Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low‐oxygen cyanobacterial mats
Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low‐oxygen cyanobacterial mats
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沉积黄铁矿硫同位素成分保留了低氧蓝藻垫下沉积物中表面微生物垫环境的特征
DOI：
10.1111/gbi.12466
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发表时间：
2021
期刊：
影响因子：
3.7
通讯作者：
Fike, David A.
中科院分区：
文献类型：
--
作者：
Gomes, Maya L.;Klatt, Judith M.;Dick, Gregory J.;Grim, Sharon L.;Rico, Kathryn I.;Medina, Matthew;Ziebis, Wiebke;Kinsman‐Costello, Lauren;Sheldon, Nathan D.;Fike, David A.
沉积黄铁矿硫同位素（δ34S）记录是古代微生物硫循环和环境条件的档案。基于现代微生物席孔隙水硫化物δ34S地球化学研究，对微生物席生态系统沉积物中黄铁矿δ34S特征进行了解释。黄铁矿的δ34S值往往能捕捉到黄铁矿形成部位孔隙水硫化物的δ34S特征。然而，微生物席是一个动态环境，其中生物地球化学循环在日循环中垂直移动。因此，有必要研究这些动力系统中黄铁矿形成位置对黄铁矿δ34S模式的影响。本文研究了休伦湖中岛天坑中硫铁矿和单硫化铁的孔隙水硫化物的δ34S变化趋势和δ34S值。该陷坑沉积物-水界面具有低氧蓝藻席生态系统，为探索早期地球环境中沉积黄铁矿δ34S特征的保存提供了有益的位置。孔隙水硫化物δ34S值全天变化高达~25‰，这是由于地表微生物群落活动的光驱动变化向下传播，影响沉积物中7.5 cm深处的孔隙水地球化学。硫酸盐储层的逐渐消耗驱动了δ34S的变化，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δ34S值与席表面附近孔隙水硫化物的δ34S值相近。我们认为，氧化硫循环和其他微生物活动促进了黄铁矿在微生物席内及其附近的形成，铁的地球化学特征限制了黄铁矿在沉积物中的进一步形成。这些结果表明，富有机质、贫铁微生物席环境中沉积的黄铁矿的原生δ34S特征捕获了席表面微生物硫循环和环境条件的信息，并且在早期成岩作用中仅受较深沉积过程的影响最小。
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.
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