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
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
Microsensor Group, Max Planck Institute for Marine Microbiology, Bremen, Germany.
Geobiology. 2022 Jan;20(1):60-78. doi: 10.1111/gbi.12466. Epub 2021 Jul 31.
The sedimentary pyrite sulfur isotope (δ S) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite δ S signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide δ S geochemistry. Pyrite δ S values often capture δ S 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 δ S patterns in these dynamic systems. Here, we present diurnal porewater sulfide δ S trends and δ S 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 δ S signatures in early Earth environments. Porewater sulfide δ S 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 δ S variability, instead of variations in average cell-specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The δ S values of pyrite are similar to porewater sulfide δ S 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 δ S 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.
沉积黄铁矿硫同位素（δS）记录是古代微生物硫循环和环境条件的档案。对微生物席生态系统中沉积的黄铁矿δS特征的解释基于对现代微生物席孔隙水硫化物δS地球化学的研究。黄铁矿δS值通常捕获黄铁矿形成位置处孔隙水硫化物的δS特征。然而，微生物席是动态环境，其中生物地球化学循环在昼夜周期中垂直变化。因此，有必要研究黄铁矿形成位置如何影响这些动态系统中的黄铁矿δS模式。在这里，我们展示了休伦湖米德岛沉洞的昼夜孔隙水硫化物δS趋势以及黄铁矿和单硫化铁的δS值。这个沉洞的沉积物 - 水界面拥有一个低氧蓝细菌席生态系统，它是探索早期地球环境中沉积黄铁矿δS特征保存情况的有用场所。由于表面微生物群落活动的光驱动变化向下传播，影响沉积物中深达7.5厘米处的孔隙水地球化学，孔隙水硫化物δS值在一天内变化高达约25‰。硫酸盐储库的逐渐消耗驱动了δS变异性，而不是沉积物不同深度处平均细胞特异性硫酸盐还原速率和/或硫化物氧化的变化。黄铁矿的δS值与微生物席表面附近的孔隙水硫化物δS值相似。我们认为，氧化硫循环和其他微生物活动促进了微生物席内及其紧邻区域的黄铁矿形成，并且铁地球化学限制了沉积物中更深层的黄铁矿进一步形成。这些结果表明，沉积在富含有机物、贫铁的微生物席环境中的黄铁矿的原始δS特征捕获了关于微生物席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仅受到深层沉积过程的最小影响。
