Name: sea surface temperature from alkenone ratios
Uploaded: 2023-04-30T06:47:01.000Z
Duration: 10 min 10 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.2.3

an-overview-of-alkenone-biomarker-analysis-for-paleothermometry

An Overview of Alkenone Biomarker Analysis for Paleothermometry

<div class="chapter_text" id="script_0">
古温度测定法（Paleothermometry）是指通过分析自然样品中特定化学物质来推算过去温度的方法，例如史前藻类遗留下来的化学成分。
藻类是一类多样化的生物，数千年来在地球的海洋和湖泊中大量存在。某些由远古藻类沉积在沉积物中的化学化合物可作为生物标志物（biomarkers）——即能够为研究人员提供有关地球历史重要信息的有机化合物。事实上，通过分析沉积物中藻类生物标志物的含量，研究人员能够确定数亿年前地球的温度。
其中一种记录来源于颗石藻（coccolithophores）的某些物种。这类藻类会根据其所处环境的温度产生不同含量的烯酮（alkenones），这是一类稳定的生物标志物。烯酮分析主要用于推算数十亿年前地球海洋表层的温度。
本视频将演示烯酮在古气候学中的应用，并介绍分离、纯化和分析烯酮以计算过去海洋表层温度的完整过程。
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<div class="chapter_text" id="script_1">
顾名思义，“烯酮古温度测定法”基于对一类称为&#160;烯酮&#160;的脂质的分析。烯酮古温度测定法所依据的烯酮是一类长链、不饱和的烷基酮，含有37个碳原子和2至4个双键。每个双键均为一个不饱和位点。在较低的海水表层温度下，产生烯酮的生物会合成比饱和烯酮更多的不饱和烯酮。饱和度与不饱和度的比值被称为烯酮不饱和指数。
通常评估的烯酮为 C37:2&#160;和 C37:3，它们分别具有37个碳原子和两个或三个双键。这些烯酮的不饱和指数，即 UK'37，与海水表层温度呈正相关。通常，气相色谱分析方法的灵敏度足以将这些烯酮彼此分离。然而，产生烯酮的藻类通常还会生成化学结构相似的脂肪酸甲酯，即烯酸酯，而该类物质使用此技术无法与烯酮区分开来。&#160;此外，来自污染的烃类污染物也可能进一步干扰色谱分析。为了准确测定烯酮的相对浓度，在分析前必须通过皂化和尿素加合的方法去除烯酸酯及未知烃类物质。
在回顾了沉积物中烯酮比值与海水表层温度之间的关系后，接下来我们来看从总脂提取物中纯化烯酮并分析其不饱和比值的技术步骤。
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<div class="chapter_text" id="script_2">
采集并提取海洋沉积物后，总脂质提取物（TLE）必须经过多步纯化过程并进行分析。首先，提取物在强碱和加热条件下进行皂化反应，将烯酮酯转化为羧酸盐和甲醇。TLE中其他存在的脂肪酸酯也会被皂化为盐和甘油。
将混合物冷却至室温后，加入水相盐溶液以促进盐和甘油的形成。随后将混合物酸化，使羧酸根阴离子质子化，生成游离脂肪酸。最后，用正己烷从混合物中萃取出烯酮和脂肪酸。
接着进行硅胶柱层析，以去除皂化产生的非极性化合物和极性脂肪酸。将干燥并完成皂化的TLE溶于正己烷后上柱。硅胶对极性化合物的保留强于非极性化合物。
首先使用非极性溶剂（如正己烷）去除非极性组分；然后使用中等极性溶剂（如二氯甲烷）洗脱烯酮，而高极性的脂肪酸及其他不需要的极性化合物则保留在柱上。
如果原始沉积物样品采自高度污染区域，则需进行尿素加合处理，以去除残留的高支链或环状烃类。将干燥后的中等极性组分溶于尿素难溶的混合溶剂（如二氯甲烷与正己烷）中，然后向TLE中加入甲醇中的浓尿素溶液，促使尿素晶体析出。
直链分子（如烯酮）可嵌入尿素晶体晶格的分子间隙中，而高度支链化或环状分子则无法嵌入，因而被排出。
待晶体生长完成后，收集尿素晶体并用非极性溶剂洗涤以去除被排出的杂质，随后将晶体溶于少量水中。再用非极性溶剂从水中萃取出烯酮用于后续分析。
</div>
<div class="chapter_text" id="script_3">
尽管此前的所有纯化步骤均未区分不同烯酮类化合物，但其沸点和分子结构的微小差异已足以在气相色谱柱上实现分离。当与火焰离子化检测器联用时，可测定样品中&#160;烯酮类化合物的相对浓度。
分子在色谱图上的保留时间（即化合物离开色谱柱所需的时间）可用于鉴定其种类。目标化合物的保留时间通过烯酮标准品进行确定。
通过分析目标峰峰面积，可确定烯酮类化合物的相对浓度。随后根据样品中 C37:2 和 C37:3&#160;的浓度计算 UK'37&#160;值。结合海水表面温度代用指标关系式与 UK'37&#160;值，分析人员即可推算出沉积物沉积时期的海水表面温度。
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<div class="chapter_text" id="script_4">
通过分析沉积物和沉积岩，可以研究地球历史的诸多不同方面。
生物地层学是通过分析所含化石来确定岩层（或地层）年代的学科。由于沉积物来源多样，同一地质时期的沉积岩在全球范围内可能具有显著不同的成分。在地球历史中，某些生物类群（如菊石）曾广泛分布于全球，并经历了快速演化。如果外观差异显著的岩层中均含有同一种菊石，则可据此建立两者之间的时代关联。结合古温度测定等技术，可从自然样品的化石记录中获取大量关于地球历史的信息。
全球海洋沉积物中普遍存在多种有孔虫（foraminifera，简称forams）。有孔虫具有碳酸钙外壳，在地球海洋中已存在数百万年。许多物种&#160;生活于海底，因此能够提供有关海洋深层区域的温度信息。有孔虫壳体中的镁钙比&#160;与温度相关，因为在较温暖的气候条件下，它们会将更多的镁元素掺入壳体中。由于有孔虫物种数量众多且丰度高，其化石记录在追踪地球历史上海洋洋流变化以及进行生物地层学研究方面具有重要价值。
当构造板块分离时，新的岩石会在板块之间形成。相应地，离散型板块边界周围的岩石特性可提供有关板块随时间运动的信息。例如，地球磁场的变化会被保存在化石、岩石和沉积物中的某些矿物内。在洋中脊两侧发现磁性变化的对称分布，这一发现极大地推动了当前对海底扩张和板块构造理论的理解。
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<div class="chapter_text" id="script_5">
您刚刚观看了 JoVE 关于烯酮古温度计的概述视频。您现在应该了解了古温度计的基本原理，以及海洋沉积物中烯酮比值与海表温度之间的关系。本系列接下来的视频将更详细地介绍这一复杂过程。
感谢观看！
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一种用于古温度测定的烯酮生物标志物分析概述

