Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks
Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks
复制标题
DOI：
10.1073/pnas.1702953114
复制
发表时间：
2017-07
期刊：
影响因子：
--
通讯作者：
Mark A. Torres;Mark A. Torres;Mark A. Torres;Nils Moosdorf;Nils Moosdorf;J. Hartmann;J. Adkins
中科院分区：
文献类型：
--
作者：
Mark A. Torres;Mark A. Torres;Mark A. Torres;Nils Moosdorf;Nils Moosdorf;J. Hartmann;J. Adkins
重要性我们汇编的数据表明，正如先前假设的那样，排出冰川的水具有不同于非冰川河流的溶质化学，反映了不同比例的矿物风化反应。在冰川风化过程中，黄铁矿氧化程度升高会产生酸性，向大气中释放碳。我们表明，这种效应可能会导致过去100万年的冰川周期中二氧化碳的变化。在地球进入和退出冰化状态的更长的数百万年时间尺度上，黄铁矿衍生的硫酸盐持续添加到海洋中可能会改变全球碳循环的平衡，使海洋-大气中的二氧化碳增加，从而提供一种负反馈机制，防止冰川失控。这一机制依赖于氧化，从而依赖于充足的氧气。冰川作用、化学风化和全球碳循环之间的联系可以引导全球气候在地质时期的演变，但甚至这个系统中反馈的方向性仍有待解决。在这里，我们汇编了来自冰川集水区的水化学数据，使用这些数据来评估与冰川风化相关的主要化学反应，并探索其对长期地球化学循环的影响。我们汇编的集水区的风化产生量高于全球平均水平，这在一定程度上是由于冰川集水区的径流较高。我们的分析支持冰川风化的主要特征是微量硫化物和碳酸盐矿物的风化。为了评估冰川风化对大气二氧化碳的影响，我们使用溶质混合模型来预测风化反应产生的碱度与溶解无机碳(DIC)的比率。与非冰期风化作用相比，冰川风化作用产生的碱度/DIC比值更有可能小于1，这表明冰川作用导致的硫化物氧化增强可能是大气中二氧化碳的来源之一。粗略计算表明，氧化通量可以改变海洋-大气二氧化碳平衡25ppm或更多，超过10Ky。在更长的时间尺度上，二氧化碳的释放可能会起到负反馈的作用，限制冰川作用的进程，这取决于岩性和大气中O2的浓度。未来关于冰川-风化-碳循环反馈的工作除了考虑硅酸盐矿物外，还应考虑微量硫化物矿物的风化作用。
Significance We compile data showing that, as hypothesized previously, waters draining glaciers have solute chemistry that is distinct from nonglacial rivers and reflects different proportions of mineral weathering reactions. Elevated pyrite oxidation during glacial weathering could generate acidity, releasing carbon to the atmosphere. We show that this effect could contribute to changes in CO2 during glacial cycles of the past million years. Over the longer, multimillion-year timescales that Earth transitions into and out of glaciated states, sustained addition of pyrite-derived sulfate to the oceans could shift the balance of the global carbon cycle toward increasing CO2 in the ocean–atmosphere, thus providing a negative-feedback mechanism preventing runaway glaciation. This mechanism depends on oxidation and thus sufficient O2. Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.