Further Test for Stable Carbon Isotopic Fractionation of Biomarkers during Diagenetic Processes and Examination of Possible Causes

生物标志物的稳定碳同位素组成已被广泛用于研究全球碳循环和古海洋学记录。然而，专家们对于成岩作用对沉积生物标志物碳同位素特征的影响一直存在很大的分歧。有很多假设，但很少有实际研究确定来自陆生高等植物的生物标志物的碳同位素组成在成岩过程中如何变化以及在多大程度上变化。在这项研究中，佐治亚大学的研究人员将试图评估和确定植物来源生物标志物的碳同位素组成在沉积成岩过程中发生变化的主要过程。有两个主要目标。第一个是通过在不同的环境条件下培养天然植物材料，研究C3和C4维管植物中各种木质素衍生的苯酚生物标志物在降解过程中的稳定碳分馏。第二个目标是检验与同位素分馏机制相关的两个具体假说：(1)分子反应部位的本征碳分馏可能是动力学相关的，是降解过程中分子同位素变化的主要原因，但分子内(反应和非反应部位之间)13C的不均匀分布可能会显著影响分子同位素分馏；(2)相同的生物标志物分子结合在不同的细胞内成分(如细胞膜和代谢储存组织)中，可能具有不同的碳同位素组成，因为它们在不同的生长阶段被生物合成，当它们以不同的速度和不同的途径降解时，可能会导致分子分馏。这项研究可能在有机地球化学、化学沉积学和古海洋学领域产生更广泛的影响。这项研究的结果可能会为评估水生和陆生植物来源的生物标志物及其同位素组成在碳循环和沉积记录中的适用性设定一个新的标准。对当前循环和过去记录的全面了解将有助于科学界预测全球气候变化的趋势。该项目还将为一名博士后助理以及研究生和本科生提供支助和培训。首席调查员还计划让暑期高中实习生参与这项研究计划。

ABSTRACTOCE-0526111The stable carbon isotopic composition of biomarkers has been widely used to study global carbon cycling and the paleoceanographic record. Among specialists, however, there has been substantial disagreement regarding the impact of diagenetic processes on the carbon isotopic signatures of sedimentary biomarkers. Assumptions abound, but there have been few actual studies to determine how and to what extent the carbon isotopic composition of biomarkers derived from terrestrial higher plants can change during diagenesis. In this study, researchers at the University of Georgia will attempt to assess and to identify the major processes by which the C isotopic composition of plant-derived biomarkers changes during sedimentary diagenesis. There are two primary objectives. The first is to study stable carbon fractionation of various lignin-derived phenol biomarkers from C3 and C4 vascular plants during degradation by incubating natural plant materials in different environmental regimes. The second goal is to test two specific hypotheses related to isotopic fraction mechanisms: (1) that the intrinsic carbon fractionation at a reaction site of a molecule may be kinetics-dependent and responsible for the most of molecular isotopic alteration during degradation, but the heterogeneous 13C distributions within molecules (between reaction and non-reaction sites) may significantly affect the molecular isotopic fractionation; and (2) that the same biomarker molecules bound in different intracellular components (e.g., cell membrane vs. metabolic storage tissue) may carry distinct carbon isotopic compositions because they are biosynthesized at different growth stages, which may result in molecular fractionation when they degrade at different rates and through different pathways.This research could have a number of broader impacts in the fields of organic geochemistry, chemical sedimentology and paleoceanography. Results from this study could potentially set a new criterion for evaluating the applicability of aquatic and terrestrial plant-derived biomarkers and their isotopic compositions in carbon cycling and sedimentary record. Comprehensive understanding for current cycling and past record will help the scientific community to predict the trend of global climate change. The project will also provide for the support and training of a postdoctoral associate and of graduate and undergraduate students. The principal investigator also plans to involve summer high-school interns in this research program.