Climate Dynamics

, Volume 23, Issue 7–8, pp 761–777 | Cite as

Bistability of the thermohaline circulation identified through comprehensive 2-parameter sweeps of an efficient climate model

  • R. Marsh
  • A. YoolEmail author
  • T. M. Lenton
  • M. Y. Gulamali
  • N. R. Edwards
  • J. G. Shepherd
  • M. Krznaric
  • S. Newhouse
  • S. J. Cox


The effect of changes in zonal and meridional atmospheric moisture transports on Atlantic overturning is investigated. Zonal transports are considered in terms of net moisture export from the Atlantic sector. Meridional transports are related to the vigour of the global hydrological cycle. The equilibrium thermohaline circulation (THC) simulated with an efficient climate model is strongly dependent on two key parameters that control these transports: an anomaly in the specified Atlantic–Pacific moisture flux (ΔF a ) and atmospheric moisture diffusivity (K q ). In a large ensemble of spinup experiments, the values of ΔF a and K q are varied by small increments across wide ranges, to identify sharp transitions of equilibrium THC strength in a 2-parameter space (between Conveyor “On” and “Off” states). Final states from this ensemble of simulations are then used as the initial states for further such ensembles. Large differences in THC strength between ensembles, for identical combinations of ΔF a and K q , reveal the co-existence of two stable THC states (Conveyor “On” and “Off”)—i.e. a bistable regime. In further sensitivity experiments, the model is forced with small, temporary freshwater perturbations to the mid-latitude North Atlantic, to establish the minimum perturbation necessary for irreversible THC collapse in this bistable regime. A threshold is identified in terms of the forcing duration required. The model THC, in a “Conveyor On” state, irreversibly collapses to a “Conveyor Off” state under additional freshwater forcing of just 0.1 Sv applied for around 100 years. The irreversible collapse is primarily due to a positive feedback associated with suppressed convection and reduced surface heat loss in the sinking region. Increased atmosphere-to-ocean freshwater flux, under a collapsed Conveyor, plays a secondary role.


Multiple Equilibrium Freshwater Flux Atlantic Sector Surface Freshwater Flux Atmospheric Moisture Transport 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This work is an output of the GENIE project of the UK Natural Environment Research Council (NERC) e-Science thematic programme (NER/T/S/2002/00217). M.Y. Gulamali, T.M. Lenton and A. Yool are funded by GENIE. R. Marsh is supported under the NERC Core Strategic Programme, “Ocean Variability and Climate”. N.R. Edwards is supported by the National Centres of Competence in Research (Climate), Switzerland. David Baker and Oz Parchment (University of Southampton) provided technical assistance by helping to achieve the first flocking of Condor pools through firewalls between UK universities. John Darlington (Imperial College) helped organise and facilitate GENIE experiments. The authors are especially grateful to Jochem Marotzke, for helpful guidance during early discussions of these experiments, and to Paul Valdes, whose original idea formed the basis of this work. We are also grateful to three anonymous referees whose suggestions considerably improved the final form of this manuscript.


