pressure is proportional to the square of the distance r from the axis. In a constant gravity field, the free surface of

6160-466: The boundary currents of the subpolar gyre. The Ross Gyre is located in the Southern Ocean surrounding Antarctica , just outside of the Ross Sea. This gyre is characterized by a clockwise rotation of surface waters, driven by the combined influence of wind, the Earth's rotation, and the shape of the seafloor. The gyre plays a crucial role in the transport of heat, nutrients, and marine life in

6272-406: The boundary layer separates and forms a toroidal vortex ring. In a stationary vortex, the typical streamline (a line that is everywhere tangent to the flow velocity vector) is a closed loop surrounding the axis; and each vortex line (a line that is everywhere tangent to the vorticity vector) is roughly parallel to the axis. A surface that is everywhere tangent to both flow velocity and vorticity

6384-423: The boundary layer will not separate and vortices will not form. However, when the boundary layer does grow beyond this critical boundary layer thickness then separation will occur which will generate vortices. This boundary layer separation can also occur in the presence of combatting pressure gradients (i.e. a pressure that develops downstream). This is present in curved surfaces and general geometry changes like

6496-453: The cases of the absence of forces, the liquid settles. This makes the water stay still instead of moving. When they are created, vortices can move, stretch, twist and interact in complicated ways. When a vortex is moving, sometimes, it can affect an angular position. For an example, if a water bucket is rotated or spun constantly, it will rotate around an invisible line called the axis line. The rotation moves around in circles. In this example

6608-437: The core (for example, by steadily turning a cylinder at the core). In free space there is no energy input at the core, and thus the compact vorticity held in the core will naturally diffuse outwards, converting the core to a gradually-slowing and gradually-growing rigid-body flow, surrounded by the original irrotational flow. Such a decaying irrotational vortex has an exact solution of the viscous Navier–Stokes equations , known as

6720-407: The core and then into the engine. Vortices need not be steady-state features; they can move and change shape. In a moving vortex, the particle paths are not closed, but are open, loopy curves like helices and cycloids . A vortex flow might also be combined with a radial or axial flow pattern. In that case the streamlines and pathlines are not closed curves but spirals or helices, respectively. This

6832-560: The depth H {\displaystyle H} , and is conserved with respect to the material derivative : In the case of the subtropical ocean gyre, Ekman pumping results in water piling up in the center of the gyre, compressing water parcels. This results in a decrease in H {\displaystyle H} , so by the conservation of potential vorticity the numerator ζ + f {\displaystyle \zeta +f} must also decrease. It can be further simplified by realizing that, in basin-scale ocean gyres,

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6944-537: The distance r . Irrotational vortices are also called free vortices . For an irrotational vortex, the circulation is zero along any closed contour that does not enclose the vortex axis; and has a fixed value, Γ , for any contour that does enclose the axis once. The tangential component of the particle velocity is then u θ = Γ 2 π r {\displaystyle u_{\theta }={\tfrac {\Gamma }{2\pi r}}} . The angular momentum per unit mass relative to

7056-400: The dynamics of fluid, a vortex is fluid that revolves around the axis line. This fluid might be curved or straight. Vortices form from stirred fluids: they might be observed in smoke rings , whirlpools , in the wake of a boat or the winds around a tornado or dust devil . Vortices are an important part of turbulent flow . Vortices can otherwise be known as a circular motion of a liquid. In

7168-550: The east coast of Madagascar, both of which are western boundary currents. South of Madagascar the two currents join to form the Agulhas Current . The Agulhas Current flows south until it joins the Antarctic Circumpolar Current, which flows east at the southern edge of the Indian Ocean Gyre. Due to the African continent not extending as far south as the Indian Ocean Gyre, some of the water in the Agulhas Current "leaks" into

7280-604: The eastern boundary Benguela Current , completing the gyre circulation. The Benguela Current experiences the Benguela Niño event, an Atlantic Ocean analogue to the Pacific Ocean's El Niño , and is correlated with a reduction in primary productivity in the Benguela upwelling zone. The Indian Ocean Gyre , located in the Indian Ocean, is, like the South Atlantic Gyre, bordered by the Intertropical Convergence Zone in

7392-408: The eastern boundary currents of the subtropical gyres streaming from the higher latitudes towards lower latitudes, corresponding to a relatively cold and dry climate (e.g., California). Currently, the core of the subtropical gyres are around 30° in both Hemispheres. However, their positions were not always there. Satellite observational sea surface height and sea surface temperature data suggest that

