Climatic and Paleoenvironmental Changes in Central Africa over the Last 300,000 Years: Evidence from the Rhizophora/Podocarpus Pollen Ratio in a Marine Core from the Gulf of Guinea

This high-resolution study expands on the initial analysis of the KW 23 core, which only covered the last 135,000 years, going back up to 300,000 years, extracted off the coast of Congo in the Gulf of Guinea, to reconstruct climatic and paleoenvironmental fluctuations in Central Africa. Fifty-eight samples were analyzed, allowing the identification of more than 150 pollen taxa. Particular attention was paid to the bioindicator taxa Rhizophora and Podocarpus, whose ecological requirements are respectively associated with warm and humid littoral conditions and cooler montane environments. Pollen diagrams were constructed using two datasets, including or excluding spores, which are often dominant in the assemblages. Variations in the Rhizophora/Podocarpus pollen ratio reveal a marked alternation between warm and cold climatic phases. This curve shows strong correspondence with the benthic foraminiferal δ1⁸O record of Melonis barleeanum, as well as with Milankovitch orbital curves and isotopic and temperature reconstructions derived from the Vostok ice core. Nine climatic zones corresponding to marine isotope stages (MIS 1 to 9) were identified. Odd-numbered stages are characterized by a high abundance of Rhizophora, reflecting warm and humid conditions favorable to mangrove development, whereas even-numbered stages are dominated by Podocarpus, indicating cooler climates and a downslope expansion of montane vegetation. These results demonstrate that the Rhizophora/Podocarpus pollen ratio is a reliable proxy for reconstructing Quaternary climatic variations in Central Africa and provide new insights into the regional expression of major global climatic oscillations.