1. Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA
2. Department of Global Ecology, Carnegie Institution of Washington, Stanford, California 94305, USA
3. Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK

Correspondence to: Mark Pagani¹ Correspondence and requests for materials should be addressed to M.P. (Email: mark.pagani@yale.edu).

Abstract

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering^{1, 2, 3, 4, 5, 6, 7}. Proxy records indicate, however, that the Earth's atmospheric carbon dioxide concentrations did not fall below about 200–250 parts per million during this period⁸. The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering. Here we investigate one possible negative feedback mechanism, occurring under relatively low carbon dioxide concentrations and in warm climates, that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals^{9, 10, 11}. We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period. These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink. Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate, our analysis indicates that the dynamic equilibrium between plants, climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years.

1. Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA
2. Department of Global Ecology, Carnegie Institution of Washington, Stanford, California 94305, USA
3. Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK

Correspondence to: Mark Pagani¹ Correspondence and requests for materials should be addressed to M.P. (Email: mark.pagani@yale.edu).

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