Improving the Accuracy of U-Th Coral Dating: A Test of Diagenetic Pathways, Models, and Effects

提高 U-Th 珊瑚测年的准确性：成岩途径、模型和效应的测试

• 批准号: 0819714
• 负责人: Laura Robinson
• 金额: $ 42万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-15 至 2012-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0819714&HistoricalAwards=false
• 关键词: Improving; Accuracy; Th; Coral; Dating

This grant will attempt to answer three key questions regarding the apparent mobility of uranium and thorium isotopes that severely compromises the accuracy of uranium-thorium dating performed on fossil corals:1) To what extent are the isotopes produced by uranium decay mobilized by the energy of alpha decay?2) Are excess uranium decay products, which are frequently observed in fossil corals, adsorbed onto the crystal surfaces?3) Can exchange of uranium between corals and water alter the isotopic composition of the coral with no change to the coral?s uranium concentration?Intellectual merit: In light of current concerns over the impacts of rising sea levels on human welfare, understanding potential magnitudes and rates of future sea level change is crucial. A well-dated and detailed history of past sea level change would provide important information in this regard. One of the premier methods for reconstructing the history of sea level is the dating of fossil corals that once grew near the sea surface. The advantages of this approach include the wide spread distribution of fossil corals, improvements in mass spectrometry allowing precise dating as far back as 600,000 years, and detailed stratigraphic correlations that can be used to determine abrupt, sub-meter scale sea-level changes. Unfortunately, these potential advantages are largely unrealized due to the widely recognized but poorly understood mobility of the uranium and thorium isotopes used for dating. Observations of systematic alteration trends in fossil corals and the idea that these trends might be explained by the systematic addition of recoil-mobilized uranium decay products have reinvigorated interest in coral diagenesis. Several models have been proposed to correct U-Th coral ages for such daughter addition, and have been shown to improve the age agreement of corals from the same fossil reef. However, the accuracy of such corrected ages remains controversial, in part because the physical mechanisms assumed by the models have not been tested directly. There is an urgent need to better understand these mechanisms, so that we might improve our understanding of past and future sea level change. This grant will undertake a series of experiments designed to test these critical assumptions.Broader Impact: The data that collected will provide fundamental information for scientists studying a broad variety of fields: carbonate chemistry, mineral-fluid interactions, paleoceanography, geochronology, and paleoclimate. Results and methods will be made available to the scientific community through publications in peer-reviewed journals and presentations at international conferences. Results and implications will be communicated to the public through interviews and talks. The team will use small-scale projects related to this research to introduce undergraduate students to laboratory techniques and the theory and practice of U-Th dating. Internships will take place through the WHOI Summer Student Fellowship Program. In addition, this proposal will support the careers of two junior scientists engaging in collaboration as a way of amplifying the impact of their combined scientific insights.

这笔赠款将试图回答有关铀和胸部同位素明显流动性的三个关键问题，这些问题严重损害了对化石珊瑚进行的铀 - 硫代的准确性：1）在多大程度上，由铀衰减的能量在多大程度上受到脉络衰减的脉络衰减的群体，这是脉络衰减的经常被静脉衰落的产品，这是在脉络上的流动？表面？3）珊瑚与水之间的铀交换可以改变珊瑚的同位素组成，而不会改变珊瑚的铀浓度？知识分子：鉴于目前对海平面上升对人类福利的影响的担忧，了解未来海平面的潜在幅度和速度是至关重要的。过去的海平面变化历史悠久且详细的历史将在这方面提供重要信息。重建海平面历史的主要方法之一是曾经在海面附近生长的化石珊瑚的日期。这种方法的优点包括化石珊瑚的广泛分布，质谱的改进，可以追溯到60万年，以及可用于确定突然的，次级尺度的海平面变化的详细地层相关性。不幸的是，由于铀和用于约会的同位素的迁移率广泛但知之甚少，因此这些潜在的优势在很大程度上是未实现的。对化石珊瑚的系统变化趋势的观察以及这些趋势可以通过系统添加后反应动物还脉衰减产物来解释的想法，这使人们对珊瑚成岩发电兴趣兴趣。已经提出了几种模型来纠正这种女儿的珊瑚年龄，并已被证明可以改善同一化石礁的珊瑚年龄一致。但是，这种校正年龄的准确性仍然存在争议，部分原因是模型假设的物理机制尚未直接测试。迫切需要更好地理解这些机制，以便我们可以提高对过去和未来海平面变化的理解。该赠款将进行一系列旨在测试这些关键假设的实验。BaroDer的影响：收集的数据将为研究各种领域的科学家提供基本信息：碳酸盐化学，矿物 - 流体相互作用，古代摄影，年代学，年代学和古气候。结果和方法将通过在国际会议上的同行评审期刊和演讲中的出版物提供给科学界。结果和含义将通过访谈和谈判传达给公众。该团队将使用与这项研究有关的小规模项目，将本科生介绍给实验室技术以及U-The约会的理论和实践。实习将通过WHOI夏季学生奖学金计划进行。此外，该提案将支持两位参与合作的初级科学家的职业，以扩大其联合科学见解的影响。