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The ocean conveyor belt

Professor Keith Hunter, of the University of Otago, explains how the ocean links several Earth systems, and is like a vast biological, chemical and geological factory. Huge currents act like conveyor belts carrying heat and material around the world.


The most important new idea that we've come up with in the last 20 or 30 years is that you can't look at things like the physics of the ocean, the chemistry of the ocean, the biology of the ocean as separate things that happen. They are all really closely interlinked. And so we think of the earth as a system. We have even coined a new phrase for it - we called it biogeochemistry, and that represents the idea that the biology, the geology, and the chemistry of the ocean are all intimately linked together.

All the oceans of the world are connected together, and we call it the global ocean amongst our scientists. We know they are connected by these currents, and we understand very well now how water, and the things that the water carries move from one basin to the other.

In a very crude sense, we talk about the North Atlantic Ocean being the start of a conveyor belt that transports water and things along, and so the water comes from the North Atlantic and goes down the Atlantic Ocean, where it mixes up again in the region of Antarctica, and then it sets off going around at high latitude in the Southern Ocean, going through the Indian Ocean and finally ending up in the Pacific. So the north of the Pacific Ocean is the other end of a long conveyor belt, just like a conveyor belt in an airport where you've got suitcases moving along. That's the way we picture the ocean. So there is a beginning and an end. You can imagine if something floating in that submarine river would take about 2,000 years to get from the Atlantic to the Pacific.

The sun controls the Earth's temperature - it's the only source of energy to speak of - so that in the beginning of the conveyor belt where you have got the North Atlantic, you are talking about an area that is covered by winds that blow across Northern Canada, which is one of the coldest parts on Earth, and so that is what cools the seawater down. That makes it colder, and more dense or heavier, and then the gravity takes over. And that drives the start if you like of the conveyor belt.

But there is a bit at the other end as well, because as the water in the North Atlantic sinks down, it's got to be replaced by other water, and that water is coming up from the Gulf of Mexico where you get the opposite thing happening. The sun is heating up the water and making it less dense, and forcing it to float on the top. And so a current of warm water heads off from the Gulf of Mexico to replace the cold water that’s falling down, and that current of warm water is called the Gulf Stream, and it's responsible for making the whole of Western Europe have a much warmer climate than it would have.

So we have this ocean circulation system - the ocean conveyor belt carries the nutrients, the chemical ingredients that are necessary for biological life, and those ingredients are put where they are by biology to suit themselves. So it’s a system of... if you like, the ocean is a fantastic biological, chemical, geological factory that is operating with all these systems. It's got 100 % recycling efficiency. If you look at it as an engineering factory, it is superbly designed.

NASA/Goddard Space Flight Centre Scientific Visualization Studio/courtesy of nasaimages.org.
Dr Sylvia Sander