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.

从中新世最佳气候条件到中新世晚期条件的过渡，即中中新世气候过渡（MMCT，约14.5-13 Ma），代表了地球晚新生代冷却的关键时期，其特征是全球温度下降约3°C，以及冰盖、大气和海洋环流的相关变化。我们的目标是调查这种气候转变的影响，在高时间分辨率的热带印度尼西亚的对流，通过获得几个十年之久的“快照”之前和之后的MMCT使用巨蛤（Tridacna）作为气候档案。这样的重建是重要的，因为它仍然没有解决是否深时间（前更新世）热带季节性增加相对于现代。此外，Tridacnas记录亚季节性极端天气事件（EWE）相关的环境变率，在高（er）CO2间隔期间的研究是有意义的，因为预期EWE增加从气候变暖。然而，过去的温度重建，通过地球化学代理，可能会受到盐度，海水成分和动力学。我们计划利用新近发展起来的双聚团同位素分析（Δ47，Δ48）和微量元素分析来提供不受这些影响的古温度。巨蛤具有良好的“深时间”保存潜力，并且由于它们的大小，非常适合通过材料密集型方法（如聚集同位素）进行（亚）季节性分辨分析。Tridacna提供每日分辨率的气候快照，并记录EWE，特别是在其元素组成（El/Ca比）。为了实现可靠的古气候重建，我们将评估贝壳沉淀动力学对Δ47，Δ48的影响，以及盐度和海水化学对在受控环境条件下培养蛤的El/Ca比值的影响。继我们以前成功的培养，三个实验将研究不同的海水钙浓度，盐度和温度的影响。随后，我们将使用LA-ICPMS、稳定和聚集同位素分析，以（亚）年到日的时间分辨率对这些壳进行多代理地球化学分析（El/Ca、δ 18 O、δ 13 C、Δ47、Δ48、87 Sr/86 Sr）。这将使我们能够评估沉淀动力学对巨蛤壳的影响（Δ47，Δ48）以及海水成分（Ca浓度和盐度/δ 18 O）对Tridacna元素和同位素组成的影响。将这些结果应用于保存异常的化石样本，我们将重建MMCT和中新世热带季节性温度变化的平均年温度变化。季节性到每日时间尺度的多代理数据将揭示极端事件的频率，例如径流或上升流事件。我们假设EWE频率和季节性降水变化减少，温度变化增加，整个MMCT冷却。总的来说，这种人类时间尺度上的古气候数据与测试气候模拟有关。