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。我们转而关注这里使用 U 的海洋领土和长链 paleothermometryk’37海表面温度代理。
最受公认和广泛应用大洋生物标志物海表面温度 (SST) 代理是 Uk’37。
Uk’37 = (C37:2) / （C37:2 + C37:3） （见赫伯特1审查）
该指数基于两种多不饱和长链烷基酮，叫脂肪酮，产生的一些类 haptophyte 藻类2，3的比例。文化4，5和核心顶部泥沙6校准研究导致发展的 Uk’37指数作为定量的 SST 代理。Prahl等人的令人惊讶的是，文化基础的校准4:
Uk’37 = 0.034(SST) + 0.039，
和米勒等人的核心顶部校准6，
Uk’37 = 0.033(SST) + 0.044，
是统计学意义上相同。
重构 Uk’37温度与各种气候和 haptophyte 的生产制度，在全球海洋7，平均每年海温相关最好。中新世早期到现代年龄8，海洋沉积物和暴露露头的隆起的海洋沉积物9暗示他们长的地质时期，非常稳定，因此有用的古气候工具检测条件。Uk’37已经习惯了在轨道11，12的时间刻度，并因此非常多才多艺的年代际10文档古海表面温度的变化。
在开阔的海面，浮游生物球石藻和Gephyrocapsa 中南美是负责大部分海面生产。为什么这些附着改变条件基于生长温度的不饱和度比现在还不得而知。它最初被认为条件被 haptophyte 细胞壁成分和他们不饱和度调整，以保持膜液，就像饱和脂肪是固体在室温，而不饱和的脂肪是流体。然而，针对这一问题的实验发现，而不是正在与细胞膜相关联，脂肪酮与细胞内的能量存储结构相关联。因此，他们在细胞内的使用仍然是一个悬而未决的问题。
最近，脂肪酮已经被发现在湖泊环境中。然而，其效用为止一直有限。比那些在海洋领域的不同海面生产者住在湖泊和因而不饱和的水温度与校准 (Uk’37) 是不同的。此外，不同于湖泊，使建立一个 ‘全球’ 不太可能是校准的这种标定方法。不幸的是，当地校准的创作是昂贵和费时，所以 U 的未来k’37湖泊也是目前很有限。
条件通常是从海洋沉积物中提取的。很多时候产生脂肪酮的同一生物生产脂肪酸甲酯的称为 alkenoates 的那些条件。这些化合物共同洗脱条件对气相色谱仪和复杂化的量化。因此，这些提取物经常会经过皂化删除 alkenoates。因为皂化反应生成羧酸，是不适合的气相色谱仪，皂化提取物中删除羧酸之后必须执行硅胶柱。脂肪酮在洗脱二氯甲烷中虽然酸左边列的中等极性酮分数出来了。最后，在极端情况下，如在沉积物中获得从污染严重的地区，像河口附近的工业中心，尿素络合法也可能需要删除 coelute 与气相色谱仪对脂肪酮的未知的化合物。
一旦被纯化总脂提取物，提取和纯化样品是在耦合到火焰电离检测器的气相色谱仪上运行。通过为每个化合物对计算机软件设计的只是这个目的 （例如安捷伦 Chemstation) 获得曲线下的面积确定相对集中的两个条件。这些区域然后放入 Uk’37比方程如上所示，得到一个 Uk’37值，范围介于 0 和 1 之间。这些 Uk’37值然后映射到使用校准所述以上的海表面温度值。
Paleothermometry 是通过特定的化学物质，在自然的样品，像那些遗留下来的史前藻类分析过去温度的计算。
藻类是形形色色的生物有了丰富在地球上的海洋和湖泊几千年。某些化学化合物，由古代藻类在泥沙沉积，作为生物标志物 — — 可以为研究者提供宝贵的洞察地球历史上的有机化合物。事实上，在沉积物中的藻类生物标志物含量的分析使得研究者可以确定地球的温度数亿年前。
一种记录来自某些种类的浮游生物。这些藻类产生不同的条件，一类鲁棒的生物标志物，基于其环境的温度。长链分析主要用来计算地球上的海洋表层海温亿万年和亿万年前。
本视频将说明如何使用条件在古气候学和描述过程的分离、 纯化，和分析条件计算过去的海表面温度。
顾名思义，”长链 paleothermometry”基于分析，如果血脂，称为脂肪酮长链 paleothermometry 基于条件;包含 37 个碳原子和 2 到 4 双键的链长、 不饱和烷基酮。每个双键是一个网站的不饱和度。在低海表面温度，长链生产者产生更多不饱和脂肪酮比饱和。向不饱和饱和的比率被称为长链不饱和指数。
通常评估的条件是 C37:2和 C37:3，分别有 37 碳原子和两个或三个双键。不饱和度指数的这些条件或 UK’37，到海表面温度呈正相关。气相色谱法是一般敏感，要彼此分开这些条件知的分析方法。然而，海面产生藻类也经常生成化学结构相似的脂肪酸甲酯或 alkenoates，不能区分脂肪酮使用这种技术。烃类污染，受污染可能也进一步搅浑色谱分析。要准确地确定相对海面浓度，alkenoates 和未知的烃之前，必须取分析法经皂化、 尿素络合法等。
既然已评审泥沙长链比率向海表面温度的关系，让我们看看他们净化从总脂提取物和不饱和度比分析技术。
一旦海洋沉积物已被收集和提取，总脂提取物或 TLE，必须通过多步纯化工艺，并分析。首先，提取液经过皂化将 alkenoates 转化为羧酸盐和甲醇使用强大的基地和热。目前在 TLE 其他脂肪酸酯将成盐和甘油皂化。
