Since the paper by Hays et al. (1976), spectral analyses of climate proxyrecords provide substantial evidence that a fraction of the climaticvariance is driven by insolation changes in the frequency ranges ofobliquity and precession variations. However, it is the variance componentscentered near 100 kyr which dominate most Upper Pleistocene climaticrecords, although the amount of insolation perturbation at the eccentricitydriven periods close to 100-kyr (mainly the 95 kyr- and 123 kyr-periods)is much too small to cause directly a climate change of ice-age amplitude.Many attempts to find an explanation to this 100-kyrcycle in climatic records have been made over the last decades. Here we showthat the double maximum which characterizes the daily irradiation receivedin tropical latitudes over the course of the year is at the origin inequatorial insolation of not only strong 95 kyr and 123 kyr periodsrelated to eccentricity, but also of a 11-kyr and a5.5-kyr periods related to precession.
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