Icebergs make the ocean cold
Ocean currents traverse all five oceans like giant rivers. They transport huge amounts of water around the globe, similar to a conveyor belt. In doing so, they ensure an exchange of heat, oxygen and nutrients all over the world. Warm water from the equator flows towards the poles, cold water from the polar regions sinks to the sea floor and flows back to the equator. This cycle balances the temperatures in the water and on land. Icebergs, ships or rubbish can also be transported by the current.
The ocean currents are driven by the different salinity and temperature of the sea water. Where sea water freezes, salt is released. The sea water under a layer of ice is therefore particularly salty - and at the same time denser and heavier. It sinks down and pulls more water with it. At a depth of several thousand meters, the water flows back into warmer regions. There it rises again and the cycle closes.
On the surface of the water, winds also set the water in motion. The wind creates a current on the surface. This current does not move exactly in the direction of the wind, but is deflected by the Coriolis force: In the northern hemisphere, the Coriolis force directs the water to the right when viewed in the direction of the current, and to the left in the southern hemisphere. The winds are also influenced by the Coriolis force.
The various influences, such as temperature differences in the water, wind and the Coriolis force, create a pattern on the surface and in the depths of the oceans that is composed of many individual currents: a worldwide cycle, also known as the "global conveyor belt" becomes.
Environmentalists estimate that 675 tons of garbage end up in the oceans every hour. About half of it is made of plastic. The bad thing about it: The plastic doesn't simply rot like plants or paper. It can float in water for centuries.
The result can already be observed in the Northeast Pacific: a plastic carpet that is as big as Central Europe floats between California and Hawaii. Sun, wind and waves have crushed plastic bags, plastic toys and plastic bottles into tiny pieces. Currents make the sea of plastic circling: the garbage drives carousel!
The huge vortex slowly rotates clockwise. It is driven by trade winds and is actually called the North Pacific Vortex. Because it carries so much rubbish with it, it has since been given a different name by oceanographers: the Great Pacific Garbage Vortex. There is now a lot more plastic spinning around here than plankton.
This is a disaster for the environment. Fish and birds eat the often poisonous plastic soup and the pollutants get into the human food chain. Some animals die miserably on the indigestible plastic particles. But the problem is not just off the west coast of the USA. In other whirlpools - in the South Pacific, the Atlantic and the Indian Ocean - a carousel made of plastic waste turns.
All my ducklings - The cruise of the rubber animals
Yellow ducks, green frogs, blue turtles - a fleet of toy animals set sail on January 10, 1992. On that day, a Chinese ship got caught in a storm in the North Pacific and lost part of its cargo: 29,000 rubber animals. Some of them washed up after months in Alaska. Others circled in an annular current in the Pacific. A few of them even got stranded in Australia, Indonesia and Chile! The manufacturer offered a reward of 100 dollars for each rubber animal found. But not only price hunters are interested in their travel routes: marine researchers can use the ducks to see how and where ocean currents run.
The world of the oceans
To this day, many secrets lie dormant in the depths of the oceans. Large parts of the world's oceans are still completely unexplored. We even know the moon better than the deep sea. But what we do know: Almost all of the water on earth - 97.5 percent to be precise - ripples in the five oceans.
The largest of all oceans is that Pacific. Its water surface measures a total of 180 million square kilometers! It makes up about half of all ocean areas. At the same time, the deepest point on earth is located in this ocean: it descends up to 11,034 meters into the Vitja Depth in the Mariana Trench, a deep-sea trench in the western Pacific.
The Atlantic is the second largest ocean. It was formed about 150 million years ago when the supercontinent Pangea broke up. With its 106 million square kilometers, it covers a fifth of the earth's surface.
The Indian ocean is mostly in the southern hemisphere. With an area of almost 75 million square kilometers, it is a good deal smaller than the Atlantic and Pacific. Its deepest point is called Diamantina Depth, which is 8,047 below sea level.
The Southern Ocean is also called the Southern or Antarctic Ocean. It includes all marine areas south of the 60th parallel in the southern hemisphere. It is considered by seafarers to be the stormiest of all seas. The large tabular icebergs floating in its water are also typical of the Southern Ocean. They broke off the ice shelf that formed around the Antarctic continent.
That's all around the North Pole Arctic Oceanalso known as the Arctic Ocean. It is the smallest of the five oceans. About two thirds of the Arctic Ocean is covered with ice in winter. However, like the ice in the Southern Ocean, its ice cover continues to melt as a result of global warming.
