The recurrence time of Dansgaard-Oeschger events and limits on the possible periodic component

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Abstract
By comparing the high-resolution isotopic records from the GRIP and NGRIP icecores, we approximately separate the climate signal from local noise to obtain an objective criterion for defining Dansgaard-Oeschger events. Our analysis identifies several additional short lasting events, increasing the total number of DO events to 27 in the period 12-90 kyr BP. The quasi-regular occurrence of the DO events could indicate a stochastic or coherent resonance mechanism governing their origin. From the distribution of waiting times we obtain a statistical upper bound on the strength of a possible periodic forcing. This finding indicates that the climate shifts are purely noise driven with no underlying periodicity.

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