An ocean gyre is a large system of circular ocean currents formed by global wind patterns and forces created by Earth’s rotation. 
 
The movement of the world’s major ocean gyres helps drive the “ocean conveyor belt.” The ocean conveyor belt circulates ocean water around the entire planet. Also known as thermohaline circulation, the ocean conveyor belt is essential for regulating temperature, salinity and nutrient flow throughout the ocean.
 
How a Gyre Forms


 
Three forces cause the circulation of a gyre: global wind patterns, Earth’s rotation, and Earth’s landmasses. Wind drags on the ocean surface, causing water to move in the direction the wind is blowing. 
 
The Earth’s rotation deflects, or changes the direction of, these wind-driven currents. This deflection is a part of the Coriolis effect. The Coriolis effect shifts surface currents by angles of about 45 degrees. In the Northern Hemisphere, ocean currents are deflected to the right, in a clockwise motion. In the Southern Hemisphere, ocean currents are pushed to the left, in a counterclockwise motion. 
 
Beneath surface currents of the gyre, the Coriolis effect results in what is called an Ekman spiral. While surface currents are deflected by about 45 degrees, each deeper layer in the water column is deflected slightly less. This results in a spiral pattern descending about 100 meters (330 feet).
 
Earth’s continents and other landmasses (such as islands) also influence the creation of ocean gyres. The massive South Pacific Gyre, for instance, includes hundreds of kilometers of open ocean. It is bounded only by the continents of Australia and South America, as well as the Equator and powerful Antarctic Circumpolar Current (ACC).
 
In contrast, the northern Indian Ocean Gyre is a much smaller ocean gyre. Unlike the South Pacific Gyre, its extent is determined largely by landmasses. The Equator forms its southern boundary, but it is bounded elsewhere by the Horn of Africa, Sri Lanka and the Indian subcontinent, and the Indonesian archipelago.
 
Types of Gyres

There are three major types of ocean gyres: tropical, subtropical, and subpolar. 
 
Subpolar gyres form in the polar regions of the planet. They sit beneath an area of low atmospheric pressure. Wind drives the currents in subpolar gyres away from coastal areas. These surface currents are replaced by cold, nutrient-rich water in a process called upwelling. The Northern Hemisphere has several subpolar gyres, bounded by islands such as Iceland, Greenland, and the Aleutians; and the northern reaches of Scandinavia, Asia, and North America.
 
Tropical gyres form near the Equator. The Coriolis effect is not present at the Equator, and winds are the primary creators of currents. For this reason, tropical gyres tend to flow in a more east-west (instead of circular) pattern. The Indian Ocean Gyre is actually two distinct tropical gyres—the northern and southern Indian Ocean Gyres.
 
Most of the world’s major gyres are subtropical gyres. These form between the polar and equatorial regions of Earth. Subtropical gyres circle areas beneath regions of high atmospheric pressure. These are placid ocean areas thousands of kilometers in diameter. Unlike coastal zones, these central regions are relatively stable. The ocean water generally stays in one place while the currents of the gyre circulate around it. 
 
Movement of Gyres
 
Gyres are comprised of ocean currents that link up as they follow the coastlines of the Earth’s continents. Each gyre has a powerful western boundary current and a weaker eastern boundary current.
 
The North Atlantic Gyre begins with the northward flow of the Gulf Stream along the East Coast of the United States. The Gulf Stream is the western boundary current of the gyre. The gyre then becomes the North Atlantic Current, which flows across the North Atlantic to Europe. Still flowing in a circular pattern, the current flows south as far as the northwestern coast of Africa, where it is known as the Canary Current—the gyre’s eastern boundary current. The gyre is completed as the North Atlantic Equatorial Current crosses the Atlantic Ocean to the Caribbean Sea. This entire circle and the water within it is the North Atlantic Gyre. 
 
Most ocean gyres are very stable and predictable. The North Atlantic Ocean Gyre always flows in a steady, clockwise path around the North Atlantic Ocean. Some gyres experience seasonal variation, however.
 
The Indian Ocean Gyre is a complex system of many currents extending from the eastern coast of Africa to the western coast of Australia. The northern part of the system circulates between the Horn of Africa and the Indonesian archipelago. It is sometimes called the Indian monsoon current.
 
The Indian monsoon current takes its name from the wind—the monsoon—that drives it. It is one of the very few currents in an ocean gyre that change direction. In the summer, the current flows clockwise, as the monsoon blows in from the southwestern Indian Ocean. In the winter, the current flows counterclockwise, as the wind blows in from the Tibetan plateau in the northeast.
 
The temperature in an ocean gyre depends on many factors, including the current. The Gulf Stream and summer monsoon current are warm currents. They are heated by the warm tropical waters of the Caribbean Sea (Gulf Stream) and equatorial Indian Ocean (summer monsoon current). The North Atlantic Current and winter monsoon current are cool currents. They are cooled by Arctic winds and ocean currents (North Atlantic) and the winter monsoon blowing from the icy Himalayas (winter monsoon current).
 
