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Astronomical pacing of late Palaeocene to early Eocene global warming events


At the boundary between the Palaeocene and Eocene epochs, about 55 million years ago, the Earth experienced a strong global warming event, the Palaeocene–Eocene thermal maximum1,2,3,4. The leading hypothesis to explain the extreme greenhouse conditions prevalent during this period is the dissociation of 1,400 to 2,800 gigatonnes of methane from ocean clathrates5,6, resulting in a large negative carbon isotope excursion and severe carbonate dissolution in marine sediments. Possible triggering mechanisms for this event include crossing a threshold temperature as the Earth warmed gradually7, comet impact8, explosive volcanism9,10 or ocean current reorganization and erosion at continental slopes11, whereas orbital forcing has been excluded12. Here we report a distinct carbonate-poor red clay layer in deep-sea cores from Walvis ridge13, which we term the Elmo horizon. Using orbital tuning, we estimate deposition of the Elmo horizon at about 2 million years after the Palaeocene–Eocene thermal maximum. The Elmo horizon has similar geochemical and biotic characteristics as the Palaeocene–Eocene thermal maximum, but of smaller magnitude. It is coincident with carbon isotope depletion events in other ocean basins, suggesting that it represents a second global thermal maximum. We show that both events correspond to maxima in the 405-kyr and 100-kyr eccentricity cycles that post-date prolonged minima in the 2.25-Myr eccentricity cycle, implying that they are indeed astronomically paced.

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Figure 1: Bulk carbonate δ 13 C and magnetic susceptibility (MS) records across the Elmo horizon at five ODP Leg 208 sites.
Figure 2: Stable isotope series of bulk sediment and single foraminifer specimens across the Elmo horizon at Site 1263.
Figure 3: Astronomical tuning of the lower Eocene sediments at Walvis ridge to two different orbital computations.

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This research used samples and data provided by the Ocean Drilling Program (ODP). This work was supported by the Netherlands Organisation for Scientific Research (L.J.L., A.S. and D.K.), Utrecht Biogeology Centre (A.S.), Deutsche Forschungsgemeinschaft (U.R.), and the National Science Foundation (J.C.Z., E.T. and J.B.). We thank the scientific and non-scientific crew of ODP Leg 208, J. Suhonen in particular, and G. Ittman, A. E. van Dijk, G. M. Ganssen, S. J. A. Jung, H. B. Vonhof, P. L. Koch, H. Brinkhuis, F. J. Hilgen, T. Kouwenhoven and J. W. Zachariasse for technical support, advice and comments.

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Correspondence to Lucas J. Lourens.

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Supplementary Notes

Supplementary Figures S1-S6, additional references and extended description of methods used and discussion on: magnetobiostratigraphy; magnetic susceptibility and CaCO3 weight% scales shown in Figure 1; spectral results and astronomical phase relations; and global significance of the Elmo horizon/ETM2 event. (PDF 3096 kb)

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Lourens, L., Sluijs, A., Kroon, D. et al. Astronomical pacing of late Palaeocene to early Eocene global warming events. Nature 435, 1083–1087 (2005).

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