Page 443 - Environment: The Science Behind the Stories

Alaska North Atlantic

Gulf Stream Azores
Kuroshio N. Pacific C. Loop Caribbean
California
North Equatorial
North Equatorial
North Equatorial CC North Equatorial CC
Monsoon
Somali
South Equatorial South Equatorial South Equatorial
North Brazil

E. Austral. Peru/Chile Brazil Benguela
Aguthas

Antarctic Circumpolar Antarctic Circumpolar Malvinas Antarctic Circumpolar

Figure 16.5 The upper waters of the oceans flow in surface currents, long-lasting and predict-
able global patterns of water movement. Warm- and cold-water currents interact with the planet’s climate
system, and people have used them for centuries to navigate the oceans. Source: Adapted from Rick Lumpkin (NOAA/
AOML).
If you released a special buoy that traveled on the surface ocean currents shown above into the Pacific
Ocean from the southeastern coast of Japan, would it likely reach The United States or Australia first?
On what currents would it be carried?

Atlantic coast and past the eastern edges of Georges Bank and (p. 473) move surface waters away from shore, raising nutri-
the Grand Banks at nearly 2 m/sec, or over 4 mph. Averaging ent-rich water from below and creating a biologically rich
70 km (43 mi) across, the Gulf Stream continues across the region. The cold water also chills the air along the coast, giv-
North Atlantic, bringing warm water to Europe and moderat- ing San Francisco its famous fog and cool summers.
ing that continent’s climate (p. 506), which otherwise would
be much colder. Figure 16.6 Currents carried a 20-m (65-ft), 188-ton dock
Besides influencing climate, ocean currents have aided from Japan to the Oregon coast. The dock was dislodged
navigation and shaped human history. Currents helped carry by the 2011 tsunami in Japan and washed ashore in Oregon
Polynesians to Easter Island (p. 24), Darwin to the Galápagos over a year later. The dock algae and invertebrates that had
(p. 68), and Europeans to the New World. Currents transport attached to the dock were removed by state wildlife officials to
heat, nutrients, pollution, and the larvae of cod and many other prevent them from becoming invasive species (pp. 106–107) in the
marine species from place to place. Currents in the Pacific western United States.
Ocean have transported debris from the tsunami that devas-
tated eastern Japan in 2011 all the way to the western coast of
the United States (Figure 16.6).

Vertical movement of water affects
marine ecosystems

Surface winds and heating also create vertical currents in
seawater. Where horizontal surface currents diverge from
one another, cold, deep waters are pulled to the surface in a
process called upwelling. Upwelled water is rich in nutrients
from the bottom, so upwellings are often sites of high pri-
mary productivity (p. 129) and lucrative fisheries. Upwellings
will occur where strong winds blow away from or parallel to
coastlines (Figure 16.7). An example is the Pacific coast of
442 North America, where north winds and the Coriolis effect

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