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

这项拟议的研究旨在开发和测试一种利用钙的稳定同位素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，这些方法不适合其他营养水平测定方法。这项研究将集中在海洋食物链上，但所开发的方法也应该适用于大陆食物链。对多种生物的初步调查表明，生物源性碳酸钙和磷酸钙在同位素上始终比源（膳食）钙轻（低于44Ca），而且营养水平的变化远远大于温度依赖分异引起的变化。提议的工作涉及PI与脊椎动物古生物学研究生之间的合作，PI拥有同位素地球化学和质谱方面的专业知识。由于生物过程似乎是决定陆地环境（包括海水）中钙稳定同位素分布的主要因素，因此拟议的研究还将对海水中钙含量在地质时期的可能变化进行初步解释。该研究计划包括三个部分：确定在现代海洋食物链的营养水平之间44Ca减少的程度，以及确定可能影响44Ca的其他因素。这些结果将对生物钙转运和固定的机制产生影响。确定化石骨骼材料如何很好地保存其原始的钙同位素组成。测量了足够多的其他类型的地质样本，以获得地球表面环境Ca循环中同位素分异的总体视图。初步资料表明，生物对轻钙同位素的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不需要保存完好的有机材料就能确定生物化石营养水平的技术，那么对于试图重建灭绝动物的生态关系的古生物学家来说，它应该会立即有用。通过增加对生物过程如何影响钙同位素定量的理解，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。一旦确定了控制陆源物质中钙同位素丰度的主要参数，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.