HR: 12:05h
AN: PP22A-08    [Abstracts]
TI: Is a Shutdown of the Thermohaline Circulation Irreversible?
AU: Yin, J
EM: yinjj@atmos.uiuc.edu
AF: Climate Research Group, Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory, Urbana, IL 61801 United States
AU: * Schlesinger, M E
EM: schlesin@atmos.uiuc.edu
AF: Climate Research Group, Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory, Urbana, IL 61801 United States
AU: Andronova, N G
EM: Natasha@atmos.uiuc.edu
AF: Climate Research Group, Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory, Urbana, IL 61801 United States
AU: Malyshev, S
EM: malyshev@Princeton.EDU
AF: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, Princeton, NJ 08544 United States
AU: Li, B
EM: binli@atmos.uiuc.edu
AF: Climate Research Group, Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory, Urbana, IL 61801 United States
AB: The thermohaline circulation (THC) in the North Atlantic plays a vital role in explaining past abrupt climate changes and in maintaining the current climate. Its remarkable nonlinear dynamics, first demonstrated by Stommel, has been supported by different types of models. This has led to concern that global warming may shut down the THC irreversibly, with consequent catastrophic climate changes, particularly for Europe. However, recent simulations by complex atmosphere/ocean general circulation models show a great suppression of the nonlinear response of the THC to external freshwater forcing. In this study a suite of models is used to investigate the nonlinear response of the THC to freshwater addition. It is found that the THC simulated by an ocean general circulation model responds very differently depending on whether it is uncoupled or coupled to an atmosphere general circulation model. The THC shuts down irreversibly in the uncoupled ocean general circulation model (OGCM) simulations, but reversibly in the coupled atmosphere/ocean general circulation model (AOGCM) simulation. This occurs because of a crucial negative feedback in the AOGCM simulation that cannot occur in the OGCM simulations. Analysis of Stommel's 2-box ocean model within different parameter regimes supports this finding. Thus, the irreversible shutdown of the THC caused by freshwater addition appears to be a model artifact rather than a likely outcome of global warming.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology
DE: 3309 Climatology (1620)
DE: 1620 Climate dynamics (3309)
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting