Text: The ocean currents and sea currents are called the oceanic circulation and they are driven in 2 ways. The first reason is that the ocean currents on the surface are driven by the wind. The other drive is the thermohaline circulation, which will be discussed first. Thermohaline circulation means that the sea currents are driven by density differences of the water caused by temperature differences and differences in salinity. Thermo refers to temperature and halien refers to salinity. First of all, remember the following two rules: - Cold water has a higher density than warm water and sinks to the bottom - Salt water has a higher density than fresh water and sinks to the bottom Seawater warms up at the equator. Then it flows towards the North Pole. Along the way, the ocean current emits a lot of heat, which warms the atmosphere, but cooling the water itself. Also, a lot of water also evaporates, but the salt remains behind. When seawater freezes and forms sea ice, the salt also remains in the seawater. In short: The density of the water is therefore increasing. Eventually this water sinks and forms deep water, causing oceanic circulation which is also called the ocean conveyer belt. The second driver of ocean currents is the wind. Just north of 30 degrees north latitude there is a westerly wind. The seawater on the surface is blown along, but due to the Coriolis effect, it deviates to the right, seen from the direction of flow. There it is influenced by the easterly trade winds, the wind currents from 30 degrees north latitude to the equator. This creates an circular ocean current also called a gyre. In this way, 2 gyres are formed in the Northern Hemisphere: those in the Atlantic Ocean and those in the Pacific Ocean. These rotate clockwise. In the southern hemisphere, the same happens, but in the opposite direction: The west wind south of 30 degrees south latitude causes the sea to flow to the east. The sea moves to the left and then follows the trade winds from the east, turning the gyres counterclockwise in the southern hemisphere. In the southern hemisphere are 3 gyres; In the atlantic and pacific oceans and also in the indian oceans. Much plastic that ends up in the oceans is carried along by the current and ends up in the gyres, where it can no longer escape due to the circular movement, and the plastic becomes fairly concentrated in a few locations. Ocean currents flowing from the equator are heated and are called warm ocean currents and generally flow along the eastern coasts of continents. Because warm water evaporates more easily, it can also rain. Thus, the east coasts of many continents often receive more precipitation than the west coasts, where there are cold ocean currents. Warm sea currents emit a lot of heat. Warm water is moved from the Gulf of Mexico to Western Europe. This warm ocean current is called the Gulf Stream. The Gulf Stream makes Western Europe much warmer than other places at the same latitude. The North Pole also receives a lot of energy in this way. Without the ocean currents, much less heat would be moved from the equator towards the North Pole and it would therefore be much colder at the North Pole. If there were no ocean currents, the heat would not be removed from the equator and it would become warmer at the equator. Around Antarctica flows the seawater in a large circle. This is called the Antarctic circumpolar current. This current prevents warm water to reach Antarctica, causing it to cool much further than the North Pole. In short, oceanic circulation is driven by differences in temperature and salinity and by wind currents, and oceanic circulation has a major impact on temperature and precipitation in coastal areas.

• published: 08 Nov 2021
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