概述了 bGDGT 古气候学的生物标志物分析
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资料来源： 实验室的杰夫卡普-马萨诸塞大学阿默斯特
在这一系列的视频，天然样品提取和纯化寻找有机的化合物，称为生物标志物，可以与相关信息对气候和环境的过去。分析的样品之一是泥沙。沉积物日积月累盆地的地质时期，地球变成行动的流体 （水或空气），泥沙流经陷运动和重力场。两种主要类型的盆地存在，（海洋和海洋） 的海洋和湖泊 （湖泊）。你可能已经猜到，非常不同类型的生活生活在这些设置，在盐度差它们之间在很大程度上驱动。在过去的几十年里，有机地球化学家发现一个工具箱的生物标志物的代理或可以用来描述气候或环境，其中一些工作在海洋环境和在其中工作的一些湖泊的化合物。我们把我们的湖泊的境界的注意力和分枝甘油二烷基甘油 tetraethers (图 1)。
在本节中我们专注于使用分枝的甘油二烷基甘油 tetrathers （图 1; brGDGTs） 和主战坦克/CBT 代理的陆地地温的分析。此代理服务器最初是由 Weijers等人描述1 ，基于在 brGDGTs 的圆环和分支结构的分布。他们发现，环化分枝 tetraethers (CBT) 与土壤 ph 值直接相关。
CBT =-日志 ((Ib + IIb) / （I + II）)
甲基化的分枝 tetraethers (MBT) 是确定的年平均气温 (MAAT) 以及在较小的程度上，土壤 ph 值。
主战坦克 = （I + Ib + Ic） / （I + Ib + Ic） + (II + IIb + IIc) + （III + IIIb + IIIc）
因此，采取在一起和校准，MBT/CBT 涉及 brGDGTs 土壤温度和 ph 值的分布。
主战坦克 = 0.122 + (0.187 x CBT) + (0.020 英寸 x MAAT)
分枝的 GDGTs 被认为是膜跨越血脂和他们的生产最初的原因归咎于厌氧 Acidobacteria 细菌生活在土壤和泥炭2-5，但随后的工作建议，也可能产生在好氧和缺氧的湖泊和海洋水列和沉积物6-9。假说，Acidobacteria 变换的甲基化成不管为了增加不饱和度降低温度响应的网站 （环化有效地去除两个氢原子） 和维持细胞膜流动性 （通过类比，饱和脂肪 （黄油） 是固体室温虽然不饱和的脂肪 （橄榄油） 是一种液体），但分枝的 GDGTs 尚未查明作为主要膜脂质在 Acidobacteria 文化。因此他们确切的起源是未知的。
校准的分枝 GDGTs 环境变量 （温度、 ph 值、 盐度、 降水等） 是广泛研究的课题。有机地球化学实验室在世界各地参与制订全球1，10和11-13区域校准分枝的 GDGTs 和 （主要） 温度之间的任务。因此，上面给出的方程定期正在细化和完善。
虽然研究了沿海的海洋沉积物，分枝的 GDGTs 通常从湖泊沉积物中提取。提取液经过硅胶柱净化从其他化合物，可能不适合 LC 或，果葡可能共同洗脱 GDGTs GDGTs。GDGTs 在甲醇洗脱的极性分数出来了。
一旦被纯化总脂提取物，提取和纯化样品是在耦合到化学电离质谱计的高性能液相色谱仪上运行。GDGTs 的相对浓度决定通过获取选定的大规模离子 (m/z; 曲线下面积图 1)每个化合物对只是这个目的 （例如安捷伦 Chemstation) 设计的计算机软件。然后把这些领域，只为所选的校准方程而且到达古地温测定。
图 1.结构的分枝的 GDGTs 用于计算温度通过 MBT/CBT 代理 （用博士岛 Castañeda，的形象而制作的权限）。请点击这里查看此图的大版本。
有机化合物称为生物标志物可用于在地球科学作为最高峰相关的信息对气候和环境的过去。
活的有机体产生这些生物标记物，为我们提供有关他们所居住的环境信息。它们可以充当代理告诉我们像地球的温度数以百万计的年前的过去的事件，有关信息。
可以用新鲜水盆地沉积物中发现的生物标志物分析地面古地温。这些生物标记物的一个关键类是分枝的甘油二烷基甘油 tetraethers 或分枝的 GDGTs。
这个视频将介绍要求调查过去的新鲜水环境变化超过数亿年的古气候学的研究领域。这将有助于澄清当前和未来的气候和环境变化。