冷却至室温的混合物后, 盐水溶液被添加到窗体盐和甘油。然后将混合物是羧基阴离子，生产脂肪酸酸化对发生作用。最后，从与正己烷混合物中提取脂肪酮和脂肪酸。
硅胶柱层析然后执行删除非极性化合物和极性的脂肪酸产生皂化法。干和皂化 TLE 是溶解在正己烷中，然后装到一个列。白炭黑比非极性的更强烈地保留极性化合物。
第一，非极性化合物被删除用非极性溶剂，如正己烷。接下来，条件被洗脱中等极性的溶剂，如二氯甲烷，在该列上留下强极性的脂肪酸和其他有害的极性化合物。
如果从一个高污染地区收集原始沉积物样本，尿素络合法执行删除任何剩余的高度分枝或循环碳氢化合物。干中极性组分溶解在强极性尿素微溶于水，DCM 和正己烷等溶剂混合物中。尿素在甲醇中的浓缩的溶液然后添加到 TLE，造成尿素晶体沉淀。
直链分子如条件融入在尿素晶体的晶格，分子之间的空间，但高度分枝和循环分子不这样做，和被驱逐。
一旦完成了晶体生长，尿素晶体是干和洗过再用非极性溶剂中，去除被驱逐的化合物。然后，晶体溶解在少量的水。从分析非极性溶剂型水中提取条件。
虽然前面的所有纯化步骤并没有区分长链物种，沸点和分子结构的小差异已足以让在气相色谱柱上的分离。当搭配火焰离子化检测器，可以确定的条件，相对浓度。
分子确定对色谱峰的保留时间，或时间需要的化合物要退出列。与长链标准确定了所需的化合物的保留时间。
脂肪酮的相对浓度均由下峰感兴趣的领域的分析。UK’37值然后计算从 C37:2和 C37:3样品中的浓度。海表面温度代理关系与 UK’37值，分析师可以解决海表面温度时的泥沙淤积。
地球历史上的许多不同方面，可以通过分析沉积物和沉积岩的调查。
生物地层学是确定图层，或地层，岩的分析目前化石年龄的研究。由于有很多的泥沙来源，从同一时期的沉积岩可能有世界各地的成分大大不同。某些物种在整个地球的历史，如亚扪人，集存在于整个世界和经历了快速发展。如果视觉上不同的岩层都包含相同品种的亚扪人，然后可以绘制各阶层之间的时间相关性。当结合技术，如 paleothermometry，可以从化石记录天然样品中确定有关地球历史上的大量信息。
许多种类的有孔虫或有孔虫，是常见于世界各地的海洋沉积物。有孔虫有碳酸钙外壳和整个地球上的海洋已经存在了数百万年。许多物种生活在海底，，从而可以提供有关海洋的较深部位的温度信息。镁钙比有孔虫对应温度，因为它们将更多的镁纳入他们的壳在温暖的气候。众多的物种和有孔虫丰度使其化石记录可用于跟踪海流在整个地球的历史中的变化和生物地层学。
当构造板块，新岩形成它们之间。相应地，一个离散板块边界的围岩属性提供有关板块运动随着时间的推移的信息。例如，地球的磁场变化都保留在一些化石、 岩石和沉积物中发现的矿物。对称变化在磁性关于洋中脊的发现大大促进了目前对海底扩张和板块构造的认识。
你刚看了朱庇特的长链 Paleothermometry 概述。现在，您应该了解 paleothermometry 的原则和长链比率在海洋沉积物对海洋表面温度的关系。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 ！
Paleothermometry is the calculation of past temperatures by analysis of specific chemicals in natural samples, like those left behind by prehistoric algae.
Algae are a diverse group of organisms that have been abundant in Earth’s oceans and lakes for millennia. Certain chemical compounds, which are deposited in sediment by ancient algae, act as biomarkers – organic compounds that can provide researchers with valuable insight into Earth’s history. In fact, analysis of algal biomarker content in sediment allows researchers to determine the Earth’s temperature hundreds of millions of years ago.
One such record comes from some species of coccolithophores. These algae produce varying amounts of alkenones, a class of robust biomarkers, based on the temperature of their environment. Alkenone analysis is primarily used to calculate the sea surface temperature of Earth’s oceans eons and eons ago.
