The sedimentary pyrite sulfur isotope (δ³⁴S) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite δ³⁴S signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide δ³⁴S geochemistry. Pyrite δ³⁴S values often capture δ³⁴S signatures of porewater sulfide at the location of pyrite formation. However, microbial mats are dynamic environments in which biogeochemical cycling shifts vertically on diurnal cycles. Therefore, there is a need to study how the location of pyrite formation impacts pyrite δ³⁴S patterns in these dynamic systems. Here, we present diurnal porewater sulfide δ³⁴S trends and δ³⁴S values of pyrite and iron monosulfides from Middle Island Sinkhole, Lake Huron. The sediment–water interface of this sinkhole hosts a low-oxygen cyanobacterial mat ecosystem, which serves as a useful location to explore preservation of sedimentary pyrite δ³⁴S signatures in early Earth environments. Porewater sulfide δ³⁴S values vary by up to ~25‰ throughout the day due to light-driven changes in surface microbial community activity that propagate downwards, affecting porewater geochemistry as deep as 7.5 cm in the sediment. Progressive consumption of the sulfate reservoir drives δ³⁴S variability, instead of variations in average cell-specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The δ³⁴S values of pyrite are similar to porewater sulfide δ³⁴S values near the mat surface. We suggest that oxidative sulfur cycling and other microbial activity promote pyrite formation in and immediately adjacent to the microbial mat and that iron geochemistry limits further pyrite formation with depth in the sediment. These results imply that primary δ³⁴S signatures of pyrite deposited in organic-rich, iron-poor microbial mat environments capture information about microbial sulfur cycling and environmental conditions at the mat surface and are only minimally affected by deeper sedimentary processes during early diagenesis.

中文翻译：

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沉积黄铁矿硫同位素组成保留了低氧蓝藻垫下方沉积物中表面微生物垫环境的特征

沉积黄铁矿硫同位素 (δ ³⁴ S) 记录是古代微生物硫循环和环境条件的档案。微生物垫生态系统沉积物中黄铁矿 δ ^{34 S 特征的解释基于对现代微生物垫孔隙水硫化物 δ 34} S 地球化学的研究。黄铁矿 δ ³⁴ S 值通常捕获黄铁矿形成位置处孔隙水硫化物的δ ^{34 S 特征。}然而，微生物垫是动态环境，其中生物地球化学循环在昼夜循环中垂直变化。因此，有必要研究黄铁矿形成的位置如何影响黄铁矿δ ³⁴这些动态系统中的 S 模式。在这里，我们展示了休伦湖中岛天坑中黄铁矿和一硫化铁的每日孔隙水硫化物 δ ³⁴ S 趋势和 δ ^{34 S 值。}该天坑的沉积物-水界面拥有一个低氧蓝藻垫生态系统，可作为探索早期地球环境中沉积黄铁矿 δ ^{34 S 特征保存的有用位置。}由于向下传播的表面微生物群落活动的光驱动变化，孔隙水硫化物 δ ³⁴ S 值全天变化高达 ~25‰，影响沉积物中深达 7.5 厘米的孔隙水地球化学。硫酸盐储层的逐步消耗驱动 δ ³⁴S 变异性，而不是沉积物中不同深度的平均细胞特异性硫酸盐还原率和/或硫化物氧化的变化。黄铁矿的δ ³⁴ S 值与垫层表面附近的孔隙水硫化物δ ^{34 S 值相似。}我们建议氧化硫循环和其他微生物活动促进黄铁矿在微生物垫中和紧邻微生物垫的形成，并且铁地球化学限制了随着沉积物深度进一步形成黄铁矿。这些结果意味着初级 δ ³⁴沉积在富含有机物、贫铁微生物垫层环境中的硫铁矿的 S 特征捕获有关垫层表面微生物硫循环和环境条件的信息，并且在早期成岩过程中受更深沉积过程的影响很小。