Giant clams as multidecadal deep-time climate snapshots – mineralization, calibration & application to the Indonesian Throughflow across the mid-Miocene transition

巨蛤作为数十年深层气候快照 â 矿化、校准

• 批准号: 518543034
• 负责人: Professor Dr. Jens Fiebig
• 金额: --
• 依托单位: Fredy and Nadine Herrmann Institute of Earth Sciences
• 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/518543034?language=en
• 关键词: Giant; clams; multidecadal; deep; time

The transition from the Miocene Climate Optimum to later Miocene conditions, the Mid-Miocene Climate Transition (MMCT, ~14.5-13 Ma), represents a key interval in Earth’s late Cenozoic cooling, characterized by ~3°C global temperature decrease and associated changes in ice cover, atmospheric and oceanic circulation. We aim to investigate the effects of this climate transition for the tropical Indonesian Throughflow at high time resolution by obtaining few decade-long ‘snapshots’ before and after the MMCT using giant clams (Tridacna) as climate archives. Such reconstructions are important as it remains unresolved whether deep-time (pre-Pleistocene) tropical seasonality was increased relative to modern. In addition, Tridacnas record sub-seasonal extreme weather event (EWE)-related environmental variability, the study of which during high(er) CO2 intervals is of interest due to the expected EWE-increase from anthropogenically-induced warming. Past temperature reconstructions via geochemical proxies, however, can be biased by salinity, seawater composition and kinetics. We plan to provide palaeotemperatures unbiased by these influences by using recently-developed dual-clumped isotopic analysis (Δ47, Δ48) and trace element analysis. Giant clams have good ‘deep-time’ preservation potential and, due to their size, are ideally suited for (sub-)seasonally-resolved analysis by material-intense methods such as clumped isotopes. Tridacna provide up to daily-resolved climate snapshots and record EWEs especially in their elemental composition (El/Ca-ratios). To enable reliable palaeoclimate reconstructions we will evaluate the influence of shell precipitation kinetics on Δ47, Δ48, and the impact of salinity and seawater chemistry on El/Ca ratios by culturing clams under controlled environmental conditions. Following on from our previous successful culturing, three experiments will investigate the influence of varying seawater Ca-concentration, salinity and temperature. Subsequently we will conduct multiproxy geochemical analyses (El/Ca, δ18O, δ13C, Δ47, Δ48, 87Sr/86Sr) of these shells at (sub)annual to daily time resolution, using LA-ICPMS, stable and clumped isotope analysis. This will allow us to assess the impact of precipitation kinetics on giant clam shells (Δ47, Δ48) and the effect of seawater compositions (Ca-concentration and salinity/δ18O) on the elemental and isotopic compositions of Tridacna. Applying these results to exceptionally-preserved fossil samples, we will reconstruct mean annual temperature variations across the MMCT and Miocene tropical seasonal temperature variability. Multiproxy data on seasonal to daily time scales will reveal the frequency of extreme e.g. runoff or upwelling events. We hypothesize a decrease in EWE-frequency and seasonal precipitation variability and an increase in temperature variability with cooling across the MMCT. Overall, such palaeoclimate data on human time-scales are relevant for testing climate simulations.

从中新世气候最佳到后新世条件的过渡，中新世的气候过渡（MMCT，〜14.5-13 MA）代表了地球晚期的新生代晚期冷却的关键间隔，其特征是〜3°C的全球温度降低，并且在冰覆盖，大气和海洋循环中的变化和相关的变化。我们的目的是通过使用巨型蛤（Tridacna）作为气候档案，在MMCT之前和之后，通过获得长达十年的“快照”来研究这种气候转变对热带印尼遍及流量的影响。这样的重建非常重要，因为是否相对于现代而增加了深度时间（Pre-Preistecene）热带季节性是否增加。此外，TridACNAS记录了亚地区的极端天气事件（EWE）相关的环境变异性，由于人为引起的变暖的预期ewe症状，对高（ER）CO2间隔期间的研究引起了人们的研究。但是，通过地球化学代理的过去温度重建可能会因盐度，海水组成和动力学而偏见。我们计划通过使用最近开发的双聚体同位素分析（Δ47，Δ48）和痕量元素分析来提供对这些影响的古植物。巨型蛤具有良好的“深度”保存潜力，并且由于其尺寸，非常适合通过材料密集型方法（例如聚类的同位素）（亚）季节性分辨的分析。 Tridacna提供了每日分辨的攀岩快照，并记录母羊，尤其是在其元素组成（El/Ca-Ratios）中。为了实现可靠的古气候重建，我们将通过在受控的环境条件下培养蛤lam来评估壳沉淀动力学对Δ47，Δ48的影响以及盐度和海水化学对EL/CA比的影响。从我们以前的成功聚类开始之后，三个实验将研究变化的海水CA浓度，盐度和温度的影响。随后，我们将使用LA-ICPMS，稳定和集群的同位素分析，对这些壳的这些壳进行多氧地球化学分析（EL/CA，Δ18O，Δ13C，Δ13C，Δ13C，Δ47，Δ48，87SR/86SR）。这将使我们能够评估降水动力学对巨型蛤壳的影响（Δ47，Δ48）以及海水成分（Ca-浓度和盐度/盐度/Δ18O）对Tridacna的元素和同位素组成的影响。将这些结果应用于保存的化石样品中，我们将重建整个MMCT和中新世热带季节性温度变化的平均年温度变化。关于季节到每日时间尺度的多氧数据数据将揭示极端的频率，例如径流或上升活动。我们假设母羊频率和季节性降水的变化降低，并且随着MMCT的冷却，温度变化的增加。总体而言，这种关于人类时间尺度的古气候数据与测试气候模拟有关。