Warm water
moves away
from coast.Cool,
nutrient-rich
water upwells
to surface.Strong trade windsCool,
nutrient-rich
water remains offshore
at great depths.Warm water stays along coast.Weak trade windsa. Coastal upwelling, where deeper waters
come to the surface, occurs in the Pacific Ocean
along the South American coast. Upwelling
provides nutrients for microscopic algae, which
in turn support a complex food web.b. Coastal upwelling weakens considerably
during years with El Niño–Southern Oscillation
(ENSO) events, temporarily reducing fish
populations.The Global Ocean 277Climate scientists observe and monitor sea surface tem-
peratures and winds to better understand and predict the
timing and severity of ENSO events. The TAO/ TRITON
array consists of 70 moored buoys in the tropical Pacific
Ocean. These instruments collect oceanic and weather
data during normal conditions and El Niño events. The
data are transmitted to scientists onshore by satellite.
Scientists at the National Oceanic and Atmospheric
Administration’s Climate Prediction Center forecasted
the 1997–1998 ENSO six months in advance, using data
from TAO/TRITON. Such forecasts give governments
time to prepare for the extreme weather changes associ-
ated with ENSO.La Niña El Niño isn’t the only periodic ocean tem-
perature event to affect the tropical Pacific Ocean. La
Niña (in Spanish, “the girl child”) occurs when the sur-
face water temperature in the eastern Pacific Ocean
becomes unusually cool and westbound trade winds be-
come unusually strong. La Niña often, but not always,
occurs after an El Niño event and is considered part of
the natural oscillation of ocean temperature.
During the spring of 1998, the surface water of
the eastern Pacific cooled 6.7°C (12°F) in just 20 days.to strong trade winds (Figure 11.3a). During an ENSO
event, however, the colder, nutrient-rich deep water is
about 150 m (490 ft) below the surface, and the warmer
surface temperatures and weak trade winds prevent
upwelling (Figure 11.3b). The lack of nutrients in the
water results in a severe decrease in the populations of
anchovies and many other marine fishes. During the
1982–1983 El Niño, one of the most damaging to fish
populations, the anchovy population decreased 99 per-
cent. Other species, such as shrimp and scallops, thrive
during an ENSO event.
ENSO alters global air currents, directing unusual,
sometimes dangerous, weather to areas far from the
tropical Pacific where it originates. By one estimate, the
1997–1998 ENSO, the strongest on record, caused more
than 20,000 deaths and $33 billion in property damage
worldwide. It resulted in heavy snows in parts of the west-
ern United States; ice storms in eastern Canada; torren-
tial rains that flooded Peru, Ecuador, California, Arizona,
and western Europe; and droughts in Texas, Australia,
and Indonesia. An ENSO-caused drought—the worst in
50 years—particularly hurt Indonesia. Fires, many delib-
erately set to clear land for agriculture, got out of control
and burned an area in Indonesia the size of New Jersey.
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