• ocean gyre
    An eddy, like this one made visible by icebergs, is part of a current. A current is part of a gyre.

    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.

    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.
    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.
  • Term Part of Speech Definition Encyclopedic Entry
    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.

    		 Encyclopedic Entry: archipelago
    Arctic Noun

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

    		 Encyclopedic Entry: Arctic
    atmospheric pressure Noun

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

    		 Encyclopedic Entry: atmospheric pressure
    biodiversity Noun

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

    		 Encyclopedic Entry: biodiversity
    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.

    		 Encyclopedic Entry: boundary
    circulate Verb

    to move around, often in a pattern.
    coast Noun

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

    		 Encyclopedic Entry: coast
    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.

    		 Encyclopedic Entry: continent
    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.

    		 Encyclopedic Entry: Coriolis effect
    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.

    		 Encyclopedic Entry: current
    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.

    		 Encyclopedic Entry: equator
    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.

    		 Encyclopedic Entry: food chain
    food web Noun

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

    		 Encyclopedic Entry: food web
    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.

    		 Encyclopedic Entry: Great Pacific Garbage Patch
    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.

    		 Encyclopedic Entry: island
    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.

    		 Encyclopedic Entry: monsoon
    nation Noun

    political unit made of people who share a common territory.

    		 Encyclopedic Entry: nation
    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.

    		 Encyclopedic Entry: nutrient
    nutrient Noun

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

    		 Encyclopedic Entry: nutrient
    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.

    		 Encyclopedic Entry: ocean conveyor belt
    ocean gyre Noun

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

    		 Encyclopedic Entry: ocean gyre
    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.

    		 Encyclopedic Entry: planet
    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.

    		 Encyclopedic Entry: plateau
    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.

    		 Encyclopedic Entry: region
    responsibility Noun

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

    object's complete turn around its own axis.

    		 Encyclopedic Entry: rotation
    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.

    		 Encyclopedic Entry: temperature
    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.

    		 Encyclopedic Entry: upwelling
    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

Producer

Caryl-Sue, National Geographic Society

Sources

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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