1. Water Mass Distribution OEAS 604 Lecture Outline 1)Thermohaline Circulation 2)Spreading pathways in ocean basins 3)T-S diagrams 4)Mixing on T-S diagrams Chapter 9 – Knauss Chapter 14 – Talley et al.

2. Thermohaline Circulation Circulation below the wind-driven currents Flow is determined by density distribution which is from temperature and salinity Circulation forced by sinking of cold dense water at high latitudes Return flow in upper water column Referred to a Meridional Overturning Circulation (MOC)

3. Water Masses Form in certain regions of the ocean Advected by ocean currents Form frontal regions were meet Water mass – a body of water with a common formation history, having its origin in a particular region of the ocean Source region – finite volume of ocean where water mass formation takes place

4. Water Mass Analysis Water type - point in n-dimensional parameter space – it is a combination of temperature, salinity, nutrients, oxygen and other tracer values Water mass – water formed in certain regions with particular temperature, salinity and other properties

5. Mixing of water masses

6. Two-point mixing Determine the mixture along line between two source waters f = fraction of water mass 1, f=1 all from water mass 1, f = 0 none from water mass 1 Tmix = fT 1 + (1-f)T 2 Smix = fS 1 + (1-f)S 2 Know Tmix, Smix, T 1, T 2, S 1, S, so solve for f

7. Track water masses Core method Gives rates of mixing and transport direction

8. Atlantic Indian Pacific T-S distribution for world oceans

9. North Atlantic and Southern Ocean NA – open to north, high latitude, limited seasonal sea ice, freshwater sources SO – bounded by continent, seasonal sea ice, no rivers, large polynyas

10. Atlantic separated Into basins with little connections

11. Indian Ocean Blocked to north Limited connection to Southern Ocean Complex bathymetry and limited openings to the east

12. Pacific Ocean Western basin Deeper Opening to north constricted by Bering Strait

13. North Atlantic Deep Water Greenland Sea Water Labrador Sea Water Mediterranean Sea Water High salinity, low temp, high oxygen Antarctic Intermediate Water Low salinity, high oxygen Antarctic Bottom Water High salinity, low temperature, average oxygen Subtropical Underwater Low oxygen

14. Antarctic Bottom Water Pathways Different varieties along western and eastern sides of basin Limited across basin exchange Flow on eastern side blocked by Walvis Ridge

15. AAIW NADW AABW East-west section in South Atlantic

16. T-S diagrams in East and West Atlantic – NADW, AAIW North Atlantic and South Atlantic Central Waters High salinity Mediterranean Sea Water WestEast

17. Annual progression of sea ice concentration in 1991, computed from the Special Sensor Microwave Imager (SSM/I) carried on the Defense Meteorological Satellite Program satellites.

18. Antarctic Circumpolar Current High speed current cores Subantarctic Front Polar Front Southern ACC Front Subtropical Front

19. Track of the Endurance (1914-1916) (from Stone 1914)

20. Bottom water formation

21. Spreading and direction of AABW

22. Intermediate and mode waters form along northern side of Polar and Subantarctic fronts

23. T-S diagram from Southern Ocean

24. AASW – Antarctic Surface Water WW – Winter Water SSW – Shelf Water HSSW – High Salinity Shelf Water ISW – Ice Shelf Water WS and RS – Bottom Water CDW - Circumpolar Deep Water

25. T-S properties of water mass change around the Southern Ocean CDW – cools and freshens

26. Spreading of Bottom water Limited exchange 90°E Ridge is a barrier

27. T-S diagram for Indian Ocean AAMW – Australian Mediterranean Water

29. Spreading of bottom water in Pacific Ocean

30. North-south section in western Pacific

31. T-S diagram from western Pacific

33. Next Class Ekman Dynamics Upwelling Chapter 7, Knauss Chapter 7, Talley et al.