The Hydrochemical Signature of Incongruent Weathering in Iceland
The Hydrochemical Signature of Incongruent Weathering in Iceland
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DOI：
10.1029/2021jf006450
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
T. Cole;M. Torres;P. Kemeny
中科院分区：
文献类型：
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作者：
T. Cole;M. Torres;P. Kemeny
玄武岩流域，如在冰岛发现的那些被认为是通过硅酸盐风化作用封存CO2的重要场所。然而，确定CO2吸收量的大小取决于准确地解释河流化学。在这里，我们汇编了来自冰岛的地球化学数据，并用它们来约束风化过程。具体来说，我们使用一个新开发的逆模型来量化来自雨水和热液流体的溶质供应，并允许可变的硅酸盐端元组成，通过第二相形成去除溶质，以及一些来自碳酸盐溶解的Ca。虽然这些过程中的一些已经考虑过以前，他们还没有被认为是一起允许我们重新确定其相对贡献。我们发现冰岛的风化作用在两个方面是不一致的。首先，原生硅酸盐的溶质释放的特点是钠的比例比预期的散装玄武岩，这可能反映了优先风化或一些贡献的韵律。这种Na富集通过第二相的优先Mg和K吸收而进一步增强。在我们的数据集中，没有样品（n = 537）需要碳酸盐溶解，即使同位素数据（δ 26 Mg，δ 30 Si，δ 44 Ca，和/或87 Sr/86 Sr）包括在内。虽然一些碳酸盐风化是允许的，硅酸盐风化可能占主导地位。我们在冰岛观察到的复杂性强调了需要逆模型来解释各种各样的过程和端元。考虑到冰岛的河流通量比同成分玄武岩风化的预期更富含Na，CO2下降的特征时间尺度可能会受到影响。
Basaltic watersheds such as those found in Iceland are thought to be important sites of CO2 sequestration via silicate weathering. However, determining the magnitude of CO2 uptake depends on accurately interpreting river chemistry. Here, we compile geochemical data from Iceland and use them to constrain weathering processes. Specifically, we use a newly developed inverse model to quantify solute supply from rain and hydrothermal fluids as well as allow for variable silicate end‐member compositions, solutes to be removed via secondary phase formation, and some Ca to be sourced from carbonate dissolution. While some of these processes have been considered previously, they have not been considered together allowing us to newly determine their relative contributions. We find that weathering in Iceland is incongruent in two ways. First, solute release from primary silicates is characterized by a higher proportion of Na than would be expected from bulk basalts, which may reflect preferential weathering or some contribution from rhyolites. This Na enrichment is further enhanced by preferential Mg and K uptake by secondary phases. No samples in our data set (n = 537) require carbonate dissolution even if isotopic data (δ26Mg, δ30Si, δ44Ca, and/or 87Sr/86Sr) are included. While some carbonate weathering is allowable, silicate weathering likely dominates. The complexity we observe in Iceland underscores the need for inverse models to account for a wide range of processes and end‐members. Given that riverine fluxes from Iceland are more Na‐rich than expected for congruent basalt weathering, the characteristic timescale of CO2 drawdown is likely affected.