This video will illustrate the use of alkenones in paleoclimatology and describe the process of isolating, purifying, and analyzing alkenones to calculate past sea surface temperature.
As its name implies, “Alkenone paleothermometry” is based on the analysis of lipids, known as alkenones. Alkenone paleothermometry is based on alkenones; long-chain, unsaturated alkyl ketones that contain 37 carbon atoms and 2 to 4 double bonds. Each double bond is a site of unsaturation. At low sea surface temperatures, alkenone producers generate more unsaturated alkenones than saturated. The ratio of saturation to unsaturation is known as the Alkenone Unsaturation Index.
The alkenones usually evaluated are C37:2 and C37:3, which have 37 carbons and two or three double bonds, respectively. The Unsaturation Index of these alkenones, or the UK’37, is positively related to sea surface temperature. The analytical method know as gas chromatography is generally sensitive enough to separate these alkenones from one another. However, alkenone-producing algae often also generate chemically-similar fatty acid methyl esters, or alkenoates, which cannot be distinguished from alkenones using this technique. Hydrocarbon contamination from pollution may also further muddy chromatographic analysis. To accurately determine relative alkenone concentration, alkenoates and unknown hydrocarbons must be removed before analysis by the methods of saponification and urea adduction.
Now that the relationship of sediment alkenone ratios to sea surface temperature has been reviewed, let’s look at the techniques for their purification from a total lipid extract and analysis of the unsaturation ratio.
Once marine sediment has been collected and extracted, the total lipid extract, or TLE, must go through a multistep purification process, and analyzed. First, the extract undergoes saponification to convert alkenoates into carboxylate salts and methanol using a strong base and heat. Other fatty acid esters present in the TLE will be saponified into salts and glycerol.
