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Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations

Sproson, Adam D.; Pogge von Strandmann, Philip A.E.; Selby, David; Jarochowska, Emilia; Frýda, Jiří; Hladil, Jindřich; Loydell, David K.; Slavík, Ladislav; Calner, Mikael; Maier, Georg; Munnecke, Axel; Lenton, Timothy M.

Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations Thumbnail


Authors

Adam D. Sproson

Philip A.E. Pogge von Strandmann

David Selby

Emilia Jarochowska

Jiří Frýda

Jindřich Hladil

David K. Loydell

Ladislav Slavík

Mikael Calner

Georg Maier

Axel Munnecke

Timothy M. Lenton



Abstract

The Ordovician (∼487 to 443 Ma) ended with the formation of extensive Southern Hemisphere ice sheets, known as the Hirnantian glaciation, and the second largest mass extinction in Earth History. It was followed by the Silurian (∼443 to 419 Ma), one of the most climatically unstable periods of the Phanerozoic as evidenced by several large scale (>5‰) carbon isotope (δ13C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187Os/188Os) and lithium (δ7Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ13C excursions. Osmium and Li isotope records resemble those previously recorded for the Hirnantian glaciation suggesting a similar causal mechanism. When combined with a new dynamic carbon-osmium-lithium biogeochemical model we suggest that astronomical forcing of the marine organic carbon cycle, as opposed to a decline in volcanic arc degassing or the rise of early land plants, resulted in drawdown of atmospheric CO2, triggering continental scale glaciation, intense global cooling and eustatic sea-level lows recognised in the geological record. Lower atmospheric pCO2 and temperatures during the Hirnantian and Silurian glaciations suppressed CO2 removal by silicate weathering, driving 187Os/188Os and δ7Li variability, supporting the existence of climate-regulating feedbacks.

Citation

Sproson, A. D., Pogge von Strandmann, P. A., Selby, D., Jarochowska, E., Frýda, J., Hladil, J., …Lenton, T. M. (2022). Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations. Earth and Planetary Science Letters, 577, Article 117260. https://doi.org/10.1016/j.epsl.2021.117260

Journal Article Type Article
Acceptance Date Oct 22, 2021
Online Publication Date Nov 4, 2021
Publication Date Jan 1, 2022
Deposit Date Jan 5, 2023
Publicly Available Date Jan 5, 2023
Journal Earth and Planetary Science Letters
Print ISSN 0012-821X
Electronic ISSN 1385-013X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 577
Article Number 117260
DOI https://doi.org/10.1016/j.epsl.2021.117260

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