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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 >Oxygen-17 excesses of the Central Namib gypcretes: spatial distribution
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Oxygen-17 excesses of the Central Namib gypcretes: spatial distribution

机译：中央纳米布石膏的氧气17过量：空间分布

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摘要

We present here sulfate oxygen isotopic data (72 samples with both δ~(18)O and δ~(17)O) systematically collected from the Central Namib Desert. Surface soils from two shore-inland (west-east) transects exhibit a gradual increase in the sulfate oxygen-17 excess (Δ~(17)O = δ~(17)O-0.52 δ~(18)O) until at ca. 70 km inland, where no continuous gypcrete deposit is observed further east (inland). The oxygen isotopic compositions for water-soluble sulfates extracted from soils and gypcretes range from 8.3 to 13.3‰ and 0.06 to 1.11‰ for δ~(18)O and Δ~(17)O, respectively. The lateral pattern is similar to what has been seen in the cold deserts of the Antarctic dry valleys. However, unlike the dry valleys, no discernible correlation is found between δ~(18)O and Δ~(17)O, or between the depth of soil horizon and Δ~(17)O in the Namib. Possible explanations include a relatively smaller component of dimethylsulfide (DMS)-derived sulfate in the total gypsum deposits and/or more active surface processes (e.g., flooding and leaching) in the Central Namib Desert than in the Antarctic cold deserts. Although current state of knowledge is insufficient to delineate quantitatively the sulfate contributions from different sources and reactions, the measurement of sulfate Δ~(17)O does identify an unmistakable atmospheric sulfate component and provides additional independent information regarding sources and reactions.
机译：我们在这里展示了从中央纳米布沙漠系统收集的硫酸盐氧同位素数据（具有δ〜（18）O和δ〜（17）O的72个样品）。来自两个沿海-内陆（西-东）样带的表层土壤逐渐显示出硫酸氧17过量（Δ〜（17）O =δ〜（17）O-0.52δ〜（18）O）逐渐增加直到。内陆70公里，在东边（内陆）没有观察到连续的石膏沉积物。从土壤和石膏中提取的水溶性硫酸盐的氧同位素组成，δ〜（18）O和Δ〜（17）O的范围分别为8.3至13.3‰和0.06至1.11‰。横向模式类似于在南极干旱谷的寒冷沙漠中所见。但是，与干旱谷地不同，在纳米布中，δ〜（18）O和Δ〜（17）O之间，土壤层深度与Δ〜（17）O之间没有明显的相关性。可能的解释包括，与南极寒冷沙漠相比，中部纳米布沙漠中总石膏沉积物中和/或更活跃的地表过程（例如洪水和浸出）中来自二甲基硫醚（DMS）的硫酸盐成分相对较小。尽管当前的知识水平不足以定量地描述来自不同来源和反应的硫酸盐贡献，但硫酸盐Δ〜（17）O的测量确实可以确定无误的大气硫酸盐成分，并提供有关来源和反应的其他独立信息。

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