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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Different sulfate sources and their post-depositional migration in Atacama soils
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Different sulfate sources and their post-depositional migration in Atacama soils

机译：阿塔卡马土壤中不同硫酸盐源及其沉积后的迁移

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Sulfate is one of the major salts accumulated in the hyperarid Atacama Desert, Chile. Its origin has been attributed to local weathering, volcanic source, sea salt, and atmosphere deposition. Previous studies concluded that atmospheric sulfate is present in the desert, but this term was poorly defined in terms of chemical origin, and its contribution to the total sulfate budget in soil is debated. The contribution of each potential sulfate source is expected to vary geographically due to different source locations. Efforts to quantify the contribution from each source have been hampered by the lack of well-defined isotopic compositions for its end-members. In this study, we discard the vague term of "atmospheric sulfate" by recognizing two major sulfate sources on the basis of their formation pathways: primary and secondary sulfate. Primary sulfate, including those from rock weathering, sea salt, and volcanic ash leachates, do not have an ~(17)O anomaly. Secondary sulfate, derived from the oxidation of reduced sulfur gases (biological or volcanic emissions) by atmospheric ozone or hydrogen peroxide, however, has an ~(17)O anomaly. We developed a method to extract water-soluble anions sequentially or entirely from bulk soil samples, and analyzed the sulfate concentrations and ~(17)O anomalies for four geographically representative soil profiles in the central Atacama Desert (23°S to 25.5°S). We found that sequential sulfate extractions on the same soil sample produce sulfate with decreasing Δ17O values. Except for a positive bulge at 20 to 50 cm in depth, there is a general increase in the Δ~(17)O value for total sulfate with soil depth for all the four soil profiles that we examined. These findings are consistent with the hypothesis that secondary sulfates (~(17)O-anomalous sulfates) are more soluble and thus preferentially leached in liquid water than primary sulfate. The finding also warns that incomplete sulfate extraction from sulfate-rich soils yields unpredictable results. We infer a Δ~(17)O value of ～4.6‰ for secondary sulfate based on data from partial sulfate extraction experiments. Total contribution of secondary sulfate in the central Atacama Desert is estimated to range from 9% to 24%, with the highest percentage in the Central Depression.
机译：硫酸盐是智利超干旱阿塔卡马沙漠中积累的主要盐之一。它的起源归因于当地的风化，火山源，海盐和大气沉积。先前的研究得出的结论是沙漠中存在大气中的硫酸盐，但是这个术语在化学来源方面定义不清，并且有人争论其对土壤中总硫酸盐预算的贡献。每种潜在的硫酸盐来源的贡献预计会因地理位置的不同而在地理位置上有所不同。由于缺乏明确的同位素组成，因此难以量化每个来源的贡献。在这项研究中，我们通过识别两种主要的硫酸盐来源（初级和次级硫酸盐）来识别它们，从而摒弃了“大气硫酸盐”这个模糊的术语。初级硫酸盐，包括岩石风化，海盐和火山灰渗滤液中的硫酸盐，没有〜（17）O异常。但是，次级硫酸盐是由大气中的臭氧或过氧化氢对还原的硫气（生物或火山排放物）进行氧化而衍生的，具有〜（17）O异常。我们开发了一种从大量土壤样品中顺序或完全提取水溶性阴离子的方法，并分析了中部阿塔卡马沙漠（23°S至25.5°S）中四个具有地理代表性的土壤剖面的硫酸盐浓度和〜（17）O异常。 。我们发现，在相同的土壤样品上连续进行硫酸盐萃取会产生Δ17O值降低的硫酸盐。在我们研究的所有四种土壤剖面中，除了在深度为20至50 cm处出现正隆起外，总硫酸盐的Δ〜（17）O值均随土壤深度的增加而普遍增加。这些发现与以下假设相符：仲硫酸盐（〜（17）O-异常硫酸盐）比伯硫酸盐更易溶于水，因此优先浸入液态水中。该发现还警告说，从富含硫酸盐的土壤中不完全提取硫酸盐会产生无法预测的结果。根据部分硫酸盐提取实验的数据，我们得出仲硫酸盐的Δ〜（17）O值为4.6‰。估计中部阿塔卡马沙漠中次生硫酸盐的总贡献量在9％到24％之间，在中部大萧条中百分比最高。

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