1. Density-Driven Downwelling and Thermohaline Circulation
Motion of the Deep Ocean - p
The Global Conveyor - p
Water Mass Characteristics - p

2. Why are deep waters
more dense than
surface waters?
p. 123

3. Temperature Profiles Across Latitude

4. Thermohaline Circulation
Thermohaline circulation is the density-driven circulation of the ocean below the pycnocline
both temperature and salinity are important in the production of bottom, deep, and intermediate water masses
p. 144

5. Intermediate, Deep, & Bottom Water Masses
water becomes more dense by lowering the temperature or by adding salt:
- winter cooling
- evaporation (water becomes saltier causing it to sink)
- seasonal sea-ice formation (a salty brine is created, which sinks)
downwelling is the sinking of dense waters
parcels of water sink to their level of neutral buoyancy below the solar-warmed surface waters thereby producing intermediate, deep, & bottom water masses

6. Thermohaline Circulationp

7. Bottom & Deep Waters p
Bottom and deep waters form only in the Atlantic today:
1. northern North Atlantic (Greenland-Norwegian Sea): North Atlantic Deep Water (NADW)
2. southern South Atlantic (Weddell Sea of Antarctica): Antarctic Bottom Water (AABW)
Deep waters of the Indian & Pacific oceans are a mix of NADW and AABW called Circumpolar Water (or “Common Water”)

8. Antarctic Intermediate Water
Gulf Stream
Med Water
Antarctic Intermediate Water
North Atlantic Deep Water
Antarctic Bottom Water

9. Water Masses
A water mass is an identifiable body of water that can be recognized by physical and chemical characteristics
temperature, salinity, density, dissolved gases, dissolved nutrients
the densest water masses are very cold and somewhat salty (AABW, NADW), or cool and very salty (MIW) p

10. Greenland-Norwegian Sea note: it is warmer in the northern
North Atlantic than in the southern
South Atlantic
Ocean
surface
Weddell Sea

11. Antarctic Intermediate Water
Gulf Stream
Med Water
Antarctic Intermediate Water
North Atlantic Deep Water
Antarctic Bottom Water

12. Greenland-Norwegian Sea note: it is saltier in the northern
North Atlantic than in the southern
South Atlantic
Ocean
surface
Weddell Sea

13. Winter cooling and sea-ice formation produces dense waters which
sink to form AABW; some of this water mixes with NADW to form
Circumpolar Water which fills the deep Pacific & Indian oceans
p. 145

15. Western Boundary Currents
Deep water masses, like near-surface currents, are influenced by the Coriolis effect resulting in strong western boundary currents
As deep waters flow equatorward beneath the pycnocline, they hug the lower continental slopes and rises on the western sides of the ocean basins

16. The Global Conveyor
The global conveyor describes the complete circuit of global ocean circulation involving the horizontal & vertical flow of near-surface & deep waters
Near-surface waters move independently of deep & intermediate waters because of the pycnocline that separates them
Downwelling & upwelling link the surface & deep ocean
p. 147

18. Global Conveyor

19. Surface currents (red) return to the Atlantic and then sink again (blue) to complete the loop of the Global Conveyor

20. Cold water holds more dissolved oxygen than warm water
Why is there so much
variation in dissolved O2
across the ocean surface?
Ocean
surface
deep & intermediate waters
acquire their physical & chemical
characteristics at the surface