沉积物积累长的地质时期，由于流体的运动和重力，在沉积盆地或低的地区，在地球的地壳。沉积盆地包括海洋，收集海洋沉积物或收集湖泊沉积的湖泊。海洋和湖泊盆地包含不同类型的生物，在盐度差它们之间在很大程度上驱动。因此，海洋和湖泊盆地含有不同的生物标志物。
分枝的 GDGTs 被认为是跨膜脂质的厌氧 acidobacteria。研究表明，生产生物膜在中更改属性响应不断变化的温度。
这种变化被引起的分枝 GDGT 的环化网站温度越低，从而提高细胞膜流动性的甲基化网站转型。然后可以到温度通过代理相关结构的转变。代理是大到无法估量的变量相关的物理现象。
此代理服务器涉及中对温度的生物标志物的甲基化或主战坦克，并不管或 CBT，数。实验导出方程可以与相关 MBT CBT 到过去的意思是每年空气温度。
研究生物标志物 GDGT 分枝和土壤温度之间的关系，湖泊沉积必须收集、 提取的三种方法之一、 纯化，并分析。
要开始学习分枝的 GDGT 生物标志物和土壤温度之间的关系，脂质分子首先提取湖泊沉积物，使用各种各样的技术。通过超声波提取是从沉积物样品获得的总脂提取物或 TLE，最简单和最便宜的方法。为此，超声波浴用于鼓动中含有有机溶剂的一小瓶的示例。甲醇和二氯甲烷的混合物用于提取生物标志物与广泛的极性。另一种提取技术采用索氏提取法。索氏提取器使胃酸反流，或连续循环，有机溶剂从圆底烧瓶向上进入凝汽器，用冷水冷却并返回。浓缩的溶剂可分为含样品的玻璃光纤顶针。一旦充分，分庭值有机溶剂回圆底烧瓶，使连续提取随着时间的推移。
这种技术很有帮助的含沙量大群众，提取和大量的标准准备仪器校准。最后，加速溶剂萃取或 ASE，是提取的商标，利用高温和压力增加萃取过程的动力学方法。ASE 仪器持有达 24 个别样品，并允许在萃取过程中的所有参数的精确控制。由于它的速度和使用简单，ASE 常用的溶剂萃取的标准方法。
一旦脂质样品提取使用这些技术之一，它是在分析制备纯化。通常情况下，硅胶柱色谱法用于净化基于其极性脂质样品。为此，小玻璃柱装有粉末的二氧化硅，称为凝胶。列然后饱和与非极性溶剂，通常正己烷，然后样品装上顶部。提取物的分离基于目标化合物的固相或溶剂相的亲和力。
极性化合物，在这种情况下分枝 GDGT 更关注极地硅比非极性正己烷。因此，非极性化合物，如碳氢化合物，中期极性的化合物，如酮和醇和强极性化合物，将旅游列以不同的速度和响应的增加极性溶剂。
洗脱剂然后收集不同馏分中。
采用高性能液相色谱法耦合到一台质谱仪，然后分析了纯化的 GDGT 或 LC 女士 LC-MS 首先分离化合物，并分析了他们基于其质量电荷比。
这使每种类型的 GDGT 使用曲线下的面积为选定的大规模离子相对浓度的测定。共计 1 组分子的分数计算是主战坦克。
CBT 会作为负面的日志使用组 1 和 2 中的分子进行计算。主战坦克和 CBT 然后插入到实验导出的方程，为了到达古地温测定。
使用生物标志物代理的古地温测定方法是有用的在地球科学中的应用范围。
第一，paleothermometry 使地球的温度在较长时间内测定。使用各种技术，地球的温度据估计在 5 亿年。这告诉我们在信封内的不同形式的生命进化的温度和通知调查对地球的生物圈、 水圈、 岩石圈和大气温度的影响，在过去，推而广之，未来。
更多最近的趋势，在地球温度也可以对记录使用 paleothermometry 构造量化。地球表面温度增加了近 1 度从 1850 年到现在与突出的气候变暖趋势在过去的两年。要了解人类活动对全球气候的影响，必须开发和用作上下文准确的古气候记录。
你刚看了朱庇特的概述的分枝甘油二烷基甘油 Tetraether Paleothermometry。现在，您应该了解如何使用分枝的 GDGT 生物标志物，以及总体技术的提取与纯化他们。以下视频在这一系列将进入更多细节关于这个复杂的过程。
谢谢观赏 ！
Procedure
References
- Weijers, J. W. H. et al. Environmental controls on bacterial tetraether membrane lipid distribution in soils, Geochimica et Cosmochimica Acta, 71(3), 703-713 (2007).