7504-920: The explanation of spring blooms of phytoplankton . Sverdrup was a member of both the United States National Academy of Sciences , the Norwegian Academies of Science , the American Academy of Arts and Sciences , and the American Philosophical Society . He served as President of the International Association of Physical Oceanography and of the International Council for the Exploration of

7616-624: The flow velocity), as well as the concept of circulation are used to characterise vortices. In most vortices, the fluid flow velocity is greatest next to its axis and decreases in inverse proportion to the distance from the axis. In the absence of external forces, viscous friction within the fluid tends to organise the flow into a collection of irrotational vortices, possibly superimposed to larger-scale flows, including larger-scale vortices. Once formed, vortices can move, stretch, twist, and interact in complex ways. A moving vortex carries some angular and linear momentum, energy, and mass, with it. In

7728-419: The fluid particles are moving in closed paths. The spiral streaks that are taken to be streamlines are in fact clouds of the marker fluid that originally spanned several vortex tubes and were stretched into spiral shapes by the non-uniform flow velocity distribution. The fluid motion in a vortex creates a dynamic pressure (in addition to any hydrostatic pressure) that is lowest in the core region, closest to

7840-409: The fluid relative to the vortex's axis. In theory, the speed u of the particles (and, therefore, the vorticity) in a vortex may vary with the distance r from the axis in many ways. There are two important special cases, however: In the absence of external forces, a vortex usually evolves fairly quickly toward the irrotational flow pattern , where the flow velocity u is inversely proportional to

7952-481: The gyre circulation. The center of the gyre is the Sargasso Sea , which is characterized by the dense accumulation of Sargassum seaweed. The South Atlantic Gyre is located in the southern hemisphere in the Atlantic Ocean, between the Intertropical Convergence Zone in the north and the Antarctic Circumpolar Current to the south. The South Equatorial Current brings water west towards South America, forming

8064-480: The gyre's strength and circulation can impact regional climate variability and may be influenced by broader climate change trends. The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system through its transport of heat and freshwater. The North Atlantic Subpolar Gyre is in a region where the AMOC is actively developed and shaped through mixing and water mass transformation. It

8176-478: The intervention of World War II meant he held the post until 1948. During 33 expeditions with the research vessel E. W. Scripps between 1938 and 1941, he produced a detailed oceanographic dataset off the coast of California. He also developed a simple theory of the general ocean circulation postulating a dynamical vorticity balance between the wind-stress curl and the meridional gradient of the Coriolis parameter,

8288-650: The lack of large landmasses breaking up the Southern Ocean . There are minor gyres in the Weddell Sea and the Ross Sea , the Weddell Gyre and Ross Gyre , which circulate in a clockwise direction. The North Atlantic Subpolar Gyre, located in the North Atlantic Ocean, is characterized by a counterclockwise rotation of surface waters. It plays a crucial role in the global oceanic conveyor belt system, influencing climate and marine ecosystems. The gyre

8400-401: The least productive waters per unit surface area in the ocean. The downwelling of water that occurs in subtropical gyres takes nutrients deeper in the ocean, removing them from surface waters. Organic particles can also be removed from surface waters through gravitational sinking, where the particle is too heavy to remain suspended in the water column. However, since subtropical gyres cover 60% of

8512-444: The liquid, if present, is a concave paraboloid . In an irrotational vortex flow with constant fluid density and cylindrical symmetry, the dynamic pressure varies as P ∞ − ⁠ K / r ⁠ , where P ∞ is the limiting pressure infinitely far from the axis. This formula provides another constraint for the extent of the core, since the pressure cannot be negative. The free surface (if present) dips sharply near

8624-444: The major source of nitrate in the nitrate-limited subtropical gyres is a result of biological, not physical, factors. Nitrogen in subtropical gyres is produced primarily by nitrogen-fixing bacteria, which are common throughout most of the oligotrophic waters of subtropical gyres. These bacteria transform atmospheric nitrogen into bioavailable forms. The Alaskan Gyre and Western Subarctic Gyre are an iron-limited environment rather than

8736-418: The majority of subtropical gyres there is a weak equatorward flow. Harald Sverdrup quantified this phenomenon in his 1947 paper, "Wind Driven Currents in a Baroclinic Ocean", in which the (depth-integrated) Sverdrup balance is defined as: Here, V g {\displaystyle V_{g}} is the meridional mass transport (positive north), β {\displaystyle \beta }