Garbage Patches
 
Ocean gyres circle large areas of stationary, calm water. Debris drifts into these areas and, due to the region’s lack of movement, can accumulate for years. These regions are called garbage patches. The Indian Ocean, North Atlantic Ocean, and North Pacific Ocean all have significant garbage patches. The garbage patch in the North Pacific Ocean is sometimes called the Pacific trash vortex or the Great Pacific Garbage Patch.
 
Garbage patches are created slowly. Marine debris makes its way into the Great Pacific Garbage Patch, for instance, from currents flowing along the west coast of North America and the east coast of Asia. Some of the debris is also dumped from ocean vessels. 
 
The circular motion of the gyre draws in the debris, mostly small particles of plastic. Eventually, the debris makes its way to the center of the gyre, where it becomes trapped and breaks down into a kind of plastic soup. 
 
Oceanographers and ecologists are concerned about garbage patches. In particular, they are studying the degradation, or breaking down, of plastics. Unlike natural substances, such as wood or metal, plastic does not disintegrate into organic substances. It simply breaks down into smaller and smaller pieces of plastic. These tiny plastic particles are as small as the algae and plankton that form the basis of the entire ocean food web. Species such as shrimp, birds, and fish consume these micro-plastics, which oftentimes kill them. The plastic chemicals can also be absorbed by predators of these species. The concentration of these chemicals increases through each trophic level of the food chain, a process known as biomagnification.
 
Garbage patches generally accumulate far from any country’s coastline, and it is nearly impossible to track the origin of marine debris. The tiny plastic particles that make up most of the patches are also very difficult and expensive to detect and remove. Few nations have accepted the responsibility of cleaning up the ocean’s garbage patches.
 
Life in a Gyre
 
Scientists are only beginning to understand the biodiversity of ocean gyres. Their calm centers have traditionally been regarded as oligotrophic, or nutrient-poor, because they have few concentrations of the organic chemicals that support producers, such as algae and plankton, in the ocean food web.
 
Researchers have recently discovered an expansion of oligotrophic regions in ocean gyres. They have correlated this expansion with increases in sea-surface temperatures—warm waters generally have far fewer nutrients than cold water.
 
The University of Hawaii is taking advantage of its position in the North Pacific Gyre to further study the gyre and factors that impact it. Scientists regularly study “the thermohaline structure, water column chemistry, currents, optical properties, primary production, plankton community structure, and rates of particle export” in this ocean gyre.
ocean gyre
An eddy, like this one made visible by icebergs, is part of a current. A current is part of a gyre.
ALOHA!
Some of the leading research on ocean gyres is being conducted at the University of Hawaii at Manoa. Scientists take regular readings of the Pacific Ocean’s temperature, chemistry, pollution, turbidity, currents, and plankton and algae communities at a deep-water research station called A Long-term Oligotrophic Habitat Assessment—ALOHA.

Horse Latitudes
Many ocean gyres are found in what are called the horse latitudes, between 30 and 35 degrees north and south. These areas are known to have calm waters and little precipitation or winds. Legend has it that the name refers to sailing ships that stalled in these latitudes, leading sailors to throw their horses overboard because they were afraid they would run out of water.

absorb
Verb

to soak up.
accumulate
Verb

to gather or collect.
algae
Plural Noun

(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.
Antarctic Circumpolar Current (ACC)
Noun

most powerful surface ocean current in the world, which rotates clockwise around the continent of Antarctica. Also called the West Wind Drift.
archipelago
Noun

a group of closely scattered islands in a large body of water.
Arctic
Noun

region at Earth's extreme north, encompassed by the Arctic Circle.
atmospheric pressure
Noun

force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth.
biodiversity
Noun

all the different kinds of living organisms within a given area.
biomagnification
Noun

process in which the concentration of a substance increases as it passes up the food chain.
bound
Verb

to limit or confine.
boundary
Noun

line separating geographical areas.
circulate
Verb

to move around, often in a pattern.
coast
Noun

edge of land along the sea or other large body of water.
complex
Adjective

complicated.
comprise
Verb

to contain or be made up of.
concentration
Noun

measure of the amount of a substance or grouping in a specific place.
consume
Verb

to use up.
continent
Noun

one of the seven main land masses on Earth.
Coriolis effect
Noun

the result of Earth's rotation on weather patterns and ocean currents. The Coriolis effect makes storms swirl clockwise in the Southern hemisphere and counterclockwise in the Northern Hemisphere.
correlate
Verb

to bring different sets of data into order, or establish a relationship or connection between them.
current
Noun

steady, predictable flow of fluid within a larger body of that fluid.
debris
Noun

