1. OCEAN CURRENTS

2. current mass of water moving from one place to another
like a river within the ocean

3. Why is Ocean Circulation Important?
Transport ~ 20% of latitudinal heat
Equator to poles
Transport nutrients and organisms
Influences weather and climate
Influences commerce
4 th century BC ,Pytheas of Massalia, a Greek ship captain, explored eastern Atlantic
Okeanos (Greek for “Great River”) because he found the ocean flowing south (Canary Current) and thought it was a river too wide to cross.

4. three types of currents
surface currents
thermohaline circulation (shallow & deep currents) wind-driven vertical currents (upwelling)

5. surface currents
occur at surface
horizontal currents

6. What causes surface currents?
WIND! Primarily caused by friction between wind and water - wind pushes water
Thermal Expansion & Gravity

7. Ocean Circulation

8. surface currents
Coriolis effect
→ Clockwise
→ Counter-clockwise 8

9. Wind-drive ocean surface currents
Wind driven surface currents
Wind-drive ocean surface currents
London = 51 deg N James Bay = 51 deg. N
Edinburgh = 55deg N, same latitude as Ontario’s Polar Bear Provincial Park
Total water in ocean surface circulation = about 100 Amazon Rivers (20 million m3/s). It requires years to complete cycle.
How fast? A few miles/hr (Gulf Stream off of Miami = 4.5 mph)
How much? Total water in ocean surface circulation = about 100 Amazon Rivers (20 million m3/s).

10. surface currents
gyre
massive circular system of wind-driven surface currents
cover whole oceans
clockwise in
Northern hemisphere
counter-clockwise
in Southern
hemisphere

11. eddies = warm core rings
surface currents
eddies = warm core rings
break off of currents and transport organisms elsewhere

12. Current Event: Gulf Oil Spill
The Gulf Loop Current enters from the Caribbean basin, moves around the Gulf of Mexico and exits out the Florida Strait, where it joins the more powerful Gulf Stream current. (msnbc.com)
Track it

13. thermohaline circulation (currents)
causes deep ocean circulation
vertical currents
temperature and salinity cause water density differences
due to density differences, water masses rise and fall

14. Sea Surface Temperature

15. Ocean Salinity
AVERAGE = 35 ppm or 3.5% denser

16. Remember that the surface circulation is driven by wind.

17. Initiating deep water circulation
A current runs from the equatorial Atlantic up the coast of the Americas.
Deflects (bounces) off landmasses.
Crosses Atlantic to warm the west coast of Europe.

18. How does ocean water change as it moves northward?
Evaporation
Cooling
Freezing

19. How do evaporation, cooling, and freezing affect salinity and density?
Evaporation and freezing increase salinity and density.
Cooling also increases density.
Water that is more dense SINKS!!!

20. thermohaline circulation (currents)
↑ salinity = ↑ density = water mass sinks
↓ temp. = ↑ density = water mass sinks

21. Water that reaches the North Atlantic is very COLD and SALTY so it SINKS!

22. Major Thermohaline Circulation
The cold, salty, really dense water starts to sink down to the bottom of the ocean in the North Atlantic, where it turns around and flows back south towards the equator of the bottom of the ocean basin.

23. It’s actually a lot more complicated with many layers of sinking & rising

24. Complex Thermohaline Circulation
North Atlantic Deep Water (NADW
15 million m3 of near surface water descend into the deep ocean each second.

25. There are certain places where the surface water typically sinks.

26. “Ocean Conveyor Belt”
Thermohaline circulation is sometimes called the “Ocean Conveyor Belt” because of it’s constant circulation in the ocean.

27. RESULTS: Heat Subsidy
Heat from tropics ends up north and south.

28. Global Warming a Problem?
What happens to the salinity and density of water when melting occurs?

29. Melting Ice a Problem?
Melting land ice may not only raise sea level but also slow circulation by “damming” water in the tropics.
As ice melts, ocean water is diluted and therefore does not sink as fast.

30. The bottom line: thermohaline circulation
When combined with surface currents, results in conveyor belt movement of water around globe

31. wind driven vertical currents = upwelling
wind blows, moves water away, causes new water to rise up to replace it