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The Astronomical Theory of Climate and the Age of the Brunhes-Matuyama Magnetic Reversal

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The Astronomical Theory of Climate and the Age of the Brunhes-Matuyama Magnetic Reversal EPSL ELSEVIER Earth and Planetary Science Letters 126 (1994) 91-108 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. 1. Introduction [PT] Present address: Centre des Faibles Radioactivit&, CNRS/CEA, Avenue de la Terrasse, BP 1, 91198 Gif-sur- Mathematically formulated early in this cen- Yvette, France. 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 92 F.C. Bassinot et al. /Earth and Planetary Science Letters 126 (1994) 91-108 theory of climate was widely accepted by Earth absolutely certain whether such a composite scientists only about 15 years ago, when Hays et record is complete and permits an accurate astro- al. [14] unambiguously showed that fluctuations nomical calibration. Furthermore, no magne- in paleoclimatic indicators in geologic records do tostratigraphy was available at site 677 and posi- contain the periods associated with the Earth's tions of the magnetic reversals were inferred from orbital components (namely, eccentricity of the biostratigraphy and oxygen isotope stratigraphy. Earth's orbit, tilt and precession of the Earth's We have addressed these uncertainties in the axis). The astronomical theory of climate brought Upper Pleistocene (last 900 kyr) by studying the important insights into the mechanisms that con- oxygen isotope record provided by the ~ 53 m trol global changes and it has also opened the long piston core MD900963 (tropical Indian way to a very powerful means for developing Ocean) in which the Brunhes-Matuyama reversal accurate geological time-scales. By fine tuning has been precisely located. The core MD900963 paleoclimatic indicators to astronomical forcing provides one of the most detailed Late Pleis- functions, Earth scientists have provided detailed tocene climatic records ever retrieved in low lati- Pliocene-Pleistocene chronologies for marine tudes. It allows us to compare in detail paleocli- sediments with a theoretical accuracy of a few matic oscillations with variations in orbital forc- thousand years [e.g., 2-5,15-18]. In the late Pleis- ing, making it possible to test the accuracy of the tocene, with the exception of Johnson's results orbitally derived timescale of Shackleton et al. [15], orbitally derived ages for the last Brunhes- [1]. Matuyama magnetic reversal (e.g., 728 ka [2]; 738 ka [3]; 734 ka [4]) have been in good agreement with the 730 ka age obtained by K/Ar ra- 2. The giant piston core MD900963: location, diochronological dating [6]. This agreement ap- biostratigraphy and magnetostratigraphy parently indicated that all the climatic variations predicted by the astronomical theory of climate Core MD900963 was collected in the In- were observed in the paleoclimatic records avail- dian Ocean, east of the Maldives platform able so far. (05°03.30'N-73°52.60'E) from a water depth of Four years ago, however, Shackleton et al. [1] 2446 m, during the MD65-SEYMAMA expedi- proposed a revised orbitally derived time-scale tion of the French R/V Marion Dufresne in 1990 for the last 2.6 Myr that differs significantly from [19]. The core liner was 52.70 m long and the previous ones below oxygen isotope stage 16 (~ sediment thickness retrieved is 51.70 m. With the 620 ka) and yields estimated ages for the last six exception of minor flow-in structures at the bot- major reversals of the Earth's magnetic field that tom of sections 3 (roughly between about 4.0 and are 5-7% older than the K/Ar radiometric val- 4.5 m) and 4 (between about 5.5 and 6.0 m), the ues [6-8]. These ages have since been confirmed sediment does not present any evidence of coring by precise Ar/Ar dating obtained on carefully disturbance. The sediment is free of turbidite selected single crystals of sanidine from lavas layers but a slump of 60 cm was found between [e.g., 9-11]. At first sight, this independent con- 26.30 and 26.90 m. Measurements performed firmation of Shackleton et al.'s age estimates within this slump interval were discarded and the suggests that several climatic oscillations pre- entire interval was eliminated in the calculation dicted by the astronomical theory of climate were of final sub-bottom depths. missing in paleoclimatic records used by former Biostratigraphy is based on calcareous nanno- investigators for the development of orbitally de- fossil and planktonic foraminifer datums studied rived timescales. However, the 120 m long oxygen at a 10 cm sampling interval. The depositional isotope record used by Shackleton et al. was not history of core MD900963 records a major hiatus retrieved in one single piece but constructed by at about 41 m, as shown by the concomitant carefully splicing together 9.5 m long hydraulic disappearance within a narrow depth range of piston cores using all the available data. It is not Helicosphaera sellii, Calcidiscus macintyrei and F.C Bassinot et aL / Earth and Planetary Science Letters 126 (1994) 91-108 93 Globigerinoides fistulosus, and the appearance of mentation rate (averaging 4.5 cm/kyr) minimized Gephyrocapsa oceanica [for details see 20]. How- smoothing of the climatic signal by bioturbation, ever, the upper 41 m of core MD900963 covers thus permitting the recovery of one of the most the entire Late Pleistocene, down to isotope stage detailed deep-sea records of Late Pleistocene cli- boundary 23.0 (Fig. 1). Isotopic stages defined by matic variability ever retrieved in low latitudes. Emiliani [21] and Shackleton and Opdyke [22] are The sedimentation rate translates into an average particularly well expressed, owing to the superpo- sample spacing of about 2.2 kyr. Unfortunately, sition of the global ice volume signal and a local the uppermost portion of the oxygen isotopic salinity effect, most probably controlled by curve does not extend into the Holocene. This changes in monsoon intensity [12]. The high sedi- suggests that the very top part of the sedimentary 8180 (%0) Paleomagnetic declination (o) 0 -1 -2 -3 -50 50 150 250 0 I I I I I I I I I I I % 10 ~-- 7 o o o oo © 20 11 © oo E % 1- ~ Y O. % 0 © C3 15 ° o 30 % 17 © 19 o B/M 21 © 40 Hiatus 50 Fig. 1. Stable oxygen isotope stratigraphy and magnetic declinations in core MD900963. 94 F.C. Bassinot et al. / Earth and Planetary Science Letters 126 (1994) 91-108 section was not preserved in the core. A loss of (~1 8 0 (%o) this type is not uncommon in piston coring [e.g., 23]. 0 -1 -2 -3 i i I,~ i I I I Paleomagnetic measurements were performed 34 with standard plastic cubes (8 cm 3) taken roughly every 75 cm along the core, from the top of the core and about 40 m. The mean sampling interval was reduced to about 15 cm around the Brun- 34.5 hes-Matuyama reversal. In addition, U-channels were measured in order to get continuous and B/M detailed records within specific intervals, selected 35 A 'ansition on the basis of the results of the single samples. E v We followed the procedure described by Nagy and Valet [24], involving measurements every 2 ,.C 35.5 cm using the high-resolution pick-up coils of a Q.
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