remains of something broken or destroyed; waste, or garbage.
deflect
Verb

to alter from a straight line.
degradation
Noun

breaking down.
detect
Verb

to notice.
determine
Verb

to decide.
disintegrate
Verb

to fall apart and disappear.
East Coast
Noun

Atlantic coast of the United States.
ecologist
Noun

scientist who studies the relationships between organisms and their environments.
Ekman spiral
Noun

rotating column of water formed as ocean surface currents are deflected by the Coriolis effect, wind, and friction forces.
Equator
Noun

imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.
essential
Adjective

needed.
expensive
Adjective

very costly.
extent
Noun

degree or space to which a thing extends.
factor
Noun

element contributing to an event or outcome.
food chain
Noun

group of organisms linked in order of the food they eat, from producers to consumers, and from prey, predators, scavengers, and decomposers.
food web
Noun

all related food chains in an ecosystem. Also called a food cycle.
fund
Verb

to give money to a program or project.
Great Pacific Garbage Patch
Noun

area of the North Pacific Ocean where currents have trapped huge amounts of debris, mostly plastics.
Gulf Stream
Noun

warm current that starts in the Gulf of Mexico and travels along the eastern coast of the U.S. and Canada before crossing the North Atlantic Ocean.
island
Noun

body of land surrounded by water.
landmass
Noun

large area of land.
marine
Adjective

having to do with the ocean.
massive
Adjective

very large or heavy.
monsoon
Noun

seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains.
nation
Noun

political unit made of people who share a common territory.
Northern Hemisphere
Noun

half of the Earth between the North Pole and the Equator.
nutrient
Noun

substance an organism needs for energy, growth, and life.
nutrient
Noun

substance an organism needs for energy, growth, and life.
ocean conveyor belt
Noun

system in which water moves between the cold depths and warm surface in oceans throughout the world. Also called thermohaline circulation.
ocean gyre
Noun

an area of ocean that slowly rotates in an enormous circle.
oceanographer
Noun

person who studies the ocean.
ocean vessel
Noun

ship, boat, submarine, or other vehicle able to travel the ocean.
oligotrophic
Adjective

having few nutrients and supporting little growth.
optical
Adjective

having to do with vision or sight.
organic
Adjective

composed of living or once-living material.
origin
Noun

source or ancestry.
particle
Noun

small piece of material.
placid
Adjective

calm.
planet
Noun

large, spherical celestial body that regularly rotates around a star.
plankton
Plural Noun

(singular: plankton) microscopic aquatic organisms.
plastic
Noun

chemical material that can be easily shaped when heated to a high temperature.
plateau
Noun

large region that is higher than the surrounding area and relatively flat.
polar
Adjective

having to do with the North and/or South Pole.
predator
Noun

animal that hunts other animals for food.
predictable
Adjective

regular or able to be forecasted.
primary
Adjective

first or most important.
producer
Noun

organism on the food chain that can produce its own energy and nutrients. Also called an autotroph.
region
Noun

any area on Earth with one or more common characteristics. Regions are the basic units of geography.
responsibility
Noun

being accountable and reliable for an action or situation.
rotation
Noun

object's complete turn around its own axis.
salinity
Noun

saltiness.
Scandinavia
Noun

region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.
seasonal
Adjective

likely to change with the seasons.
significant
Adjective

important or impressive.
Southern Hemisphere
Noun

half of the Earth between the South Pole and the Equator.
stable
Adjective

steady and reliable.
stationary
Adjective

unmoving.
subcontinent
Noun

large section of a continent.
subpolar gyre
Noun

circulating ocean current that forms at high latitudes beneath an area of low atmospheric pressure, where wind drives currents away from coastal areas.
substance
Noun

physical material.
subtropical gyre
Noun

circulating ocean current that forms between Earth's polar and equatorial regions, beneath an area of high atmospheric pressure.
temperature
Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.
thermohaline circulation
Noun

ocean conveyor belt system in which water moves between the cold depths and warm surface in oceans throughout the world.
trophic level
Noun

one of three positions on the food chain: autotrophs (first), herbivores (second), and carnivores and omnivores (third).
tropical gyre
Noun

circulating ocean current that forms in equatorial regions and tends to flow mostly east-west.
upwelling
Noun

process in which cold, nutrient-rich water from the bottom of an ocean basin or lake is brought to the surface due to atmospheric effects such as the Coriolis force or wind.
variation
Noun

difference.
vortex
Noun

column of rotating fluid, such as air (wind) or water.
water column
Noun

area reaching from the sediment of a body of water to its surface.
wind
Noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

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Editors

Melissa MacPhee, National Geographic Society
Caryl-Sue, National Geographic Society

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Caryl-Sue, National Geographic Society

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The source of the material in the first slide (Ocean Currents) is the COMET® Website at http://meted.ucar.edu/ of the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s) with the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (DOC). ©1997-2014 University Corporation for Atmospheric Research. All Rights Reserved.

Last Updated

Oct. 4, 2014

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