Geoscience Reference
In-Depth Information
That extraordinary eighteenth-century politician, postmaster,
printer, author, inventor, satirist, musician, civic activist, diplomat,
and scientist Benjamin Franklin—a man with such a wide reach that
he was called the most accomplished American of his age—realized
from these measurements that something was stirring in those depths.
If the ocean was still, the Sun's heat would slowly reach through to
the ocean depths, and warm them through to the ocean floor. He
realized that, therefore, they could not be still. The cold deep water
must have travelled across as a submerged current from the far polar
regions.
He pondered the question of the mysteriously variable transatlan-
tic crossing times, too, interrogating experienced ships' captains
about the courses they took, about which voyages were fast and which
were slow. He found out enough to plot on a map of the Atlantic a
mass of water that continually flowed across this ocean from west to
east, creating an adverse current of some 5 kilometres an hour to
those who tried to sail against it. He called it the Gulf Stream. His
map—even though he reprinted it a couple of times—was ignored
virtually completely, as was, for a long time, his advice to ships' cap-
tains on how best to steer a path around the current. This did not
dampen Franklin's innovative spirits in oceanography. Late in his life
he published a series of novel ideas on ship design, including a soup
bowl designed to keep stable in rough seas. Creature comforts, he
knew, were important in a sailor's life.
What, though, was driving the ocean currents that were the object
of his curiosity?
Driving the Currents
The prime driver of this movement is, one way or another, the Sun.
Some 174 petawatts of energy continually shine down on the Earth.
A petawatt is one of those words that give little sense of its meaning,
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