Microbial alteration of geochemical and isotope proxies in fine-grained carbonate sediments

细粒碳酸盐沉积物中地球化学和同位素代理的微生物改变

• 批准号: 318969578
• 负责人: Professor Dr. Gernot Arp
• 金额: --
• 依托单位: Abteilung Geobiologie
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/318969578?language=en
• 关键词: Microbial; alteration; geochemical; isotope; proxies

While there is a strongly increasing knowledge on microbial effects on the primary precipitation of carbonates, the subsequent alteration of trace element and stable isotope signals in ordinary carbonate muds during early diagenesis is still poorly understood. Earlier studies provided partially contradicting results, with only minor diagenetic changes at shallow sediment depths despite of changes in pore water chemistry on the on hand side, or clear dissolution and recrystallization features on the other side. Likewise, stable isotope composition has been reported to change with changing pore waters, without a significant shift in bulk mineralogical composition of the sediment. Indeed, the bulk effect of microbial processes such as heterotrophic CO2 release, sulfide oxidation, sulfate reduction and ammonification on pore water carbonate mineral saturation states, and hence carbonate crystallites, is discussed controversially. One reason might be that sedimentological studies commonly rather focus solely on chemical and physicochemical changes of pore water, whereas geomicrobiological studies include, if at all, only fragmentary pore water data. In the present project proposal, a combined approach of pore water analyses (full and balanced analyses incl. trace elements), mineralogical and isotope analyses, plus NGS-based metagenomic and metatranscriptomic analyses of sediment microbial communities is developed to trace changes in fine-grained primary carbonates at shallow sediment depth in a tropical lagoonal setting on the atoll of Aldabra, a site that has been proposed as a potential analogue of lithographic limestone deposition. The phylogenetic and functional composition of microbial communities will be traced from the sediment/water interface to anoxic conditions at shallow sediment depth at cm to dm-scale, and correlated with exopolymer degradation and pore water saturation states. The sediments will be screened for corrosion and recrystallization of existing carbonate crystallites as well as syntaxial growth or even new precipitation, supplemented with delta 13C and delta 18O analyses. These traditional stable isotope measurements are complemented by delta 26Mg and delta 44Ca analyses (ZP 0 and TP 9) to assess their susceptibility with respect to pore water changes and microbial activity. The study provides an important basis to assess traditional stable isotope signals in the fossil record, which are widely used as palaeoenvironmental proxies, as well as a test for the use of non-traditional isotopes for tracing diagenetic pathways in a natural setting.

虽然有一个强烈增加的知识微生物对碳酸盐的初次沉淀的影响，在早期成岩作用期间，在普通碳酸盐泥浆中的微量元素和稳定同位素信号的后续变化仍然知之甚少。早期的研究提供了部分矛盾的结果，只有轻微的成岩作用的变化，在浅沉积物深度，尽管在一方面的孔隙水化学的变化，或明确的溶解和重结晶功能的另一边。同样，据报道，稳定同位素组成随着孔隙沃茨的变化而变化，而沉积物的大量矿物组成没有显著变化。事实上，大量的微生物过程，如异养CO2释放，硫化物氧化，硫酸盐还原和氨化孔隙水碳酸盐矿物饱和状态，因此碳酸盐微晶的影响，是有争议的讨论。原因之一可能是沉积学研究通常只侧重于孔隙水的化学和物理化学变化，而地质微生物学研究则只包括零碎的孔隙水数据。在本项目建议书中，采用了孔隙水分析（全面和平衡分析，包括为了追踪Aldabra环礁热带泻湖环境中浅沉积物深度细粒原生碳酸盐的变化，开发了基于NGS的宏基因组学和宏转录组学的沉积物微生物群落分析，Aldabra环礁被认为是石印石灰石沉积的潜在模拟物。微生物群落的系统发育和功能组成将被追溯到从沉积物/水界面到缺氧条件下，在浅沉积物深度在厘米至厘米尺度，并与外聚合物降解和孔隙水饱和状态。将对沉积物进行筛选，以了解现有碳酸盐微晶的腐蚀和重结晶以及同轴生长甚至新的沉淀，并辅以δ 13 C和δ 18 O分析。这些传统的稳定同位素测量补充了δ 26 Mg和δ 44 Ca分析（ZP 0和TP 9），以评估其对孔隙水变化和微生物活性的敏感性。这项研究为评估化石记录中被广泛用作古环境代用指标的传统稳定同位素信号提供了重要依据，并为在自然环境中使用非传统同位素追踪成岩途径提供了测试。