Page 61 - (DK) Ocean - The Definitive Visual Guide

SURFACE CURRENTS 59

PEOPLE
BENJAMIN FRANKLIN

The American statesman and
inventor Benjamin Franklin
(1706–90) made one of the
earliest studies of an ocean
current, publishing a map of the
Gulf Stream’s course. He became
interested in it after the British
postal authorities asked him why
American postal ships crossed the
Atlantic faster than English ships.
The answer was that American
ships were utilizing an eastward
extension of the Gulf Stream.

Boundary Currents

The currents at the edges of gyres are called boundary currents. Those on
the western side of gyres are strong, narrow, and warm—they move heat
energy away from the equator. Examples of these currents are the Gulf
Stream and the Brazil Current in the southwestern Atlantic.
Eastern boundary currents are weaker, broader cold currents
that move water back toward the tropics. Examples are the
Benguela Current off southwest Africa and the California
Current. At the gyre boundaries close to the equator are
warm, west-flowing equatorial currents. Other currents feed
into or out of the main gyres. These include, for example,
the warm North Atlantic
Drift, an offshoot of the
Gulf Stream, and cold
currents that bring water
down from the Arctic,
such as the Oyashio and
East Greenland currents.
WARM CURRENT
Satellite devices can detect COLD CURRENT
phytoplankton levels in the In this satellite view, sea
water, which can be related ice is visible flowing past the
to temperature. Here, yellow Kamchatka Peninsula in the cold
and red indicate high levels Oyashio Current. Eddies within
of plankton and the warm the current have produced spiral
Brazil Current. patterns in the sea ice.

Meeting of Currents

In a few areas, warm and cold currents meet and interact. Examples
include the meeting of the warm Gulf Stream with the cold Labrador
Current off the eastern seaboard of the US and Canada, and the
meeting of the cold Oyashio Current with the warm Kuroshio Current
to the north of Japan. At these confluences, the denser water in the cold
current dives beneath the water in the warm current, usually producing
some turbulence. This can trigger an upward flow of nutrient-rich
waters from the sea floor, encouraging the growth of plankton, and
producing good feeding grounds for fish, sea birds, and mammals.
SEA SMOKE
Dolphins cavort amid
steep waves. The
OPPOSING CURRENTS “sea smoke” is
The warm Brazil Current on the left, created when water
and the colder Falklands Current on vapor is added to
the right, each carry differently colored cold air drifting
populations of plankton. across the boundary
between cold and
warm currents. INTRODUCTION