Terrestrial sediment flux and upwelling intensity in the anthropogenic era recorded by stable Ba isotopes and rare earth elements in tropical coral skeletons

由于海水变暖和人类活动引起的海水化学变化，珊瑚受到压力。因此，根据珊瑚本身的记录量化河流径流、沙尘通量和季节性上涌强度的过去变化的能力对珊瑚保护至关重要，同时也为人为土地利用和气候变化的历史提供了宝贵的见解。然而，对陆地沉积物通量和上升流强度常用的珊瑚元素/钙代用物（例如Ba/Ca比值）的解释可信度有限，因为会出现与海水化学变化无关的异常峰值。近年来，珊瑚骨架中的稳定Ba同位素和稀土元素（REE）已成为记录河流输入变化的新工具，并已被应用于改进对珊瑚元素/Ca冲突记录的解释。组合稳定Ba同位素和REE同位素的巨大价值在于它们各自的特定同位素分馏和化学性质，它们不受生物矿化效应的影响，而生物矿化效应会影响所有ca归一化元素的比例。通过结合稳定的Ba同位素和REE (Ba-REE)，我们将开发一个更可靠和广泛适用的沉积物通量和上升流代理。我们实验室在分析方法方面的最新进展现在可以常规测量海水和珊瑚骨架中稳定的Ba同位素和极低的REE浓度。在受河流径流、沙尘通量和上升流季节性波动影响较大的特定地点，从珊瑚和同时期海水中生成Ba-REE的月分辨时间序列数据。我们将在季节时间尺度上对珊瑚和海水之间的Ba同位素分馏和REE分配进行直接校准，并将组合珊瑚Ba-REE代理应用于仪器时代的短记录。这项工作将对SPP2299优先计划的目标做出重大贡献，SPP2299优先计划旨在通过使用新的地球化学和同位素工具，在月度到季节性的时间尺度上，加强我们对热带海洋气候变率及其对珊瑚礁生态系统影响的理解。

Corals are under stress from warming seawater and changes in seawater chemistry caused by human activities. Therefore, the ability to quantify past changes in river runoff, dust flux and seasonal upwelling intensity based on records of corals themselves is pivotal for coral protection, while at the same time providing valuable insights into the history of anthropogenic land use and climatic variability. However, the confidence in interpretation of the commonly used coral element/Ca proxies for terrestrial sediment fluxes and upwelling intensity, e.g., Ba/Ca ratios, is limited due to the occurrence of anomalous peaks that are not related to changes in seawater chemistry. Recently, stable Ba isotopes and rare earth elements (REE) in coral skeletons have been developed as novel tools to record past changes in riverine inputs and have been applied to improve the interpretation of the conflicting coral element/Ca records. The great value of combined stable Ba isotopes and REE lies in their specific isotope fractionation and chemical properties, respectively, which are independent from biomineralisation effects that can influence all Ca-normalized elemental ratios. By combining stable Ba isotopes and REE (Ba-REE) we will develop a more robust and widely applicable proxy for sediment fluxes and upwelling. Recent advances in analytical methods by our laboratory now allow the routine measurement of stable Ba isotopes and the very low REE concentrations in seawater and coral skeletons. Monthly resolved time series data of Ba-REE will be generated from coral and contemporaneous seawater at specific locations that are significantly affected by seasonal fluctuations in river runoff, dust flux and upwelling. We will perform the direct calibration of Ba isotope fractionation and REE partitioning between coral and seawater on seasonal timescales and apply the combined coral Ba-REE proxy to short records from the instrumental era. The proposed work will significantly contribute to the goals of Priority Program SPP2299 aiming at enhancing our understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world by using novel geochemical and isotopic tools at monthly to seasonal timescales.