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

DePaolo 9526997拟议的研究试图开发和测试一种使用稳定的钙同位素来评估营养水平的新方法，并将这种方法应用于化石生物，特别是脊椎动物，这些生物不适用于其他确定营养水平的方法。这项研究将重点放在海洋食物链上，但开发的方法也应该适用于大陆食物链。对各种生物的初步调查表明，生物来源的碳酸钙和磷酸钙的同位素值始终比来源(饮食)钙的轻(低44Ca)，而且由于依赖温度的分馏作用，营养水平的变化要比变化大得多。拟议的工作涉及在同位素地球化学和质谱学方面拥有专业知识的PI和一名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包括海水在内的陆地环境中钙稳定同位素分布的主要因素，拟议的研究还将允许初步解释海水44Ca随地质时间的可能变化。研究计划包括三个部分：确定现代海洋食物链中营养级别之间44Ca减少的程度，以及确定其他可能影响44Ca的因素。这些结果将对生物钙的运输和固定机制有一定的指导意义。确定化石骨骼材料如何保存其原始的钙同位素组成。测量足够多的其他类型的地质样品，以全面了解地球表面环境中钙循环的同位素分馏。初步数据表明，轻钙同位素的生物清除作用是控制海水钙同位素值的主要因素之一。如果我们成功地建立了一种技术来确定化石生物的营养水平，而不需要保存完好的有机材料，这应该会立即对古生物学家试图重建灭绝动物的生态关系有用。通过增加对生物加工如何影响钙同位素配给的理解，拟议的研究将阐明一个可能重要但鲜为人知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随地质时间的变化可能提供一种新的古海洋学工具。

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.