来源：马萨诸塞大学阿默斯特分校 Jeff Salacup 实验室&#160;
在本系列视频中，研究人员提取并纯化了天然样品，以寻找一类称为生物标志物的有机化合物，这些化合物能够提供有关过去气候与环境的信息。所分析的样品之一是沉积物。沉积物在地质历史时期中不断堆积于盆地——即地球表面的凹陷区域，沉积物在流体（水或空气）运动和重力作用下被输送至此。盆地主要分为两种类型：海洋型（海洋和海）和湖泊型（湖泊）。可以预见，由于两者盐度差异显著，其中生存的生物类型也大不相同。在过去的几十年中，有机地球化学家开发出一系列生物标志物代用指标，即可用于表征气候或环境的化合物，其中一些适用于海洋环境，另一些则适用于湖泊环境。本文将重点关注海洋环境，以及利用Uk'37海表温度代用指标进行烯酮古温度测定的方法。
目前最成熟且应用最广泛的开阔海域生物标志物海表温度（SST）代用指标是 Uk'37。
Uk'37 = (C37:2) / (C37:2 + C37:3)（参见 Herbert1 的综述）
该指数基于由某些定鞭藻类藻类产生的一类多不饱和长链烷基酮（称为烯酮）的两种组分之间的比值2,3培养4,5&#160;和表层沉积物核心6&#160;校准研究促成了U的开发k'37 指数作为定量SST代用指标。Prahl基于培养的校准方法令人惊叹 等4:
Uk'37 = 0.034(SST) + 0.039
以及穆勒的岩心顶部校准 等6,
Uk'37 = 0.033(SST) + 0.044
在统计学上完全相同。
重建的Uk'37温度与全球海洋不同气候和颗石藻生产力条件下年均海表温度（SST）的相关性最佳7。在早始新世至今的海洋沉积物岩芯8以及抬升的海洋沉积露头9&#160;中均检测到烯酮，表明其在地质时间尺度上具有极高的稳定性，因而可作为有效的古气候代用指标。Uk'37已被用于记录从十年际10&#160;到轨道尺度11,12&#160;的古海表温度变化，因此具有很高的适用性。
在开阔海域中，颗石藻 Emiliania huxleyi 和 Gephyrocapsa oceanica 是绝大多数烯酮类化合物的生产者。目前尚不清楚这些定鞭藻为何会根据生长温度改变烯酮的不饱和度比例。最初人们认为烯酮是定鞭藻细胞壁的组成部分，其不饱和度的调节是为了维持膜的流动性，类似于饱和脂肪在室温下呈固态，而不饱和脂肪则呈液态。然而，针对这一问题开展的实验发现，烯酮并非与细胞膜相关，而是与细胞内的能量储存结构相关联。因此，烯酮在细胞内的具体功能仍是一个未解之谜。
最近，在湖泊环境中发现了烯酮。然而，其应用迄今仍受到限制。与海洋环境中的烯酮生产者不同，湖泊中的烯酮生产者导致水温与不饱和度（Uk'37）之间的校准关系存在差异。此外，不同湖泊之间的校准关系各不相同，因此建立“全球性”校准关系的可能性较低。遗憾的是，建立局部校准关系成本高昂且耗时较长，因此目前Uk'37在湖泊中的应用前景也受到限制。
烯酮通常从海洋沉积物中提取。产生烯酮的同种生物往往还会产生烯酮的脂肪酸甲酯，即称为烯酮酸酯。这些化合物在气相色谱中与烯酮共洗脱，从而干扰烯酮的准确定量。因此，提取物通常需要经过皂化处理以去除烯酮酸酯。由于皂化反应会产生不适合直接进行气相色谱分析的羧酸，因此在皂化后必须使用硅胶柱层析，将羧酸从提取物中去除。烯酮会随中等极性的酮组分在二氯甲烷洗脱液中流出，而羧酸则保留在柱上。最后，在某些极端情况下，例如从高度污染区域（如靠近工业中心的河口）获取的沉积物样品，可能还需要进行尿素加合处理，以去除在气相色谱中与烯酮共洗脱的未知化合物。
在总脂质提取物纯化后，将提取并纯化的样品通过与火焰离子化检测器联用的气相色谱仪进行分析。使用专为此目的设计的计算机软件（如 Agilent Chemstation），通过获取每种化合物色谱峰的积分面积，确定两种烯酮的相对浓度。然后将这些面积代入上述 Uk'37 比率计算公式，得到介于 0 到 1 之间的 Uk'37 值。随后，利用上述描述的校准方法，将这些 Uk'37 值转换为对应的海表温度值。
<div class="chapter_text" id="script_0">
古温度测定法（Paleothermometry）是指通过分析自然样品中特定化学物质来推算过去温度的方法，例如史前藻类遗留下来的化学物质。
藻类是一类多样化的生物，在地球的海洋和湖泊中已大量存在数千年。某些由远古藻类沉积在沉积物中的化学化合物可作为生物标志物——即能够为研究人员提供地球历史重要信息的有机化合物。事实上，通过对沉积物中藻类生物标志物成分的分析，研究人员能够确定数亿年前地球的温度。
其中一种记录来源于某些颗石藻（coccolithophores）物种。这类藻类会根据其生存环境的温度产生不同量的烯酮（alkenones），这是一类稳定的生物标志物。烯酮分析主要用于推算数十亿年前地球海洋表层的温度。
本视频将展示烯酮在古气候学中的应用，并介绍分离、纯化和分析烯酮以计算过去海洋表层温度的实验流程。
</div>
<div class="chapter_text" id="script_1">