Even if we live a few hundred kilometers away from them, oceans are very important to us. Their currents and the evaporation of sea water have an enormous influence on our weather. A large part of the air we breathe is also created in the world's oceans: algae that live here convert carbon dioxide into oxygen when exposed to sunlight.
How does the salt get into the sea?
Anyone who has swallowed water while bathing in the sea knows from their own experience: Sea water tastes salty. And when the water evaporates, a fine white layer of salt often sticks to the skin. This is because, on average, seawater consists of 3.5 percent salt. For one liter of sea water that is 35 grams or about one and a half heaped tablespoons of salt. But how does the salt actually get into the sea?
Many of these salts come from the rocks of the earth's crust. Rainwater dissolves salts from the rock and takes them with it. It washes them into rivers and into the groundwater. This is how salts are washed into the sea. Because relatively little salt is transported, the river water is hardly salty. Only in the sea does the concentration increase. Because there are also salts from the ocean floor and submarine volcanoes. When the sea water evaporates, all of these salts are left behind. That is why washed-out salts have been accumulating in the oceans for millions of years.
The salinity is not the same in all seas. The more water evaporates, the more salty the water becomes. The Red Sea contains more salt than the Pacific. And the Dead Sea in the Middle East - actually a lake - is so salty with a salt content of around 30 percent that you can lie in it without sinking. The Baltic Sea, on the other hand, is rather poor in salt: because of the low temperature, very little water evaporates there. In addition, many rivers flow into the inland sea and feed it with fresh water. That is why the Baltic Sea is much less salty than the Dead Sea.
Where do icebergs come from?
Although icebergs float in the sea, they are not made of frozen sea water, but of fresh water. Because they come from the huge glaciers of the polar regions. The polar glaciers protrude into the sea at the edges. Pieces of them break off regularly - the icebergs. It is also said that the glacier “calves”. And because ice is lighter than water, it drifts around in the sea without sinking.
The polar seas are cold between –4 and 0 degrees Celsius. That is why the icebergs only thaw very slowly. When the current drives them into warmer waters, they melt a little faster. Nevertheless, large icebergs grow to be decades old.
Some icebergs are huge and flat: the tabletop icebergs. They arise when the glaciers on the coast slide far out into the sea. Then large ice sheets float on the sea, but they are still connected to the glacier. This “ice shelf” can be between 200 and 1,000 meters thick. The largest areas of ice shelf are in Antarctica, on the coasts of Greenland and Alaska. When large pieces of ice break off, they swim out into the polar sea as tabular icebergs.
Icebergs are very dangerous for shipping because only their tip is visible above water. Most of the iceberg is underwater. Ships must keep a sufficiently large safe distance from the white giants so that they are not damaged by the sharp edges of the iceberg.
But there is also ice that freezes from sea water: First, ice floes from salt water form on the surface of the water. When these ice floes are pushed together, a coherent ice sheet is created - the pack ice.
The first seafarers to cross the Atlantic were puzzled on their return: Why was their ship faster on the route from America to Europe than the other way around? Today we know the solution: a sea current in the North Atlantic propelled the ship on its way to Europe - the Gulf Stream.
The Gulf Stream is a powerful ocean current in the Atlantic. It is up to 200 kilometers wide. The amount of water that it transports exceeds the amount of water that flows into the sea from all the rivers on earth by more than a hundred times. The Gulf Stream is fed by warm ocean currents near the equator. The Gulf Stream begins north of the Bahamas. From here it initially moves over 1,000 kilometers north along the American east coast.
Westerly winds and Coriolis force force the current northeast at North Carolina level. On its way towards Europe, the Gulf Stream continues to lose speed. It no longer moves in a dead straight line, but meanders forward. Parts of the stream split off and flow back. The ice-cold Labrador Current finally gets in his way from the north; the Gulf Stream continues to lose strength and heat. Evaporation increases the salt content and density of the water until the Gulf Stream finally descends east of Greenland. Parts of its water masses flow from here as deep currents in the direction of the South Atlantic and Indian Ocean.
The Gulf Stream is very important for Europe: it acts like central heating on our climate. Without its warmth, the winters in Western and Central Europe would be much harder. It is only because of him that ports in Northern Europe are ice-free all year round - except on the Baltic Sea, where the current does not reach. We owe even the fact that palm trees and lemon trees thrive on England's south-west coast to the mighty and warm Gulf Stream.
