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Abstract

An ocean general circulation model coupled to a nonlinear energy
balance model of the atmosphere and a statistical feedback model for
wind stress shows a temporary collapse of the ’conveyor belt’-type
thermohaline circulation in response to a prescribed meltwater input
of 500 years duration. The thermohaline circulation of the Atlantic
reverses. The associated changes in ocean heat transport lead to a
strong cooling in the North. Atlantic and in Europe. Due to the
windstress feedback, the mode without North Atlantic deepwater
formation is slightly unstable and the system slowly returns to the
’conveyor belt’ overturning mode.
The circulation changes leave a strong imprint in geochemical
tracers included in the model simulations. Radiocarbon chronologies
are strongly affected, showing a rapidly advancing radiocarbon
’clock’ when formation of North Atlantic deepwater collapses and a
very slowly moving radiocarbon ’clock’ when the conveyor-belt
overturning starts again. In the deep Atlantic, the changes in the
origin of the water masses lead to a rapid increase of the
differences in radiocarbon ages relative to the surface waters. 6180
shows a similar time evolution as salinity, but the errors in the
reconstruction of salinity from 6180 are typically larger than 1 psu
during meltwater input. Much of the meltwater signal in sea water is
obscured in carbonate shells due to the temperature effect.