Global cooling forced increase in marine strontium isotopic ratios: Importance of mica weathering and a kinetic approach

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• 作者：Gaojun Li ; Jun Chen ; Junfeng Ji ; Lianwen Liu ; Jiedong Yang ; Xuefen Sheng
• 关键词：climate ; marine ⁸⁷Sr/⁸⁶Sr ; mica ; geochemical cycle ; kinetics
• 刊名：Earth and Planetary Science Letters
• 出版年：2007
• 出版时间：28 February 2007
• 年：2007
• 卷：254
• 期：3-4
• 页码：303-312
• 全文大小：407 K

文摘

The knowledge of how and why marine ⁸⁷Sr/⁸⁶Sr ratios changed helps understand the impacts of many processes on the global biogeochemical cycle in the geological past. Here we examine the possible influence of global cooling on the evolution of marine ⁸⁷Sr/⁸⁶Sr curve by a kinetic approach. The importance of mica weathering is emphasized due to its high content of radiogenic strontium and low activation energy in weathering reaction. Since the activation energy determines the sensitivity of weathering rate in response to temperature changes, global cooling will increase the ⁸⁷Sr/⁸⁶Sr ratio of continental flux by relatively preferential weathering of mica. Based on the average strontium contents and ⁸⁷Sr/⁸⁶Sr ratios of the mica minerals in the exposed upper continental crust, a kinetic model is established to survey the response of riverine ⁸⁷Sr/⁸⁶Sr to the changes of global temperatures. The model result indicates that the increase of riverine ⁸⁷Sr/⁸⁶Sr caused by global cooling can solely account for most of the increase in seawater ⁸⁷Sr/⁸⁶Sr since 3.4 Myr B.P. This finding emphasizes that the weathering kinetics is an important mechanism relating the global climate change to marine ⁸⁷Sr/⁸⁶Sr curve; and the marine ⁸⁷Sr/⁸⁶Sr curve should be used with great care in the climate-weathering-tectonic connections.