顾名思义，“烯酮古温度计”是基于对一类称为烯酮的脂质进行分析。烯酮古温度计的原理依赖于烯酮——一类长链、不饱和的烷基酮，含有37个碳原子和2至4个双键。每个双键均为一个不饱和位点。在较低的海水表层温度下，烯酮生产者会生成比饱和烯酮更多的不饱和烯酮。饱和与不饱和的比例被称为烯酮不饱和指数。
通常评估的烯酮为C37:2和C37:3，它们分别具有37个碳原子和两个或三个双键。这些烯酮的不饱和指数，即UK'37，与海水表层温度呈正相关。通常，气相色谱这一分析方法的灵敏度足以将这些烯酮彼此分离。然而，产生烯酮的藻类通常还会生成化学结构相似的脂肪酸甲酯，即烯酸酯，而该技术无法将其与烯酮区分开来。&#160;此外，来自污染的烃类污染物也可能进一步干扰色谱分析。为了准确测定烯酮的相对浓度，必须在分析前通过皂化和尿素加合的方法去除烯酸酯及未知烃类。
在回顾了沉积物中烯酮比值与海水表层温度之间的关系后，接下来我们来看从总脂提取物中纯化烯酮以及测定其不饱和比值的技术方法。
</div>
<div class="chapter_text" id="script_2">
采集并提取海洋沉积物后，总脂质提取物（TLE）必须经过多步纯化过程并进行分析。首先，提取物在强碱和加热条件下进行皂化反应，将烯酮酯转化为羧酸盐和甲醇。TLE 中存在的其他脂肪酸酯也将被皂化为盐和甘油。
将混合物冷却至室温后，加入水相盐溶液以形成盐和甘油。随后将混合物酸化，使羧酸根阴离子质子化，生成游离脂肪酸。最后，使用正己烷从混合物中萃取烯酮和脂肪酸。
接着进行硅胶柱层析，以去除皂化产生的非极性化合物和极性脂肪酸。将干燥后的皂化 TLE 溶于正己烷，然后上样至层析柱。硅胶对极性化合物的保留能力强于非极性化合物。
首先，使用非极性溶剂（如正己烷）洗脱并去除非极性化合物。随后，使用中等极性溶剂（如二氯甲烷）洗脱烯酮，而高极性的脂肪酸及其他不需要的极性化合物则保留在柱上。
如果原始沉积物样品采自高度污染区域，则需进行尿素加合反应，以去除任何残留的高度支链化或环状烃类。将干燥的中等极性组分溶于尿素溶解度极低的混合溶剂（如二氯甲烷与正己烷）中。然后向 TLE 中加入浓的甲醇尿素溶液，促使尿素晶体析出。
直链分子（如烯酮）可嵌入尿素晶体晶格分子间的空隙中，而高度支链化和环状分子则无法嵌入，因而被排出晶体外。
待晶体生长完成后，收集尿素晶体并用非极性溶剂洗涤，以去除被排出的杂质。随后将晶体溶于少量水中，再用非极性溶剂从水中萃取烯酮用于后续分析。
</div>
<div class="chapter_text" id="script_3">
尽管此前的所有纯化步骤均未区分不同烯酮类化合物，但其沸点和分子结构上的微小差异已足以在气相色谱柱上实现分离。当与火焰离子化检测器联用时，可测定样品中&#160;烯酮类化合物的相对浓度。
分子在色谱图上的保留时间（即化合物流出色谱柱所需的时间）可用于鉴定其种类。目标化合物的保留时间通过烯酮标准品确定。
通过分析目标色谱峰下的面积，可确定烯酮类化合物的相对浓度。随后根据样品中 C37:2 和 C37:3 的浓度计算 UK'37 值。结合海水表面温度代用指标关系式与所测得的 UK'37 值，分析人员即可推算出沉积物沉积时的海水表面温度。
</div>
<div class="chapter_text" id="script_4">
通过分析沉积物和沉积岩，可以研究地球历史的诸多不同方面。
生物地层学是通过分析岩石中所含化石来确定岩层（或地层）年代的研究方法。由于沉积物来源多样，同一地质时期的沉积岩在全球范围内可能具有显著不同的组成。在地球历史中，某些生物类群（如菊石）在全球范围内广泛分布，并经历了快速演化。如果外观迥异的岩层均含有同一种菊石物种，则可据此建立两者之间的时代关联。结合古温度测量等技术，可从天然样品的化石记录中获取大量关于地球历史的信息。
全球海洋沉积物中普遍存在多种有孔虫（foraminifera，简称 forams）。有孔虫具有碳酸钙外壳，在地球海洋中已存在数百万年。许多物种&#160;生活于海底，因此能够提供有关海洋深层区域的温度信息。有孔虫壳体中的镁钙比&#160;与温度相关，因为在较温暖的气候条件下，它们会将更多的镁元素掺入壳体中。有孔虫物种的多样性及其丰度使其化石记录在追踪地球历史上海洋洋流变化以及生物地层学研究中具有重要价值。
当构造板块分离时，其间的区域会形成新的岩石。相应地，离散型板块边界周围的岩石特性可提供关于板块随时间运动的信息。例如，地球磁场的变化会被保存在化石、岩石和沉积物中的某些矿物内。在洋中脊两侧发现的磁性对称变化，对当前海底扩张和板块构造理论的建立起到了重要推动作用。
</div>
<div class="chapter_text" id="script_5">
您刚刚观看了 JoVE 关于烯酮古温度计的概述视频。您现在应该理解了古温度计的基本原理，以及海洋沉积物中烯酮比值与海表温度之间的关系。本系列的后续视频将更详细地介绍这一复杂过程。
感谢观看！
</div>

