Pasquier Virgil, Sansjofre Pierre, Rabineau Marina, Revillon Sidonie, Houghton Jennifer, Fike David A
Laboratoire Géosciences Océan, UMR CNRS-6538, Institut Universitaire Européen de la Mer, Université Bretagne Occidentale, 29280 Plouzane, France;
Laboratoire Géosciences Océan, UMR CNRS-6538, Institut Universitaire Européen de la Mer, Université Bretagne Occidentale, 29280 Plouzane, France.
Proc Natl Acad Sci U S A. 2017 Jun 6;114(23):5941-5945. doi: 10.1073/pnas.1618245114. Epub 2017 May 22.
The sulfur biogeochemical cycle plays a key role in regulating Earth's surface redox through diverse abiotic and biological reactions that have distinctive stable isotopic fractionations. As such, variations in the sulfur isotopic composition (δS) of sedimentary sulfate and sulfide phases over Earth history can be used to infer substantive changes to the Earth's surface environment, including the rise of atmospheric oxygen. Such inferences assume that individual δS records reflect temporal changes in the global sulfur cycle; this assumption may be well grounded for sulfate-bearing minerals but is less well established for pyrite-based records. Here, we investigate alternative controls on the sedimentary sulfur isotopic composition of marine pyrite by examining a 300-m drill core of Mediterranean sediments deposited over the past 500,000 y and spanning the last five glacial-interglacial periods. Because this interval is far shorter than the residence time of marine sulfate, any change in the sulfur isotopic record preserved in pyrite (δS) necessarily corresponds to local environmental changes. The stratigraphic variations (>76‰) in the isotopic data reported here are among the largest ever observed in pyrite, and are in phase with glacial-interglacial sea level and temperature changes. In this case, the dominant control appears to be glacial-interglacial variations in sedimentation rates. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records, especially associated with intervals of substantial sea level change. This work provides an important perspective on the origin of variability in such records and suggests meaningful paleoenvironmental information can be derived from pyrite δS records.
硫生物地球化学循环通过各种具有独特稳定同位素分馏的非生物和生物反应，在调节地球表面氧化还原方面发挥着关键作用。因此，地球历史上沉积硫酸盐和硫化物相的硫同位素组成（δS）变化可用于推断地球表面环境的实质性变化，包括大气氧的增加。此类推断假定各个δS记录反映了全球硫循环的时间变化；这一假设对于含硫酸盐矿物可能有充分依据，但对于基于黄铁矿的记录则不太确定。在此，我们通过研究一段300米长的地中海沉积物钻孔岩芯来探究海洋黄铁矿沉积硫同位素组成的其他控制因素，该岩芯沉积于过去50万年，跨越了最后五个冰期 - 间冰期。由于这个时间间隔远短于海洋硫酸盐的停留时间，保存在黄铁矿中的硫同位素记录（δS）的任何变化必然对应于局部环境变化。本文报道的同位素数据中的地层变化（>76‰）是黄铁矿中观测到的最大变化之一，并且与冰期 - 间冰期海平面和温度变化同步。在这种情况下，主要控制因素似乎是沉积速率的冰期 - 间冰期变化。这些结果表明，沉积硫同位素记录存在重要但先前被忽视的沉积控制因素，特别是与海平面大幅变化的时期相关。这项工作为这类记录变化的起源提供了重要视角，并表明可以从黄铁矿δS记录中获取有意义的古环境信息。
