1. Music today: Little Mermaid, “Under the Sea” WELCOME OSU MOMS!!

2. Deep Ocean Circulation
Motion in the Ocean, Part 2, or
Who wants to ride the Great Conveyor Belt?

3. Surface Circulation

4. How does the Deep Ocean respond to Surface Circulation?
The main gyres move heat and salt
Resulting DENSITY variations lead to vertical flow (sinking)
Formation of “water masses”, characterized by Temperature, Salinity

5. Density Variation in Sea Water
Isopycnals = constant density

6. North Atlantic Circulation

7. Density-Driven Water Flow
Called “Thermohaline Circulation”, because temperature and salinity together determine density of seawater “Thermo” = temperature “haline” = salt

8. Where does the Ocean’s Deepest Water Come From?
The densest seawater is cold and salty
This is formed at high latitudes in the North and South Atlantic: North Atlantic Deep Water (NADW) Antarctic Bottom Water (AABW)

9. Density of Sea Water
NADW * *
AABW

10. Density Rules!

11. Deep Water Masses

12. Water Masses and ocean mixing

13. Mediterranean Water

14. Mediterranean Water

15. Mediterranean Water

16. Deep Atlantic Circulation

17. Tracers in the Ocean Track the motion (direction and velocity)
14C, cosmic rays in the upper atmos (half-life is 5700 years) 3H, nuclear weapons testing (half-life is 12.5 years) CFCs, chlorinated fluoro-carbons

18. The Great Conveyor Belt

19. Closing Isthmus of Panama and onset of the Ice Ages?

20. Consequences of Global Flow
Ocean turnover is about 1500 years (time for a round trip on the conveyor belt)
Deep water (made in the polar Atlantic) contains abundant O2 and CO2
The high O2 content promotes oxidation of bottom sediments
The CO2 content controls CCD (Carbonate Compensation Depth)

21. Carbon Cycle and Global Warming
The temperature of bottom water formation determines how much CO2 is dissolved in deep ocean water
The rate of overturn of the oceans determines the “burial rate” of C from the atmosphere
Organic C accumulates in sediments, depending on the O2 content of deep ocean

22. Carbon Cycle and Global Warming
Organic C in sediments is reduced to CH4 (methane gas)
Methane gas migrates upward and can be trapped as frozen “gas hydrates” near the ocean floor

23. Gas Hydrates

24. Gas Hydrates

25. Gas Hydrates

26. Gas Hydrates

27. Climate Change Concerns
What happens when sea level falls? (negative feed-back)
What happens when deep water warms? (positive feed-back)
Both effects liberate gas hydrates (CH4), which combines with O2 to form CO2, ultimately reaching the atmosphere

28. Deep Ocean Circulation
The ocean has an enormous capacity to absorb and release greenhouse gases
So, the rate, temperature and composition of seawater circulating through the deep ocean is vitally important in assessing long term climate change