Page 445 - Environment: The Science Behind the Stories

to the west strengthen, and weather patterns are affected in
Equator
opposite ways. ENSO cycles are periodic but irregular, occur-
ring every 2–8 years. Scientists are exploring whether the
globally warming air and sea temperatures (Chapter 18) may
Pacific
Ocean Convective loop be increasing the frequency and strength of these cycles.

Equator Winds Movement Climate change is altering ocean chemistry
Indonesia of water Scientists today are learning a great deal about how global
climate change will affect ocean chemistry and biology. The
oceans absorb carbon dioxide (CO ) from the atmosphere, as
2
we first saw in the carbon cycle (see Figure 5.17, p. 140). As
our civilization pumps excess carbon dioxide into the atmos-
Peru phere by burning fossil fuels for energy and removing vegeta-
Upwelling of deep,
tion from the land, the buildup of atmospheric CO is causing
cold water
2
the planet to grow warmer, setting in motion many changes
and consequences (Chapter 18).
The oceans have soaked up roughly a third of the excess
CO that we’ve added to the atmosphere, and this has slowed
(a) Normal conditions 2
global climate change. However, there are two concerns.
One is that the ocean’s surface water may soon become satu-
rated with as much CO as it can hold. Once it reaches this
2
Increased convection
limit, then climate change will accelerate as the oceans will
Winds
Equator no longer remove large amounts of carbon dioxide from the
Movement atmosphere.
Indonesia of water Winds
The second concern is that as ocean water soaks up CO ,
2
it becomes more acidic. As ocean acidification proceeds,
many sea creatures have difficulty forming shells because the
chemicals they need to create them are less available. This
Peru process is harming corals in particular (see The Science behind
The STory, pp. 446–447). Corals build reefs, which are hubs for
Deep, cold water
marine biodiversity and provide billions of dollars’ worth of
stays below
surface
ecosystem services. Because of the decline of coral reefs, sci-
entists are warning that ocean acidification is shaping up to be
one of most damaging consequences of global climate change.
(b) El Niño conditions
Marine and Coastal Ecosystems
Figure 16.9 El Niño conditions occur every 2 to 8 years,
causing marked changes in weather patterns. In these
diagrams, red and orange colors denote warmer water, and blue With their variation in topography, temperature, salinity, nutri-
and green colors denote colder water. Under normal conditions ents, and sunlight, marine and coastal environments feature a
(a), prevailing winds push warm surface waters toward the western variety of ecosystems. Regions of ocean water differ greatly,
Pacific. Under El Niño conditions (b), winds weaken, and the warm and some zones support more life than others. The uppermost
water flows back across the Pacific toward South America, like 10 m (33 ft) of water absorbs 80% of solar energy, so nearly
water sloshing in a bathtub. This shuts down upwelling along the all of the oceans’ primary productivity occurs in the top layer,
American coast and alters precipitation patterns regionally and or photic zone. Generally, the warm, shallow waters of con-
globally. Adapted from National Oceanic and Atmospheric Administration, tinental shelves are most biologically productive and support
Tropical Atmospheric Ocean Project.
the greatest species diversity. Habitats and ecosystems occur-
ring between the ocean’s surface and floor are termed pelagic,
occurred shortly after Christmas. Coastal industries such as whereas those that occur on the ocean floor are called benthic.
Peru’s anchovy fisheries are devastated by El Niño events, Most marine and coastal ecosystems are powered by solar
and the 1982–1983 El Niño alone caused over $8 billion in energy, with sunlight driving photosynthesis by phytoplankton
economic losses worldwide. El Niño events alter weather in the photic zone. Yet even the darkest ocean depths host life.
patterns around the world, creating rainstorms and floods As we survey marine and coastal ecosystems, keep in
in areas that are generally dry (such as southern California) mind that they are part of a web of interconnected freshwa-
and causing drought and fire in regions that are typically ter and marine aquatic systems (see Figure 15.3, p. 410) that
moist (such as Indonesia). exchange water, organisms, sediments, pollutants, and other
La Niña events are the opposite of El Niño events; in a dissolved substances with one another. Hence, the topics we
La Niña event, unusually cold waters rise to the surface and discuss in this chapter are greatly influenced by those in fresh-
444 extend westward in the equatorial Pacific when winds blowing water ecosystems, and vice versa.

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