Geology Reference
In-Depth Information
0
°
30
°
E60
°
E
90
°
E
120
°
E
150
°
E
180
°
150
°
W
120
°
W
90
°
W 0
°
W30
°
W
Greenland
ARCTIC OCEAN
Beaufort
Sea
Barents
Sea
Greenland
Sea
Greenland
Sea
North
Sea
ASIA
60
°
N
Bering
Sea
Sea of
Japan
EUROPE
NORTH
PACIFIC
OCEAN
NORTH
ATLANTIC
OCEAN
NORTH
AMERICA
Andaman
Sea
Yellow
Sea
Gulf of
Mexico
30
°
N
Red Sea
Mediterranean
Sea
Caribbean Sea
Arabian
Sea
AFRICA
Equator
Equator
SOUTH
AMERICA
Java
Sea
Coral
Sea
INDIAN
OCEAN
SOUTH
ATLANTIC
OCEAN
AUSTRALIA
SOUTH
PACIFIC
OCEAN
30
°
S
60
°
S
Numeric Data for the Oceans
Surface
Water
Average
Maximum
Area
Volume
Depth
Depth
Ocean* (million km
2
)
(million km
3
)
(km)
(km)
ANTARCTICA
Pacifi c
180
700
4.0
11.0
Atlantic
93
335
3.6
9.2
Indian
77
285
3.7
7.5
Arctic
15
17
1.1
5.2
Source
: P. R. Pinet, 1992
. Oceanography
(St. Paul, MN: West, 1992)
.
*Excludes adjacent seas, such as the Caribbean Sea and Sea of Japan,
which are marginal parts of oceans.
◗
Figure 9.2
The Seafl oor This map shows the four oceans and
many of the seas, which are marginal parts of oceans. The seafl oor
constitutes the largest part of Earth's surface.
he greatly underestimated the width of the Atlantic Ocean. Con-
trary to popular belief, he was not attempting to demonstrate
Earth's spherical shape; its shape was well accepted by then. The
controversy was over Earth's circumference and the shortest
route to China; on these points, Columbus's critics were correct.
These and similar voyages added considerably to the
growing body of knowledge about the oceans, but truly scien-
tifi c investigations did not begin until the late 1700s. At that
time, Great Britain was the dominant maritime power, and to
maintain that dominance, the British sought to increase their
knowledge of the oceans. So, scientifi c voyages led by Captain
James Cook were launched in 1768, 1772, and 1777. From 1831
until 1836, the HMS
Beagle
sailed the seas. Aboard was Charles
Darwin, who is well known for his views of organic evolu-
tion, but who also proposed a theory on the evolution of coral
reefs. In 1872, the converted British warship HMS
Challenger
began a four-year voyage to sample seawater, determine oce-
anic depths, collect samples of seafl oor sediment and rock, and
name and classify thousands of species of marine organisms.
During these voyages, many oceanic islands previ-
ously unknown to Europeans were visited. And even though
exploration of the oceans was limited, it was becoming
increasingly apparent that the seafloor was not flat and
featureless as formerly believed. Indeed, scientists discovered
that the seafl oor has varied topography just as continents
do, and they recognized such features as oceanic trenches,
submarine ridges, broad plateaus, hills, and vast plains.
Measuring the length of a weighted line lowered to the sea-
floor was the first method for determining ocean depths.
Now scientists use an instrument called an
echo sounder
,
which detects sound waves that travel from a ship to the sea-
fl oor and back (
◗
Figure 9.3). Depth is calculated by know-
ing the velocity of sound in water and the time required for
the waves to reach the seafl oor and return to the ship, thus
yielding a continuous profi le of seafl oor depths along the
ship's route.
Seismic profi ling
is similar to echo sounding,
but is even more useful. Strong waves from an energy source
refl ect from the seafl oor, and some of the waves penetrate
seafl oor layers and refl ect from various horizons back to the
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