A New Method of Assessing Trophic Levels in Fossil Organisms Using Calcium Stable Isotopes

DePaolo 9526997 拟议的研究旨在开发和测试一种使用钙的稳定同位素评估营养级的新方法，并将这种方法应用于化石生物，特别是脊椎动物，而不适用于其他营养级确定方法。 这项研究将侧重于海洋食物链，但所制定的方法也应适用于大陆食物链。 各种生物的初步调查表明，生物碳酸钙和磷酸钙是一贯的同位素轻（低44Ca）比源（饮食）钙，营养水平的变化是远远大于由于温度依赖性分馏的变化。 提议的工作涉及在同位素地球化学和质谱方面具有专业知识的PI与脊椎动物古生物学研究生之间的合作。 由于生物处理似乎是决定钙稳定同位素在陆地环境（包括海水）中分布的主要因素，因此拟议的研究还将允许初步解释海水44Ca在地质时期的可能变化。 研究计划包括三个部分： 确定44Ca在现代海洋食物链中营养级之间减少的程度，并确定可能影响44Ca的其他因素。 这些结果将对生物钙运输和固定的机制有一定的影响。 确定化石骨骼材料如何保持其原始的钙同位素组成。 测量足够多的其他类型地质样品，以全面了解地球表面环境Ca循环中的同位素分馏。 初步数据表明，生物对轻钙同位素的清除是海水钙同位素值的主要控制因素之一。 如果我们成功地建立了一种不需要保存完好的有机物质就能确定化石生物的营养级的技术，它应该会对试图重建灭绝动物生态关系的古生物学家立即有用。 通过增加对生物加工如何影响钙同位素比率的理解，拟议的研究将阐明一个可能重要但知之甚少的稳定同位素系统的工作原理。 一旦控制陆地物质中钙同位素丰度的主要参数被量化，海洋44Ca在地质时期的变化可能会提供一个新的古海洋学工具。

DePaolo 9526997 The proposed research seeks to develop and test a new method of assessing trophic level using stable isotopes of calcium, and to apply this method to fossil organisms, particularly vertebrates, not amenable to other methods of trophic level determination. The study will focus on marine food chains, but the method developed should apply to continental food chains as well. A preliminary survey of a variety of organisms suggests that biogenic calcium carbonate and calcium phosphate is consistently isotopically lighter (lower 44Ca) than source (dietary) calcium, and that the trophic level shifts are much greater than shifts due to temperature-dependent fractionation. The work proposed involves collaboration between the PI, who has expertise in isotope geochemistry and mass spectrometry, and a graduate student in vertebrate paleontology. Because biological processing appears to be a major factor determining the distribution of calcium stable isotopes in terrestrial settings, including seawater, the proposed research will also allow preliminary interpretation of possible changes in seawater 44Ca over geologic time. The research plan consists of three parts: Determining the extent to which 44Ca decreases between trophic levels in modern marine food chains, and identifying other factors that can influence 44Ca. These results will have implications for the mechanisms of biological Ca transport and fixation. Establishing how well fossil skeletal materials preserve their original calcium isotopic makeup. Measuring enough other types of geological samples to get an overall view of isotopic fractionation in the Ca cycle of the earth's surface environment. Preliminary data indicate that biological scavenging of light calcium isotope is one of the main controls on the calcium isotopic value of seawater. If we are successful in establishing a technique for determining the trophic level of fossil organisms that does not require well-preserved organic material, it should be immediately useful to paleontologists attempting to reconstruct the ecological relationships of extinct animals. By increasing understanding of how biological processing affects calcium isotopic rations, the proposed research will illuminate the workings of a possibly important, but little understood, stable isotope system. Once the major parameters controlling calcium isotope abundaces in terrestrial materials are quantified, changes in the ocean 44Ca through geologic time may provide a new paleoceanographic tool.