Atmospheric carbon dioxide concentrations over the past 60 million years

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Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60 Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.

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Figure 1: Sea surface pH for the past 60 Myr.
Figure 2: Sea surface alkalinity for the past 60 Myr.
Figure 3: Record of atmospheric carbon dioxide for the past 60 Myr.
Figure 4: Carbon dioxide levels and Cenozoic climate change.


  1. 1

    Arrhenius, S. On the influence of carbonic acid in the air upon the temperature on the ground. Phil. Mag. 41, 237–279 (1896).

  2. 2

    Chamberlin, T. C. An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis. J. Geol. 7, 545– 584 (1898).

  3. 3

    Owen, R. M. & Rea, D. K. Sea floor hydrothermal activity links climate to tectonics—the Eocene carbon dioxide greenhouse. Science 227, 166–169 ( 1985).

  4. 4

    Berner, R. A., Lasaga, A. C. & Garrels, R. M. The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years. Am. J. Sci. 283, 641–683 (1993).

  5. 5

    Kerrick, D. M. & Caldeira, K. Metamorphic CO2 degassing from orogenic belts. Chem. Geol. 145, 213 –232 (1998).

  6. 6

    Brady, P. V. The effect of silicate weathering on global temperature and atmospheric CO 2. J. Geophys. Res. 96, 18101– 18106 (1991).

  7. 7

    Worsley, T. R., Moore, T. L., Fraticelli, C. M. & Scotese, C. R. Phanerozoic CO2 levels and global temperatures inferred from changing paleogeography. Geol. Soc. Am. (Special Paper) 288, 57–73 (1994).

  8. 8

    Raymo, M. E. & Ruddiman, W. F. Tectonic forcing of late Cenozoic climate. Nature 359, 117– 122 (1992).

  9. 9

    Berger, W. H. & Vincent, E. Deep-sea carbonates: reading the carbon-isotope signal. Geologische Rundschau 75, 249–269 (1986).

  10. 10

    McGowran, B. Silica burp in the Eocene ocean. Geology 17, 857–860 (1989).

  11. 11

    Beck, A., Sinha, A., Burbank, D. W., Seacombe, W. J. & Khan, S. in Late Paleocene—Early Eocene Climatic and Biotic Events in the Marine and Terrestrial Records (eds Aubry, M-P., Lucas, S. G. & Berggren, W. A.) 103– 117 (Columbia Univ. Press, New York, 1998).

  12. 12

    Kakihana, H., Kotaka, M., Satoh, S., Nomura, M. & Okamoto, M. Fundamental studies on the ion exchange separation of boron isotopes. Bull. Chem. Soc. Jpn 50, 158–163 (1977).

  13. 13

    Hemming, N. G. & Hanson, G. N. Boron isotope composition and concentration in modern marine carbonates. Geochim. Cosmochim. Acta 56, 537–543 (1992).

  14. 14

    Hemming, N. G., Reeder, R. J. & Hanson, G. N. Mineral-fluid partitioning and isotopic fractionation of boron in synthetic calcium carbonate. Geochim. Cosmochim. Acta 59, 371–379 ( 1995).

  15. 15

    Spivack, A. J., You, C. F. & Smith, H. J. Foraminiferal boron isotope ratios as a proxy for surface ocean pH over the past 21 Myr. Nature 363, 149–151 (1993).

  16. 16

    Sanyal, A., Hemming, N. G., Hanson, G. N. & Broecker, W. S. Evidence for a higher pH in the glacial ocean from boron isotopes in foraminifera. Nature 373, 234– 236 (1995).

  17. 17

    Sanyal, A. et al. Oceanic pH control on the boron isotopic composition of foraminifera: evidence from culture experiments. Paleoceanography 11, 513–517 ( 1996).

  18. 18

    Sanyal, A., Hemming, N. G., Broecker, W. S. & Hanson, G. N. Changes in pH in the eastern equatorial Pacific across Stage 5-6 boundary based on boron isotopes in foraminifera. Glob. Biogeochem. Cycles 11, 125–133 ( 1997).

  19. 19

    Palmer, M. R., Pearson, P. N. & Cobb, S. J. Reconstructing past ocean pH-depth profiles. Science 282, 1468–1471 ( 1998).

  20. 20

    Pearson, P. N. & Palmer, M. R. Middle Eocene seawater pH and atmospheric carbon dioxide concentrations. Science 284, 1824–1826 ( 1999).

  21. 21

    Bralower, T. J. et al. Late Paleocene to Eocene paleoceanography of the equatorial Pacific Ocean: Stable isotopes recorded at Ocean Drilling Program Site 865, Allison Guyot. Paleoceanography 10, 841– 865 (1995).

  22. 22

    Pearson, P. N. & Shackleton, N. J. Neogene multispecies planktonic foraminifer stable isotope record, Site 871, Limalok Guyot. Proc. ODP Sci. Res. 144, 401– 410 (1995).

  23. 23

    Israelson, C., Buchardt, B., Haggerty, J. A. & Pearson, P. N. Carbonate and pore water geochemistry of pelagic caps at Limalok and Lo-En guyots, western Pacific. Proc. ODP Sci. Res. 144, 737–743 (1995).

  24. 24

    Opdyke, B. N. & Pearson, P. N. Geochemical analysis of multiple planktonic foraminifer species at discrete time intervals. Proc. ODP Sci. Res. 144, 993–995 (1995).

  25. 25

    Coxall, H. K., Pearson, P. N., Shackleton, N. J. & Hall, M. A. Hantkeninid depth adaptation: an evolving life-strategy in a changing ocean. Geology 28, 87–90 (2000).

