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Climate Dynamics

, Volume 27, Issue 7–8, pp 715–725 | Cite as

Tropical versus high latitude freshwater influence on the Atlantic circulation

  • Heiko Goelzer
  • Juliette Mignot
  • Anders Levermann
  • Stefan Rahmstorf
Article

Abstract

We investigate the model sensitivity of the Atlantic meridional overturning circulation (AMOC) to anomalous freshwater flux in the tropical and northern Atlantic. Forcing in both locations leads to the same qualitative response: a positive freshwater anomaly induces a weakening of the AMOC and a negative freshwater anomaly strengthens the AMOC. Strong differences arise in the temporal characteristics and amplitude of the response. The advection of the tropical anomaly up to the deep water formation area leads to a time delayed response compared to a northern forcing. Thus, in its transient response, the AMOC is less sensitive to a constant anomalous freshwater flux in the tropics than in the north. This difference decreases with time and practically vanishes in equilibrium with constant freshwater forcing. The equilibrium response of the AMOC shows a non-linear dependence on freshwater forcing in both locations, with a stronger sensitivity to positive freshwater forcing. As a consequence, competitive forcing in both regions is balanced when the negative forcing is about 1.5 times larger than the positive forcing. The relaxation time of the AMOC after termination of a freshwater perturbation depends significantly on the AMOC strength itself. A strong overturning exhibits a faster relaxation to its unperturbed state. By means of a set of complementary experiments (pulse-perturbations, constant and stochastic forcing) we quantify these effects and discuss the corresponding time scales and physical processes.

Keywords

Atlantic Meridional Overturn Circulation North Atlantic Deep Water Deep Water Formation Global Warming Scenario Convection Site 
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.

Notes

Acknowledgments

A.L. and J.M. were funded by the Comer foundation. We are indebted to two anonymous reviewers for their comments that greatly helped to improved the manuscript.

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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Heiko Goelzer
    • 1
  • Juliette Mignot
    • 2
  • Anders Levermann
    • 1
  • Stefan Rahmstorf
    • 1
  1. 1.Potsdam Institute for Climate Impact ResearchPotsdamGermany
  2. 2.Laboratoire ďOcéanographie et du Climat: Expérimentations et Approches NumériquesInstitut Pierre Simon Laplace, Unité mixte de Recherche CNRS/IRD/UPMCParis Cedex 05France

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