Page 201 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

20°
0°
20°
Canaries
ATLANTIC Current 20°
North Equatorial Current OCEAN
100°E
120°E 140°E
Winds
Ocean currents
Message in a bottle and toys
Typhoon Ioke
Simulated distribution of tsunami debris
160°E 180°
500 1000 KILOMETRES
160°W 140°W
ARCTIC OCEAN
120°W 100°W
Dana Point, California 1992
mohaline circulation hauls larger volumes of water. (Figure 16.4 illustrates the ocean’s physical structure and profiles of temperature, salinity, and dissolved gases; note that temperature and salinity vary with depth.)
To picture the THC, imagine a continuous chan­ nel of water beginning with the flow of the Gulf Stream and the North At­ lantic Drift (Figure 6.18). When this warm, salty water mixes with the cold water of the Arctic Ocean, it cools, increases in den­ sity, and sinks. The cold water downwelling in the North Atlantic, on either side of Greenland, produces the deep current that then
Hong Kong
0° 100°E
Cargo spill, 1994
Mogmog, Equator Micronesia
1995
Westerlies PACIFIC OCEAN
40°
North Pacific Current
Tropic of Cancer
North Equatorial Current Equatorial Countercurrent
PACIFIC OCEAN
South Equatorial Current
Tropic of Capricorn
West Wind Drift
40°
40°
Falkland Current
Benguela Current 20°
40°
Animation
Ocean Circulation
80°N
North Equatorial Current
INDIAN OCEAN
Equatorial Countercurrent
South Equatorial Current
Equator
CORAL S E A
Peru Current
South Equatorial Current
West Wind Drift
60°
0 1500
3000 KILOMETRES
Antarctic Circumpolar Current 60° Antarctic Circle
80°
Chapter 6 atmospheric and Oceanic Circulations 165 80° 40° 60° 80° 100° 120° 140° 160° 180° 160° 140° 120° 100° 80° 60° 40° 20° 0° 80°
Warm currents
Arctic Circle
Labrador Current
North Atlantic Drift
60°
(after U.S. Hydrographic Office)
60°
Cool currents January conditions
based on 30-year record
m
ea
r
t
S
f
l
u
G
ROBINSON PROJECTION
80°
▲Figure 6.18 Major ocean currents. [after the U.S. naval Oceanographic Office.]
In other regions with an accumulation of water— such as at the western end of an equatorial current, or in the Labrador Sea, or along the margins of Antarctica— the excess water gravitates downward in a downwelling current. These are the deep currents that flow vertically and along the ocean floor and travel the full extent of the ocean basins, redistributing heat energy and salinity over the globe.
Thermohaline Circulation—
The Deep Currents
0
Route of the drifting toys (approximate)
60°N
40°N
20°N
Route of a message in
a bottle (approximate, assuming only a partial
circuit around the Pacifific Gyre)
100°W
California Current
Kuroshio
160°E 180°
Northeast trade winds
160°W
140°W
120°W
Kuroshio
▲Figure 6.19 Transport of marine debris by Pacific Ocean currents. The paths of a message in a bottle, toy rubber duckies, and Typhoon ioke show the movement of currents around the Pacific gyre. The distribution of debris from the 2011 Japan tsunami is a computer simulation based on expected winds andcurrentsthroughJanuary7,2012.[nOaa.]
Pacific high
Differences in temperatures and salinity (the amount of salts dissolved in water) produce density differences important to the flow of deep currents on Earth known as thermohaline circulation, or THC (thermo- refers to temperature and -haline refers to salinity). Travelling at slower speeds than wind­driven surface currents, the ther­