Ocean gyre

In oceanography, a gyre (/ˈdʒaɪər/) is a large system of ocean surface currents that flow in a circle. These currents are pushed into circular paths by the wind.

Gyres are formed because of the Coriolis effect. This is a natural force that helps control how water moves around the planet. Together with other forces like vorticity and friction, they create the special circular patterns we see in the ocean from the wind stress curl (torque).

The word gyre can describe any kind of spinning motion in the air or water, even ones made by humans. But when people talk about gyres most often, they mean the big, important systems in our oceans that help move water all around the world.

Formation

The largest ocean gyres are driven by wind. Their places and movements are set by global wind patterns: easterlies near the tropics and westerlies at midlatitudes. These winds create a twist that moves water in a circle. This circular motion is called Ekman pumping in warmer areas and Ekman suction in colder areas. Ekman pumping pushes water up in the center of the gyre, while Ekman suction pulls water down.

Gyres are not the same all over. The edges, especially on the west side, move faster than the middle. This happens because of how the Earth spins and how water moves. In warm parts of the ocean, water piles up in the middle of the gyre. This makes the water level higher in the center and creates fast currents on the west side.

Biogeochemistry

Depending on where they are in the world, ocean gyres can be places where lots of living things grow or where very few grow. Each gyre has its own special mix of plants and animals, but they can be grouped by where they are located.

Some gyres, called cyclonic gyres, help bring nutrients up from deep in the ocean, so more plants and animals can live there. Other gyres, called anticyclonic gyres, push water down, which takes nutrients away from the surface. Because of this, these areas are sometimes called "ocean deserts" since very little grows there. Even though these areas don’t produce much on their own, they cover such a large part of the ocean that they still add a lot to the ocean’s overall life.

How much life grows in the ocean depends a lot on nutrients like nitrogen and phosphorus, as well as sunlight. When these nutrients and sunlight are present in the right amounts, tiny plants called plankton grow and produce oxygen.

In some places, like near Alaska, the ocean has lots of nutrients but still doesn’t grow much plankton. This is because those areas need a special nutrient called iron, which usually comes from dust blowing in from land.

The North Atlantic Subpolar Gyre plays a big role in taking in carbon dioxide from the air. Tiny plants there use this carbon dioxide in the spring and summer, but they don’t grow as much in the spring as we might expect.

Ocean gyres usually have about five or six levels of living things that depend on each other for food. Small plants called phytoplankton are at the bottom, and bigger animals, like small fish and squid, eat them. These small animals then become food for even larger ocean creatures.

Native Polynesian knowledge of ocean patterns

Indigenous Polynesian people have a special connection to the Pacific Ocean. Their knowledge helps them understand the land and water around them. This knowledge is different for each person and community, but it is very important for taking care of the environment.

Long ago, Polynesians traveled across the Pacific Ocean to places like Hawaii and New Zealand. They used the stars, winds, and ocean currents to find their way. These travelers knew a lot about the ocean currents, including those that form the North Pacific Gyre, and their navigation methods are still used today.

The Māori people, who came from Polynesia and live in New Zealand, also have a strong link to the ocean. They believe the sea is the source of all life and has energy called Tangaroa. This energy shows up in different ways, like strong currents or calm waters. The Māori have many stories passed down about navigating the Southern and Antarctic Oceans. Today, researchers are working to combine this traditional knowledge with modern science to help protect the ocean and support indigenous communities in New Zealand.

Threats

Climate change

Ocean currents help move heat and water around the world, shaping the climate in different areas. For example, some currents bring warm, moist air to places like East China and Japan, making the weather mild and rainy. Other currents bring cooler, drier air to places like California.

Scientists have noticed that big ocean currents are slowly moving toward the poles over the past few decades. This matches what computer models predict with global warming. In past cold periods, some currents were closer to the equator than they are today. These changes show that warming is affecting ocean currents.

As the ocean takes in more carbon dioxide, it becomes more acidic. This change harms small sea creatures that build shells or skeletons from a substance called calcium carbonate. It also affects the growth of tiny plants in the ocean, which are important for feeding many sea animals.

Overfishing and ecosystem disruption

Overfishing is putting pressure on the animals that live near ocean currents. Big fishing fleets often fish near these areas because they have more food. Heavy fishing has caused some fish populations to drop sharply. This does not just affect the fish being caught; it also changes the whole balance of sea life. When top predators or important smaller fish are removed, other species can grow too fast, changing the ecosystem. In areas where food is already scarce, overfishing can make these changes even worse.

Deep-sea mining

Deep-sea mining is a new threat that could harm the deep ocean. Mining looks for valuable materials on the ocean floor, which lies inside big ocean currents. Mining stirs up mud and chemicals, which can cover sea creatures and disrupt the deep sea’s delicate balance. Because deep-sea animals and plants grow and change very slowly, it may take a long time for them to recover, if they can recover at all.