Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction
Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction
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DOI：
10.1016/j.gca.2021.02.037
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发表时间：
2021-06-10
影响因子：
5
通讯作者：
Mason, Andrew J.
中科院分区：
文献类型：
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作者：
Day, Christopher C.;von Strandmann, Philip A. E. Pogge;Mason, Andrew J.
我们报告了洞穴模拟碳酸盐沉淀实验中Li的测量结果，以便：i)评估适用于洞穴生长的预期同位素分选因子，以及ii)有助于更广泛地了解碳酸盐中锂的结合。实验装置密切模仿自然过程（例如，由CO2脱气驱动的沉淀，低离子强度溶液，薄溶液膜），但在实验室环境中允许控制生长条件（温度，pCO(2)，滴速，碳酸盐饱和度指数和初始溶液的组成）。对于主要的一批方解石生长实验，我们的平均1000ln α（方解石溶液）是-8.5 +/- 2（2 sigma）。1000ln α对洞穴内生长条件的低灵敏度对于使用洞穴样品重建风化强度是令人鼓舞的。在不同温度下，方解石饱和度指数在0.1 ~ 0.6之间，生长速率独立变化，对D（Li）和1000ln α均无显著影响。对于整个生长条件范围（考虑所有温度和方解石饱和度指数），我们观察到1000ln α的小而显著的下降，我们不将其归因于温度。基于研究间比较，我们定义LogDLi = 0.09(+/- 0.04) x GR - 3.2(+/- 0.2)，其中GR为生长速率，单位为10(-8)mmol cm(-2) s（-1）。这与先前定义的在较低的增长率范围内的关系类似。在本研究的整个生长速率范围内，在rho = 0.018水平上，1000ln alpha = -0.13 (+/- 0.04) x GR - 7.1（+/- 0.3）是显著的，与表面捕获控制一致。未来的实验应该测试诸如生长速率和pH等因素，独立于其他变量，以进一步评估它们在定义1000ln alpha中的作用。在20摄氏度的实验中，随着[Mg]（溶液）的增加，方解石、高镁方解石（HMC）和文石的α值为1000ln。我们对这三种矿物学的1000ln alpha值在-7.3和-10.7之间。特别是对于HMC和文石，在实验室和自然环境中生长的CaCO3的1000ln alpha值与其他公布的值非常一致。与大量碳酸盐、底栖有孔虫和腕足动物的测量结果一致，这表明碳酸盐矿物学之间的1000ln α差异可能并不总是像一些早期研究所表明的那样大。(C) 2021 Elsevier Ltd版权所有。
We report Li measurements from cave-analogue carbonate-precipitation experiments in order to: i) assess the expected isotope fractionation factors applicable to speleothem growth, and ii) contribute to the wider understanding of lithium incorporation in carbonates. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2 degassing, low ionic strength solution, thin solution film) but within a laboratory setting that allows for controlled growth conditions (temperature, pCO(2), drip rate, carbonate saturation index and the composition of the initial solution). For the main batch of calcite growth experiments our average 1000ln alpha(calcite-solution )is -8.5 +/- 2(2 sigma). This low sensitivity of 1000ln alpha to in-cave growth conditions is encouraging for weathering intensity reconstruction using speleothem samples. At each temperature, growth rate was varied independently with calcite saturation indices ranging between 0.1 and 0.6, with no significant impact on either D(Li) or 1000ln alpha. For the full range of growth conditions (considering all temperatures and calcite saturation indices) we observe a small but significant decrease in 1000ln alpha, which we do not attribute to temperature. Based on an inter-study comparison we define LogDLi = 0.09(+/- 0.04) x GR - 3.2(+/- 0.2), where GR is growth rate in units of 10(-8) mmol cm(-2) s(-1). This is similar to the previously defined relationship over a reduced range of growth rates. Over this study's full range of growth rates, 1000ln alpha = -0.13 (+/- 0.04) x GR - 7.1(+/- 0.3) is significant at the rho = 0.018 level, consistent with a surface entrapment control. Future experiments should test factors such as growth rate and pH, independently of other variables, to further assess their role in defining 1000ln alpha. A subset of 20 degrees C experiments, with increasing [Mg](solution), provides 1000ln alpha for calcite, high-magnesian calcite (HMC) and aragonite. Our values of 1000ln alpha for these three mineralogies range between -7.3 and -10.7. For HMC and aragonite in particular there is close agreement with other published values of 1000ln alpha for CaCO3 grown in laboratory and in natural settings. In agreement with measurements in bulk carbonates, benthic foraminifera and brachiopods, this suggests that differences in 1000ln alpha between carbonate mineralogies may not always be as large as suggested by some earlier studies. (C) 2021 Elsevier Ltd. All rights reserved.