Hominins, including Homo sapiens, are thought to have responded to climatic and environmental fluctuations by developing morphologically and behaviorally adaptable traits. Moreover, paleoclimatic variability in Africa is important to quantify in order to understand the impacts of future global warming on particularly sensitive regions. However, we lack long, high-resolution, well-dated records of rainfall from Africa that we can compare to understand the effects of external climate mechanisms on different regions and timescales. Here I will discuss hydrogen isotopic records from plant waxes (δDwax) from lacustrine and marine sediment cores that together capture the long-term-, orbital-, and millennial-scale hydroclimate of eastern Africa. We find that Africa became progressively drier throughout the Plio-Pleistocene with a step-wise response to the growth of Northern Hemisphere ice sheets and the associated feedbacks. Precession and eccentricity drove rainfall cycles, indicating that the modulation of monsoon strength by low-latitude insolation was the dominant control on climate and environment for millions of years. However, there is evidence that high-latitude processes influenced orbital-scale climate fluctuation more recently in the late-Pleistocene when glacial-interglacial cycles were strongest. Further, millennial-scale variability is higher during glacial periods, suggesting that high-latitude processes affected tropical hydroclimate by way of different processes at different timescales. These high-resolution geochemical records of rainfall provide the context required to examine the complex relationship between our human ancestors and their environment. I will also talk about expanding this endeavor by including a new West African study that captures transitions such as the mid-Miocene Climate Optimum that are important to the study of the Sahel environmental response to global warming.
Rachel Lupien, LDEO, Columbia University (Website)