Goethite Internal Thermometry - Improvements and Applications

地球的气候在时间尺度上的变化从几十年到数百万年不等，这是对太阳的输出、大陆的排列、海洋环流和大气成分等因素的反应。我们对过去气候的了解大多来自对矿物质的分析，这些矿物质记录了它们生长的环境条件。例如，极地冰构成了几十万年前的气候档案，而海洋生物的碳酸盐骨架也携带着类似的信息，可以追溯到数亿年前。目前，人们对大陆上深时间的环境条件知之甚少，主要是因为人们所知的携带古气候记录的材料很少，无法确定准确的形成年龄。最近的研究表明，矿物针铁矿——一种在大陆岩石风化过程中产生的常见氧化铁——可以用辐射法测定年代，并包含其形成温度的记录。该奖项将通过开发一种高效和自动化的技术来评估针铁矿形成温度，探索这种表征大陆古气候的新方法，一旦建立起来，将使用该技术来完善该方法的温度校准，并将其应用于过去6600万年的针铁矿标本套件，这些标本来自欧洲、巴西和澳大利亚的地方。最终的结果将是一种改进的分析方法，以及来自大陆的第一个数百万年的古温度记录。这项工作将支持一名研究生，也将吸引当地社区学院的学生参与这项工作的科学以及即将开发的自动分析系统的开发和编程。针铁矿（FeOOH）是含铁矿物与含氧地层和地表水相互作用形成的。在风化环境中，这种非常不溶性的相形成、生存和积累，成为铁粒、蛛丝、古土壤和红土的主要成分。最近的两项进展表明，针铁矿可以提供一种独特的古温度记录，例如在大陆内部，几乎没有其他的古温度计存在。首先，用(U-Th)/He法测定针铁矿的年代，不确定度为5%。1500多个日期的汇编表明，针铁矿的形成跨越了整个新生代（0-66 Ma），几乎没有中断。其次，两个晶体学上不同的氧位点在18O/16O中具有易于测量的温度依赖对比，从而允许单相古温度学。该项目将通过三项任务将这两项进展联系起来，这些任务旨在改进和完善针铁矿内部测温方法，并首次以系统的方式应用该方法。任务一是设计和建造一条新的氧气提取线，可以完全自动化和高效地处理针铁矿标本。这是实现该项目所需的大量氧同位素分析的关键一步。任务2是通过分析在比以前工作更多样化的温度和化学条件下生长的合成针铁矿来改进针铁矿内部温度计的校准。这项任务将提高针铁矿内部温度的不确定性，并将确定任何尚未识别的衍生温度的二次控制。任务3包括对针铁矿内部测温档案的第一次系统调查。将对三组已经确定年代的针铁矿进行古温度分析（共约100个样品）：来自亚马逊盆地深部风化硫化物矿床的表生针铁矿、来自中欧的针铁矿芯岩和来自西澳大利亚神秘的通道铁矿床的针铁矿。从每一个地点，我们将获得连续跨越数百万年的氧同位素数据。这些记录将使研究人员能够评估针铁矿温度估计的内部一致性，并首次以高时间分辨率记录来自三个不同大陆的整个新生代的古温度。第四个任务是让社区成员参与到这个项目中来，同时教会他们一项有用的技能。首席研究员将领导为期3天的Labview短期课程，这是一种编程语言，从根本上实现了所提议的工作。参加课程的有竞争力的学生将包括来自当地高中和/或社区大学的个人。短期课程将介绍针铁矿内部温度测量的科学和方法，并将从建议的分析工作中提取编码示例和练习。在短期课程结束时，其中一名学生将被选中进行为期十周的实习，为拟议的提取线开发/记录Labview代码。该项目的更传统的更广泛的影响包括支持一个博士生，改进和验证一个全新的可以广泛应用的古气候工具，从以前未研究过的地区创造新的古气候记录，这些记录将在地球科学和其他领域有用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Earth's climate varies over timescales from tens of years to millions of years in response to factors such as the sun's output, the arrangement of continents, ocean circulation, and the composition of the atmosphere. Much of what we know about past climate comes from analysis of minerals that carry a record of environmental conditions under which they grew. For example, polar ice constitutes an archive of climate extending back hundreds of thousands of years, while the carbonate skeletons of marine organisms carry similar information extending to hundreds of millions of years ago. At present, little is known about environmental conditions on the continents in deep time, primarily because few materials are known that carry a record of paleoclimate and for which an accurate formation age can be determined. Recent work indicates that the mineral goethite, a common iron oxide produced during weathering of continental rocks, can be radiometrically dated and also contains a record of its formation temperature. This award will explore this new method of characterizing continental paleoclimate by developing an efficient and automated technique to assess goethite formation temperature, and, once established, will use that technique to refine the temperature calibration of the method and apply it to suites of dated goethite specimens spanning the last 66 million years from localities in Europe, Brazil, and Australia. The end product will be an improved analytical methodology and amongst the first multimillion year paleotemperature records from the continents. The work will support a graduate student and will also engage students from a local community college in both the science of the undertaking and in the development and programming of the automated analytical system to be developed.Goethite (FeOOH) is formed when Fe-bearing minerals interact with oxygen-bearing