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Ocean Circulation Deep Thermohaline currents

Ocean Circulation Deep Thermohaline currents. Density = mass/volume (gr/cm 3 ) D ( ρ ) ~(T, S). Density Layered Ocean! Surface layer – Ekman Spiral Pycnocline Layer – Geostrophic curr. Deep Ocean – Thermohaline curr. Ocean Circulation. Surface Circulation  Wind Driven

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Ocean Circulation Deep Thermohaline currents

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  1. 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 PlotsRepresent the influence of TS on density (iso-picnolines)

  14. TS Plot example

  15. Example: CTD Hydrographic Survey

  16. Example: CTD Casts Line ‘A’ T S D http://tabs.gerg.tamu.edu/gomoms/ctddata.html

  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 (1000-2000m) • Deep Waters (2000-5000m) • Bottom Waters (over ocean bottom)

  21. Atlantic Deep Waters • AABW • Antarctic Atlantic Bottom Water • -1.9 oC - 34.6 o/oo (cold & “fresh”) • Forms in the Weddell Sea, during southern winter ice formation • NADW • North Atlantic Deep Water • 4 oC - 34.9 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 • Antarctic Intermediate Water • 2.2 oC - 33.8 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 - 35.5 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 - 36 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. MediterraneanIntermidiate 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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