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Improved efficiency of the biological pump as a trigger for the Late Ordovician glaciation


The first of the ‘Big Five’ Phanerozoic mass extinctions occurred in tandem with an episode of glaciation during the Hirnantian Age of the Late Ordovician. The mechanism or change in the carbon cycle that promoted this glaciation, thereby resulting in the extinction, is still debated. Here we report new, coupled nitrogen isotope analyses of bulk sediments and chlorophyll degradation products (porphyrins) from the Vinini Creek section (Vinini Formation, Nevada, USA) to show that eukaryotes increasingly dominated marine export production in the lead-up to the Hirnantian extinction. We then use these findings to evaluate changes in the carbon cycle by incorporating them into a biogeochemical model in which production is increased in response to an elevated phosphorus inventory, potentially caused by enhanced continental weathering in response to the activity of land plants and/or an episode of volcanism. The results suggest that expanded eukaryotic algal production may have increased the community average cell size, leading to higher export efficiency during the Late Katian. The coincidence of this community shift with a large-scale marine transgression increased organic carbon burial, drawing down CO2 and triggering the Hirnantian glaciation. This episode may mark an early Palaeozoic strengthening of the biological pump, which, for a short while, may have made eukaryotic algae indirect killers.

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Fig. 1: Late Ordovician chronology, stable isotope, lipid biomarker, and sea-level stratigraphic records from Vinini Creek, Nevada, USA.
Fig. 2: Model predictions.


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We gratefully acknowledge X. Wang (Johns Hopkins University) for valuable discussions on the execution and C++ code modification of the COPSE model. J.S. acknowledges financial support from Z. T. Guo and the China Scholarship Council. We thank D. T. Johnston and J. J. Kharbush for helpful discussions, and B. D. A. Naafs, S. J. Hurley and S. J. Carter for assistance with sample preparation and machine use. We thank A. J. Kaufman for his help with bulk N-isotopic analysis of Vinini Creek samples. We thank D. Hu for the bulk N-isotope analysis of XY-5 samples. This study was supported by the National Natural Science Foundation of China (grant numbers 41520104007 and 41330102). A.P. received support from the NASA Astrobiology Institute and the Gordon and Betty Moore Foundation.

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Authors and Affiliations



J.S. and A.P. designed the paper. J.S., G.A.H. and S.D.W. performed the biomarker analysis. J.S. and K.C. performed the bulk sediment analysis. J.S., A.P. and Y.G.Z. contributed to the data interpretation. D.L., S.C.F. and Y.S. collected the samples and provided a robust stratigraphic framework. J.S., A.P. and Y.G.Z. designed the biogeochemical model. J.S. wrote code and performed model simulations. J.S. and A.P. wrote the manuscript, with inputs from G.A.H., Y.G.Z., S.C.F. and S.D.W.

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Correspondence to Jiaheng Shen or Ann Pearson.

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Shen, J., Pearson, A., Henkes, G.A. et al. Improved efficiency of the biological pump as a trigger for the Late Ordovician glaciation. Nature Geosci 11, 510–514 (2018).

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