Ocean currents are mainly caused by the wind, the rotation of the Earth, and differences in temperature and salinity of the water in the oceans.
The Earth constantly rotates on itself, and this has consequences for the oceans. Due to this rotation, a force called Coriolis force emerges. This force deflects water movements: to the right in the northern hemisphere and to the left in the southern hemisphere. The oceans do not follow a simple straight path, but rather take curved trajectories. Specifically, this force helps create large circulation systems called oceanic gyres, which permanently shape ocean currents.
The wind blows across the surface of the oceans and creates what are called surface currents. These currents carry the water with them, much like when you blow on a cup of coffee to move the foam on the surface. The phenomenon extends to about 100 meters deep. The large, regular winds, such as the trade winds or westerlies, create vast, consistent, and well-organized movements at the surface of the oceans. Because of the Earth's rotation, French currents do not go straight; instead, they take a slightly deviated path. This phenomenon is called the Coriolis force. This is how large oceanic whirlpools, or gyres, are born, mixing the water over thousands of kilometers.
The temperature and salinity make seawater more or less dense, which causes significant movements in the oceans. Warm water, being lighter, stays on the surface, while cold water, being heavier, sinks to the depths. The same goes for salinity: very salty water is denser, so it sinks, whereas fresh or less salty water floats above. The combination of these differences creates a permanent circulation known as thermohaline circulation, comparable to a gigantic conveyor belt that stirs the oceans worldwide. This circulation greatly influences the global climate, as it transports heat, oxygen, and nutrients over long distances across the oceans, directly affecting marine environments and even our weather.
The tides we observe every day are mainly caused by the gravitational attraction of the Moon (and also a bit of the Sun). As water constantly moves, it deforms, forming "humps," creating daily rises and falls in sea level. As they move, these masses of water generate regular currents, which primarily influence the seas close to the coasts or straits. Some areas of the globe even experience very strong currents, known as tidal currents, capable of transporting significant amounts of sediments and nutrients essential to marine ecosystems. Ultimately, alongside the large ocean currents caused by other phenomena, the effect of the tide may not be gigantic on a global scale, but it remains essential near the coasts, even shaping local marine life.
Continents act as barriers that redirect and shape the path of ocean currents. For example, when water encounters a landmass, it changes direction, creating loops called gyres. The particular position of South America strongly influences the powerful ocean current known as the Antarctic Circumpolar Current, which quietly circles Antarctica precisely because it has no continent in its way. In contrast, the narrowness of certain passages between continents causes impressive accelerations, such as that observed at the Strait of Gibraltar. Without continents positioned as they are, ocean currents would certainly look very different.
El Niño and La Niña are periodic oceanic phenomena related to variations in ocean currents in the equatorial Pacific Ocean. They can affect climates and weather conditions around the world, causing droughts or heavy rainfall.
The Gulf Stream, a warm ocean current located in the Atlantic Ocean, carries an estimated amount of water about 100 times greater than all the rivers in the world combined! It is thanks to this powerful current that Europe enjoys a temperate climate.
Some ocean currents form gigantic whirlpools called gyres. In the North Pacific Ocean, the Great Pacific Garbage Patch, an accumulation of plastic waste, has formed precisely in such a gyre area.
The Antarctic Ocean is traversed by the Antarctic Circumpolar Current, the only ocean current that flows freely all around the globe without interruption by continents. It plays a major role in global climate regulation.
Surface currents are primarily generated by wind and influenced by the rotation of the Earth; they are found in the upper layers of the ocean. In contrast, deep currents are mainly caused by differences in temperature and salinity; they form at the poles and circulate slowly at the bottom of the oceans.
The Antarctic Circumpolar Current (ACC), also known as the westerly winds current, is considered the most powerful ocean current in the world. It completely encircles Antarctica and plays a critical role in global thermal regulation.
Ocean currents influence the distribution of nutrients, organisms, and temperatures in the ocean. They promote the mixing of nutrient-rich waters to the surface, allowing marine ecosystems to thrive and affecting the migrations of marine species.
Indirectly, human activities such as greenhouse gas emissions influencing climate change can affect ocean currents. For example, increased melting of polar ice alters the density and salinity of the oceans, potentially disrupting global ocean circulation.
Yes, ocean currents play a major role in regulating the climate by transporting warm and cold waters around the globe. For example, the Gulf Stream helps to temper the climate in Western Europe by bringing warm water from the Caribbean.
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