An ocean gyre is a large system of circular ocean current s formed by global wind patterns and forces created by Earth’s rotation

How a Gyre Forms

Three forces cause the circulation of a gyre: global wind patterns, Earth’s rotation, and Earth’s landmass es. Wind drags on the ocean surface, causing water to move in the direction the wind is blowing.

The Earth’s rotation deflect s, 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).

In contrast, the northern Indian Ocean Gyre is a much smaller ocean gyre. Unlike the South Pacific Gyre, its extent is determine d 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 gyre s 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 gyre s 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 gyre s. 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 comprise d 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 circulate s 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 factor s, 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 vessel s.

The circular motion of the gyre draws in the debris, mostly small particle s 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.

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 nation s 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 producer s, such as algae and plankton, in the ocean food web.

Researchers have recently discovered an expansion of oligotrophic regions in ocean gyres. They have correlate d this expansion with increases in sea-surface temperatures—warm waters generally have far fewer nutrients than cold water.