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Ocean Circulation Changes

Ocean Circulation Changes. Gerrit Lohmann Carbon Course 9. January 2006 @PEP, University of Bremen, Germany. Box Model: terrerstrial carbon cycle. Oceanic inorganic carbon cycle. Ca CO 3 sediments and rocks weathering. Topics. Long-term carbon cycle: sediments & rocks

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Ocean Circulation Changes

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  1. Ocean Circulation Changes Gerrit Lohmann Carbon Course 9. January 2006 @PEP, University of Bremen, Germany

  2. Box Model: terrerstrial carbon cycle

  3. Oceanic inorganic carbon cycle

  4. Ca CO3 sediments and rocks weathering

  5. Topics • Long-term carbon cycle: sediments & rocks • Ocean circulation, carbon cycle & climate • Ecosystem

  6. North Atlantic: Ice Core and Marine Data YD H1 H2 Role of the Ocean Circulation? GISP2: Grootes et al. 2000Bard et al. 2000

  7. Ocean Circulation Methaphor conversion surface deep

  8. Carbon flux deserts High production upwelling

  9. ``13-C Conveor Belt´´

  10. Stommel (1961) Box Model Heat, freshwater surface fluxes

  11. Stommel Box Model: Advection • Advection=Transport: q T2 from low to high latitudes, contributes to T1 • q T1 from high to low latitudes, contributes to T2 • ``upstream scheme´´: Transport along the velocity direction (also ``upwind scheme´´)

  12. Stommel Box Model: Advection • Advection=Transport: q T2 from low to high latitudes, contributes to T1 • q T1 from high to low latitudes, contributes to T2 • ``upstream scheme´´: Transport along the velocity direction (also ``upwind scheme´´) • d/dt T1 ~ q T2 • d/dt T2 ~ q T1 • d/dt (T1-T2) = -q (T1-T2) + Fluxes

  13. Stommel Box Model: Fluxes • ``Restoring´´: Relaxation towards local temperatures • d/dt T1 ~ -r (T1 –T10) • d/dt T2 ~ -r (T2 – T20) • d/dt (T1-T2) = -q (T1-T2) -r (T1-T2 -T10+T20 ) • ``Flux for Salinity´´: P-E (precipitation-evaporation) • dS/S0 = (P-E)/h

  14. advection noise Surface fluxes Temperature: Salinity:

  15. Stommel (1961) Box Model Heat, freshwater surface fluxes Z: Depth Y: meridional direction

  16. Salinity loop • S2 low • q low • q S1 low • S2 low ------------- Positive feedback

  17. Temperature loop • T2 high (high latitude warming) • q low • q T1 low • T2 low ------------- Negative feedback -> stable

  18. Feedback Loops

  19. What is ``wrong´´ with q ?

  20. Geostrophic motion • Flow is driven by the basic pressure gradient force (PGF) and only after the flow is initiated does the Coriolis force act. • After about a day the flow has accelerated sufficiently for the PGF and Coriolis force to balance giving the geostrophic wind.

  21. Stommel (1961) Box Model gyre

  22. Stommel (1961) box model On-mode Off-mode

  23. Thermohaline circulation hysteresis Hysteresis intercomparison Rahmstorf, et al.GRL, 2005 Intermediate complexity models

  24. Box Models • Stommel‘s model was almost completey ignored (25 years) • Rooth, 1982: Two hemisphere counterpart, unaware of the Stommel (1961) model • Rooth suggested to F. Bryan: test with a GCM

  25. What do we learn? • Multiple equilibria: robust feature of box models, GCMs • Fundamental destabilizing mechanism: salinity feedback (feedback loop) • Stability –Hysteresis Now: • Stability depends on the basic state ?

  26. North Atlantic: Ice Core and Marine Data YD H1 H2 Role of the Ocean Circulation? GISP2: Grootes et al. 2000Bard et al. 2000

  27. Ocean Circulation Methaphor conversion surface deep

  28. Conveyor belt Warm water route

  29. Conveyor belt Cold water route

  30. Conceptual Model of the THC (~ Rooth) S1> S2 Present Cold & Warm water route South- Equator North- Atlantic S1< S2 Glacial Cold water route

  31. Predicted Change of the THC Rahmstorf, Nature 1999

  32. Predicted Change of the THC by several Climate Models after IPCC, 2001

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