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.

从中新世气候最佳状态到晚中新世条件的转变，即中中新世气候转变（MMCT，~14.5-13 Ma），代表了地球新生代晚期变冷的关键时期，其特征是全球温度下降~3°C和相关变化我们的目标是通过获取气候变化前后数十年的“快照”，以高时间分辨率研究这种气候转变对热带印度尼西亚穿流的影响。 MMCT 使用砗磲作为气候档案，因为深时（更新世前）热带季节性相对于现代是否有所增加仍然悬而未决。此外，砗磲记录了次季节极端天气事件（EWE）。 - 相关的环境变化，由于通过地球化学重建过去的温度，预计 EWE 会增加，因此在高（ER）CO2 间隔期间进行研究很有意义。然而，代理可能会受到盐度、海水成分和动力学的影响，我们计划通过使用最近开发的双簇同位素分析（Δ47、Δ48）和微量元素分析来提供不受这些影响的古温度。 -时间'保存潜力，并且由于其大小，非常适合通过材料密集型方法（例如丛集）进行（亚）季节解析分析砗磲提供每日解析的气候快照并记录 EWE，特别是其元素组成（El/Ca 比率），为了实现可靠的古气候重建，我们将评估壳降水动力学对 Δ47、Δ48 的影响以及继我们之前的成功培养之后，通过在受控环境条件下培养蛤来研究盐度和海水化学对 El/Ca 比率的影响。随后，我们将使用 LA-ICPMS 以（次）年到日的时间分辨率对这些贝壳进行多代理地球化学分析（El/Ca、δ18O、δ13C、Δ47、Δ48、87Sr/86Sr）。 、稳定和团簇同位素分析这将使我们能够评估降水动力学对巨蛤壳的影响。 （Δ47、Δ48）以及海水成分（Ca 浓度和盐度/δ18O）对砗磲元素和同位素成分的影响将这些结果应用于保存完好的化石样本，我们将重建 MMCT 和 MMCT 的年平均温度变化。中新世热带季节性温度变化。季节性到每日时间尺度的多代理数据将揭示极端径流或上升流事件的频率。总体而言，人类时间尺度上的古气候数据与测试气候模拟相关。