  1. Annan JD, Hargreaves JC, Edwards NR, Marsh R (2004) Parameter estimation in an intermediate complexity earth system model using an ensemble Kalman filter. Ocean Model (in press)Google Scholar
  2. Brittain J, Darwin IF (2003) Tomcat: the definitive guide. O’Reilly and Associates, UK, p 332Google Scholar
  3. Broecker WS (1998) Paleocean circulation during the last deglaciation: a bipolar seesaw? Paleoceanography 13:119–121CrossRefGoogle Scholar
  4. Cubasch U, Meehl GA, Boer GJ, Stouffer RJ, Dix M, Noda A, Senior CA, Raper S, Yap KS (2001) Projections of future climate change. Climate change 2001: the scientific basis. In: Houghton JT, Ding Y, Griggs DJ, Noguer M, Linden PJvd , Dai X, Maskell K, Johnson CA (eds) Contribution of working group I to the third assessment report of the intergovernmental panel on climate change. Cambridge University Press, London, pp 525–582Google Scholar
  5. Curry R, Dickson RR, Yashayaev I (2003) A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426:826–829CrossRefPubMedGoogle Scholar
  6. Delworth T, Manabe S, Stouffer RJ (1993) Interdecadal variations of the thermohaline circulation in a coupled ocean-atmosphere model. J Climate 6:1993–2011CrossRefGoogle Scholar
  7. Edwards NR, Marsh R (2004) An efficient climate model with three-dimensional ocean dynamics. Clim Dyn (submitted)Google Scholar
  8. Edwards NR, Shepherd JG (2002) Bifurcations of the thermohaline circulation in a simplified three-dimensional model of the world ocean and the effects of interbasin connectivity. Clim Dyn 19:31–42CrossRefGoogle Scholar
  9. Edwards NR, Willmott AJ, Killworth PD (1998) On the role of topography and wind stress on the stability of the thermohaline circulation. J Phys Oceanogr 28:756–778CrossRefGoogle Scholar
  10. Epema DHJ, Livny M, van Dantzig R, Evers X and Pruyne J (1996) A worldwide flock of Condors: load sharing among workstation clusters. Future Gener Comput Syst 12:53–65CrossRefGoogle Scholar
  11. Foster I, Kesselman C, Tuecke S (2001) The anatomy of the grid: enabling scalable virtual organizations. Int J High Perform Comput Appl 15:200–222Google Scholar
  12. Gulamali MY, Lenton TM, Yool A, Price AR, Marsh RJ, Edwards NR, Valdes PJ, Watson JL, Cox SJ, Krznaric M, Newhouse S, Darlington J (2003) GENIE: delivering e-Science to the environmental scientist, Proceedings of the UK e-Science All Hands Meeting 2003, pp 145–152Google Scholar
  13. Huybrechts P, DeWolde J (1999) The dynamic response of the Greenland and Antarctic ice sheets to multiple-century climatic warming. J Climate 12:2169–2188CrossRefGoogle Scholar
  14. Latif M (2001) Tropical Pacific/Atlantic Ocean interactions at multi-decadal timescales. Geophys Res Lett 28:529–542CrossRefGoogle Scholar
  15. Latif M, Roeckner E, Mikolajewicz U, Voss R (2000) Tropical stabilisation of the thermohaline circulation in a greenhouse warming simulation. J Climate 13:1809–1813CrossRefGoogle Scholar
  16. Lenderink G, Haarsma R (1994) Variability and multiple equilibria of the thermohaline circulation associated with deep water formation. J Phys Oceanogr 24:1480–1493CrossRefGoogle Scholar
  17. Litzkow M, Tannenbaum T, Bashley J, Livny M (1997) Checkpoint and migration of UNIX processes in the Condor distributed processing system. Technical report 1346, Computer Sciences Department, University of Wisconsin-Madison, MadisonGoogle Scholar
  18. Manabe S, Stouffer RJ (1997) Coupled ocean-atmosphere model response to freshwater input: comparison to Younger Dryas event. Paleoceanography 12:321–336CrossRefGoogle Scholar
  19. Marotzke J (1996) Analysis of thermohaline feedbacks. NATO ASI series I44:334–378Google Scholar
  20. Oort AH (1983) Global atmospheric circulation statistics, 1958–1973. NOAA Professional Paper 14Google Scholar
  21. Rahmstorf S (1994) Rapid climate transitions in a coupled ocean-atmosphere model. Nature 372:82–85CrossRefGoogle Scholar
