1. Ocean Currents
Ocean water circulates in currents caused by wind and by density differences
Currents are the flow of water between areas of different surface levels or different densities

2. Ocean Currents
Ocean water moves constantly sideways, up, down because it is:
Blown by wind
Moved by density differences
Heated unevenly
Evaporated unevenly
Affected by Earth’s rotation (Coriolis)
Pulled by sun & moon
The Ocean: A Driving Force for Weather and Climate

3. CURRENTS Currents are important because they:
moderate climates (transfer heat)
mix nutrients and gases
transport larvae and plankton
Warm air from equator flows toward poles, drives air circulation, makes wind, moves water
Continents deflect east-west water movement, but not air
NASA
NOAA

4. Coriolis Effect
Water near ocean surface moves to the right of wind direction in Northern Hemisphere
Water near ocean surface moves to the left of wind direction in Southern Hemisphere

6. Coriolis Effect Coriolis Effect Causes currents to move
Clockwise in the Northern Hemisphere
Counterclockwise in the Southern Hemisphere
Coriolis Effect

7. Surface Currents Affect the uppermost 10% of world ocean
Some rapid & riverlike, some slow and diffuse
Largest organized into gyres

8. The circular patterns of surface water currents are called gyres
The circular patterns of surface water currents are called gyres. The characteristics of a current depend upon where the water is coming from in the gyre.

9. Western boundary currents are located on the western side of oceans.
Eastern boundary currents are located on the eastern side of the OCEAN - not the continent.
East Coast of United States
Gulf Stream
in red
Western boundary currents are located on the western side of oceans.
Florida

10. Comparison of Boundary Currents
Western
Eastern
currents bring warm water from the equator
1. currents bring cold water from the poles
2. high salinity;
low oxygen content
2. low salinity; high oxygen content
3. nutrient poor, infrequent upwelling
3. nutrient rich due to upwelling
4. lower biomass
4. high biomass

11. Surface Currents

12. Effect of Surface Currents on Climate
Surface currents distribute heat worldwide
Warm water flows to higher latitudes transfers heat to the air and cools
Moves back to low latitudes
Absorbs heat
Repeats

13. Vertical Movement Upwelling – upward movement of water
Can be caused by wind blowing parallel to shore or offshore (Coastal Upwelling)
Brings nutrients

15. Vertical Movement
Downwelling – downward movement of water – caused by:
Increase in surface water density
Wind blowing parallel to shore or onshore (Coastal Downwelling)
Brings dissolved gases and nutrients to deeper ocean

17. DENSITY DRIVEN CURRENTS
AKA THERMOHALINE CURRENTS

18. Thermohaline currents found on the ocean floor.
“Thermo” refers to temperature and “haline” refers to salinity.
NASA
Water slows down below the pycnocline (area defining water masses of different densities) to 1-2 meters/day.
Cold water sinks at the poles and crawls toward the rising warmer water at the equator.
NASA

19. Density Structure of the Ocean
Salt water weighs 2-3% more than pure water
Cold, salty water is more dense than warm, less salty water
Much of the ocean can be divided into three density zones:
surface, pycnocline & deep

20. Density Zones Surface or Mixed Zone
Temperature, salinity & density constant due to currents and waves
In contact with atmosphere
Exposed to sunlight
Least dense water
2% all of ocean water
~150 meters deep

21. Density Zones Pycnocline aka Thermocline aka Halocline
Density increases with depth, temperature decreases, salinity increases
Isolates surface water from denser layer below
18% of all ocean water

22. Density Zones Deep Zone Below pycnocline Depth below 1000 m
Little change with depth
Very cold (1-3C) and stable
80% of all ocean water

23. Density stratification in the ocean – surface layer does not mix with bottom layer