How many gyres are formed in the open oceans

Activity: Build a Drifter. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate? Question Set: What is a Mammal?

Further Investigations: What is a Mammal? Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Purchase a membership! Flow meters are small, often handheld devices used to measure current flow. Water current spins a propeller as it moves past the meter. The amount the propeller spins can be correlated with current speed.

Some meters can also report the direction of water flow. Flow meters are useful in smaller bodies of water. Clod cards are small blocks of plaster or a similar type of material used to measure relative flow rate between sites. As water current flows over the blocks, they dissolve. The faster the water flow, the more the clod cards dissolve. Clod cards are useful tools for measuring water flow near ocean bottom. Shallow water drifters float near the surface of the water and are pushed by the predominant surface current.

The distance traveled, time, and direction of a drift can be measured by an observer or GPS device. The picture is a Davis drifter, which uses underwater sails moved by current flow. Deep ocean drifters flow with the current below the surface. They are programmed to descend to a predetermined depth for several days and then rise to the surface. While underwater, they record their position and then transmit information back to scientists when they surface.

Deep ocean drifters are useful for long-term deployment in deep water as they can surface and sink through many cycles. An ADCP emits sound pulses underwater and then measures the frequency of the sound bouncing back off of the water particles.

If the water particles are moving away from the ADCP, then the frequency will be longer. If the particles are moving toward the ADCP, then the frequency will be shorter. ADCPs are useful for measuring flow in bays. They can also be mounted on the bow of ships.

Shore-based current meters send out sound signals and measure the frequency of sound bouncing back. These instruments bounce sound off wind induced surface currents. Shore-based current meters are useful when measuring surface currents. They are formed primarily by wind blowing across the surface of the ocean and by differences in the temperature, density and pressure of water and are steered by Earth's rotation as well as the location of the continents and topography of the ocean bottom.

Gyres are spiraling circulations thousands of miles in diameter and rimmed by large, permanent ocean currents. Eddies are smaller, temporary loops of swirling water that can travel long distances before dissipating.

Wind is the primary force that creates and moves surface currents; Earth's rotation plays an important role in steering the water's motion. Persistent subtropical high pressure systems centered at about 30 degrees north and south latitude create patterns of strong winds known as the trades and the westerlies.

Friction between the air and the water sets the sea surface in motion. As this topmost layer of water moves, it pulls on the water directly beneath it, which in turn pulls on the layer of water beneath that to create the beginnings of an ocean current.

The resulting motion is not in line with the wind, however. Earth's rotation causes an apparent force known as the Coriolis effect to deflect straight-line movement across the surface about 45 degrees to the right in the Northern Hemisphere and 45 degrees to the left in the Southern Hemisphere. In addition, each successive layer of water is slightly deflected from the motion of the one above, like a deck of cards fanned out.

This forms a phenomenon called an Ekman spiral that was first described by Swedish mathematician Vagn Walfrid Ekman in , but it was not until the late s that a team from WHOI first observed it in the open ocean. The net wind-driven movement of water, known as Ekman transport, creates a bulge in each ocean basin that is as much as three feet one meter higher than mean global sea level.

The force of gravity pulling on this large mass of water creates a pressure gradient similar to that in an atmospheric high pressure system which in turn leads to a stable, rotating mass of water. Five permanent subtropical gyres can be found in the major ocean basins—two each in the Atlantic and Pacific Oceans and one in the Indian Ocean—turning clockwise in the Northern Hemisphere and counterclockwise in the Southern.

Smaller counterclockwise gyres centered at around 60 degrees north latitude are created by the prevailing winds around permanent sub-Arctic low-pressure systems. Another subpolar gyre, the only one centered on a landmass, circles Antarctica driven by the near-constant westerly winds that blow over the Southern Ocean, unimpeded by land. The subtropical gyres are surrounded by four linked currents: two boundary currents oriented roughly north-south at their eastern and western edges and two east-west currents at the northern and southern extent of the gyre.

Western boundary currents are also among the fastest non-tidal ocean currents on Earth, reaching speeds of more than five miles per hour 2. As these warm western boundary currents slow and spread out, they turn east to form the most poleward currents of their associated gyre. In the north, they also act as the southern boundary of the sub-polar gyres, permitting the exchange of water between the subtropics and the Arctic.

In the south, the Antarctic Circumpolar Current connects to the southern subtropical gyres through these currents in a similar way. The colder eastern boundary currents, which flow from the high latitudes toward the equator, are the slowest and most diffuse currents around the gyre. As they reach the equator, they turn west and pick up speed, driven by the trade winds and heat from the tropical sun. Eddies are relatively small, contained pockets of moving water that break off from the main body of a current and travel independently of their parent.

They can form in almost any part of a current, but are especially pronounced in western boundary currents. Once the fast-moving currents leave the confining influence of land, they become unstable and, like a fire hose with no one holding it, begin to meander and bend. If a current becomes so tightly bent that it doubles back on itself, that section of flow may "pinch off" and separate from the main body of the current like an oxbow bend in a river.

These swirling features can take the shape of warm-core masses of warm water turning in colder ocean waters or cold-core masses of cold water in warm eddies and can travel for months across hundreds or thousands of miles of open ocean. Eddies also form in the mid-ocean, far from boundary currents. Their genesis results from an instability process in which large-scale mean flows are constantly breaking down into smaller scale features. The atmosphere behaves in much the same way: energy is put into the system on the planetary scale it is warm at the equator and cold at the poles , which creates large-scale flow that spawns the storms and fronts we know as weather.

In that sense, ocean eddies are analogous to atmospheric weather—although their spatial scales are smaller and temporal scales longer because of differences between air and water. Currents, gyres and eddies transport water and heat long distances and help promote large-scale mixing of the ocean. Strong currents and eddies also influence shipping routes and have been known to damage oil platforms.

Powerful offshore currents and weaker coastal currents shape the land by contributing to beach erosion and the movement of barrier islands. Knowledge of how and where these phenomena occur as well as how they might be changing is sought by fishing fleets to locate schools of fish, by the Coast Guard to respond to search-and-rescue emergencies or oil spills, and by policy makers to help formulate marine conservation plans.

Western boundary currents such as the Gulf Stream carry large amounts of heat from tropical waters to the north. This flow is part of the thermohaline circulation, or ocean conveyor and helps distributes heat around the planet. Since these currents come from the equator, they are warm water currents, bringing warm water to the higher latitudes and distributing heat throughout the ocean. At the same time, between o latitude the westerlies move surface water towards the east.

The Coriolis Effect and the presence of the continents deflect the currents towards the equator, creating eastern boundary currents on the eastern side of the ocean basins. These currents come from high latitude areas, so they deliver cold water to the lower latitudes. Together, these currents combine to create large-scale circular patterns of surface circulation called gyres. In the Northern Hemisphere the gyres rotate to the right clockwise , while in the Southern Hemisphere the gyres rotate to the left counterclockwise.

The Kuroshio flows into the North Pacific Current which moves east towards North America, where it becomes the California Current to complete the gyre. Near Antarctica the circulation is somewhat different. Because there is little in the way of continental land masses between o south, the surface current created by the westerly winds can make its way completely around the Earth, creating the Antarctic Circumpolar Current ACC or West Wind Drift WWD that flows from west to east Figure 9.

The Antarctic Circumpolar Current is the only current that connects all of the major ocean basins, and in terms of the amount of water that it transports, it is the largest surface current on Earth.