来源：杰夫·萨拉库普实验室 - 马萨诸塞大学阿默斯特分校  
在本系列视频中，天然样品被提取并……

古温度测定法是通过分析自然样品中特定化学物质（例如史前藻类遗留的物质）来计算过去温度的方法。藻类是一类多样化的生物，在地球的海洋和湖泊中已存在数千年之久。某些由远古藻类沉积在沉积物中的化学化合物可作为生物标志物——即能够为研究人员提供有关地球历史重要信息的有机化合物。事实上，通过分析沉积物中藻类生物标志物的含量，研究人员能够推断出数亿年前地球的温度。其中一个记录来自某些颗石藻物种。这些藻类会根据其所处环境的温度产生不同数量的烯酮，烯酮是一类稳定的生物标志物。烯酮分析主要用于计算数十亿年前地球海洋的表层海水温度。本视频将阐述烯酮在古气候学中的应用，并描述分离、纯化和分析烯酮以计算过去海表温度的过程。顾名思义，“烯酮古温度计”是基于一类称为“烯酮”的脂质分析。烯酮古温度计的原理依赖于烯酮——一类长链、不饱和的烷基酮，含有37个碳原子和2至4个双键。每个双键均为一个不饱和位点。在较低的海表温度下，烯酮生产者生成的不饱和烯酮多于饱和烯酮。饱和度与不饱和度的比值被称为烯酮不饱和指数。通常评估的烯酮是 C37:2 和 C37:3，它们分别具有 37 个碳原子和两个或三个双键。这些烯酮的不饱和指数，即 UK'37，与海表温度呈正相关。通常采用的分析方法为气相色谱法，其灵敏度足以将这些烯酮彼此分离。然而，产生烯酮的藻类通常也会生成化学结构相似的脂肪酸甲酯，即烯酸酯，而该技术无法区分烯酮与烯酸酯。此外，来自污染的烃类污染物可能进一步干扰色谱分析。为了准确测定烯酮的相对浓度，必须在分析前通过皂化和尿素加合的方法去除烯酸酯及未知烃类物质。在回顾了沉积物中烯酮比值与海表温度之间的关系后，让我们来探讨如何从总脂质提取物中纯化烯酮并分析其不饱和度比值的技术。采集并提取海洋沉积物后，必须对总脂质提取物（TLE）进行多步纯化处理并加以分析。首先，提取物需经过皂化反应，在强碱和加热条件下将烯酸酯转化为羧酸盐和甲醇。TLE 中存在的其他脂肪酸酯也将在此过程中被皂化为相应的盐和甘油。将混合物冷却至室温后，加入水性盐溶液以生成盐和甘油。随后将混合物酸化，使羧酸根阴离子质子化，生成脂肪酸。最后用己烷从混合物中萃取烯酮和脂肪酸。随后通过硅胶色谱法去除皂化产生的非极性化合物和极性脂肪酸。将干燥并完成皂化的总脂质提取物溶解于正己烷中，然后上样至色谱柱。硅胶对极性化合物的保留强于非极性化合物。首先，使用非极性溶剂（如正己烷）去除非极性化合物。接着，用中等极性的溶剂（如二氯甲烷）洗脱烯酮，使强极性的脂肪酸及其他不需要的极性化合物保留在柱上。如果原始沉积物样品采自高度污染区域，则需进行尿素加合处理，以去除任何残留的高度支链化或环状烃类。将干燥后的中等极性组分溶解于尿素溶解度极低的溶剂混合物中，例如二氯甲烷（DCM）和正己烷。然后向总提取物（TLE）中加入甲醇中的浓尿素溶液，促使尿素晶体析出。直链分子（如烯酮）可嵌入尿素晶体晶格的分子间隙中，而高度支链化和环状的分子则无法嵌入，并被排出。晶体生长完成后，将尿素晶体干燥，然后用非极性溶剂洗涤以去除排出的化合物。随后，将晶体溶解于少量水中。使用非极性溶剂从水中萃取烯酮用于分析。尽管此前的所有纯化步骤均未区分不同烯酮类物质，但因其沸点和分子结构存在微小差异，足以在气相色谱柱上实现分离。当与火焰离子化检测器联用时，可测定烯酮的相对浓度。