8848-470: The most limiting. Lack of nutrients in the surface waters of subtropical gyres is related to the strong downwelling and sinking of particles that occurs in these areas as mentioned earlier. However, nutrients are still present in these gyres. These nutrients can come from not only vertical transport, but also lateral transport across gyre fronts. This lateral transport helps make up for the large loss of nutrients due to downwelling and particle sinking. However,

8960-543: The most to the least, China, Indonesia, Philippines, Vietnam, Sri Lanka, Thailand, Egypt, Malaysia, Nigeria, and Bangladesh, largely through the rivers Yangtze , Indus , Yellow , Hai , Nile , Ganges , Pearl , Amur , Niger , and the Mekong , and accounting for "90 percent of all the plastic that reaches the world's oceans". Asia was the leading source of mismanaged plastic waste , with China alone accounting for 2.4 million metric tons. Vortex In fluid dynamics ,

9072-711: The north and the Antarctic Circumpolar Current to the south. The South Equatorial Current forms the northern boundary of the Indian Ocean Gyre as it flows west along the equator towards the east coast of Africa. At the coast of Africa, the South Equatorial Current is split by Madagascar into the Mozambique Current , flowing south through the Mozambique Channel, and the East Madagascar Current , flowing south along

9184-528: The northern boundary of the South Atlantic gyre. Here, the water moves south in the Brazil Current , the western boundary current of the South Atlantic Gyre. The Antarctic Circumpolar Current forms both the southern boundary of the gyre and the eastward component of the gyre circulation. Eventually, the water reaches the west coast of Africa, where it is brought north along the coast as a part of

9296-567: The northern boundary of the South Pacific Gyre, the South Equatorial Current flows west towards southeast Asia and Australia. There, it turns south as it flows in the East Australian Current , a western boundary current. The Antarctic Circumpolar Current again returns the water to the east. The flow turns north along the western coast of South America in the Humboldt Current , the eastern boundary current that completes

9408-606: The northward flowing Alaska Current and the southward flowing California Current . The Alaska Current is the eastern boundary current of the subpolar Alaska Gyre, while the California Current is the eastern boundary current that completes the North Pacific Gyre circulation. Within the North Pacific Gyre is the Great Pacific Garbage Patch , an area of increased plastic waste concentration. The South Pacific Gyre , like its northern counterpart,

9520-445: The number of trophic levels is the size of the phytoplankton , which are generally small in nutrient limited gyres. In low oxygen zones, oligotrophs are a large percentage of the phytoplankton. At the intermediate level, small fishes and squid (especially ommastrephidae ) dominate the nektonic biomass. They are important for the transport of energy from low trophic levels to high trophic levels. In some gyres, ommastrephidae are

9632-508: The ocean is heavily dependent on the presence of nutrients and the availability of sunlight. Here, nutrients refers to nitrogen, nitrate, phosphate, and silicate, all important nutrients in biogeochemical processes that take place in the ocean. A commonly accepted method for relating different nutrient availabilities to each other in order to describe chemical processes is the Redfield, Ketchum, and Richards (RKR) equation. This equation describes

9744-455: The ocean surface, their relatively low production per unit area is made up for by covering massive areas of the Earth. This means that, despite being areas of relatively low productivity and low nutrients, they play a large role in contributing to the overall amount of ocean production. In contrast to subtropical gyres, subpolar gyres can have a lot of biological activity due to Ekman suction upwelling driven by wind stress curl. Subpolar gyres in

9856-792: The ocean. The Māori believe that the sea is the source of all life and is an energy, called Tangaroa. This energy could manifest in many different ways, like strong ocean currents, calm seas, or turbulent storms. The Māori have a rich oral history of navigation within the Southern Ocean and Antarctic Ocean and a deep understanding their ice and ocean patterns. A current research project is aimed at consolidating these oral histories. Efforts are being made to integrate TEK with Western science in marine and ocean research in New Zealand. Additional research efforts aim to collate indigenous oral histories and incorporate indigenous knowledge into climate change adaptation practices in New Zealand that will directly affect

9968-410: The outer boundary of the Ross Gyre. Further, the gyre is intensified by a westward ocean stress anomaly over its southern boundary. The ensuing southward Ekman transport anomaly raises sea surface heights over the continental shelf and accelerates the westward throughflow by increasing the cross-slope pressure gradient. The sea level pressure center may have a greater impact on the Ross Gyre transport or

