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      Atmospheric carbon dioxide concentrations over the past 60 million years

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      Nature
      Springer Science and Business Media LLC

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          Abstract

          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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          Most cited references34

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          The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years

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            Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene

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              XXXI.On the influence of carbonic acid in the air upon the temperature of the ground

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                Author and article information

                Journal
                Nature
                Nature
                Springer Science and Business Media LLC
                0028-0836
                1476-4687
                August 2000
                August 17 2000
                August 2000
                : 406
                : 6797
                : 695-699
                Article
                10.1038/35021000
                10963587
                12b19da8-fc14-4617-8396-6fef95a5003a
                © 2000

                http://www.springer.com/tdm

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