After cooling the mixture to room temperature, an aqueous salt solution is added to form salts and glycerol. The mixture is then acidified to protonate the carboxylate anions, producing fatty acids. Finally, the alkenones and fatty acids are extracted from the mixture with hexane.
Silica gel chromatography is then performed to remove both apolar compounds and the polar fatty acids produced by saponification. The dried and saponified TLE is dissolved in hexane and then loaded onto a column. Silica retains polar compounds more strongly than apolar ones.
First, apolar compounds are removed with an apolar solvent, like hexane. Next, alkenones are eluted by a moderately polar solvent, such as dichloromethane, leaving the highly polar fatty acids and other unwanted polar compounds on the column.
If the original sediment sample was collected from a highly polluted area, urea adduction is performed to remove any remaining highly branched or cyclic hydrocarbons. The dried mid-polarity fraction is dissolved in a solvent mixture in which the strongly polar urea is minimally soluble, such as DCM and hexane. A concentrated solution of urea in methanol is then added to the TLE, causing urea crystals to precipitate.
Straight-chain molecules such as alkenones fit into the spaces between molecules in the urea crystal lattice, but highly branched and cyclic molecules do not, and are expelled.
Once crystal growth has finished, the urea crystals are dried and then washed with an apolar solvent to remove expelled compounds. Then, the crystals are dissolved in a small amount of water. The alkenones are extracted from the water with an apolar solvent for analysis.
While all previous purification steps did not differentiate between alkenone species, small differences in boiling point and molecular structure are sufficient for separation on a gas chromatography column. When paired with a flame-ionization detector, relative concentrations of the alkenones, can be determined.
Molecules are identified on the chromatogram by their retention time, or the time needed for the compound to be exit the column. The retention times of the desired compounds are ascertained with alkenone standards.
The relative concentrations of the alkenones are determined from analysis of the areas under the peaks of interest. The UK’37 value is then calculated from the concentrations of C37:2and C37:3 in the sample. With the sea surface temperature proxy relationship and the UK’37 value, the analyst can solve for sea surface temperature at the time of the sediment deposition.
Many different facets of Earth’s history can be investigated by analysis of sediment and sedimentary rock.
Biostratigraphy is the study of determining the ages of layers, or strata, of rock by analysis of the fossils present. As there are many sources of sediment, sedimentary rocks from the same time period may have dramatically different compositions around the world. Certain sets of species throughout Earth’s history, such as the ammonites, existed worldwide and underwent rapid evolution. If visually dissimilar rock strata both contain the same species of ammonite, then a temporal correlation between the strata can be drawn. When combined with techniques such as paleothermometry, extensive information about Earth’s history can be determined from fossil records in natural samples.
Many species of foraminifera, or forams, are found in marine sediments worldwide. Forams have calcium carbonate shells and have existed throughout Earth’s oceans for millions of years. Many species live on the ocean floor, and thus can provide temperature information about deeper parts of the ocean. The magnesium to calcium ratio of forams corresponds to temperature, as they incorporate more magnesium into their shells in warmer climates. The multitude of species and the abundance of forams makes their fossil record useful for tracking changes in ocean currents throughout Earth’s history and for biostratigraphy.
As tectonic plates diverge, new rock forms between them. Correspondingly, the properties of the rock surrounding a divergent plate boundary provide information about plate movements over time. For instance, changes in Earth’s magnetic field are preserved in some minerals found in fossils, rock, and sediment. The discovery of symmetric changes in magnetism about mid-ocean ridges significantly contributed to the current understanding of seafloor spreading and plate tectonics.
You’ve just watched JoVE’s Overview of Alkenone Paleothermometry. You should now understand the principles of paleothermometry and the relationship of alkenone ratios in marine sediment to sea surface temperature. The following videos in this series will go into more detail about this complex process.
Thanks for watching!
