Moving the Waters - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 99

The mass of surface water is moving. Partly, the water mass is
pushed by the arrival of other water masses, mostly from off the coast
of Africa. Much later on in the journey it will be pulled from the
north. Mainly, here, it is being dragged by winds.
The winds first keep the water pushed against the coastline of
Florida and then the eastern seaboard of the US. The water here is
moving north at nearly 10 kilometres per hour—about twice human
walking speed. Somewhere off Cape Hatteras it begins to cross the
ocean, as the winds begin to blow mainly to the east. At this point it
forms part of one of the most spectacular migrations on the planet.
The water here forms a river about a hundred kilometres wide and
a kilometre deep, carrying some 150 million cubic metres of water
per second—that is 150 sverdrups—on a journey across the Atlantic.
This is the Gulf Stream, essentially as mapped and codified by Ben-
jamin Franklin. That water is, incidentally, carrying with it enough
heat to supply current human energy needs 100 times over, if it
could be tapped. Even without active exploitation, it keeps north-
west Europe warm.
Once the Gulf Stream has arrived in the seas around Iceland and
Greenland, its heat given up to warm these cold northerly lands, it
begins to chill and sink—and so the great journey, where we started,
begins once more. For now, this great current system is a constant
part of the Earth's geophysiology. It was not always so—and it will
likely not be with us forever in the future.
Rerouting Ocean Currents
The world's ocean currents—far larger than any rivers—seem sol-
idly fixed, as permanent as the landmasses that adjoin them. Take
the mighty Gulf Stream for instance (Fig. 9). The heat it trans-
ports—almost 1.5 petawatts—dwarfs that produced by human
activity, and ultimately helps keep north-west Europe pleasantly