8.5.1: Ocean Currents

At the beginning of this Chapter, we listed two more ocean sources from which energy can be harvested. One of them are ocean currents. Not tidal currents we have already talked about – those flowing forth and back in the same rhythm as the tides around the globe. But there are also permanent current always flowing in the same direction. The most famous of them is perhaps the warm Gulf Current, which emerges from the Gulf of Mexico, flows along the coast of North America, then traverses the Atlantic and flows along the coasts of Europe.

Figure \(\PageIndex{1}\): An interesting map of global currents, prepared in 1943 for the US Navy (source: Wikimedia Commons).

Another current we Oregonians should all know is the cold Alaska Cur- rent, flowing along the US West Coast. Because of this current, the Oregon beaches are not crowded even at the hottest summer days. Compare Oregon beaches with those in Croatia, a Mediterranean country at about the same latitude as Oregon, and with its coast famous for its beauty, at places looking like “Oregon’s twin coast”. And please click on this and see what happens at Croatian beaches where there is easy access to water!

So, one can see that a cold current can significantly influence the climate at the coast. But at the coast only? Think of the Corvallis and the whole Willamette Valley: the summers are mild, with not too many really hot days. Think of what’s going on at the same latitude East Coast.

Then, in Pacific Northwest we experience the cooling effect of Alaska Cur- rent. Then we can expect that a warm current should have an opposite effect, right? And it’s indeed what happens. In Europe, countries located close to the Atlantic Coast benefit from the warming effect of the Gulf Stream. Especially, Scandinavian countries. Take, for example cities at the Norwegian ocean coast, and cities (well, settlements...) at the western coast of Greenland, where there is no Gulf Stream. One can find “pairs” which have a very similar latitude: for instance, Narvik, Norway, and Rodebay, Greenland – the average winter temperature in the latter is about 6^◦C lower. Well, six degrees Celsius (over 10 degrees Fahrenheit) makes a big difference.

The Gulf Stream, because of its width ( 100 km), depth (800 to 1200 m) and speed (about 2,5 m/s at the surface) carries an enormous amount of energy. So, it may be tempting idea to extract some of it. For instance, good conditions for extracting energy from the Gulf Stream do exist at the coasts of Florida. The ocean over there is not very deep, one can install turbines at the bottom, exactly the same way as can be done with tidal stream turbines, discussed in the preceding Section. And in contrast to tidal streams, which flow one way, than pause, then the other way, than pause, and so on – the Gulf Stream flows with a constant power 24 hours/day. So, much more convenient than with tidal streams, isn’t it? According to some estimates, the power harnessed from the Gulf Stream could easily supply 50% of the power consumed in all Florida State...

Nice and tempting? Perhaps. But the Author of this text categorically refuses to discuss it any further. In the Author’s opinion, playing with permanent ocean currents may have far-reaching and dangerous consequences. Why? Because we still don’t know exactly what is the “motor” propelling those currents. We know that it’s principally a “thermal engine”, fueled by solar power and wind power (which, in turn, also is converted solar power). Water warmed up by Sun expands in volume, so some part of it has to flow away. Well, it can not flow away permanently, it must be substituted by cold water from the depths. And, indeed, in addition to surface currents, there are also deep water currents flowing in opposite directions.

Presently, at the best, we have only what physicists call a “qualitative understanding” (and students usually call a “conceptual understanding”) of the motors setting all those currents in motion. We are not able to say what may happen if we start extracting energy from the Gulf Stream near the coasts of North America. Are we sure that nothing wrong is going to happen to the path of the Stream several thousand miles away? To the part flowing along the coasts of Scandinavia? As long as we don’t have comprehensive quantitative model of global ocean currents, enabling one to calculate the effects of any “human intervention” into the power of the currents, it certainly better not to try meddling into the forces of nature that keep the current running. How do we know that they are not sensitive to “stealing” some power from them? Europe would never forgive America if some irresponsible experimenting “switched off” the heat the Gulf Stream has been delivering to it for many thousands of years.

Well, one can ask, if the Author is so strongly against harnessing the power of Gulf Stream and other major global ocean currents, why doesn’t he oppose exploiting tidal currents? Here, the answer is easy. The mechanism propelling the tidal streams are pretty well understood. And every tidal stream is not a global, but a local phenomenon. Such currents never flow very far: with the speed of 2 m/s, like the stream in the Cook Strait, the water flows perhaps 10 miles during the high tide, then 10 miles the other way during the low tide, and so on. And during each such cycle the streams dissipate their energy, due to friction, erosion, creation of waves, etc. If some part of the energy were not extracted by turbines, it would be lost anyway.