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首页> 外文期刊>Geochimica et Cosmochimica Acta: Journal of the Geochemical Society and the Meteoritical Society >Deposition, accumulation, and alteration of Cl-, NO3-, ClO4- and ClO3- salts in a hyper-arid polar environment: Mass balance and isotopic constraints
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Deposition, accumulation, and alteration of Cl-, NO3-, ClO4- and ClO3- salts in a hyper-arid polar environment: Mass balance and isotopic constraints

机译：高干旱极性环境中Cl-，NO3-，ClO4-和ClO3-盐的沉积，积累和改变：质量平衡和同位素约束

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The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl-, NO3-, ClO4- and ClO3- in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl- and NO3- isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO4-/NO3- ratios and NO3- isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO3-/ClO4- in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO3-, possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from similar to 10 to 30 kyr near the glacier to 70-200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization. (C) 2016 Elsevier Ltd. All rights reserved.
机译：南极麦克默多干旱谷（MDV）的多年冻土/沉积物中的盐分可用作干旱沙漠地球化学过程和古气候重建的替代物。以前对MDV多年冻土中盐分的分析主要是在沿海地区进行的，在该地区，多年冻土受到水过程和海洋和平流层源混合投入的影响。我们通过评估大学谷地的多年冻土/沉积物来扩展这项工作，该谷地位于液态水的运输和海洋影响最小的超干区。我们确定了在干燥和冰结水泥质土壤/沉积物，雪和冰川冰中的Cl-，NO3-，ClO4-和ClO3-的丰度，并确定了Cl-和NO3-的同位素特征。数据与升华之前的盐分沉积，核武器试验的结果均不一致，而是指向主要是平流层源以及取决于基质的不同程度的沉积后转化，从裸露土壤的最小变化到雪和冰川冰中的显着变化（光降解和/或挥发）。干燥多年冻土层中的离子丰度表明，在当前的气候条件下，垂直传输受到限制，这可能是由于融雪的渗透所致。 ClO4- / NO3-比例和NO3-同位素组成随深度和位置的细微变化可能反映了与运输有关的分馏和沉积历史。与沉积和其他干旱系统相比，表层土壤中ClO3- / ClO4-的低摩尔比表明，ClO3-在沉积后的损失很大，这可能是由于铁矿物质的还原，这可能对火星上的氧-氯物种有重要影响。盐的累积量随沿山谷的距离而变化，并且基于多种方法的表观累积时间范围从接近冰川的10至30 kyr到接近山谷口的70至200 kyr。盐的年龄相对较小，而冰胶沉积物中阴离子的浓度相对较低且均一，这表明要么是近期除盐的机制，要么是相对较现代的永冻土（<100万年）。总之，我们的结果表明，大学谷地近地表盐是平流层源的最终成员，这些平流层源不经过生物过程或广泛的迁移。 （C）2016 Elsevier Ltd.保留所有权利。

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