Global climate stabilisation by chemical weathering during the Hirnantian glaciation
Pogge von Strandmann, PAE
European Association of Geochemistry
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Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled “weathering thermostat” has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (δ7Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma). We find a positive δ7Li excursion, suggestive of a silicate weathering decline. Using a coupled lithium-carbon model, we show that initiation of the glaciation was likely caused by declining CO2 degassing, which triggered abrupt global cooling, and much lower weathering rates. This lower CO2 drawdown during the glaciation allowed climatic recovery and deglaciation. Combined, the data and model provide support from the geological record for the operation of the weathering thermostat.
This study and PPvS were funded by NERC advanced research fellowship NE/I020571/2 and ERC Consolidator grant 682760 - CONTROLPASTCO2. AD thanks the support of the Natural Science and Engineering Council of Canada (Discovery Grant). TML was supported by NERC (NE/N018508/1). DS acknowledges the Total Endowment Fund. Michael Melchin is thanked for reading an earlier version of the manuscript. This manuscript was greatly improved by reviews from Lee Kump, Jerome Gaillardet and an anonymous reviewer.
This is the final version of the article. Available from European Association of Geochemistry via the DOI in this record.
vol. 3, no. 2