Bridging the gap between laboratory measurements and field estimations of silicate weathering using simple calculations
Bridging the gap between laboratory measurements and field estimations of silicate weathering using simple calculations
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使用简单的计算弥合硅酸盐风化的实验室测量和现场估计之间的差距
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
Chen Zhu
中科院分区：
文献类型：
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作者：
J. Ganor;Peng Lu;Zuoping Zheng;Chen Zhu
实验室中观察到的硅酸盐矿物的风化速率通常比现场研究推断的高出五个数量级。简单的计算表明，即使在标准的实验室实验中完全模拟了现场条件，也不可能测量在现场观察到的矿物缓慢溶解速度。由于无法测量典型野外条件下的溶解速率，因此应根据现场条件外推可用数据。为此，结合25℃下自然风化少长石的远离平衡溶解速率和80℃时偏离平衡对新鲜钠长石溶解速率的影响，建立了斜长石在野外溶解的速率定律。与通常认为实验室实验预测的溶解速率快于野外实验相反，基于该速率定律的模拟表明，实验室溶解实验预测的溶解速率实际上比野外观测的慢。这种差异是由于次生矿物的沉淀作用影响原生矿物的饱和度，从而影响其溶解速度。事实上，在模拟中加入高岭石沉淀可以显著提高斜长石的溶解速度。此外，在模拟中观察到了低长石溶解和高岭石沉淀之间的强烈耦合。我们建议，这样的耦合也必须存在于场中。因此，任何预测野外溶解速率的尝试都需要知道次生矿物的沉淀速率。
Weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies. Simple calculations show that even if the field conditions were fully simulated in standard laboratory experiments, it would be impossible to measure the slow rates of mineral dissolution that are observed in the field. As it is not possible to measure the dissolution rates under typical field conditions, one should extrapolate the available data to the field conditions. To do this, a rate law for the dissolution of plagioclase in the field was formulated by combining the far from equilibrium dissolution rate of weathered natural oligoclase at 25°C with the effect of deviation from equilibrium on dissolution rate of fresh albite at 80°C. In contrast to the common view that laboratory experiments predict dissolution rates that are faster than those in the field, the simulation based on this rate law indicates that laboratory dissolution experiments actually predict slower rates than those observed in the field. This discrepancy is explained by the effect of precipitation of secondary minerals on the degree of saturation of the primary minerals and therefore on their dissolution rate. Indeed, adding kaolinite precipitation to the simulation significantly enhances the dissolution rate of the plagioclase. Moreover, a strong coupling between oligoclase dissolution and kaolinite precipitation was observed in the simulation. We suggest that such a coupling must exist in the field as well. Therefore, any attempt to predict the dissolution rate in the field requires knowledge of the rate of the secondary mineral precipitation.