Sensitivity of thermohaline circulation to decadal and multidecadal variability

Lorenzo, M. N., Taboada, J. J., and Iglesias, I. 2009. Sensitivity of thermohaline circulation to decadal and multidecadal variability. – ICES Journal of Marine Science, 66: 1439–1447. In this paper, stochastic freshwater inputs with different variabilities are introduced into an Earth Model of Intermediate Complexity to study their effect on the behaviour of the thermohaline circulation (THC). The variability in the stochastic signal was set to be either decadal or multidecadal (70 years), based on intensity modulation of the El Niño-Southern Oscillation (ENSO) phenomenon. The results demonstrate a weakening of the THC in both the decadal and the multidecadal cases. This weakening results in a reduction in air surface temperature, mainly in the North Atlantic. Moreover, the 500-mb stream function also weakens. This causes lower rainfall in Western Europe, except in the areas most influenced by the Gulf Stream. Sea surface temperature is reduced significantly in the area around Greenland, whereas sea surface salinity is reduced around Greenland and in the Gulf Stream, but increased in the Labrador Sea and in Hudson Strait. The latter effects are more marked in the case where the variability of the inputs is multidecadal. The main implication of these results is that the natural decadal or multidecadal variability in freshwater inputs could have noticeable effects on the fate of the THC, which may be superimposed on the effects of climate change.