10080-431: The presence of western boundary current solutions over eastern boundary current solutions can be found again through the conservation of potential vorticity. Considering again the case of a subtropical northern hemisphere gyre, the return flow must be northward. In order to move northward (an increase in planetary vorticity f {\displaystyle f} ), there must be a source of positive relative vorticity to

10192-457: The process of photosynthesis and respiration and the ratios of the nutrients involved. The RKR Equation for Photosynthesis and Respiration: With the correct ratios of nutrients on the left side of the RKR equation and sunlight, photosynthesis takes place to produce plankton (primary production) and oxygen. Typically, the limiting nutrients to production are nitrogen and phosphorus with nitrogen being

10304-445: The reduced pressure may also draw matter from that surface into the core. For example, a dust devil is a column of dust picked up by the core of an air vortex attached to the ground. A vortex that ends at the free surface of a body of water (like the whirlpool that often forms over a bathtub drain) may draw a column of air down the core. The forward vortex extending from a jet engine of a parked airplane can suck water and small stones into

10416-437: The relative vorticity ζ {\displaystyle \zeta } is small, meaning that local changes in vorticity cannot account for the decrease in H {\displaystyle H} . Thus, the water parcel must change its planetary vorticity f {\displaystyle f} accordingly. The only way to decrease the planetary vorticity is by moving the water parcel equatorward, so throughout

10528-533: The relative vorticity and have a valid northward return flow in the northern hemisphere subtropical gyre. Due to friction at the boundary, the velocity of flow must go to zero at the sidewall before reaching some maximum northward velocity within the boundary layer and decaying to the southward Sverdrup transport solution far away from the boundary. Thus, the condition that ∂ v / ∂ x > 0 {\displaystyle \partial v/\partial x>0} can only be satisfied through

10640-413: The rigid-body flow to the irrotational state. Vortex structures are defined by their vorticity , the local rotation rate of fluid particles. They can be formed via the phenomenon known as boundary layer separation which can occur when a fluid moves over a surface and experiences a rapid acceleration from the fluid velocity to zero due to the no-slip condition . This rapid negative acceleration creates

10752-400: The rotation of the bucket creates extra force. The reason that the vortices can change shape is the fact that they have open particle paths. This can create a moving vortex. Examples of this fact are the shapes of tornadoes and drain whirlpools . When two or more vortices are close together they can merge to make a vortex. Vortices also hold energy in its rotation of the fluid. If the energy

10864-481: The seafloor's topography. Like the Ross Gyre, the Weddell Gyre plays a critical role in the movement of heat, nutrients, and marine life in the Southern Ocean. Insights into the behavior and variability of the Weddell Gyre are crucial for comprehending the interaction between ocean processes in the southern hemisphere and their implications for the global climate system. This gyre is formed by interactions between

10976-418: The small populations of plankton that live there. The North Atlantic Subpolar Gyre is an important part of the ocean's carbon dioxide drawdown mechanism. The photosynthesis of phytoplankton communities in this area seasonally depletes surface waters of carbon dioxide, removing it through primary production. This primary production occurs seasonally, with the highest amounts happening in summer. Generally, spring

11088-461: The stars, winds, and ocean currents to know where they were on the ocean and where they were headed. These navigators were intimately familiar with Pacific currents that create the North Pacific gyre and this way of navigating continues today. Another example involves the Māori people who came from Polynesia and are an indigenous group in New Zealand. Their way of life and culture has strong connections to

11200-550: The system. The relative vorticity in the shallow-water system is: Here v {\displaystyle v} is again the meridional velocity and u {\displaystyle u} is the zonal velocity. In the sense of a northward return flow, the zonal component is neglected and only the meridional velocity is important for relative vorticity. Thus, this solution requires that ∂ v / ∂ x > 0 {\displaystyle \partial v/\partial x>0} in order to increase

11312-572: The throughflow, depending on its location and strength. This gyre has significant effects on interactions in the Southern Ocean between waters of the Antarctic margin, the Antarctic Circumpolar Current, and intervening gyres with a strong seasonal sea ice cover play a major role in the climate system. The Ross Sea is the southernmost sea on Earth and holds the United States' McMurdo Station and Italian Zuchelli Station . Even though this gyre

