Download Currents Under the Surface

24.2
Currents Under the Surface
Unlike surface currents, which are driven by wind, deep ocean currents are
driven by gravity and differences in density. A density current is heavier
and denser than surrounding water; such dense water masses sink from
the surface toward the bottom of the ocean where they circulate in the
deep ocean for 500 to 2000 years before resurfacing.
KEY IDEA
Deep ocean currents are driven by
properties that determine the
density of water, such as salinity
and temperature.
Density Currents
KEY VOCABULARY
Density currents can be found in all the world’s oceans. As shown in the
map below, the deep currents connect with global surface currents to form
a complete path of circulation. This circulation of ocean water is an
efficient heat-transport system. Similar to the conveyor belt at a grocery
store check-out line, the circulating currents transport warm water to
colder areas and cold water to warmer areas. For this reason, the global
circulation of ocean currents is often modeled as a Global Conveyor Belt.
Density currents move very slowly compared to surface currents.
Despite their slow movement, they are important to marine animals living
in the deep ocean. Density currents retain the oxygen absorbed at the
surface layer, as well as the temperature, salinity, and density. Such deep
currents are the only source of oxygen for deep-sea life.
• density current
• upwelling
SURFACE AND DEEP CURRENTS
This simple model of ocean current
circulation is called the Global
Conveyor Belt. The model gives you a
sense of how water moves from polar to
equatorial regions.
Surface and Deep Currents
0°
30°E
60°E
90°E
120°E
150°E
180°
150°W
Cold, salty deep currrents
Warm, less-salty, surface currents
Arctic Circle
30°N
Tropic of Cancer
Equator
0°
0°
Tropic of Capricorn
30°S
30°S
60°S
60°S
Antarctic Circle
90°W
536
30°W
Unit 6 Earth’s Oceans
180°
150°W