The rubbish in the sea goes on a merry-go-roundGeology and Geography
Every hour, 675 tonnes of rubbish end up in the world’s oceans, environmentalists estimate. About half of this is plastic. The bad thing about it is that the plastic does not simply rot like plants or paper. It can float in the water for centuries.
The result can already be observed in the Northeast Pacific: Between California and Hawaii, a carpet of plastic the size of Central Europe is floating. Sun, wind and waves have ground plastic bags, plastic toys and plastic bottles into tiny pieces. Currents make the sea of plastic gyrate: The rubbish goes on a merry-go-round!
The huge vortex rotates slowly in a clockwise direction. It is driven by trade winds and is actually called the North Pacific Gyre. Because it carries so much rubbish, however, oceanographers have since given it another name: the Great Pacific Garbage Vortex. In the meantime, there is much more plastic than plankton.
This is a disaster for the environment. Fish and birds eat the often toxic plastic soup and the pollutants get into the human food chain. Some animals die miserably from the indigestible plastic particles. But the problem is not only off the west coast of the USA. A merry-go-round of plastic waste is also spinning in other ocean eddies – in the South Pacific, the Atlantic and the Indian Ocean.
All My Ducklings – The Cruise of the Rubber Animals
Yellow ducks, green frogs, blue turtles – on 10 January 1992, a fleet of toy animals set sail. On that day, a Chinese ship was caught in a storm in the North Pacific and lost part of its cargo: 29,000 rubber animals. Some of them washed up in Alaska months later. Others circled on a ring current in the Pacific.
A few of them even stranded in Australia, Indonesia and Chile! The manufacturer offered a reward of 100 dollars for each rubber animal found. But it is not only prize hunters who are interested in their travel routes: marine researchers can recognise from the duck finds how and where ocean currents run.
Like huge rivers, ocean currents cross all five oceans. They transport enormous masses of water around the globe, similar to a conveyor belt. In this way, they ensure an exchange of heat, oxygen and nutrients all over the earth. Warm water from the equator flows towards the poles, cold water from the polar regions sinks to the ocean 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.
Ocean currents are driven by the different salinity and temperature of seawater. Where seawater freezes, salt is released. The seawater under a layer of ice is therefore particularly salty – and at the same time denser and heavier. It sinks to the bottom, dragging other masses of water with it. At a depth of several thousand metres, the water flows back into warmer regions. There it rises again and the cycle closes.
At the water surface, additional winds set the water in motion. The wind causes 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 steers the water to the right, as seen in the direction of the current, and in the southern hemisphere it steers it to the left. Winds are also influenced by the Coriolis force.
The various influences, such as temperature differences of the water, wind and the Coriolis force, create a pattern at the surface and in the depths of the oceans that is made up of many individual currents: a worldwide cycle that is also called the “global conveyor belt”.
The world of the oceans
Many secrets still 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. What we do know, however: Almost all the water on this earth – 97.5 per cent to be exact – laps in the five oceans.
The largest of all oceans is the Pacific. Its water surface measures a total of 180 million square kilometres! This means that it accounts for about half of all ocean surfaces. At the same time, this world ocean is home to the deepest place on earth: it descends up to 11,034 metres into the Witja Deep in the Mariana Trench, a deep-sea trench in the western Pacific.
The Atlantic Ocean is the second largest ocean. It was formed about 150 million years ago when the primeval continent of Pangaea broke apart. With its 106 million square kilometres, it covers one fifth of the earth’s surface.
Most of the Indian Ocean lies in the southern hemisphere. With an area of just under 75 million square kilometres, it is a good deal smaller than the Atlantic and Pacific Oceans. Its deepest point is called the Diamond Low, which lies 8,047 below sea level.
The Southern Ocean is also called the Southern or Antarctic Ocean. It includes all sea areas south of the 60th parallel in the southern hemisphere. Sailors consider it the stormiest of all seas. Typical of the Southern Ocean are also the large tabular icebergs that float in its waters. They have broken off from the ice shelf that has formed around the Antarctic continent.
Around the North Pole lies the Arctic Ocean, also 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. But its ice cover, like the ice of the Southern Ocean, continues to melt due to global warming.
Even if we live several hundred kilometres away from them: Oceans are of great importance to us. Their currents and the evaporation of seawater have an enormous influence on our weather. A large part of the air we breathe is also produced in the oceans: Algae that live here convert carbon dioxide into oxygen when exposed to sunlight.
Oil spill in the Gulf of Mexico
A fortnight ago, the oil rig “Deepwater Horizon” exploded in the Gulf of Mexico. Since then, millions of litres of crude oil have been leaking into the sea every day. The viscous soup now threatens the coasts in the southeast of the USA in particular. The damage to the environment can hardly be estimated.
On 20 April, the Deepwater Horizon oil platform caught fire and sank two days later. Eleven workers were killed in the explosion, 115 could be rescued. What threatens after this disaster is a devastating oil spill in the Gulf of Mexico. For days, diving robots have been trying to seal the leaks at a depth of 15,000 metres.
But all attempts to stop the escaping crude oil have failed so far. Efforts to prevent the oil spill from spreading also failed to achieve the desired success. High swells, for example, hindered the deployment of floating barriers to contain the spreading oil slick: The oil continues to drift towards the coast. A state of emergency has already been declared in the US states of Louisiana, Mississippi, Florida and Alabama.
Experts expect billions of dollars in damage. About half of the sum will have to be used to clean up the polluted coasts. Huge losses in tourism and fishing are also expected.
The danger of deep-sea drilling
Just a hundred years ago, rich oil deposits were comparatively easy to discover and the oil was easy to extract. Today, however, many of these oil wells have already been exploited. But because our energy needs are constantly increasing, oil fields that are difficult to access are now also being developed. These include oil deposits in the deep sea, which lie at depths of more than 500 metres. In order to reach the oil, floating drilling platforms are set up.
Raw material is extracted from these drilling platforms – also called “offshore extraction”. This type of oil extraction, however, involves a great deal of effort and carries high risks, as the Deepwater Horizon accident showed. But as long as demand continues to rise, oil must be sought ever deeper – now at depths of up to 3,000 metres.
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