What is the Coriolis Force?
Airplanes flying from New York to Frankfurt have a lot of tailwind. The wind that drives them blows from west to east at a height of about 10 kilometers. Jetstream is the name of this strong air current that can reach speeds of up to 500 km / h. Their direction is the result of the so-called Coriolis force.
It is named after the French scientist Gaspard Gustave de Coriolis, who was the first to examine it mathematically in 1835. The cause of the Coriolis force is the rotation of the earth around its own axis: At the equator, the earth rotates at 1670 kilometers per hour to the east; in the direction of the poles, the speed continues to decrease. When air masses flow from the equator to the North Pole, they take the momentum to the east and then move faster than the earth's surface. Viewed from the surface of the earth, it looks as if they are diverted from their north course to the east - i.e. to the right. Conversely, air masses that flow from the pole to the equator are overtaken by the surface of the earth, so they are deflected on their southward course to the west - also to the right.
On the way to the South Pole, the directions are reversed: Air masses on the way to the Pole are diverted from their south course to the east, i.e. to the left - just like the air masses on the north course towards the equator, which are diverted to the west. So the Coriolis force leads to a right deflection in the northern hemisphere and a left deflection in the southern hemisphere, the stronger the closer you get to the poles.
In this way the Coriolis force influences the global wind system, the great air currents on earth. It therefore has a major influence on the weather: In our latitudes, for example, the air flows towards the North Pole and is therefore deflected to the east. With us, the wind mostly comes from the west, from the Atlantic, and therefore brings more humid air with moderate temperatures. The jet streams also owe their direction to the Coriolis force.
Even tropical cyclones several 100 kilometers in diameter are created with the help of the Coriolis force. Because through them, hot, humid air begins to rotate until it grows into a destructive vortex. The Coriolis force not only affects large air masses, it also deflects ocean currents. This explains why the warm Gulf Stream drifts to the right on its way north and heats large parts of Northern Europe.
The global wind system
The air masses of the atmosphere flow around the globe: They rise and fall, meet and mix. However, this does not happen wildly, but the winds follow a very specific pattern. This global wind system (also called planetary circulation) is influenced primarily by radiation from the sun and by the Coriolis force.
The tireless cycle of air begins at the equator, where warm air rises constantly. A whole chain of low pressure areas, the so-called equatorial low pressure trough, forms on the ground. The ascended air moves at a great height towards the poles. Because it cools down on the way, it sinks again in the subtropics at about 30 ° north and south latitudes and flows back on the ground as a trade wind towards the equator. The entire wind cycle around the equator was described by the English scientist George Hadley as early as 1753 and is therefore called the "Hadley cell". (Meteorologists call a "cell" a circular flow of air.)
Air masses also circulate around the poles and form the two “polar cells”: Because cold air sinks to the ground at the pole, a high pressure area is created at this point. From here, cold air flows on the ground towards the equator. As soon as this air mass has warmed up sufficiently, it rises again: A whole series of lows arise around the 60th parallel, the subpolar low pressure trough. The air that rises here flows back up to the pole.
Between the polar cell and the Hadley cell, roughly between the 30th and 60th degrees of latitude, the air masses of the polar regions and the Passat Zone meet: this is where the third large wind cell has spread. It is also called the "Ferrel cell" after its discoverer, the American William Ferrel. Because cold and warm air masses meet in this region, the weather here is often changeable and rainy, which we know well in Central Europe. The wind comes predominantly from the west. That is why the region between the 40th and 60th parallel is called the west wind zone in Europe. The wind also comes from the west at high altitudes: At the border to the polar cell, strong high-altitude winds flow that are turned by the Coriolis force and directed to the east - the so-called jet streams.
So three major wind cycles have built up on each hemisphere: the Hadley cell, the Ferrel cell and the polar cell. Why there are just three is related to the speed of the earth's rotation. What would happen if the earth rotated much more slowly can be simulated with the computer: Then the warm air would simply rise at the equator, cool down at the pole and flow back on the ground. There would only be one large wind cell in each hemisphere. However, the faster the earth is rotated in the computer model, the more wind cells split off. When simulating the actual rotational speed of the earth, the computer also comes to the conclusion that there are exactly three large wind cells in each hemisphere.
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