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Zusammenfassung:
The oscillatory behaviour of the climate system on decadal timescales before the instrumental record is hard to quantify. However, knowledge of this variability is important for putting current changes in context and for supporting reliable future predictions. Here we investigate the recurrent component of Holocene climate variability in the North Atlantic sector from 10,500 to 2,000 years ago by conducting a frequency analysis of both an annually laminated climate record from a lake in England and outputs from a long transient simulation of the Atlantic meridional overturning circulation. We find consistent decadal variability over the past 6,700 years and before 8,500 years before present, probably reflecting predominance of solar and ocean forcings. Between these dates, climate variability was dampened on decadal timescales. Our results suggest that meltwater discharge into the North Atlantic and the subsequent hydrographic changes, from the opening of the Hudson Bay until the final collapse of the Laurentide Ice Sheet, disrupted the decadal cyclic signals for more than a millennium. Given the current acceleration of the Greenland Ice Sheet melting in response to global warming, this study provides long-term evidence of potential challenges predicting future patterns of the climate system.
