Bovee R J, Pearson A
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.
Geobiology. 2014 Nov;12(6):529-41. doi: 10.1111/gbi.12099. Epub 2014 Sep 8.
Planktonic sulfur bacteria growing in zones of photic zone euxinia (PZE) are important primary producers in stratified, sulfur-rich environments. The potential for export and burial of microbial biomass from anoxic photic zones remains relatively understudied, despite being of fundamental importance to interpreting the geologic record of bulk total organic carbon (TOC) and individual lipid biomarkers. Here we report the relative concentrations and carbon isotope ratios of lipid biomarkers from the water column and sediments of meromictic Mahoney Lake. The data show that organic matter in the central basin sediments is indistinguishable from material at the lake shoreline in both its lipid and carbon isotopic compositions. However, this material is not consistent with either the lipid profile or carbon isotope composition of biomass obtained directly from the region of PZE. Due to the strong density stratification and the intensive carbon and sulfur recycling pathways in the water column, there appears to be minimal direct export of the sulfur-oxidizing planktonic community to depth. The results instead suggest that basinal sediments are sourced via the littoral environment, a system that integrates an indigenous shoreline microbial community, the degraded remains of laterally rafted biomass from the PZE community, and detrital remains of terrigenous higher plants. Material from the lake margins appears to travel downslope, traverse the strong density gradient, and become deposited in the deep basin; its final composition may be largely heterotrophic in origin. This suggests an important role for clastic and/or authigenic minerals in aiding the burial of terrigenous and mat-derived organic matter in euxinic systems. Downslope or mineral-aided transport of anoxygenic, photoautotrophic microbial mats may have been a significant sedimentation process in early Earth history.
在光合带富硫区（PZE）生长的浮游硫细菌是分层、富硫环境中的重要初级生产者。尽管缺氧光合带微生物生物量的输出和埋藏潜力对于解释总有机碳（TOC）和单个脂质生物标志物的地质记录至关重要，但这方面的研究仍相对较少。在此，我们报告了常年分层的马奥尼湖水柱和沉积物中脂质生物标志物的相对浓度和碳同位素比值。数据显示，中心盆地沉积物中的有机质在脂质和碳同位素组成上与湖岸线的物质难以区分。然而，这种物质与直接从PZE区域获得的生物量的脂质谱或碳同位素组成均不一致。由于水柱中强烈的密度分层以及密集的碳和硫循环途径，硫氧化浮游群落向深处的直接输出似乎极少。相反，结果表明盆地沉积物来自沿岸环境，该系统整合了本地岸线微生物群落、PZE群落横向漂流生物量的降解残骸以及陆地高等植物的碎屑残骸。来自湖边缘的物质似乎沿坡下滑，穿过强烈的密度梯度，并沉积在深盆地中；其最终组成可能在很大程度上源于异养。这表明碎屑和/或自生矿物在富硫系统中协助陆地和席状衍生有机质埋藏方面发挥了重要作用。在早期地球历史中，缺氧光合自养微生物席的下坡或矿物辅助运输可能是一个重要的沉积过程。
