Page 441 - Environment: The Science Behind the Stories

Figure 16.2 The world’s oceans are connected
Arctic Ocean
in a single vast body of water but are given dif-
ferent names. The Pacific Ocean is the largest and,
like the Atlantic and Indian Oceans, includes both
tropical and temperate waters. The Arctic and South-
Atlantic Mediterranean Sea
Ocean Pacific ern Oceans include the waters in the polar regions.
Gulf of Mexico Persian Gulf Ocean Many smaller bodies of water are named as seas or
gulfs; a selected few are shown here.
Caribbean
Sea
Indian Coral Sea
Ocean

Southern
Ocean

To comprehend underwater geographic features, we can boundary, where one slab of crust dives beneath another in the
examine a stylized map (Figure 16.3) that reflects bathymetry process of subduction (p. 53).
(the measurement of ocean depths) and topography (physical Wherever reefs, volcanism, or other processes create phys-
geography, or the shape and arrangement of landforms). In ical structure underwater, life thrives. Marine animals make
bathymetric profile, gently sloping continental shelves under- use of physical structure as habitat, and topographically com-
lie the shallow waters bordering the continents. Continental plex areas often make for productive fishing grounds. Georges
shelves vary tremendously in width but average 80 km (50 mi) Bank and the Grand Banks are examples; they are essentially
wide, with an average slope of just 1.9 m/km (10 ft/mi). These huge underwater mounds formed during the ice ages when
shelves drop off at the shelf-slope break, where the continen- glaciers dumped debris at their southernmost extent. As cli-
tal slope angles more steeply downward to the deep ocean mate warmed and the glaciers retreated, sea level rose, and
basin below. these hilly areas were submerged in the ocean’s salty water.
Some island chains, such as the Florida Keys, are formed
by reefs (pp. 449–450) and lie atop the continental shelf. Ocean water contains high concentrations
Others, such as the Aleutian Islands, which curve across the of dissolved salts
North Pacific from Alaska toward Russia, are volcanic in ori-
gin. The Aleutians are also the site of a deep trench that, like Ocean water contains approximately 96.5% H O by mass.
2
the Mariana Trench, formed at a convergent tectonic plate Most of the remainder consists of ions from dissolved salts

Continental shelf Figure 16.3 A stylized bathymetric
Shelf-slope break profile shows key geologic features
of the submarine environment.
Continental slope Shallow water exists around the edges
Continental rise of continents over the continental shelf,
which drops off at the shelf-slope break.
Oceanic ridge Volcanic The steep continental slope gives way to
island arc the more gradual continental rise, all of
which are underlain by sediments from the
continents. Vast areas of seafloor are flat
abyssal plain. Seafloor spreading occurs
at oceanic ridges, and oceanic crust is
subducted in trenches (p. 53). Volcanic
activity along trenches may give rise to
island chains such as the Aleutian Islands.
Features on the left side of this diagram
Sediment
are more characteristic of the Atlantic
Ocean, and features on the right side of
the diagram are more characteristic of
the Pacific Ocean. Thurman, Harold V.; Trujilo,
Alan P., 2002. Essentials of Oceanography, 7th Ed.
Trench Adapted and Electronically reproduced by permis-
sion of Pearson Education, Inc., Upper Saddle
440 River, New Jersey.

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