African climate changes during C4 plant evolution and expansion

在这个工作包（TP 2）中，我们建议建立详细的记录植被变化的非洲大陆调查陆源植物脂质生物标志物和它们的分子，碳和氢，同位素签名。这些分析将结合东赤道和南大西洋海洋沉积物岩心样本的花粉组合进行。在第一阶段（1-3年），我们专注于中新世中期至晚期，涵盖C4草原的大规模扩张。在第二阶段（4-6年），我们将研究从始新世晚期到渐新世早期的时间间隔，当C4植物进化。C4植物的进化和扩张都主要与大气CO2水平的降低有关，根据CO2阈值模型。而对于始新世/渐新世的间隔下降的CO2水平进行了重建，中新世pCO 2水平的估计值和检测到的C4草原的扩张之间存在不匹配。这种对比反过来又指出了其他环境因素对大规模植被变化的重要性，如降水量和季节性。为了解决这一差异，我们将应用新的化合物特定的氢同位素分析陆地脂质生物标志物，使大陆水文条件的准确评估。脂质生物标志物与花粉记录的详细比较将允许不同组成的C4植被之间的区别。此外，我们将建立有机地球化学记录过去海表面温度（SST）的变化在东南大西洋解开大陆环境变化和海洋变化之间的气候联系。在这方面，本TP获得的结果将直接与TP 4中生成的海洋代用数据相比较。在整个研究单元内，该TP与TP 01一起提供陆地植被和气候参数的数据库，以定量验证所获得的全球碳和水循环模拟结果。

In this workpackage (TP 2) we propose to establish detailed records of vegetation changes on the African continent by investigating terrigenous plant lipid biomarkers and their molecular, carbon and hydrogen, isotopic signatures. These analyses will be conducted in combination with pollen associations on samples from marine sediment cores in the eastern equatorial and southern Atlantic. In the first phase (year 1-3) we focus on the middle to Late Miocene, covering the large-scale expansion of C4 grasslands. In the second phase (year 4-6) we will investigate the interval from the Late Eocene to the Early Oligocene, when C4 plants evolved. Both evolution and expansion of C4 plants have yet mainly been linked to decreasing atmospheric CO2 levels according to the CO2-treshold model. While for the Eocene/Oligocene interval falling C02 levels were reconstructed a mismatch exists between estimates of Miocene pCO2 levels and the detected expansion of C4 grasslands. This contrast, in turn, points to the significance of other environmental factors for large-scale vegetation changes, such as amount and seasonality of precipitation. In order to resolve this discrepancy, we will apply novel compound-specific hydrogen isotope analyses on terrestrial lipid biomarkers, which enable accurate assessment of continental hydrological conditions. A detailed comparison of lipid biomarker with pollen records will allow the distinction between C4 vegetations of different composition. In addition, we will establish organic-geochemical records of past sea-surface temperature (SST) changes in the south-eastern Atlantic to unravel climatic linkages between the continental environmental changes and oceanographic variations. In this respect, the results obtained by this TP will directly be comparable to the marine proxy data generated in TP 4. Within the entire Research Unit, this TP, in conjunction with TP 01, provides the data base of terrestrial vegetation and climate parameters to quantitatively validate the obtained modelling results on the global carbon and water cycle.