Collaborative Research: Validation of the lacustrine branched GDGT paleothermometer

过去大陆温度的重建提供了对地球气候系统及其对内部和外部强迫机制的敏感性的重要见解。这种重建为观测到的和预测的未来气候变化提供了地质背景，并揭示了太阳辐照度变化、火山活动和温室气体浓度等各种强迫对全球气候的影响。沉积物中保存的有机分子为推断过去气候提供了一种工具，在空间和时间上都有广泛的应用。一个有前途的和最近开发的技术的基础上组装的支链甘油二烷基甘油四醚（brGDGT），由细菌产生的膜脂，有可能扩大了解过去的大陆温度在各种气候制度，时间尺度和沉积环境。brGDGT代表了一个重要的气候档案，因为它们在湖泊中分布广泛且丰富，它们表现出与水温和pH值相关的结构差异，并且它们可以在湖泊沉积物中保存很长一段时间（数百万年）。然而，它还没有严格的评估，如果brGDGT提供了一个通用的方法，过去的温度重建和环境参数以外的温度和pH值的潜在影响尚未进行评估。通过进行基本的现场和实验室实验，研究人员将阐明brGDGT对环境压力的结构反应，并研究氧气暴露，降解和微生物群落结构对brGDGT分布的影响。这项研究是必要的，基础性的工作，以验证在湖泊中使用的brGDGT古温度计。调查人员将与尤里卡合作！女孩，Inc。的霍利奥克，MA提供环境地球化学的实践夏季研讨会，作为为期一个月的暑期科学夏令营的一部分，旨在鼓励初中和高中女生追求STEM领域的职业生涯。支链甘油二烷基甘油四醚（brGDGT）是无处不在的化合物，在各种陆地环境中发现，包括土壤，河流和湖泊。以前的研究，包括研究人员所做的工作，已经确定这些化合物的甲基化程度对温度敏感，预示着brGDGT分布可以作为过去温度变化的代表。然而，许多挑战和未解决的问题限制了brGDGT温度计的应用。这些包括未知的生物来源（S），缺乏第一原则的证据表明，brGDGT结构响应环境强迫，成岩蚀变和/或氧暴露的敏感性的证据。该项目旨在通过实地和实验室方法解决其中一些基本挑战。在实验室环境中，研究人员将维持和操纵围隔实验，以确定brGDGT甲基化和环化是否响应于温度和pH值。在现场，他们将监测目标湖泊中的brGDGT通量，并进行受控降解实验。脂质分析将与Illumina MiSeq测序配对，以了解微生物群落结构如何影响brGDGT分布。最后，他们将对一组湖泊沉积物进行探索性统计分析，以研究brGDGT分布在不同沉积和气候条件下的表现。该项目的结果将构成对brGDGT的理解的根本性进步，并提高将其用作古温度计的能力。

The reconstruction of past continental temperatures provides critical insights into the Earth's climate system and its sensitivity to internal and external forcing mechanisms. Such reconstructions provide geological context for observed and projected future climate changes, and reveal the impact of diverse forcings, such as changes in solar irradiance, volcanic events, and greenhouse gas concentrations, on global climate. Organic molecules preserved in sediments provide a tool for inferring past climate that may be widely applicable in both space and time. A promising and recently developed technique based on assemblages of branched glycerol dialkyl glycerol tetraethers (brGDGTs), membrane lipids produced by bacteria, has the potential to expand understanding of past continental temperatures across a variety of climatic regimes, time scales, and depositional environments. brGDGTs represent an important climate archive because they are widespread and abundant in lakes, they exhibit structural differences related to water temperature and pH, and they can be preserved for long periods of time (millions of years) in lake sediments. However, it has not been rigorously assessed if brGDGTs provide a universal method for past temperature reconstruction and the potential influence of environmental parameters other than temperature and pH has not yet been evaluated. Through conducting fundamental field and laboratory experiments, the investigators will elucidate the structural response of the brGDGTs to environmental stresses and investigate the impacts of oxygen exposure, degradation, and microbial community structure on brGDGT distributions. This research represents necessary, fundamental work to validate the use of the brGDGT paleothermometer in lakes. Investigators will partner with the Eureka! Program of Girls, Inc. of Holyoke, MA to offer hands-on summer workshops in environmental geochemistry, as part of a month-long summer science camp designed to encourage middle and high school girls to pursue careers in STEM fields.Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are ubiquitous compounds, found in a variety of terrestrial environments includes soils, rivers, and lakes. Previous research, including work done by the investigators, has established that the degree of methylation of these compounds is sensitive to temperature, auguring the use of brGDGT distributions as a proxy for past temperature changes. However, a number of challenges and unresolved issues limit the application of a brGDGT thermometer. These include unknown biological source(s), a lack of first-principles evidence that brGDGT structures respond to environmental forcings, and evidence for diagenetic alteration and/or sensitivity to oxygen exposure. This project aims to address some of these fundamental challenges via both a field and laboratory-based approach. In a lab setting, researchers will maintain and manipulate mesocosm experiments to determine whether brGDGT methylation and cyclization responds to temperature and pH. In the field, they will monitor brGDGT fluxes in a target lake and conduct controlled degradation experiments. Lipid analyses will be paired with Illumina MiSeq sequencing in order to understand how microbial community structure influences brGDGT distributions. Finally, they will conduct exploratory statistical analyses on a set of lake sediments to study how brGDGT distributions behave in different sedimentary and climatic regimes. The results of this project will constitute a fundamental advance in the understanding of brGDGTs and improve the ability to use them as a paleothermometer.