11424-533: The upper few hundred meters of the ocean. The gyre gains energy from winds in the south and loses energy in the north over a mean annual cycle. The strong atmospheric circulation in the autumn, combined with significant areas of open water, demonstrates the effect that wind stress has directly on the surface geostrophic currents. The Beaufort Gyre and the Transpolar Drift are interconnected due to their relationship in their role in transporting sea ice across

11536-440: The vortex axis is therefore constant, r u θ = Γ 2 π {\displaystyle ru_{\theta }={\tfrac {\Gamma }{2\pi }}} . The ideal irrotational vortex flow in free space is not physically realizable, since it would imply that the particle speed (and hence the force needed to keep particles in their circular paths) would grow without bound as one approaches

11648-402: The vortex axis. Indeed, in real vortices there is always a core region surrounding the axis where the particle velocity stops increasing and then decreases to zero as r goes to zero. Within that region, the flow is no longer irrotational: the vorticity ω → {\displaystyle {\vec {\omega }}} becomes non-zero, with direction roughly parallel to

11760-450: The vortex axis. The Rankine vortex is a model that assumes a rigid-body rotational flow where r is less than a fixed distance r 0 , and irrotational flow outside that core regions. In a viscous fluid, irrotational flow contains viscous dissipation everywhere, yet there are no net viscous forces, only viscous stresses. Due to the dissipation, this means that sustaining an irrotational viscous vortex requires continuous input of work at

11872-466: The vortex would persist forever. However, real fluids exhibit viscosity and this dissipates energy very slowly from the core of the vortex. It is only through dissipation of a vortex due to viscosity that a vortex line can end in the fluid, rather than at the boundary of the fluid. Harald Sverdrup (oceanographer) Harald Ulrik Sverdrup (15 November 1888 – 21 August 1957) was a Norwegian oceanographer and meteorologist . He served as director of

11984-430: The vorticity ω → {\displaystyle {\vec {\omega }}} must not be confused with the angular velocity vector of that portion of the fluid with respect to the external environment or to any fixed axis. In a vortex, in particular, ω → {\displaystyle {\vec {\omega }}} may be opposite to the mean angular velocity vector of

12096-429: The vorticity vector is defined to be the direction of the axis of rotation of this imaginary ball (according to the right-hand rule ) while its length is twice the ball's angular velocity . Mathematically, the vorticity is defined as the curl (or rotational) of the velocity field of the fluid, usually denoted by ω → {\displaystyle {\vec {\omega }}} and expressed by

12208-845: The wind, or follow the flow of ocean currents, often ending up in the middle of oceanic gyres where currents are weakest. Within garbage patches, the waste is not compact, and although most of it is near the surface of the ocean, it can be found up to more than 30 metres (100 ft) deep in the water. Patches contain plastics and debris in a range of sizes from Microplastics and small scale plastic pellet pollution , to large objects such as fishing nets and consumer goods and appliances lost from flood and shipping loss. Garbage patches grow because of widespread loss of plastic from human trash collection systems. The United Nations Environmental Program estimated that "for every square mile of ocean" there are about "46,000 pieces of plastic". The 10 largest emitters of oceanic plastic pollution worldwide are, from

12320-480: The world's major ocean gyres are slowly moving towards higher latitudes in the past few decades. Such feature show agreement with climate model prediction under anthropogenic global warming. Paleo-climate reconstruction also suggest that during the past cold climate intervals, i.e., ice ages, some of the western boundary currents (western branches of the subtropical ocean gyres) are closer to the equator than their modern positions. These evidence implies that global warming

12432-559: Was CEO of Store Norske Spitsbergen Kulkompani . Sverdrup was a student at Bergen Cathedral School in 1901 before graduating in 1906 at Kongsgård School in Stavanger . He graduated cand. real. in 1914 from University of Oslo . He studied under Vilhelm Bjerknes and earned his Dr. Philos. at the University of Leipzig in 1917. He was the scientific director of the North Polar expedition of Roald Amundsen aboard

12544-1072: Was awarded the William Bowie Medal by the American Geophysical Union , the Alexander Agassiz Medal of the National Academy of Sciences , the Patron's Medal of the Royal Geographical Society , the Vega Medal by the Swedish Society for Anthropology and Geography and the Swedish Order of the Polar Star . The Sverdrup , a unit describing the volume of water transport in ocean currents ,

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