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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-135
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
25 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
A comparison of two astronomical tuning approaches for the Oligocene-Miocene Transition from Pacific Ocean Site U1334 and implications for the carbon cycle
Helen M. Beddow1, Diederik Liebrand2, Douglas S. Wilson3, Frits J. Hilgen1, Appy Sluijs1, Bridget S. Wade4, and Lucas J. Lourens1 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands
2PalaeoClimate.Science, 3501 AB, Utrecht (province), The Netherlands
3Department of Earth Science University of California, Santa Barbara, CA 93106-9630, USA
4Department of Earth Sciences, Faculty of Mathematical and Physical Sciences, University College London, Gower Street, London, WC1E 6BT, UK
Abstract. Astronomical tuning of sediment sequences requires both unambiguous cycle-pattern recognition in climate proxy records and astronomical solutions, and independent information about the phase relationship between these two. Here we present two astronomically tuned age models for the Oligocene-Miocene Transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning approaches have on astronomically calibrated ages and the geologic time scale. These age models are based on different phase-assumptions between climate proxy records and eccentricity: the first age model is based on an inverse and in-phase assumption of CaCO3 weight (wt %) to Earth's orbital eccentricity, the second age model is based on an inverse and in-phase assumption of benthic foraminifer stable carbon isotope ratios (δ13C) to eccentricity. The phase-assumptions that underpin these age models represent two end-members on the range of possible tuning options. To independently test which tuned age model and tuning assumptions are correct, we assign their ages to magnetostratigraphic reversals identified in anomaly profiles. Subsequently we compute tectonic plate-pair spreading rates based on the tuned ages. These alternative spreading rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n–C6Cn.1r, which are not based on astronomical tuning in the latest iteration of the Geologic Time Scale. Furthermore, it provides independent evidence that the relatively large (several 10,000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity, constitute a real feature of the Oligocene-Miocene climate system and carbon cycle. The age constraints from Site U1334 thus provide independent evidence that the delayed responses of the Oligocene-Miocene climate-cryosphere system and carbon cycle resulted from increased nonlinear feedbacks to astronomical forcing.

Citation: Beddow, H. M., Liebrand, D., Wilson, D. S., Hilgen, F. J., Sluijs, A., Wade, B. S., and Lourens, L. J.: A comparison of two astronomical tuning approaches for the Oligocene-Miocene Transition from Pacific Ocean Site U1334 and implications for the carbon cycle, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-135, in review, 2017.
Helen M. Beddow et al.
Helen M. Beddow et al.
Helen M. Beddow et al.

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Short summary
We present two astronomy-based time scales for climate records from the Pacific Ocean. These records range from 24 to 22 million years ago; a time period when Earth was warmer than today and the only land-ice was located on Antarctica. We use tectonic plate-pair spreading rates to test the two time scales, which shows that the carbonate record yields the best time scale. In turn, this implies that Earth’s climate system and carbon cycle responded slowly to changes in incoming solar radiation.
We present two astronomy-based time scales for climate records from the Pacific Ocean. These...
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