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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 >Organic sulfur fluxes and geomorphic control of sulfur isotope ratios in rivers
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Organic sulfur fluxes and geomorphic control of sulfur isotope ratios in rivers

机译：河流中硫同位素比的有机硫磺助熔剂和均匀控制

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Pyrite oxidation plays a critical role in the relationship between weathering and climate, and its impact on the global carbon cycle has previously been constrained through inversion models utilizing observations of river sulfate (SO42-) and its S-34/S-32 isotope ratio (delta S-34(SO4)). However, measurements from some rivers have suggested that delta S-34(SO4) can be substantially impacted by processes such as microbial sulfate reduction and/or sulfur assimilation and cycling, rather than simply reflecting a weighted mixture of lithologic sulfur sources. To study the prevalence and controls on SO42- transformations, we measured dissolved major element concentrations and delta S-34(SO4) in river water samples from throughout western Iceland. Our analyses focused on samples from a small catchment hosting the Efri Haukadalsa river, a system with relatively uniform and isotopically constrained basaltic bedrock. We also measured sediment delta S-34 and sulfur speciation using sulfur K-edge X-ray absorption spectroscopy on sediment and vegetation samples from this catchment. Values of dissolved delta S-34(SO4) in the Efri Haukadalsa ranged from 2.5 parts per thousand to 23.7 parts per thousand and had a linear relationship with Cl-/SO42- ratios, indicating that SO42- predominantly derived from basalt weathering and meteoric precipitation. The lower delta S-34(SO4) values were found in fluvial valleys with V-shaped cross sections, while higher values of delta S-34(SO4) occurred in U-shaped, glacially eroded valleys with thick alluvial fills blanketing the valley floor. Spectroscopic observations identified organic sulfur phases in suspended river sediment, floodplain deposits, and vegetation. Mass balance calculations quantified the organic sulfur flux as less than 10% of SO42- export, and sediment delta S-34 values were comparable to river delta S-34(SO4). We interpreted these isotopic and chemical patterns as reflecting differences in the availability of unweathered bedrock across the Efri Haukadalsa catchment, with V-shaped valleys having greater access to fresh sulfide-bearing minerals than alluviated U-shaped valleys; this interpretation is in contrast to one in which the elevated delta S-34(SO4) values reflect fractionation during sulfur transformations along alluvial reaches. These results validated the application of river inversion models for constraining weathering fluxes and affirmed that pyrite oxidation globally, even in the presence of river sulfur cycling, modulates the abundance of atmospheric carbon dioxide. (C) 2021 Elsevier B.V. All rights reserved.
机译：黄铁矿氧化在风化和气候之间的关系中起着关键作用，其对全球碳循环的影响此前已通过利用硫酸河（SO42-）及其S-34/S-32同位素比值（δS-34（SO4））观测的反演模型得到限制。然而，一些河流的测量表明，三角洲S-34（SO4）可能会受到微生物硫酸盐还原和/或硫同化和循环等过程的实质性影响，而不仅仅是反映岩性硫源的加权混合。为了研究SO42转化的患病率和控制措施，我们测量了冰岛西部河水样本中溶解的主要元素浓度和δS-34（SO4）。我们的分析集中在埃弗里·霍卡达尔萨河所在的一个小集水区的样本上，这是一个具有相对均匀且同位素受限的玄武岩基岩的系统。我们还使用硫K边X射线吸收光谱法对该流域的沉积物和植被样品测量了沉积物三角洲S-34和硫形态。埃弗里-豪卡达尔萨地区溶解的δS-34（SO4）值在2.5‰到23.7‰之间，与Cl-/SO42-比值呈线性关系，表明SO42-主要来源于玄武岩风化和大气降水。较低的三角洲S-34（SO4）值出现在具有V形横截面的河谷中，而较高的三角洲S-34（SO4）值出现在覆盖谷底的U形冰川侵蚀河谷中。光谱观测确定了悬浮河流沉积物、漫滩沉积物和植被中的有机硫相。质量平衡计算将有机硫通量量化为SO42-出口量的10%以下，沉积物delta S-34值与河流delta S-34（SO4）值相当。我们将这些同位素和化学模式解释为反映了埃弗里-豪卡达尔萨流域未风化基岩的可用性差异，V形山谷比冲积U形山谷更容易获得新鲜的含硫化物矿物；这种解释与升高的三角洲S-34（SO4）值反映沿冲积河段硫转化期间的分馏形成对比。这些结果验证了河流反演模型在限制风化通量方面的应用，并确认了全球范围内的黄铁矿氧化，即使在河流硫循环的情况下，也会调节大气中二氧化碳的丰度。（c）2021爱思唯尔B.V.保留所有权利。

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