- Damste, J. S. S. et al. 13,16-Dimethyl Octacosanedioic Acid (iso-Diabolic Acid), a Common Membrane-Spanning Lipid of Acidobacteria Subdivisions 1 and 3. Appl Environ Microb, 77, 4147-4154 (2011).
- Hopmans, E. C. et al. A novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids, Earth and Planetary Science Letters, 224(1-2), 107-116 (2004).
- Weijers, J. W. H. et al. Membrane lipids of mesophilic anaerobic bacteria thriving in peats have typical archaeal traits. Environ Microbiol, 8, 648-657 (2006).
- Weijers, J. W. H., Schouten, S., Spaargaren, O. C., Damste, J. S. S. Occurrence and distribution of tetraether membrane lipids in soils: Implications for the use of the TEX86 proxy and the BIT index. Organic Geochemistry, 37, 1680-1693 (2006).
- Chappe, B., Albrecht, P., Michaelis, W. Polar Lipids of Archaebacteria in Sediments and Petroleums. Science, 217, 65-66 (1982).
- Peterse, F. et al. Constraints on the application of the MBT/CBT palaeothermometer at high latitude environments (Svalbard, Norway). Organic Geochemistry, 40, 692-699 (2009).
- Tierney, J. E., Russell J. M. Distributions of branched GDGTs in a tropical lake system: Implications for lacustrine application of the MBT/CBT paleoproxy, Organic Geochemistry, 40(9), 1032-1036 (2009).
- Zhu, C. et al. Sources and distributions of tetraether lipids in surface sediments across a large river-dominated continental margin. Organic Geochemistry, 42, 376-386 (2011).
- Pearson, E. J. et al. A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes. Geochimica et Cosmochimica Acta. 75, 6225-6238 (2011).
- Damste, J. S. S., Ossebaar, J., Schouten, S., Verschuren, D. Altitudinal shifts in the branched tetraether lipid distribution in soil from Mt. Kilimanjaro (Tanzania): Implications for the MBT/CBT continental palaeothermometer. Organic Geochemistry, 39, 1072-1076 (2008).
- Loomis, S. E., Russell, J. M., Ladd, B., Street-Perrott, F. A., Damste, J. S. S. Calibration and application of the branched GDGT temperature proxy on East African lake sediments. Earth and Planetary Science Letters, 357, 277-288 (2012).
- Tierney, J. E. et al. Environmental controls on branched tetraether lipid distributions in tropical East African lake sediments. Geochimica et Cosmochimica Acta, 74, 4902-4918 (2010).
Transcript
Organic compounds called biomarkers can be used in Earth Science as paleothermometers to relate information on climates and environments of the past.
Living organisms produce these biomarkers, which provide us with information about the environment in which they lived. They can act as a proxy to tell us information about past events, like the Earth’s temperature millions of years ago.
Terrestrial paleotemperature can be analyzed using biomarkers found in sediment from fresh-water basins. One key class of these biomarkers are branched glycerol dialkyl glycerol tetraethers, or branched GDGTs.
This video will introduce the area of study, called paleoclimatology, which investigates past changes in fresh-water environments over hundreds of millions of year. This helps elucidate current and future climate and environmental changes.
Sediments accumulate over geologic time, due to fluid movement and gravity, in sedimentary basins, or low areas in the Earth’s crust. Sedimentary basins include oceans, which collect marine sediment, or lakes, which collect lacustrine sediment. Marine and lacustrine basins contain different types of organisms, driven in large part by the difference in salinity between them. Thus, marine and lacustrine basins contain different biomarkers.
