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Ocean currents
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The winds blowing over the surface of the ocean cause the water to move in __________
Poor Philip! How did he end up on a deserted island in the middle of the sea? He needs to get home, but how? He doesn’t have a phone, but he has a pencil, some paper, a glass bottle - and a brilliant idea! He decides to write a message asking for help, and put it in the bottle.
Then he has to throw the bottle into the sea, as far as he can. Hopefully someone will find it and come and save him. It’s a few days later and Philip is losing hope. Look, a boat! They found Philip’s message.
He’s saved! But how did that message get to the people on the boat? The water in the sea is constantly moving, and a stream of water must have carried the bottle to another island! Such streams flow continuously from one place to another, just like rivers on land. They are OCEAN CURRENTS.
Ocean currents are driven by the wind, the rotation of the Earth, the temperature, and the amount of salt in the water. Winds blow over the surface of the ocean, causing the water to move in the same direction as the wind. The wind moves the top layer of water, and the top layer then drags some of the lower layers along with it. This type of movement in the ocean is a SURFACE CURRENT. Because of the rotation of the Earth, surface currents flow in very specific ways.
They flow clockwise in the Northern Hemisphere, and anticlockwise in the Southern Hemisphere. But, surface currents aren’t the only currents; there are some that run much deeper below the surface! We call these DEEP OCEAN CURRENTS. [But] What keeps the water in deep ocean currents moving? It’s mostly the difference in temperature, and the amount of salt in the water, with some help from the wind, and the rotation of the Earth! Let’s look at the Gulf Stream as an example.
The Gulf Stream starts in the Gulf of Mexico. The water there is very warm, and because of that, it rises to the surface. Once at the surface, this water is directed by the wind and the rotation of the Earth towards Europe. When the stream reaches Europe it travels north, where the warm water loses much of its heat into the air, and also some of the water evaporates, leaving the salt behind. Together, this makes the water both colder and saltier.
Low temperature and high salt content makes the water much heavier. This causes it to plunge down to the bottom of the Atlantic Ocean, creating the world’s highest underwater waterfall: 3505 metres high! This waterfall is continuously pulling more water which is flowing north from the Gulf of Mexico, creating a constant stream stretching across the globe. By moving masses of warm and cold water from one place to another, currents affect the climate and marine ecosystems all around the planet. It’s very lucky for Philip that we have ocean currents, because he is now on his way home.