Global climate stabilisation by chemical weathering during the Hirnantian glaciation

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 (δ 7 Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma).We find a positive δ 7 Li 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 CO 2 degassing, which triggered abrupt global cooling, and much lower weathering rates.This lower CO 2 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.