Branched GDGTs are thought to be membrane-spanning lipids of anaerobic acidobacteria. Research suggests that the producing organisms change membrane properties in response to changing temperature.
This change is caused by the transformation of methylated sites on the branched GDGT’s to cyclized sites at colder temperatures, thereby enhancing membrane fluidity. This change in structure can then be correlated to temperature through a proxy. Proxies are measureable physical phenomena that are correlated to immeasurable variable.
This proxy relates the number of methylations or MBT, and cyclizations, or CBT, in the biomarker to temperature. An experimentally-derived equation can relate MBT and CBT to the past Mean Annual Air Temperature.
To study the relationship between branched GDGT biomarkers and soil temperature, lacustrine sediment must be collected, extracted by one of three techniques, purified, and analyzed.
To begin studying the relationship between branched GDGT biomarkers and soil temperature, the lipid molecules are first extracted from lacustrine sediments, using a variety of techniques. Extraction via sonication is the simplest and least expensive method of obtaining the total lipid extract, or TLE, from a sediment sample. For this, an ultrasonic bath is used to agitate the sample in a vial containing organic solvent. A mixture of methanol and dichloromethane is used to extract biomarkers with a wide range of polarities. Another extraction technique utilizes Soxhlet extraction. A Soxhlet extractor enables the reflux, or continuous cycling, of organic solvent from a round-bottom flask upward into a condenser, which is cooled by cold water and returned. The condensed solvent falls into a glass fiber thimble containing the sample. Once full, the chamber siphons the organic solvent back into the round-bottom flask, enabling continuous extraction over time.
This technique is helpful in the extraction of large sediment masses, and the preparation of large volumes of standards for instrument calibration. Finally, accelerated solvent extraction, or ASE, is a trademarked method of extraction that utilizes high temperature and pressure to increase the kinetics of the extraction process. The ASE instrument holds up to 24 individual samples, and allows for precise control of all parameters in the extraction process. Due to its speed and simplicity of use, ASE is commonly used as the standard method of solvent extraction.
Once the lipid sample is extracted using one of these techniques, it is purified in preparation for analysis. Typically, silica gel column chromatography is used to purify the lipid sample based on its polarity. For this, a small glass column is loaded with a fine powder of silica, called a gel. The column is then saturated with an apolar solvent, typically hexane, and then the sample loaded on the top. The separation of the extract is based on the affinity of the target compound for either the solid phase or the solvent phase.
Polar compounds, in this case branched GDGT’s, are more attracted to the polar silica than the apolar hexane. Thus, the apolar compounds, such as hydrocarbons, the mid-polar compounds, such as ketones and alcohols, and the highly polar compounds, will travel the column at different rates and in response to solvents of increasing polarity.
The eluents are then collected in separate fractions.
The purified GDGT’s are then analyzed using high performance liquid chromatography coupled to a mass spectrometer, or LC-MS. LC-MS first separates the compounds, and then analyzes them based on their mass-to-charge ratio.
This enables the determination of the relative concentration of each type of GDGT using the area under the curve for the selected mass ion. MBT is calculated as the fraction of the group 1 molecules to the total.
CBT is then calculated as a negative log using molecules in groups 1 and 2. MBT and CBT are then plugged into an experimentally-derived equation, in order to arrive at a paleotemperature determination.
The determination of paleotemperature using biomarker proxies is useful in a range of applications in earth science.
First, paleothermometry enables the determination of the Earth’s temperature over long periods of time. Using various techniques, the temperature of Earth has been estimated as far back as 500 million years. This tells us the envelope of temperature within which different forms of life evolved and informs investigations of the effects of temperature on Earth’s biosphere, hydrosphere, lithosphere, and atmosphere in the past, and by extension, the future.
More recent trends in the Earths temperature can also be quantified against records constructed using paleothermometry. The Earths surface temperature has increased by nearly 1 degree from 1850 to the present with an accentuated warming trend in the last two decades. To understand the anthropogenic impact on global climate, accurate paleoclimate records must be developed and used as context.
You’ve just watched JoVE’s Overview of Branched Glycerol Dialkyl Glycerol Tetraether Paleothermometry. You should now understand how the branched GDGT biomarkers are used, and the overall technique of extracting and purifying them. The following videos in this series will go into more detail about this complex process.
Thanks for watching!