In
oceanography
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
, a gyre () is any large system of circulating
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, s ...
s, particularly those involved with large
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
movements. Gyres are caused by the
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 ...
; planetary
vorticity
In continuum mechanics, vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point (the tendency of something to rotate), as would be seen by an observer located at that point and traveling along wi ...
, horizontal friction and vertical friction determine the circulatory patterns from the ''
wind stress
In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a f ...
curl
cURL (pronounced like "curl", UK: , US: ) is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various network protocols. The name stands for "Client URL".
History
cURL was fi ...
'' (
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
).
''Gyre'' can refer to any type of
vortex
In fluid dynamics, a vortex ( : 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 th ...
in an
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
or a
sea
The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...
,
even one that is human-created, but it is most commonly used in terrestrial
oceanography
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
to refer to the major
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
systems.
Major gyres
The following are the five most notable ocean gyres:
[The five most notable gyres](_blank)
PowerPoint Presentation
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Indian Ocean Gyre
The Indian Ocean gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyor belt. The Indian Ocean gyre is composed of two major curr ...
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North Atlantic Gyre
The North Atlantic Gyre of the Atlantic Ocean is one of five great oceanic gyres. It is a circular ocean current, with offshoot eddies and sub-gyres, across the North Atlantic from the Intertropical Convergence Zone (calms or doldrums) to the part ...
*
North Pacific Gyre
The North Pacific Gyre (NPG) or North Pacific Subtropical Gyre (NPSG), located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, locate ...
*
South Atlantic Gyre
The South Atlantic Gyre is the subtropical gyre in the south Atlantic Ocean. In the southern portion of the gyre, northwesterly (or southeastward-flowing) winds drive eastward-flowing currents that are difficult to distinguish from the northern ...
*
South Pacific Gyre
__NOTOC__
The Southern Pacific Gyre is part of the Earth's system of rotating ocean currents, bounded by the Equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South America to the east. The center of ...
They flow
clockwise
Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite ...
in the Northern hemisphere, and
counterclockwise
Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite ...
in the Southern hemisphere.
Other gyres
Tropical gyres
![Currents](https://upload.wikimedia.org/wikipedia/commons/c/c2/Currents.svg)
Tropical gyres are less unified and tend to be mostly east–west with minor north–south extent.
* Atlantic Equatorial Current System (two counter-rotating circulations)
* Pacific Equatorial Current System
* Indian Monsoon Gyres (two counter-rotating circulations in northern Indian Ocean)
Subtropical gyres
Subtropical gyres are formed by an intricate process involving both
Coriolis force and
Ekman transport. As global winds, caused by Earth's rotation, blow across the ocean surface they are acted upon by Coriolis causing movement to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. These winds cause frictional surface currents as the wind transfers energy to the ocean allowing the water to move in a circular motion. As Ekman transport acts on these circular currents the net transport of water is actually 90 degrees which drives regions of convergence, allowing water to pile up in the center of the ocean basin forming a bulge.
The center of a subtropical gyre is a high pressure zone, while the outer edges of the gyre are a low pressure zone. This difference in pressure causes a pressure gradient allowing the diffusion of water from the high pressure zone in the bulge to the low pressure zone on the outer edges of the gyre.The movement of water does not flow directly down the bulge in the center but around it due to Coriolis causing circulation around the high pressure zone in a clockwise motion in the
northern hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
and a counterclockwise motion in the
southern hemisphere.Thus, Resulting in the rotation of the gyre. The gyre has a stable circulation of water around it due to the exact balance between Ekman force and Coriolis. These gyres contribute to the
Geostrophic Flow
A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern ...
of the ocean resulting in the overall
Ocean circulation model
Ocean general circulation models (OGCMs) are a particular kind of general circulation model to describe physical and thermodynamical processes in oceans. The oceanic general circulation is defined as the horizontal space scale and time scale larg ...
of the Earth. The movement of subtropical gyres cause areas of
downwelling
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the ''sinking'' limb of a convecti ...
in the ocean resulting in regions of lower productivity.
This build-up of water in the center creates flow towards the equator in the upper of the ocean, through rather complex dynamics. This flow is returned towards the pole in an intensified western
boundary current
Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.
Eastern boundary currents
Eastern boundary currents are ...
. The boundary current of the
North Atlantic Gyre
The North Atlantic Gyre of the Atlantic Ocean is one of five great oceanic gyres. It is a circular ocean current, with offshoot eddies and sub-gyres, across the North Atlantic from the Intertropical Convergence Zone (calms or doldrums) to the part ...
is the
Gulf Stream
The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...
, of the
North Pacific Gyre
The North Pacific Gyre (NPG) or North Pacific Subtropical Gyre (NPSG), located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, locate ...
the
Kuroshio Current
The , also known as the Black or or the is a north-flowing, warm ocean current on the west side of the North Pacific Ocean basin. It was named for the deep blue appearance of its waters. Similar to the Gulf Stream in the North Atlantic, the Ku ...
