Sulfur isotopes in coal constrain the evolution of the Phanerozoic sulfur cycle
Sulfur isotopes in coal constrain the evolution of the Phanerozoic sulfur cycle
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DOI：
10.1073/pnas.1306450110
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发表时间：
2013-05-21
影响因子：
11.1
通讯作者：
Canfield, Donald E.
中科院分区：
文献类型：
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作者：
Canfield, Donald E.
硫酸盐是现代海水中第二丰富的阴离子（仅次于氯离子），其循环与地球表面的有机物和氧气循环密切相关。例如，微生物还原硫化物会氧化大量的有机碳，随后硫化物与铁反应产生黄铁矿，黄铁矿埋藏在沉积物中是大气的重要氧气来源。在地球历史上，海水硫酸盐的浓度和硫循环的运行经历了动态变化，我们对这段历史的理解主要基于对海水硫酸盐和沉积黄铁矿的同位素记录的解释。然而，同位素记录并没有给出古代硫循环的完整画面。这是因为，在标准同位素质量平衡模型中，变量多于约束。通常情况下，在解释同位素记录和缺乏更好的信息时，人们假设进入海洋的硫酸盐的同位素组成随着时间的推移保持不变。有人认为，这一假设有一个约束，在过去的390马从煤中硫的同位素组成。事实上，这些成分与现代输入海洋的地表水成分并无实质性差异。当应用到质量平衡模型，这些结果支持以前的解释硫循环操作和反对最近的建议，硫酸盐一直是一个次要的球员硫循环通过古生代Eon。
Sulfate is the second most abundant anion (behind chloride) in modern seawater, and its cycling is intimately coupled to the cycling of organic matter and oxygen at the Earth's surface. For example, the reduction of sulfide by microbes oxidizes vast amounts of organic carbon and the subsequent reaction of sulfide with iron produces pyrite whose burial in sediments is an important oxygen source to the atmosphere. The concentrations of seawater sulfate and the operation of sulfur cycle have experienced dynamic changes through Earth's history, and our understanding of this history is based mainly on interpretations of the isotope record of seawater sulfates and sedimentary pyrites. The isotope record, however, does not give a complete picture of the ancient sulfur cycle. This is because, in standard isotope mass balance models, there are more variables than constraints. Typically, in interpretations of the isotope record and in the absence of better information, one assumes that the isotopic composition of the input sulfate to the oceans has remained constant through time. It is argued here that this assumption has a constraint over the last 390 Ma from the isotopic composition of sulfur in coal. Indeed, these compositions do not deviate substantially from the modern surface-water input to the oceans. When applied to mass balance models, these results support previous interpretations of sulfur cycle operation and counter recent suggestions that sulfate has been a minor player in sulfur cycling through the Phanerozoic Eon.