ELSEVIER Earth and Planetary Science Letters 126 (1994) 91-108 EPSL The astronomical theory of climate and the age of the Brunhes-Matuyama magnetic reversal Franck C. Bassinot a,1, Laurent D. Labeyrie b, Edith Vincent a, Xavier Quidelleur c Nicholas J. Shackleton d, Yves Lancelot a a Laboratoire de Gdologie du Quaternaire, CNRS-Luminy, Case 907, 13288 Marseille cddex 09, France b Centre des Faibles Radioactivit&, CNRS/CEA, Avenue de la Terrasse, BP 1, 91198 Gif-sur-Yvette, France c Institut de Physique du Globe, Laboratoire de Pal~omagn&isme, 4 Place Jussieu, 75252 Paris c~dex 05, France d Department of Quaternary Research, The Godwin Laboratory, Free School Lane, Cambridge CB2 3RS, UK Received 3 November 1993; revision accepted 30 May 1994 Abstract Below oxygen isotope stage 16, the orbitally derived time-scale developed by Shackleton et al. [1] from ODP site 677 in the equatorial Pacific differs significantly from previous ones [e.g., 2-5], yielding estimated ages for the last Earth magnetic reversals that are 5-7% older than the K/Ar values [6-8] but are in good agreement with recent Ar/Ar dating [9-11]. These results suggest that in the lower Brunhes and upper Matuyama chronozones most deep-sea climatic records retrieved so far apparently missed or misinterpreted several oscillations predicted by the astronomical theory of climate. To test this hypothesis, we studied a high-resolution oxygen isotope record from giant piston core MD900963 (Maldives area, tropical Indian Ocean) in which precession-related oscillations in t~180 are particularly well expressed, owing to the superimposition of a local salinity signal on the global ice volume signal [12]. Three additional precession-related cycles are observed in oxygen isotope stages 17 and 18 of core MD900963, compared to the SPECUAP composite curves [4,13], and stage 21 clearly presents three precession oscillations, as predicted by Shackleton et al. [1]. The precession peaks found in the 3180 record from core MD900963 are in excellent agreement with climatic oscillations predicted by the astronomical theory of climate. Our ~180 record therefore permits the development of an accurate astronomical time-scale. Based on our age model, the Brunhes- Matuyama reversal is dated at 775 + 10 ka, in good agreement with the age estimate of 780 ka obtained by Shackleton et al. [1] and recent radiochronological Ar/Ar datings on lavas [9-11]. We developed a new low-latitude, Upper Pleistocene ~180 reference record by stacking and tuning the 3180 records from core MD900963 and site 677 to orbital forcing functions. [PT] Present address: Centre des Faibles Radioactivit&, CNRS/CEA, Avenue de la Terrasse, BP 1, 91198 Gif-sur- Yvette, France. 1. Introduction Mathematically formulated early in this cen- tury by Milutin Milankovitch, the astronomical 0012-821X/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0012-821X(94)00127-K