The effect of temperature on experimental and natural chemical weathering rates of granitoid rocks
The effect of temperature on experimental and natural chemical weathering rates of granitoid rocks
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DOI：
10.1016/s0016-7037(99)00250-1
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发表时间：
1999-10
影响因子：
5
通讯作者：
A. White;A. Blum;T. Bullen;D. Vivit;M. Schulz;J. Fitzpatrick
中科院分区：
文献类型：
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作者：
A. White;A. Blum;T. Bullen;D. Vivit;M. Schulz;J. Fitzpatrick
研究了气候温度变化（5-35°C）对化学风化的影响，并利用含新鲜和风化花岗岩的流动柱和基于年溶质排放的流域自然花岗岩风化进行了实验研究。尽管新鲜花岗岩的Na和Si实验出水浓度明显高于风化花岗岩，但随着温度的升高，Na和Si浓度的增加比例相似。Si和Na表现出相当的平均表观活化能（Ea），分别为56和61 kJ/mol，这与在较大温度范围内测量长石溶解的实验结果相似。利用全球分布的86个花岗岩类流域溶质排放通量的扩展数据库，建立了一个温度-降水耦合模型，得出了Si的表观活化能（51 kJ/mol），这也与实验研究得出的结果相当。这种相关性强化了温度确实显著影响天然硅酸盐风化速率的证据。由于黑云母的快速氧化/溶解，与流域排放相比，柱状研究中流出的钾离子浓度相对于其他阳离子有所升高。K浓度对温度的敏感性较低，导致较低的平均值（27 kJ/mol），表明黑云母中较低能量层间部位的K损失。在较低温度下，黑云母的初始阳离子释放明显快于斜长石的阳离子释放。这与报道的在寒冷的冰川流域相对于温暖的温带环境中较高的K/Na比率相一致。随着温度的升高，相对于黑云母，斜长石释放的放射性较小的Sr增加，导致柱状流出物中87sr /86Sr比值相应降低。使用流出液K/Na比、Sr浓度和黑云母和斜长石的87sr /86Sr比进行简单的混合计算，近似于黑云母/斜长石在较高温度（35°C）下溶解的化学计量阳离子比，但随着温度的降低，黑云母的相对比例逐渐高估。Ca、Mg和Sr浓度密切相关，与温度没有一致的趋势，并且受风化黑云母中微量方解石或交换的控制。流域模式无法区分这些物种的气候信号，这与实验研究中观察到的较低的温度依赖性有关。
The effects of climatic temperature variations (5–35°C) on chemical weathering are investigated both experimentally using flow-through columns containing fresh and weathered granitoid rocks and for natural granitoid weathering in watersheds based on annual solute discharge. Although experimental Na and Si effluent concentrations are significantly higher in the fresh relative to the weathered granitoids, the proportional increases in concentration with increasing temperature are similar. Si and Na exhibit comparable average apparent activation energies (Ea) of 56 and 61 kJ/mol, respectively, which are similar to those reported for experimental feldspar dissolution measured over larger temperature ranges. A coupled temperature–precipitation model, using an expanded database for solute discharge fluxes from a global distribution of 86 granitoid watersheds, produces an apparent activation energy for Si (51 kJ/mol), which is also comparable to those derived from the experimental study. This correlation reinforces evidence that temperature does significantly impact natural silicate weathering rates. Effluent K concentrations in the column study are elevated with respect to other cations compared to watershed discharge due to the rapid oxidation/dissolution of biotite. K concentrations are less sensitive to temperature, resulting in a lower average Eavalue (27 kJ/mol) indicative of K loss from lower energy interlayer sites in biotite. At lower temperatures, initial cation release from biotite is significantly faster than cation release from plagioclase. This agrees with reported higher K/Na ratios in cold glacial watersheds relative to warmer temperate environments. Increased release of less radiogenic Sr from plagioclase relative to biotite at increasing temperature produces corresponding decreases in87Sr/86Sr ratios in the column effluents. A simple mixing calculation using effluent K/Na ratios, Sr concentrations and87Sr/86Sr ratios for biotite and plagioclase approximates stoichiometric cation ratios from biotite/plagioclase dissolution at warmer temperatures (35°C), but progressively overestimates the relative proportion of biotite with decreasing temperature. Ca, Mg, and Sr concentrations closely correlate, exhibit no consistent trends with temperature, and are controlled by trace amounts of calcite or exchange within weathered biotite. The inability of the watershed model to differentiate a climate signal for such species correlates with the lower temperature dependence observed in the experimental studies.