Sedimentary Pyrite Formation in a Seasonally Oxygen‐Stressed Estuary: Potential Imprints of Microbial Ecology and Position‐Specific Isotope Fractionation
Sedimentary Pyrite Formation in a Seasonally Oxygen‐Stressed Estuary: Potential Imprints of Microbial Ecology and Position‐Specific Isotope Fractionation
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DOI：
10.1029/2022jg007324
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发表时间：
2023-04
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通讯作者：
Kalev G. Hantsoo;M. Gomes;S. Malkin;D. Brenner;W. Kenney
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作者：
Kalev G. Hantsoo;M. Gomes;S. Malkin;D. Brenner;W. Kenney
沉积黄铁矿记录是重建古环境条件必不可少的，但这些记录可能会受到氧浓度和温度的季节性波动的影响，这可能会影响生物扰动，硫化物通量和硫化物氧化微生物（SOMs）的分布。为了研究季节性氧胁迫如何影响硫化物（<2 cm）黄铁矿的形成，我们测量了切萨皮克湾生物扰动浅滩和缺氧通道的时间序列浓度和黄铁矿硫的硫同位素（δ 34 S）组成以及潜在的前体化合物。我们还测量了放射性同位素深度剖面，以估计沉积速率和生物扰动强度。结果表明，净黄铁矿降水仅限于夏季和初秋在这两个网站。与非生物扰动部位相比，轻度生物扰动部位的黄铁矿浓度更高，并且对前体化合物浓度的反应性明显更强。这种差异可能是由两个网站之间的优势SOM社区的差异。尽管如此，相似的黄铁矿δ 34 S值意味着SOM群落的变化对这里的硫铁矿δ 34 S值的影响有限。然而，我们发现，黄铁矿δ 34 S值是一致的，并远远低于同时代的前体化合物在这两个网站。稳态模型表明，S8-多硫化物池中的平衡位置特定同位素分馏（PSIF）效应可以在黄铁矿和零价硫的δ 34 S值之间产生4.3-7.3‰的差距。这项研究表明，SOM社区可能有不同的影响，黄铁矿积累的季节性动态系统中，PSIF在多硫化物池可能会留下一个印记，黄铁矿同位素记录。
Sedimentary pyrite records are essential for reconstructing paleoenvironmental conditions, but these records may be affected by seasonal fluctuations in oxygen concentration and temperature, which can impact bioturbation, sulfide fluxes, and distributions of sulfide oxidizing microbes (SOMs). To investigate how seasonal oxygen stress influences surficial (<2 cm) pyrite formation, we measured time‐series concentrations and sulfur isotope (δ34S) compositions of pyrite sulfur along with those of potential precursor compounds at a bioturbated shoal site and an oxygen‐deficient channel site in Chesapeake Bay. We also measured radioisotope depth profiles to estimate sedimentation rates and bioturbation intensities. Results show that net pyrite precipitation was restricted to summer and early autumn at both sites. Pyrite concentration was higher and apparently more responsive to precursor compound concentration at the mildly bioturbated site than at the non‐bioturbated site. This disparity may be driven by differences in the dominant SOM communities between the two sites. Despite this, the sites' similar pyrite δ34S values imply that changes in SOM communities have limited effects on surficial pyrite δ34S values here. However, we found that pyrite δ34S values are consistently and anomalously lower than coeval precursor compounds at both sites. A steady‐state model demonstrates that equilibrium position‐specific isotope fractionation (PSIF) effects in the S8‐polysulfide pool can create a 4.3–7.3‰ gap between δ34S values of pyrite and zero‐valent sulfur. This study suggests that SOM communities may have distinct effects on pyrite accumulation in seasonally dynamic systems, and that PSIF in the polysulfide pool may leave an imprint in pyrite isotope records.