Calibration of the phosphate δ18O thermometer for SIMS analyses to reconstruct ancient seawater temperatures

校准用于 SIMS 分析的磷酸盐 δ18O 温度计以重建古代海水温度

• 批准号: 470134482
• 负责人: Professor Dr. Thomas Wotte
• 金额: --
• 依托单位: Lehrstuhl für Paläontologie / Stratigraphie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/470134482?language=en
• 关键词: Calibration; phosphate; 18O; thermometer; SIMS

Oxygen isotope (δ18O) studies on marine biological precipitated phosphate (bioapatite) provide a valuable tool for reconstructing temperatures of (paleo)seawater. Whereas the conventional oxygen isotope analysis of bioapatite via IRMS (isotope ratio mass spectrometry) requires large sample volumes of > 1 mg, this volume is essentially reduced during in situ SIMS (secondary ion mass spectrometry) analysis. Such a reduction of sample size also minimizes the risk of contamination of the primary oxygen isotope signal. Despite this obvious advantage, some critical points probably influencing the final interpretation of data: (1) There seems to be an offset between oxygen isotope values generated via SIMS and IRMS, as SIMS probably not only liberates oxygen isotopes related to the PO43− group. Whether (and if so, to what extent) non-PO43− related oxygen isotopes bias the final δ18O values or whether this reported offset is only an artefact of sample alteration, needs clarification. (2) Equations necessary for reconstructing the (paleo)seawater temperatures are based on data from IRMS analyses. But, are these thermometer equations also applicable for SIMS data? (3) In order to calibrate the oxygen isotope values from bioapatite generated by SIMS, Durango apatite is commonly used as the primary isotope standard. Even if its homogeneity in δ18O is generally accepted, there are still doubts questioning this presumption. This project aims to clarify these critical aspects to calibrate and establish a phosphate δ18O thermometer for SIMS analyses from bioapatite, allowing a precise calculation of seawater temperatures. For the successful realization of the project, we want to analyze teeth of sharks grown up during standardized seawater conditions. Requirements necessary, are given by commercial aquariums. Why we want to use sharks? Sharks are the ideal provider for marine bioapatite, as (1) their teeth are principally composed of flour-apatite, which is most resistant against secondary alteration, and (2) shark teeth are changed continuously and are thus important fossils from marine and terrestrial environments. To determine oxygen isotope fractionation between bioapatite of teeth and seawater, different shark species of the same aquarium will be investigated. On the other hand, the influence of variations in seawater temperature, pH-value, and oxygen isotopic composition on distinct shark species will be detected by using eight basins of four commercial aquariums.Results of our research will be a fundamental base for calculating seawater temperatures of the geological past, using oxygen isotopes of fossil bioapatite generated via SIMS analysis. Therefore, our project is an important contribution towards a better understanding of the interaction between atmosphere, hydrosphere, and biosphere throughout the Earth’s history.

海洋生物沉淀磷酸盐（生物磷灰石）的氧同位素（δ 18 O）研究为恢复（古）海水温度提供了有价值的工具。然而，通过IRMS（同位素比质谱法）进行的生物磷灰石的常规氧同位素分析需要> 1 mg的大样品体积，而在原位西姆斯（二次离子质谱法）分析期间，该体积基本上减小。样品大小的这种减小还使初级氧同位素信号的污染风险最小化。尽管有这个明显的优势，一些关键点可能会影响数据的最终解释：（1）通过西姆斯和IRMS产生的氧同位素值之间似乎存在偏移，因为西姆斯可能不仅释放与PO43−基团相关的氧同位素。非PO43 −相关的氧同位素是否（如果是，在多大程度上）使最终的δ 18 O值产生偏差，或者这种报告的偏移是否只是样品改变的假象，需要澄清。(2)重建（古）海水温度所需的方程是基于IRMS分析的数据。但是，这些温度计方程也适用于西姆斯数据吗？(3)为了校准由西姆斯产生的生物磷灰石的氧同位素值，杜兰戈磷灰石通常被用作主要同位素标准。即使它的δ18O均一性被普遍接受，仍然有人质疑这一假设。该项目旨在澄清这些关键方面，以校准和建立用于生物磷灰石西姆斯分析的磷酸盐δ 18 O温度计，从而精确计算海水温度。为了成功实现该项目，我们希望分析在标准化海水条件下生长的鲨鱼牙齿。必要的要求，由商业水族馆给出。我们为什么要用鲨鱼？鲨鱼是海洋生物磷灰石的理想提供者，因为（1）它们的牙齿主要由最抗次生蚀变的粉磷灰石组成，（2）鲨鱼牙齿不断变化，因此是海洋和陆地环境中的重要化石。为了测定鲨鱼牙齿和海水中生物磷灰石的氧同位素分馏，将对同一水族箱中不同种类的鲨鱼进行调查。另一方面，利用4个商业性水族馆的8个水池，研究海水温度、pH值、氧同位素组成的变化对鲨鱼种类的影响，为通过西姆斯分析生物磷灰石化石的氧同位素，推算地质年代的海水温度奠定基础。因此，我们的项目是对更好地了解整个地球历史上大气圈，水圈和生物圈之间的相互作用的重要贡献。