Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record
Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record
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DOI：
10.1073/pnas.1218874110
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发表时间：
2013-07-09
影响因子：
11.1
通讯作者：
Johnston, David T.
中科院分区：
文献类型：
--
作者：
Leavitt, William D.;Halevy, Itay;Johnston, David T.
中生代大气氧含量与有机碳和黄铁矿硫的埋藏历史有关。然而，硫循环仍然受到很大的限制，导致O-2预算的不确定性。在这里，我们提出的实验链接的分馏的多个硫同位素的微生物硫酸盐还原的速率的幅度。这些数据表明，这种分馏是由电子供体（有机质）的可用性，而不是由电子受体（硫酸盐），沉积埋藏环境之间的变化的环境约束的浓度控制。通过将这些结果与黄铁矿埋藏的沉积物生物地球化学模型相结合，我们发现在过去200 Ma中观察到的硫同位素分馏与浅海底环境的面积范围之间存在很强的关系。我们将其解释为微生物硫酸盐还原速率对富含有机物的海底环境的可用性的全球依赖性。然而，在早/中古生代分馏未能与陆棚面积。我们认为，这种脱钩反映了较浅的古氧化还原边界，主要局限于水柱在早古生代。这两种状态之间的过渡开始于石炭纪，并在三叠纪-侏罗纪边界附近结束，表明O-2对石炭纪上升的长期响应。总之，这些结果奠定了基础脱钩硫酸盐还原速率的变化，从全球平均记录的黄铁矿埋藏，突出了当地性质的沉积过程如何影响全球记录。这一区别极大地改善了我们对S循环及其与大气氧历史关系的理解。
Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O-2 budgets. Here we present experiments linking the magnitude of fractionations of the multiple sulfur isotopes to the rate of microbial sulfate reduction. The data demonstrate that such fractionations are controlled by the availability of electron donor (organic matter), rather than by the concentration of electron acceptor (sulfate), an environmental constraint that varies among sedimentary burial environments. By coupling these results with a sediment bio-geochemical model of pyrite burial, we find a strong relationship between observed sulfur isotope fractionations over the last 200 Ma and the areal extent of shallow seafloor environments. We interpret this as a global dependency of the rate of microbial sulfate reduction on the availability of organic-rich sea-floor settings. However, fractionation during the early/mid-Paleozoic fails to correlate with shelf area. We suggest that this decoupling reflects a shallower paleoredox boundary, primarily confined to the water column in the early Phanerozoic. The transition between these two states begins during the Carboniferous and concludes approximately around the Triassic-Jurassic boundary, indicating a prolonged response to a Carboniferous rise in O-2. Together, these results lay the foundation for decoupling changes in sulfate reduction rates from the global average record of pyrite burial, highlighting how the local nature of sedimentary processes affects global records. This distinction greatly refines our understanding of the S cycle and its relationship to the history of atmospheric oxygen.