通过保留时间（即化合物流出色谱柱所需的时间）在色谱图上对分子进行鉴定。目标化合物的保留时间通过烯酮标准品确定。通过分析目标峰下面积，确定烯酮的相对浓度。然后根据样品中C37:2和C37:3的浓度计算UK'37值。结合海水表面温度代用指标关系式与UK'37值，分析人员可推算出沉积物沉积时的海水表面温度。通过分析沉积物和沉积岩，可以研究地球历史的诸多不同方面。生物地层学是通过分析岩石中所含化石来确定岩层或地层年代的研究方法。由于沉积物来源多样，同一地质时期的沉积岩在全球范围内可能具有显著不同的成分。在地球历史的某些时期，某些生物类群（例如菊石）在全球广泛分布，并经历了快速演化。如果外观差异显著的岩层中均含有相同的菊石物种，则可据此建立这些岩层之间的时间关联。当该方法与古温度测定等技术结合使用时，便可从自然样品的化石记录中获取关于地球历史的大量信息。全球海洋沉积物中广泛分布着多种有孔虫（foraminifera），也称为有孔虫类（forams）。有孔虫具有碳酸钙外壳，已在地球海洋中生存了数百万年。许多物种栖息在海底，因此能够提供有关海洋深层区域的温度信息。有孔虫体内镁与钙的比值与其生存环境的温度相关，因为在较温暖的气候条件下，它们会将更多的镁元素结合到外壳中。由于有孔虫物种丰富且数量众多，其化石记录在追踪地球历史上海洋洋流变化以及生物地层学研究中具有重要价值。当构造板块分离时，板块之间会形成新的岩石。相应地，离散型板块边界周围岩石的性质提供了关于板块随时间运动的信息。例如，地球磁场的变化会被化石、岩石和沉积物中某些矿物所记录。在洋中脊两侧发现磁性呈对称变化的现象，极大地促进了当前对海底扩张和板块构造理论的理解。您刚刚观看了 JoVE 关于烯酮古温度计的概述视频。现在，您应该理解了古温度计的基本原理，以及海洋沉积物中烯酮比值与海表温度之间的关系。本系列的后续视频将更详细地介绍这一复杂过程。感谢观看！

Education

教育

JoVE Science Education

Environmental Sciences

环境科学

Earth Science

地球科学

概述了 Paleothermometry 长链生物标志物分析

sea surface temperature from alkenone ratios

Sea surface temperature can be reconstructed from alkenone ratios preserved in marine sediment. Alkenones are long-chain, unsaturated alkyl ketones made by some haptophyte algae, especially coccolithophores such as Emiliania huxleyi and Gephyrocapsa oceanica in the open ocean. The most widely used proxy is the U K'37 index, which compares the C37:2 and C37:3 alkenones. Because the ratio changes with growth temperature, it can be used to estimate past sea surface temperature.