  26. 26

    Taylor, S. R. & McLennan, S. M. The Continental Crust: Its Composition and Evolution (Blackwell Scientific, Oxford, 1985).

  27. 27

    Zachos, J. C., Lohmann, K. C., Walker, J. C. G & Wise, S. W. Abrupt climate change and transient climates during the Paleogene: a marine perspective. J. Geol. 101, 191– 213 (1993).

  28. 28

    Hemming, N. G., Guilderson, T. P. & Fairbanks, R. G. Seasonal variations in the boron isotopic composition of coral: A productivity signal? Glob. Biogeochem. Cycles 12, 581–586 (1998).

  29. 29

    Jorgensen, B. B. et al. Symbiotic photosynthesis in a planktonic foraminiferan, Globigerinoides sacculifer (Brady) studied with microelectrodes. Limnol. Oceanogr. 30, 1253–1267 (1985).

  30. 30

    Rink, S. et al. Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa. Mar. Biol. 131, 583–595 (1998).

  31. 31

    Millero, F. J. Thermodynamics of the carbon dioxide system in the oceans. Geochim. Cosmochim. Acta 59, 661–677 (1995).

  32. 32

    Van Andel, T. J. Mesozoic-Cenozoic calcite compensation depth and the global distribution of calcareous sediments. Earth Planet. Sci. Lett. 26, 187–194 (1975).

  33. 33

    Wanninkhof, R., Lewis, E., Feely, R. A. & Millero, F. J. The optimal carbonate dissociation constants for determining surface water p CO 2 from alkalinity and total inorganic carbon. Mar. Chem. 65, 291–301 ( 1999).

  34. 34

    Kiehl, J. T. & Dickinson, R. E. A study of the radiative effects of enhanced atmospheric CO2 and CH4 on early Earth surface temperatures. J. Geophys. Res. 92, 2991– 2998 (1987).

  35. 35

    Shackleton, N. J. Palaeogene stable isotope events. Palaeogeogr. Palaeoclimatol. Palaeoecol. 57, 91–102 ( 1986).

  36. 36

    Miller, K. G., Fairbanks, R. G. & Mountain, G. S. Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion. Paleoceanography 2, 1–19 (1987).

  37. 37

    Zachos, J. C., Stott, L. D. & Lohmann, K. C. Evolution of early Cenozoic temperatures. Paleoceanography 9, 353–387 (1994).

  38. 38

    Frakes, L. A., Francis, J. E. & Syktus, J. I. Climate Modes of the Phanerozoic (Cambridge Univ. Press, Cambridge, 1992).

  39. 39

    Ritchie, J. D. & Hitchen, K. in Correlation of the Early Paleogene in Northwest Europe (eds Knox, R. W. O., Corfield, R. M. & Dunay, R. E.) 63–78 (Special Publication 101, Geological Society, 1996).

  40. 40

    Sloan, L. C. et al. Possible methane-induced polar warming in the early Eocene. Nature 357, 320–322 (1992).

  41. 41

    Dickens, G. R., O'Neill, J. R., Rea, D. K. & Owen, R. M. Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene. Paleoceanography 10, 965–971 (1995).

  42. 42

    Thomas, E., Zachos, J. C. & Bralower, T. S. in Warm Climates in Earth History (eds Huber, B. T., MacLeod, K. S. & Wing, S. C.). 132–160 (Cambridge Univ. Press, Cambridge, 2000).

  43. 43

    Wing, S. L., Bao, H. & Koch, P. L. in Warm Climates in Earth History (eds Huber, B. T., MacLeod, K. S. & Wing, S. C.). 197–237 (Cambridge Univ. Press, Cambridge, 2000).

  44. 44

    Paytan, A., Kastner, M., Campbell, D. & Thiemens, M. H. Sulfur isotopic composition of Cenozoic seawater sulfate. Science 282, 1459–1462 ( 1998).

  45. 45

    Broecker, W. S. & Sanyal, A. Does atmospheric CO2 police the rate of chemical weathering? Glob. Biogeochem. Cycles 12, 403–408 ( 1998).

  46. 46

    Wright, J. D., Miller, K. G. & Fairbanks, R. G. Early and middle Miocene stable isotopes; Implications for deepwater circulation and climate. Paleoceanography 7, 357–389 (1992).

  47. 47

    Pagani, M., Arthur, M. A. & Freeman, K. H. Miocene evolution of atmospheric carbon dioxide. Paleoceanography 14, 273– 292 (1999).

  48. 48

    Crowley, T. J. in Warm Climates in Earth History (eds Huber, B. T., MacLeod, K. S. & Wing, S. C.). 425–444 (Cambridge Univ. Press, Cambridge, 2000).

  49. 49

    Berggren, W. A., Kent, D. V., Swisher, C. C. & Aubry, M.-P. A revised Cenozoic geochronology and chronostratigraphy. 129– 212 (Special Publication 54, Society of Economic Paleontologists and Mineralogists, 1995).

  50. 50

    Pearson, P. N. Planktonic foraminifer biostratigraphy and the development of pelagic caps on guyots in the Marshall Islands group. Proc. ODP Sci. Res. 144, 21–59 (1995).

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The authors contributed equally to this work. Samples were provided by the Ocean Drilling Program. We thank S. Cobb for assistance in sample preparation. This work was supported by the Natural Environment Research Council. P.N.P. is supported by a Royal Society University Research Fellowship.

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Correspondence to Paul N. Pearson.

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