, of the
South Atlantic Gyre
The South Atlantic Gyre is the subtropical gyre in the south Atlantic Ocean. In the southern portion of the gyre, northwesterly (or southeastward-flowing) winds drive eastward-flowing currents that are difficult to distinguish from the northern ...
the
Brazil Current
The Brazil Current is a warm water current that flows south along the Brazilian south coast to the mouth of the Río de la Plata.
Description
This current is caused by diversion of a portion of the Atlantic South Equatorial Current from where ...
, of the
South Pacific Gyre
__NOTOC__
The Southern Pacific Gyre is part of the Earth's system of rotating ocean currents, bounded by the Equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South America to the east. The center of ...
the
East Australian Current
The East Australian Current (EAC) is a warm, southward, western boundary current that is formed from the South Equatorial Current (SEC) crossing the Coral Sea and reaching the eastern coast of Australia. At around 15° S near the Australian co ...
, and of the
Indian Ocean Gyre
The Indian Ocean gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyor belt. The Indian Ocean gyre is composed of two major curr ...
the
Agulhas Current
The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
.
Subpolar gyres
Subpolar gyres form at high latitudes (around
60°). Circulation of surface wind and ocean water is counterclockwise in the Northern Hemisphere, around a
low-pressure area
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
, such as the persistent
Aleutian Low
The Aleutian Low is a semi-permanent low-pressure system located near the Aleutian Islands in the Bering Sea during the Northern Hemisphere winter. It is a climatic feature centered near the Aleutian Islands measured based on mean sea-level press ...
and the
Icelandic Low
The Icelandic Low is a semi-permanent centre of low atmospheric pressure found between Iceland and southern Greenland and extending in the Northern Hemisphere winter into the Barents Sea. In the summer, it weakens and splits into two centres, on ...
. Surface currents generally move outward from the center of the system. This drives the
Ekman transport, which creates an
upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...
of nutrient-rich water from the lower depths.
Subpolar circulation in the southern hemisphere is dominated by the
Antarctic Circumpolar Current
The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feat ...
, due to the lack of large landmasses breaking up the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
. There are minor gyres in the
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha ...
and the
Ross Sea
The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who vi ...
, the
Weddell Gyre
The Weddell Gyre is one of the two gyres that exist within the Southern Ocean. The gyre is formed by interactions between the Antarctic Circumpolar Current (ACC) and the Antarctic Continental Shelf. The gyre is located in the Weddell Sea, and r ...
and
Ross Gyre
The Ross Gyre is one of the two gyres that exist within the Southern Ocean. The gyre is located in the Ross Sea, and rotates clockwise. The gyre is formed by interactions between the Antarctic Circumpolar Current and the Antarctic Continental She ...
, which circulate in a clockwise direction.
Biological desert
![Mollweide Cycle](https://upload.wikimedia.org/wikipedia/commons/1/1d/Mollweide_Cycle.gif)
Gyres are sometimes described as "ocean deserts" or more precisely "biological deserts", a concept that uses the concept of
desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
in the sense of an environment lacking life and not necessarily water. Other places that are called oceanic deserts are
hypoxic
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the t ...
or
anoxic waters
Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anox ...
such as
dead zones.
Climate change
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, 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 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 is very likely to push the large-scale ocean gyres towards higher latitudes.
Major Ocean Currents Drifting Poleward
''www.loe.org'', accessed 5 December 2021
The influence of the Coriolis effect on westward intensification
Pollution
See also
* Anticyclone
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...
* Cyclone
In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anti ...
* Ecosystem of the North Pacific Subtropical Gyre
The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Souther ...
* Eddy
Eddie or Eddy may refer to:
Science and technology
*Eddy (fluid dynamics), the swirling of a fluid and the reverse current created when the fluid flows past an obstacle
* Eddie (text editor), a text editor originally for BeOS and now ported to Lin ...
* Fluid dynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...
* Geostrophic current
A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern ...
* Skookumchuck Skookumchuck () is a Chinook Jargon term that is in common use in British Columbia English and occurs in Pacific Northwest English. '' Skookum'' means "strong" or "powerful", and "chuck" means water, so ''skookumchuck'' means "rapids" or "whitewa ...
* ''Volta do mar
, , or (the phrase in Portuguese means literally 'turn of the sea' but also 'return from the sea') is a navigational technique perfected by Portuguese navigators during the Age of Discovery in the late fifteenth century, using the dependable p ...
''
* 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 ( ). ''Vo ...
References
External links
5 Gyres – Understanding Plastic Marine Pollution
SIO 210: Introduction to Physical Oceanography – Global circulation
SIO 210: Introduction to Physical Oceanography – Wind-forced circulation notes
North Pacific Gyre Oscillation
— Georgia Institute of Technology
*
{{Physical oceanography
Aerodynamics
Fluid dynamics
Oceanic gyres
Fisheries science