Monday, August 10, 2009

Follow the Water

My latest research sidetrack has come in the form of water analysis. Dallas Murphy's interesting account of the work of oceanography, To Follow The Water, has many interesting things to say about the movement of water. He points out that the Gulf Stream causes something like 36 Sverdrup units to go northward from the Caribbean region to the North Atlantic, keeping Europe warm and preventing an Ice Age. A Sverdrup unit is one million cubic metres of water per second. It's an awe-inspiring figure.

More to the point, while we can measure the large movements, the currents and vortices, they still remain susceptible to chaos at the local level. In late 2004, the meridional overturning circulation (in which cooling high-density salt water sinks and less-dense salt water rises in the ocean) appeared to have slowed for a while. Headlines saying that the Gulf Stream had stopped sprouted like a virulent disease. Of course, if the Gulf Stream really had stopped, we'd all be in serious trouble.

All the major oceans have these huge currents, one cycle in each hemisphere, with branches. If these currents were rivers, they'd be really huge rivers. The Gulf Stream is about 100 km wide and 1.2 km deep. It transports 1.4 petawatts of heat; that's a million billion joules per second and is about 100 times the energy consumption of the entire human race. If only we could tap it!

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