Mathematics – Logic
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.126...91b&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 126, no. 1-3, p. 91-108
Mathematics
Logic
249
Climate Change, Earth (Planet), Equatorial Regions, Geochronology, Geomagnetism, Magnetic Fields, Oxygen Isotopes, Pacific Ocean, Argon Isotopes, Indian Ocean, Planetary Evolution, Potassium Isotopes, Radioactive Decay
Scientific paper
Below oxygen isotope stage 16, the orbitally derived time-scale developed by Shackleton et al. from Ocean Drilling Program (ODP) site 677 in the equatorial Pacific differs significantly from previous ones, 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. 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 delta O-18 are particularly well expressed, owing to the superimposition of a local salinity signal on the global ice volume signal. Three additional precession-related cycles are observed in oxygen isotope stages 17 and 18 of core MD900963, compared to the SPECMAP composite curves, and stages 21 clearly presents three precession oscillations, as predicted by Shackleton et al. The precession peaks found in the delta O-18 record from core MD900963 are in excellent agreement with climatic oscillations predicted by the astronomical theory of climate. Our delta O-18 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. and recent radiochronological Ar/Ar datings on lavas. We developed a new low-latitude, Upper Pleistocene delta O-18 reference record by stacking and tuning the delta O-18 records from core MD900963 and site 677 to orbital forcing functions.
Bassinot Franck C.
Labeyrie Laurent D.
Lancelot Yves
Quidelleur Xavier
Shackleton Nicholas J.
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