The U K'37 proxy was developed from both culture studies and core-top sediment calibration work. The culture-based relationship reported by Prahl and colleagues and the core-top relationship reported by Müller and colleagues are statistically very similar. Reconstructed U K'37 temperatures tend to match mean annual sea surface temperature across many ocean settings. Alkenones are also stable enough to be found in marine sediment cores from the early Eocene to modern deposits and in exposed outcrops of uplifted marine sediment. That long record makes them useful for studying climate change across both short and long time scales.

Scientists first thought alkenones were part of algal cell walls and helped control membrane fluidity, similar to how unsaturated fats stay fluid. Later work showed that alkenones are associated with energy storage structures inside the cell instead. Their exact role in the cell is still not fully known. Alkenones have also been found in lakes, but lacustrine use is more limited because the producers are different and the calibration between temperature and unsaturation changes from one lake to another. A single global lake calibration is unlikely, and making local calibrations takes time and money.

Marine sediment samples usually need several cleanup steps before analysis. Alkenone-producing algae often make alkenoates, which are fatty acid methyl esters that can co-elute with alkenones on a gas chromatograph and make quantification harder. To remove them, the total lipid extract is saponified, which converts the alkenoates into carboxylic acids and salts. The mixture is then acidified, and the resulting fatty acids are separated from the alkenones by silica gel chromatography. In polluted samples, such as sediment from estuaries near industrial centers, urea adduction may also be needed to remove unknown compounds that co-elute with the target molecules.

After purification, the sample is analyzed by gas chromatography with a flame ionization detector. The alkenones are identified by retention time using standards, and the areas under the peaks are used to determine the relative amounts of C37:2 and C37:3. Those values are inserted into the U K'37 equation to obtain a number between 0 and 1. A temperature calibration then converts that value into sea surface temperature at the time the sediment was deposited. This approach helps researchers study past ocean climates using biomarkers preserved in natural samples.

Alkenone paleothermometry is one part of a larger field of paleothermometry, which uses chemicals in sediments and rocks to estimate past temperatures. Algal biomarkers can preserve climate information from hundreds of millions of years ago. Sediment records can also be compared with other tools from Earth science, including biostratigraphy, which uses fossils to match rock layers by age. For example, ammonites can link separate strata, and foraminifera can provide temperature clues because their magnesium-to-calcium ratio changes with warmer water. Together with evidence from magnetism in rocks and sediment, these methods help scientists rebuild Earth’s history and track processes such as seafloor spreading and plate tectonics.

Sea Surface Temperature from Alkenone Ratios

sea-surface-temperature-from-alkenone-ratios

determining spatial orientation of rock layers with the brunton compass

determining-spatial-orientation-rock-layers-with-brunton

Measuring Rock Layer Strike and Dip

The Brunton compass is used to measure the spatial orientation of rock layers and other rock features. Many rock units show planar surfaces or linear features. These include bedding surfaces, fault surfaces, fracture surfaces, joint surfaces, foliation, and mineral alignment. These measurements give geologists the raw data they need to study how rock units formed and how they changed over time. The directions are recorded as strike and dip. Strike is the direction of a flat surface, and dip...

using topographic maps to generate topographic profiles

using-topographic-maps-to-generate-topographic-profiles

Reading Contour Lines on Topographic Maps

Topographic maps show Earth’s surface in a plan view, which means an overhead view. They give a clear look at land shape from above. These maps are a standard way to represent three-dimensional terrain on a flat page. Contour lines are the key feature of a topographic map. Each line connects places with the same elevation, or height above sea level. The spacing between contour lines is called the elevation interval, and it depends on how much detail the map shows and on the land itself. <br...

making a geologic cross section

Reading Geologic Maps in 3D

Geologic maps show rock units at Earth’s surface and help geologists infer what lies below it. They began in Europe in the mid-to-late 18th century and have since become a key tool for studying rock distribution, subsurface structure, and changes through time. A modern geologic map is a data-rich, two-dimensional plan view built on a topographic map. On these maps, color variations mark specific rock units. The lines where one unit meets another are called contacts. Geologic maps also use...

physical properties of minerals i: crystals and cleavage

physical-properties-of-minerals-i-crystals-and-cleavage

Mineral Crystal Shapes and Cleavage

Mineral crystal shapes and cleavage reveal how a mineral is built at the atomic level. These physical properties are measurable and visible traits that help identify minerals. They include color, streak, magnetic properties, hardness, crystal growth form, and crystal cleavage. Each of these properties is specific to a mineral. They are tied to the mineral’s chemical make-up and atomic structure. Crystal growth form and crystal cleavage both come mainly from the repeated pattern of basic atomic...

physical properties of minerals ii: polymineralic analysis

physical-properties-of-minerals-ii-polymineralic-analysis

Mineral Clues for Rock Identification

Mineral color, streak, luster, hardness, magnetism, and acid reaction help identify minerals and rocks. These physical properties can be seen or measured in hand samples and in the field. They are tied to a mineral’s chemical makeup and, to a lesser extent, its atomic structure. The video also explains why these clues work for rocks as well as minerals. Rocks are made of mineral grains, and most rocks contain more than one mineral type, which means they are polymineralic. Some rocks are...

