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.Comment: 9 figure
