Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing



Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO2, p CO 2 )1. Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (12–5 Myr ago), an interval with p CO 2 values of only 200–350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere2,3 and warmer-than-modern temperatures on the continents4. Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low p CO 2 12–5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data5,6,7,8,9,10, reveal a long-term trend of thermocline shoaling in the equatorial Pacific since 13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between p CO 2 , sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs11,12.

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Figure 1: Late Neogene oceanic conditions and atmospheric p CO 2 .
Figure 2: Sites used in this study.


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We thank the Ravelo laboratory group for discussions. We also thank J. Zachos and P. Koch for comments on the manuscript. L. Lajoie, P. Talmage and T. M. Aung assisted in sample preparation and analysis. D. Andreasen and R. Franks provided analytical support. This research used samples and/or data provided by the Integrated Ocean Drilling Program (IODP). Funding for this research was provided by NSF grant OCE0902047.

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J.P.L. and A.C.R. did the primary data analysis and wrote the paper with intellectual feedback from all authors. J.P.L. generated alkenone temperature reconstructions; J.P.L., P.S.D., H.L.F., A.C. and M.W.W. analysed foraminifera δ18O.

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Correspondence to Jonathan P. LaRiviere.

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The authors declare no competing financial interests.

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LaRiviere, J., Ravelo, A., Crimmins, A. et al. Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing. Nature 486, 97–100 (2012).

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