igneous volcanic rock

How Volcanic Rock Forms From Lava

Volcanic rock forms when magma reaches Earth’s surface and cools. It is a type of igneous rock, which means it comes from cooling and crystallization of molten material. When magma is on the surface, it is called lava. Magma is molten rock that is usually between about 800 °C and 1,200 °C. It forms inside Earth through three main melting processes. These are the addition of heat, the addition of volatiles, and decompression. Each way of making magma can produce a different kind of magma. That...

igneous intrusive rock

Magma Cooling and Igneous Rock

Igneous rocks form when hot liquid rock, called magma, cools and crystallizes. Magma temperatures typically range from about 800 °C to 1,200 °C. These rocks record the freezing of molten material inside Earth.

an overview of bgdgt biomarker analysis for paleoclimatology

an-overview-of-bgdgt-biomarker-analysis-for-paleoclimatology

Sediment Biomarkers for Past Climate Records

Sediment biomarkers can record past climate conditions, and branched GDGTs are one example used to study temperature in freshwater basins. These organic compounds are extracted from natural samples, purified, and then measured to help reconstruct environments from the past. In paleoclimatology, scientists use these records to better understand climate change over time. Sediments build up over geologic time in sedimentary basins, which are low areas in the Earth’s crust where material is...

an overview of alkenone biomarker analysis for paleothermometry

Sea surface temperature can be reconstructed from alkenone ratios preserved in marine sediment. Alkenones are long-chain, unsaturated alkyl ketones made by some haptophyte algae, especially coccolithophores such as Emiliania huxleyi and Gephyrocapsa oceanica in the open ocean. The most widely used proxy is the U K'37 index, which compares the C37:2 and C37:3 alkenones. Because the ratio changes with growth temperature, it can be used to estimate past sea surface temperature. The U K'37 proxy...

sonication extraction of lipid biomarkers from sediment

sonication-extraction-of-lipid-biomarkers-from-sediment

How Organic Carbon Becomes Biomarkers

Organic material and inorganic material are chemically different. In an ecosystem, living material includes leaves, fungi, bark, and tissue. Non-living material includes rocks, their minerals, oxygen, water, and metals. Organic matter contains carbon linked to other carbon and hydrogen molecules, which sets it apart from inorganic matter. Carbon is especially flexible in the kinds of bonds it can form. Its valence range from -4 to +4 lets it make up to four separate covalent bonds with nearby...

soxhlet extraction of lipid biomarkers from sediment

soxhlet-extraction-of-lipid-biomarkers-from-sediment

Large-Volume Sediment Extraction for Standards

Large-volume sediment extraction is used to isolate compounds for chemical standards. These standards help labs track the performance, accuracy, and precision of instruments over time. That way, a measurement made today can be compared with one made a year later. Because standards must be checked over long periods, labs often need large amounts of material. Many chemical standards can be bought from companies such as Sigma-Aldrich and Fisher. But some natural compounds needed for paleoclimatic...

extraction of biomarkers from sediments - accelerated solvent extraction

extraction-of-biomarkers-from-sediments-accelerated-solvent-extraction

Sediment biomarkers can help scientists reconstruct past air and water temperatures. In this method, a group of organic biomarkers called glycerol-dialkyl glycerol-tetraethers, or GDGTs, is studied in modern sediments and in older sediment layers of known age. GDGTs are produced by a suite of archaea and bacteria. Their distribution changes in a predictable way in response to temperature. That pattern lets researchers use sediment records to track how climate changed over time. These...

conversion of fatty acid methyl esters by saponification for uk'37 paleothermometry

conversion-fatty-acid-methyl-esters-saponification-for-uk-37

Saponification for Cleaner GC-FID Analysis

Saponification helps clean up complex lipid samples before gas chromatography analysis. A total lipid extract, or TLE, from an organic solvent extraction can contain hundreds or even thousands of compounds. Researchers may only need a few target compounds. They may also need to remove unwanted material that gets in the way or co-elutes, meaning it comes off the gas chromatograph at the same time as another compound. This sample cleanup supports measurement on a gas chromatograph coupled to a...

purification of a total lipid extract with column chromatography

purification-of-a-total-lipid-extract-with-column-chromatography

Separating Lipid Classes by Column Chromatography

Column chromatography is used to separate lipid classes in a total lipid extract. A total lipid extract, or TLE, is often a complex mixture made up of hundreds or even thousands of compounds. Researchers may only need a few target compounds, so they remove the compounds they are not studying. Those target compounds can belong to different classes, including alkanes, ketones, alcohols, and acids. In some studies, a sample may contain many compounds, but only a small set matters for analysis.

removal of branched and cyclic compounds by urea adduction for uk'37 paleothermometry

removal-branched-cyclic-compounds-urea-adduction-for-uk-37

Urea Adduction Separates Lipid Shapes

Urea adduction separates straight-chain lipids from branched and cyclic compounds in a total lipid extract. Researchers use this step when they want only a small set of target molecules from a sample that may contain hundreds or even thousands of compounds. For paleothermometry, the target compounds are the alkenones used in U k'37 and the isoprenoidal glycerol dialkyl glycerol tetraethers, or GDGTs, used in MBT/CBT. Together, these organic paleothermometers depend on only six compounds: two...

earth science

该系列专题包括地质学、地球化学等。各种示范, 包括矿物的物理化学性质和岩石形成的分析。

Learn how alkenone biomarkers in marine sediment are purified and measured with gas chromatography to estimate past sea surface temperature using the U K'37 proxy.

