Geoscience Reference
In-Depth Information
fig. 9. NASA reconstruction of the Gulf Stream and eddies coming off the
main currents. Warm water from the Gulf of Mexico flows along the eastern
coast of North America before it diverts across the North Atlantic at Cape
Hatteras.
warm. Something that large must be a permanent part of our
planet's machinery, surely?
It turns out that switching an ocean current on or off, or rerouting
it, is geologically commonplace. One way to do it is with truly geo-
logical slowness—for instance, as oceans change their shape and con-
tinents shift, come into contact with each other, and move apart. The
coming together of the Americas, with the rise above sea level of the
Panama isthmus, is a classic example. This growing strip of land throt-
tled back, and then cut off, the broadly circumequatorial current that
used to flow between the north and south Americas, with conse-
quences that might—via a chain of knock-on effects—have encour-
aged ice to grow in the far north, and hence plunge the world into an
ice age.
Another means is more subtle, but just as effective—and often far
quicker. One can keep the geometrical shape of the ocean basins the
same, but alter the composition of the water within them. This has
been a recurrent pattern in the North Atlantic, and its history is
written in ice.
The ice layers that, year by year, have covered Greenland with its
3-kilometre-thick carapace of ice have preserved within them a finely
Search WWH ::




Custom Search