Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations
Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations
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锇和锂同位素证据表明风化反馈与轨道有机碳埋藏和志留纪冰川有关
DOI：
10.1016/j.epsl.2021.117260
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发表时间：
2022
影响因子：
5.3
通讯作者：
Lenton Timothy M.
中科院分区：
文献类型：
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作者：
Sproson Adam D.;Pogge von Strandmann Philip A.E.;Selby David;Jarochowska Emilia;Frida Jiri;Hladil Jindrich;Loydell David K.;Slavik Ladislav;Calner Mikael;Maier Georg;Munnecke Axel;Lenton Timothy M.
奥陶纪(∼487年至443Ma)以南半球大面积冰盖的形成而告终，这是地球历史上第二大大灭绝。紧随其后的是志留纪(∼443-419 Ma)，这是显生宙气候最不稳定的时期之一，与进一步灭绝事件有关的几次大尺度(>；5‰)碳同位素(δ13C)扰动就是明证。尽管经过了几十年的研究，但这些环境不稳定的原因仍然是个谜。在这里，我们提供了海相沉积岩的Os(187Os/188Os)和Li(δ7Li)同位素测量，涵盖了志留纪δ13C的四次漂移。Os和Li的同位素记录类似于之前为赫南提冰川记录的记录，表明了类似的原因机制。结合一个新的动态碳-锶-锂生物地球化学模型，我们认为，海洋有机碳循环的天文强迫，而不是火山弧脱气的减少或早期陆地植物的上升，导致了大气中二氧化碳的减少，触发了大陆尺度的冰川作用，强烈的全球冷却和地质记录中确认的海平面低点。Hirnantian冰期和志留纪冰期较低的大气PCO2和温度抑制了硅酸盐风化对CO2的去除，驱动了187Os/188Os和δ7Li变率，支持了气候调节反馈的存在。
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 (δ 13 C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187 Os/188 Os) and lithium (δ 7 Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ 13 C 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 CO 2, triggering continental scale glaciation, intense global cooling and eustatic sea-level lows recognised in the geological record. Lower atmospheric pCO 2 and temperatures during the Hirnantian and Silurian glaciations suppressed CO 2 removal by silicate weathering, driving 187 Os/188 Os and δ 7 Li variability, supporting the existence of climate-regulating feedbacks.