Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 4 2006 10.5194/cpd-2-519-2006 http://www.clim-past-discuss.net/2/519/2006/ http://www.clim-past-discuss.net/2/519/2006/cpd-2-519-2006.html http://www.clim-past-discuss.net/2/519/2006/cpd-2-519-2006.pdf 519 533 2006-07-24 Equatorial insolation: from precession harmonics to eccentricity frequencies A. Berger M. F. Loutre J. L. Mélice Université catholique de Louvain, Institut d’Astronomie et de Géophysique G. Lemaître, 2 Chemin du Cyclotron, 1348 Louvain-la-Neuve, Belgium Department of Oceanography, University of Cape Town, Rondebosch 7701, South Africa Since the paper by Hays et al. (1976), spectral analyses of climate proxy records provide substantial evidence that a fraction of the climatic variance is driven by insolation changes in the frequency ranges of obliquity and precession variations. However, it is the variance components centered near 100 kyr which dominate most Upper Pleistocene climatic records, although the amount of insolation perturbation at the eccentricity driven 100-kyr period is much too small to cause directly a climate change of ice-age amplitude. Many attempts to find an explanation to this 100-kyr cycle in climatic records have been made over the last decades. Here we show that the double maximum which characterizes the daily irradiation received in tropical latitudes over the course of the year is at the origin in equatorial insolation of not only a strong 100-kyr, but also of a 11-kyr and a 5.5-kyr periods related respectively to eccentricity and to precession.