Modelling tempo-spatial signatures of Heinrich Events: influence of the climatic background state

Different sea surface temperature (SST) reconstructions for the Last Glacial Maximum are applied to a hybrid-coupled climate model. The resulting oceanic states are perturbed by North Atlantic meltwater inputs in order to simulate the effect of Heinrich Events on the Atlantic thermohaline circulation (THC) and SST. The experiments show that both the Atlantic SST signature of the meltwater event and the time span of THC recovery strongly depend on the climatic background state. Data-model comparison reveals that the overall spatial signature of SST anomalies is captured much better in the glacial meltwater experiments than in an analogous experiment under present-day conditions. In particular, a breakdown of the modern THC would induce a much stronger temperature drop in high northern latitudes than did Heinrich Events during the ice age. Moreover, our results suggest that the present-day circulation can settle into a stable ‘off’ mode, whereas the glacial THC was mono-stable. Mono-stability may serve as an explanation for the recovery of the THC after Heinrich Event shutdowns during the Last Glaciation.