1. Deep Thermohaline currents
Ocean Circulation
Deep Thermohaline currents

2. Density = mass/volume
(gr/cm3)
D (ρ) ~(T, S)

3. Density Layered Ocean! Surface layer – Ekman Spiral
Pycnocline Layer – Geostrophic curr.
Deep Ocean – Thermohaline curr.

4. Ocean Circulation Surface Circulation  Wind Driven
Ekman Transport and Geostrophic Currents
Surface layer and Picnocline zone
0 – 50,100m / 50,100m - ~1000m
Affects ~25% of total water mass
Fast (1-2 m/s)

5. Surface Geostrophic and Deep Thermohaline Circulation

6. Ocean Circulation Surface Circulation  Wind Driven
Ekman Transport and Geostrophic Currents
Surface layer and Picnocline zone
0 – 50,100m / 50,100m - ~1000m
Affects ~25% of total water mass
Fast (1-2 m/s)
Deep Circulation  Density Driven
Thermohaline Circulation
Below Picnocline zone (>~1000m)
Affects ~75% of total water mass
Slow (~ m/day)

7. Deep Thermohaline Circulation
T, S are CONSERVATIVE properties
TS properties attained at the surface
Change only by mixing
(Non-Conservative Properties)
O2, Nutrients
Oceans are layered according to water densities!!!

8. H20: Temperature and Density

9. Seawater: Temperature and Density

10. Seawater: Ice Formation

11. Seasonal changes of surface layer thermocline
Surface seasonal thermocline
Deep permanent thermocline

12. Latitudinal changes of surface layer salinity

13. TS Plots Represent the influence of TS on density (iso-picnolines)

14. TS Plot example

15. Example: CTD Hydrographic Survey

16. Example: CTD Casts Line ‘A’

17. Example: TS Diagram for CTD Line A

18. Deep Thermohaline Circulation
So… where do Deep Waters Form?
TS properties attained at the surface
TS properties remain remarkably constant
TS properties only altered by water mixing

19. Deep Water Formation

20. Major Water Masses – Thermohaline Circulation
Central Waters (0-1000m)
Intermediate Waters ( m)
Deep Waters ( m)
Bottom Waters (over ocean bottom)

21. Atlantic Deep Waters AABW NADW Antarctic Atlantic Bottom Water
-1.9 oC o/oo (cold & “fresh”)
Forms in the Weddell Sea, during southern winter ice formation
NADW
North Atlantic Deep Water
4 oC o/oo (“warm” & saline)
Forms by cooling of saline Atlantic surface waters during northern winters, in the Norwegian and Greenland Seas

22. Atlantic Deep Waters AIW MIW Antarctic Intermediate Water
2.2 oC o/oo (cold & “fresh”)
Forms in sub-polar regions, in the Antarctic Convergence zone
Extends Northward up to 25oN
(NAIW – North Atlantic Intermediate Water)
MIW
Mediterranean Intermediate Water
11.9 oC o/oo (warm and very saline)
Spills from Mediterrenan over the Gibraltar Sill
Forms a tongue in the Atlantic ~1000m deep

23. Atlantic Surface Waters
NACW
North Atlantic Central Water
24 oC o/oo (very warm & very saline)
Surface waters, low density

24. Atlantic Deep Water Masses

25. Atlantic Deep Water Masses

26. Weddell Sea – formation AABW

27. Weddell Sea

28. Mediterranean Intermidiate Water

29. Tracing Deep water masses TS Diagrams

30. Coriolis Effect on Thermohaline Circulation

31. North Atlantic Deep Conveyer belt – 1000 year cycles

32. Conveyor Belt “engine”

33. North Atlantic Deep Conveyer belt – 1000 year cycles

34. Pacific Ocean Thermohaline Circulation