Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. All over the world, the oceans are changing in profound ways. The reason is accelerating winds. Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. Like a balloon, the light warm air floats upward, leaving a slight vacuum below, which pulls in cooler, denser air from the sides. The cooler air coming into the space left by the warm air is wind. This hotter air rises up at the equator and as colder air moves in to take its place, winds begin to blow and push the ocean into waves and currents.
Wind is not the only factor that affects ocean currents. The Earth is a sphere that spins on its axis in a counterclockwise direction when seen from the North Pole.
The further towards one of the poles you move from the equator, the shorter the distance around the Earth. This means that objects on the equator move faster than objects further from the equator. While wind or an ocean current moves, the Earth is spinning underneath it. As a result, an object moving north or south along the Earth will appear to move in a curve, instead of in a straight line. Wind or water that travels toward the poles from the equator is deflected to the east, while wind or water that travels toward the equator from the poles gets bent to the west.
The Coriolis Effect bends the direction of surface currents. The third major factor that determines the direction of surface currents is the shape of ocean basins Figure When a surface current collides with land, it changes the direction of the currents. Imagine pushing the water in a bathtub towards the end of the tub. When the water reaches the edge, it has to change direction.
Figure Currents are created by wind, and their directions are determined by the Coriolis effect and the shape of ocean basins. As water in the Mediterranean evaporates, it leaves the salt behind.
This super salty ocean water then bleeds into the Atlantic via the thin mouth of the Mediterranean, also known as the Strait of Gibraltar. When cold, salty water circulates the globe and gradually becomes warmer, it begins to rise. Scientists worry that the melting ice caused by global warming may weaken the global conveyer belt by adding extra fresh water in the Arctic.
A study found that the massive ocean current that courses around the Atlantic Ocean, called the Atlantic Meridional Overturning Circulation, has decreased in strength by about 15 percent since AD and is now the weakest it has been in 1, years. Ironically, despite an overall increase in global temperatures, many places in North America and Europe may get colder as a result.
Not all currents occur at such a large scale. Individual beaches may have rip currents that are dangerous to swimmers. Rip currents are strong, narrow, seaward flows of water that extend from close to the shoreline to outside of the surf zone. Rip currents are formed when there are alongshore variations in wave breaking. In particular, rip currents tend to form in regions with less wave breaking sandwiched between regions of greater wave breaking. This can occur when there are gaps in sand bars nearshore, from structures like piers or jetties, or from natural variations in how waves are breaking.
Rip currents can move faster than an Olympic swimmer can swim, at speeds as fast as eight feet 2. At these speeds, a rip current can easily overpower a swimmer trying to return to shore. Instead of attempting to swim against the current, experts suggest not to fight it and to swim parallel to shore. Unseen by the human eye, thousands of microscopic animals hitch rides across oceans on an oceanic highway.
These animals, called zooplankton, move at the whim of ocean currents. The currents enable the young creatures to find their way to hospitable places where they grow into adults. Other ocean creatures hitch rides on currents using floating debris, like mats of seaweed, tree trunks, and even plastic. They use these havens to survive the otherwise perilous open ocean. After the tsunami that prompted the Fukushima Daiichi power plant meltdown in Japan, debris from the Japanese coast began washing ashore on the West coast of North America, bringing with it over Japanese species.
It also ensures the diversity of genetics within a population, an important factor for keeping species resistant and resilient to hardships like disease and environmental disasters. Currents also influence where large adult species can and want to go. Turtles and whales migrate annually to the plentiful waters of Georges Bank off the coast of New England, a place that is productive because of the warm waters brought north from the equator.
Sculpting seawater into crested shapes, waves move energy from one area to another. When waves crash onshore they can make a significant impact to the landscape by shifting entire islands of sand and carving out rocky coastlines.
Storm waves can even move boulders the size of cars above the high tide line, leaving a massive boulder hundreds of feet inland. Until recently, scientists attributed the placement of these rogue boulders to past tsunami damage, however, a study upended this notion by carefully recording the movement of boulders along a swath of rocky coastline in Ireland over a time period in which no tsunamis occurred.
In addition to over 1, mid-sized boulders, many reaching over tons in weight, scientists recorded the movement of a ton boulder the same weight as 90 full-sized African elephants , showing that storm waves moved it over 8 feet 2. A wave forms in a series of crests and troughs. The crests are the peak heights of the wave and the troughs are the lowest valleys.
A wave is described by its wavelength or the distance between two sequential crests or two sequential troughs , the wave period or the time it takes a wave to travel the wavelength , and the wave frequency the number of wave crests that pass by a fixed location in a given amount of time.
When a wave travels, it is passing through the water, but the water barely travels, rather it moves in a circular motion. Waves on the ocean surface are usually formed by wind.
When wind blows, it transfers the energy through friction. The faster the wind, the longer it blows, or the farther it can blow uninterrupted, the bigger the waves. Therefore, a wave's size depends on wind speed, wind duration, and the area over which the wind is blowing the fetch. This variability leads to waves of all shapes and sizes. The smallest categories of waves are ripples, growing less than one foot.
The largest waves occur where there are big expanses of open water that wind can affect. These large wave sites attract surfers, although occasionally, waves get just too big to surf. Some of the biggest waves are generated by storms like hurricanes. In , Hurricane Ivan created waves that averaged around 60 feet 18 meters high and the largest were almost feet In , hurricane Dorian also created a wave over feet high in the northern Atlantic.
To sailors, they look like walls of water. No one knows for sure what causes a rogue wave to appear, but some scientists think that they tend to form when different ocean swells reinforce one another. One was recorded by a buoy in and measured A classic tsunami wave occurs when the tectonic plates beneath the ocean slip during an earthquake. The physical shift of the plates force water up and above the average sea level by a few meters. From a single tectonic plate slip, waves radiate outwards in all directions moving away from the earthquake.
When a tsunami reaches shore, it begins to slow dramatically from contact with the bottom of the seafloor. As the leading part of the wave begins to slow, the remaining wave piles up behind it, causing the height of the wave to increase. In fact, more than 40 percent of plastic is used only once before it is thrown away, where it lingers in the environment for a long, long time.
It often breaks down into smaller and smaller particles, called microplastics, which can be ingested by both animals and people. Fortunately, there are things we can do to help—like stop using plastic bags, straws, and bottles, recycling when we can, and disposing of waste properly. Use these classroom resources to teach about ocean plastics and check back for more coming later this year!
Scientists across the globe are trying to figure out why the ocean is becoming more violent and what, if anything, can be done about it. Ocean currents, including the ocean conveyor belt, play a key role in determining how the ocean distributes heat energy throughout the planet, thereby regulating and stabilizing climate patterns.
A current is the steady, predictable movement of a fluid within a larger body of that fluid. Fluids are materials capable of flowing and easily changing shape. A gyre is a circular ocean current formed by the Earth's wind patterns and the forces created by the rotation of the planet. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Rubber Duck on the Beach A rubber duck washed up on the beach after being carried out in the ocean.
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