Reconstructing tropical African hydrology using hydrogen isotope ratios of lacustrine sedimentary biomarkers: a calibration transect across Cameroon

古叶蜡脂质中的氢同位素特征（D）可能记录了古植物水的同位素特征，这可能间接反映了降雨的同位素特征。在几个中高纬度湖泊环境中收集的材料表明，叶蜡（D）和源水（D）之间存在紧密的关系。相反，对于热带地区，植被和水文系统中与同位素分馏相关的过程与高纬度地区有很大的不同，尚未提供此代理的校准研究。在这里，我建议分析化合物特定的氢同位素比值的脂质沉积在湖泊沉积物从热带非洲。本项目的总体目标是：I.确定水文气候因素和植物生理过程，决定了氢同位素组成的叶蜡脂生物标志物在热带地区，II。为在热带非洲定量应用特定化合物的氢同位素制定一个强有力的框架。为此，将沿着横跨喀麦隆的南北向样带分析来自活植物、土壤、活浮游植物和近期湖泊表层沉积物的生物标志物的D值。然后将这些值与该样带沿线湖水、树液水和降雨沿着的D值进行比较。选择这个10°长的纬度样带是因为它是独特的，因为它包含了广泛的对比鲜明的植被类别和气候，是热带非洲的代表。这项校准将是第一次在热带地区进行的研究。热带地区是地球大气对流的主要热量和水蒸气来源，准确重建其过去的气候动力学在很大程度上依赖于新的、经过充分校准的气候代用指标。

Hydrogen isotope signatures ((D) in ancient leaf-wax lipids potentially record isotopic properties of ancient plant water, which may indirectly reflect isotopic signatures of rainfall. There is a tight relationship between leaf-wax (D and source-water (D as demonstrated for material collected in several mid- and high-latitude lacustrine environments. In contrast, for the tropical realm, where both vegetation and processes associated with isotope fractionation in the hydrologic system strongly differ from those at higher latitudes, calibration studies for this proxy are not yet available. Here, I propose to analyse the compound-specific hydrogen isotope ratios of lipids deposited in lake sediments from tropical Africa. The overall aim of this project is to: I. Identify the hydro-climatological factors and plant physiological processes that determine the hydrogen isotopic composition of leaf-wax lipid biomarkers in the tropical realm, II. Develop a robust framework for the quantitative application of compound-specific hydrogen isotopes in tropical Africa. For this purpose, (D values of biomarkers from living plants, soils, living phytoplankton and recent lake surface sediments will be analyzed along a N-S transect spanning Cameroon. These values will be then compared with the (D values of lake water, water from tree sap, and rainfall along this transect. This 10°-long latitudinal transect was chosen because it is unique as it encompasses a wide range of contrasting vegetation classes and climates that are representative for tropical Africa. This calibration will be the first study in the tropical realm. The tropics are the main source of heat and water vapour for Earth’s atmospheric convection, and the accurate reconstruction of their past climatic dynamics strongly rely on new, adequately calibrated climate-proxy.