Impact of geogenic CO2 on the depth distribution of and feedstock provision for deep microbial communities in the Hartousov mofette system in NW Bohemia

Hartoušov mofette系统位于Cheb盆地北部（NW Bohemia, Czech Republic），是一个以CO2为主的呼出地幔气体弥漫性脱气结构，d13C特征相对较重（-2‰）。从生物地球化学和微生物学的角度来看，这些CO2渗漏为微生物群落形成了一个有趣而独特的生命栖息地，强烈的地质CO2通量为本地微生物群落形成了特定的碳和能量来源。因此，本研究的目的是利用有机地球化学、同位素地球化学和生物地球化学方法研究CO2脱气对大气系统浅层和深层微生物群落及其碳和能量来源的影响。2016年春季，GFZ在Hartoušov mofette油田钻了一个108.5米深的井，恢复了整个沉积序列，一直到风化的基底。在陆相渐新统向湖相中新统过渡的78.5 m深度处，发生了一次CO2吹出，表明在该深度段存在一种“CO2储层”，而湖相粘土可能起到一种封印作用。对这个“封印”下面的矿物基质的研究表明，它与上升的二氧化碳相互作用。在陆相渐新世深部沉积中，地源CO2刺激了带状钙镁菱铁矿的沉淀，而在“CO2储层”剖面中，由于孔隙水中CO2浓度高，碳酸盐被溶解。整体有机质的d13C信号和首次研究的过去微生物生物标志物的复合特定d13C信号显示，湖相中新世泥岩以下沉积物的d13C信号明显较重，表明在更深的岩心层段，上升的地源CO2也对有机基质产生了影响。虽然我们的初步结果提供了深层地下成因CO2与矿物和有机基质之间相互作用的指示，但需要进一步的研究来验证这些相互作用并了解所涉及的过程。

The Hartoušov mofette system located in the northern Cheb Basin (NW Bohemia, Czech Republic) represents a diffuse degassing structure of exhaling mantle derived gases dominated by CO2 with a relative heavy d13C signature (-2 ‰). From a biogeochemical and microbiological point of view these CO2 seeps form an interesting and unique life habitat for microbial communities with intense geogenic CO2 fluxes forming a particular carbon and energy source for the indigenous microbial community. Thus, the aim of the current study is the investigation of the impact of degassing CO2 on the shallow and deep microbial communities in the mofette system and their carbon and energy sources using organic-geochemical, isotope geochemical and biogeochemical approaches. In spring 2016 the GFZ drilled a 108.5 m deep borehole into the Hartoušov mofette field recovering the entire sedimentary successions down to the weathered basement. In 78.5 m depth at the transition from terrestrial Oligocene to lacustrine Miocene claystones a CO2 blow out occurred suggesting a kind of “CO2 reservoir” at this depth interval, whereas the lacustrine claystones might act as a kind of seal. Investigations on the mineral matrix below this “seal” suggest an interaction with the ascending CO2. In the deeper terrestrial Oligocene deposits the geogenic CO2 appears to stimulate the precipitation of zoned calcium-magnesium siderites, while in the “CO2 reservoir” section carbonates are dissolved due to the high CO2 concentrations in the pore water. The d13C signal of the bulk organic matter and the compound specific d13C signal of the first investigated past microbial biomarkers reveal significantly heavier d13C signals for the deposits below the lacustrine Miocene claystones, indicating an influence of the ascending geogenic CO2 also on the organic matrix in the deeper core interval. Although our first results provide indications on the interaction between the geogenic CO2 and the mineral and organic matrix in the deep subsurface, further investigations are necessary to verify these interactions and to understand the involved processes.