81
T
he warm Gulf Stream current
that flows eastward across
the North Atlantic Ocean
is one of the greatest movements
of water on Earth. It is driven
east by prevailing westerly winds,
and is part of a great loop that
then recrosses the Atlantic to the
Caribbean. The current had been
known since 1513, when Spanish
explorer Juan Ponce de León found
his ship moving back north off
Florida despite winds blowing him
south. But it was only properly
charted in 1770, by US statesman
and scientist Benjamin Franklin.Local advantage
As deputy postmaster of the British
American colonies, Franklin was
fascinated by why it took British
packet ships delivering mail two
weeks longer to cross the Atlantic
than American merchant ships.
Already famous for his invention of
the lightning conductor, he asked
Nantucket whaling captain Timothy
Folger why this might be. Folger
explained that American captains
knew of the west–east current. Theycould spot it by whale migrations,
differences in temperature and color,
and the speed of surface bubbles,
and so they crossed over the current
to escape it, while the westbound
British packet ships battled against
it all the way.
With Folger’s aid, Franklin
charted the current’s course as it
flowed along the east coast of North
America from the Gulf of Mexico to
Newfoundland and then streamed
east across the Atlantic. He also
gave the Gulf Stream its name. ■EXPANDING HORIZONS
A STRONG CURRENT
COMES OUT OF THE
GULF OF FLORIDA
BENJAMIN FRANKLIN (1706–1790)
IN CONTEXT
BRANCH
Oceanography
BEFORE
c.2000 BCE Polynesian
seafarers use ocean currents to
cross between Pacific islands.
1513 Juan Ponce de Léon
is the first to describe the
strong currents of the Atlantic
Ocean’s Gulf Stream.
AFTER
1847 US naval officer Matthew
Maury publishes his chart of
winds and currents, compiled
by studying ships’ logs and
charts in naval archives.
1881 Prince Albert I of
Monaco realizes that the Gulf
Stream is a gyre (loop) and
splits in two—one branch
flowing north toward the
British Isles, and the other
south to Spain and Africa.
1942 Norwegian
oceanographer Harald
Sverdrup develops a theory
of general ocean circulation.
Franklin’s chart was published in
1770 in Britain, but it would be years
before British captains learned to use
the Gulf Stream to cut sailing times.See also: George Hadley 80 ■ Gaspard-Gustave de Coriolis 126 ■
Robert FitzRoy 150–55