Sea Surface Temperature from Alkenone Ratios | JoVE K12

Pennsylvania State Academic Standards

Earth and Space Science

3.3.9-12.I

History of Earth

3.3.9-12.F

3.3.9-12.G

3.3.9-12.J

Weather and Climate

3.3.9-12.E

Louisiana Student Standards for Science

High School

Earth’s Systems

HS-ESS2-1

HS-ESS2-3

HS-ESS2-4

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Physical Geology

Minerals

properties-minerals-hardness-luster-cleavage-streak-crystal-shape

Properties of minerals (hardness, luster, cleavage, streak, crystal shape, fluorescence, flammability, density/specific gravity, malleability)

Earth's History

The geologic rock record

Plate Tectonics

Internal Earth

Historical review

Virginia  Standards of Learning

HIgh School

ES.5

ES.5.a

ES.9

ES.9.a

ES.10

ES.10.d

Texas Essential Knowledge and Skills

Earth Systems Science

112.49.c.11

112.49.c.11.E.

Alabama Course of Study Science

9-12.ESS.2.5.d

Florida Department of Education

SC.912.E.6

SC.912.E.6.3

SC.912.E.7

SC.912.E.7.7

Georgia Standards of Excellence

Geology

Geologic Time

SG3.a

new-york-state-science-learning-standards

New York State Science Learning Standards

Physical Science

HS. Structure and Properties of Matter

HS-PS1-10.

HS. Waves and Electromagnetic Radiation

HS-PS4-5.

Life Science

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

HS-LS1-6.

HS-LS2-4.

Earth and Space Sciences

HS-ESS2-2.

HS-ESS2-6.

HS-ESS2-7.

Jeff Salacup

Overview

Principles of Alkenone Paleothermometry

Alkenone Purification

Analysis of Relative Alkenone Concentrations

Applications

Summary

Igneous Volcanic Rock

Source: Laboratory of Alan Lester - University of Colorado Boulder
Igneous rocks are the products of cooling and crystallization of magma. Volcanic rocks ...

The Carbon Cycle

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among ...

Igneous Intrusive Rock

Source: Laboratory of Alan Lester - University of Colorado Boulder
Igneous rocks are products of the cooling and crystallization of high temperature ...

Using Topographic Maps to Generate Topographic Profiles

Source: Laboratory of Alan Lester - University of Colorado Boulder
Topographic maps are &#34;plan-view&#34; representations of Earth&#39;s ...

Determining Spatial Orientation of Rock Layers with the Brunton Compass

Source: Laboratory of Alan Lester - University of Colorado Boulder
Most rock units exhibit some form of planar surfaces or linear features. Examples ...

Making a Geologic Cross Section

Source: Laboratory of Alan Lester - University of Colorado Boulder
Geologic maps were first made and utilized in Europe, in the mid-to-late 18th century. ...

Use models to explain how mantle convection powers plate tectonics.

ESS.EES.2.1

Analyze and interpret data to predict locations of volcanoes and earthquakes based on plate boundaries.

ESS.EES.2.2

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
Throughout this series of videos, natural samples were extracted and ...

Topographic Surveying and Contours

Topographic surveying is critical for documenting the Earth's surface, focusing on capturing elevations, slopes, and natural and man-made features. It is ...

Plotting of Topographic Maps

Topographic maps represent the Earth's surface features using contour lines, which connect points of equal elevation to create a two-dimensional ...

Methods of Obtaining Topography

Topography involves measuring and mapping land elevations, natural features, and artificial structures to create accurate representations of the terrain. ...

Use models to explain how plate tectonics influence topography.

The Soil Ecosystem

Plants obtain inorganic minerals and water from the soil, which acts as a natural medium for land plants. The composition and quality of soil depend not ...

Conditions on Early Earth

What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited ...

The Water Cycle

The Earth&rsquo;s hydrosphere includes all of the areas where the storage and movement of water occurs. Since water is the basis of all living processes, ...

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of ...

The Phosphorus Cycle

Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, ...

The Sulfur Cycle

Sulfur, an important element in the chemical makeup of proteins, is recycled through the atmosphere and aquatic and terrestrial environments. Found in the ...

Bioremediation

Bioremediation is the use of prokaryotes, fungi, or plants to remove pollutants from the environment. This process has been used to remove harmful toxins ...

Carry out investigations to explain how the rock cycle and rates of weathering, erosion, and soil formation influence Earth's systems.

ESS.EES.2.4

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

Analyze and interpret data to explain how volcanic activity influences changes in Earth's atmosphere, geosphere, biosphere, and hydrosphere.

ESS.EES.2.5

Analyze how the geosphere is shaped by plate tectonics and the rock cycle.

Sea Surface Temperature from Alkenone Ratios

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