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Deep Thermohaline currents

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Presentation on theme: "Deep Thermohaline currents"— Presentation transcript:

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


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