Global climate stabilisation by chemical weathering during the Hirnantian glaciation
Global climate stabilisation by chemical weathering during the Hirnantian glaciation
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DOI：
10.7185/geochemlet.1726
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发表时间：
2017-06
期刊：
影响因子：
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通讯作者：
P. V. Strandmann;A. Desrochers;M. Murphy;A. Finlay;D. Selby;T. Lenton
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作者：
P. V. Strandmann;A. Desrochers;M. Murphy;A. Finlay;D. Selby;T. Lenton
硅酸盐岩石的化学风化作用是大气中二氧化碳减少的主要机制。因此，影响风化的过程是控制全球气候的核心。长期以来，人们一直建议使用温度控制的“风化恒温器”来稳定长期气候，但没有来自地质记录的明确证据。在这里，我们使用锂同位素（δ7Li）来评估在一个重要的气候冷却期——奥陶世末希尔南天冰期（~445 Ma）——硅酸盐风化的影响。我们发现一个正的δ7Li偏移，暗示了硅酸盐风化作用的减弱。利用锂-碳耦合模型，我们发现冰川的开始可能是由于二氧化碳脱气减少引起的，这引发了全球突然变冷，并且风化速率大大降低。在冰期，二氧化碳的减少使气候恢复和冰川消融成为可能。数据和模型的结合为风化恒温器的运行提供了地质记录的支持。
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.