  22. Rahmstorf S (1995a) Multiple convection patterns and thermohaline flow in an idealized OGCM. J Climate 8:3028–3039CrossRefGoogle Scholar
  23. Rahmstorf S (1995b) Bifurcations of the Atlantic thermohaline circulation in response to changes in the hydrological cycle. Nature 378:145–149CrossRefGoogle Scholar
  24. Rahmstorf S (1996) On the freshwater forcing and transport of the Atlantic thermohaline circulation. Clim Dyn 12:799–811CrossRefGoogle Scholar
  25. Rahmstorf S (2000) The thermohaline ocean circulation—a system with dangerous thresholds. Clim Change 46:247–256CrossRefGoogle Scholar
  26. Rahmstorf S, Ganopolski A (1999) Long-term global warming scenarios computed with an efficient coupled climate model. Clim Change 43:353–367CrossRefGoogle Scholar
  27. Schiller A, Mikolajewicz U, Voss R (1997) The stability of the North Atlantic thermohaline circulation in a coupled ocean-atmosphere general circulation model. Clim Dyn 13:325–347CrossRefGoogle Scholar
  28. Schmittner A, Appenzeller C, Stocker TF (2000) Enhanced Atlantic freshwater export during El Nino. Geophys Res Lett 27:1163–1166CrossRefGoogle Scholar
  29. Stocker TF (1998) The seesaw effect. Science 282:61–62CrossRefGoogle Scholar
  30. Stouffer RJ, Dixon KW, Gregory JM, Spelman MJ, Hurlin W (2004) A coupled model intercomparison of the climate response to freshwater input in the north Atlantic Ocean. Geophys Res Abstr 6:1254Google Scholar
  31. Thain D, Tannenbaum T, Livny M (2003) Condor and the grid. In: Berman F, Hey AJG, Fox G (eds) Grid computing: making the global infrastructure a reality.Wiley, New York, pp 299–335Google Scholar
  32. Thorpe RB, Gregory JM, Johns TC, Wood RA, Mitchell JFB (2001) Mechanisms determining the Atlantic thermohaline circulation response to greenhouse gas forcing in a non-flux-adjusted coupled climate model. J Climate 14:3102–3116CrossRefGoogle Scholar
  33. Vellinga M (1998) Multiple equilibria in ocean models as a side effect of convective adjustment. J Phys Oceanogr 28:621–633CrossRefGoogle Scholar
  34. Wang H, Birchfield GE (1992) An energy-salinity balance climate model: water vapor transport as a cause of changes in the global thermohaline circulation. J Geophys Res 97:2335–2346Google Scholar
  35. Weaver AJ, Eby M, Wiebe EC, Bitz CM, Duffy PB, Ewen TL, Fanning AF, Holland MM, MacFadyen A, Matthews HD, Meissner KJ, Saenko O, Schmittner A, Wang HX, Yoshimori M (2001) The UVic Earth System Climate Model: model description, climatology, and applications to past, present and future climates. Atmos Ocean 39:361–428Google Scholar
  36. Wood RA, Keen AB, Mitchell JFB, Gregory JM (1999) Changing spatial structure of the thermohaline circulation in response to atmospheric CO2 forcing in a climate model. Nature 399:572–575CrossRefGoogle Scholar
  37. Yang F, Kumar A, Schlesinger ME, Wang W (2003) Intensity of hydrological cycles in warmer climates. J Climate 16:2419–2423CrossRefGoogle Scholar
  38. Zaucker F, Broecker WS (1992) The influence of atmospheric moisture transport on the fresh water balance of the Atlantic drainage basin: general circulation model simulations and observations. J Geophys Res 97:2765–2773Google Scholar

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • R. Marsh
    • 1
  • A. Yool
    • 1
    Email author
  • T. M. Lenton
    • 2
    • 3
  • M. Y. Gulamali
    • 4
  • N. R. Edwards
    • 5
  • J. G. Shepherd
    • 1
  • M. Krznaric
    • 4
  • S. Newhouse
    • 4
  • S. J. Cox
    • 6
  1. 1.Southampton Oceanography CentreSouthamptonUK
  2. 2.Centre for Ecology and HydrologyEdinburghUK
  3. 3.School of Environmental SciencesUniversity of East AngliaNorwichUK
  4. 4.London e-Science CentreImperial CollegeLondonUK
  5. 5.Physics InstituteUniversity of BernBernSwitzerland
  6. 6.School of Engineering SciencesUniversity of SouthamptonSouthamptonUK

Personalised recommendations