ground and surface waters. In weathering environments, this very insoluble phase forms, survives and accumulates, becoming a major constituent of ferricretes, gossans, paleosols and laterites. Two recent advances suggest that goethite can provide a unique record of paleotemperatures in settings, such as continental interiors, where almost no alternative paleothermometer exists. First, using the (U-Th)/He method goethite can be dated with an uncertainty 5%. A compilation of more than 1500 dates reveals that goethite formation spans, almost without interruption, the entire Cenozoic Era (0-66 Ma). Second, the two crystallographically-distinct oxygen sites have a readily-measured temperature-dependent contrast in 18O/16O, allowing single-phase paleothermometry. This project will link these two advances by undertaking three tasks designed to improve and refine the goethite-internal thermometry method, and to apply it in a systematic way for the first time. Task 1 is to design and build a new oxygen extraction line that can process goethite specimens in a completely automated and efficient way. This is a critical step to permit the large number of oxygen isotopic analyses required by this project. Task 2 is to refine the calibration of the goethite internal thermometer by analyzing synthetic goethites grown under a more diverse range of temperature and chemical conditions than previous work. This task will improve the uncertainty on goethite-internal temperatures, and will identify any as-yet unrecognized secondary controls on derived temperatures. Task 3 consists of the first systematic investigation of the goethite internal thermometry archive. Three suites of already-dated goethites will be analyzed for paleotemperature (total ~100 samples): supergene goethites from a deeply weathered sulfide deposit in the Amazon basin, goethite pisoliths from Central Europe, and goethites from the enigmatic Channel Iron Deposits of Western Australia. From each of these localities we will obtain oxygen isotope data that continuously spans many millions of years. These records will allow the researchers to assess internal consistency of the goethite temperature estimates, and to document for the first time paleotemperatures at high temporal resolution over the entire Cenozoic from three different continents. A fourth task is designed to engage members of the community with this project and simultaneously to teach them a useful skill. The principal investigator will lead a 3-day short-course in Labview, a programming language that fundamentally enables the proposed work. Competitively-selected students participating in the course will include individuals from local high schools and/or community colleges. The short-course will introduce the science and the approaches of goethite-internal thermometry, and coding examples and exercises will be drawn from the proposed analytical work. At the end of the short course one of these students will be selected for a ten-week internship to develop/document Labview code for the proposed extraction line. More traditional Broader Impacts of this project include support for a PhD student, refinement and verification of an entirely new paleoclimate tool that can be broadly applied, and creation of new paleoclimate records from previously unstudied areas that will be useful in geoscience and beyond.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.