A combination of palynology and geochemical proxies to investigate Pliocene environmental and climate changes in tropical West Africa and east equatorial Atlantic

This dissertation investigates the long-term vegetation, environmental and climate changes in West Africa and in the eastern equatorial Atlantic during the Pliocene, in order to identify the links between low latitude environmental variability to the global Pliocene climate reorganization, related to changes in the atmospheric circulation, ocean gateway closure, the Northern Hemisphere Glaciation and orbital forcings

Eine Kombination aus Palynologie und geochemischen Proxies Pliozän Umwelt- und Klima zu untersuchen Veränderungen im tropischen Westafrika und im Osten äquatorialen atlantisch

This dissertation investigates the long-term vegetation, environmental and climate changes in West Africa and in the eastern equatorial Atlantic during the Pliocene, in order to identify the links between low latitude environmental variability to the global Pliocene climate reorganization, related to changes in the atmospheric circulation, ocean gateway closure, the Northern Hemisphere Glaciation and orbital forcings

XRF scanning, revisited composite depth and age model of ODP Site 159-959 (1.8-6.2 Ma)

In this study, new high-resolution XRF data from ODP Site 959 (3°37'N, 2°44'W) have been used to investigate the relationship between paleoenvironmental changes in West Africa and sedimentation in the tropical east Atlantic Ocean. Fe intensity data have been used to build a 91 meter composite depth record that has been astronomically tuned allowing the development of a detailed age model from 6.2 to 1.8 Ma. Based on this new stratigraphy we studied the variations of Ti/Al, Ti/Ca and Al/Si ratios, proxies for aeolian vs. fluvial supply, as dust indicator and fine vs. coarse grain size, respectively. We discuss sedimentation patterns at ODP Site 959 associated to the environmental changes from the late Miocene until the early Pleistocene. During the interval corresponding to the earlier stages of the Messinian Salinity Crisis our proxy records indicate enhanced run-off from the West African continent and major supply of fine material at ODP Site 959, suggesting a stronger monsoon and increased precipitation during eccentricity minima. A long-term decrease of river supply is documented after 5.4 Ma towards the early Pleistocene. From the increased values and variability of Ti/Al ratios we suggest that after 3.8 Ma dust started to reach the study site probably as a result of the southward shift of the Intertropical Convergence Zone during winter. Between 3.2 and 2.9 Ma ODP Site 959 Ti/Ca ratios exhibit three maxima corresponding to eccentricity maxima similarly to other dust records of northern Africa. This suggests continent-wide aridity or larger climate variability during that interval. Eccentricity forcing (405 kyr and 100 kyr) and precession frequencies are found in the entire studied interval. The variations of Ti/Al ratio suggest stronger seasonality between 5.8 and 5.5 Ma and after 3.2 Ma

XRF scanning, pollen and spores of ODP Site 108-659

Pliocene vegetation dynamics and climate variability in West Africa have been investigated through pollen and XRF-scanning records obtained from sediment cores of ODP Site 659 (18°N, 21°W). The comparison between total pollen accumulation rates and Ti/Ca ratios, which is strongly correlated with the dust input at the site, showed elevated aeolian transport of pollen during dusty periods. Comparison of the pollen records of ODP Site 659 and the nearby Site 658 resulted in a robust reconstruction of West African vegetation change since the Late Pliocene. Between 3.6 and 3.0 Ma the savannah in West Africa differed in composition from its modern counterpart and was richer in Asteraceae, in particular of the Tribus Cichorieae. Between 3.24 and 3.20 Ma a stable wet period is inferred from the Fe/K ratios, which could stand for a narrower and better specified mid-Pliocene (mid-Piacenzian) warm time slice. The northward extension of woodland and savannah, albeit fluctuating, was generally greater in the Pliocene. NE trade wind vigour increased intermittently around 2.7 and 2.6 Ma, and more or less permanently since 2.5 Ma, as inferred from increased pollen concentrations of trade wind indicators (Ephedra, Artemisia, Pinus). Our findings link the NE trade wind development with the intensification of the Northern Hemisphere glaciations (iNHG). Prior to the iNHG, little or no systematic relation could be found between sea surface temperatures of the North Atlantic with aridity and dust in West Africa