What don't we understand about past rainfall changes in Africa and Arabia during the Pliocene?

Past hydroclimate change in Africa and the Arabian Peninsula plays a vital role in early human evolution and dispersal. Although arid today, North Africa and the Arabian Peninsula experienced periodic humid intervals, during which strengthened rainfall driven by astronomical forcing (chiefly eccentricity-modulated precessional cycles) transformed the Saharo-Arabian desert into a vegetated landscape cross-cut by rivers and lakes. The relationship between hydroclimate variability and hominid evolution is strongly debated and continuous palaeoclimate reconstructions are required to provide a context for understanding evolutionary outcomes on land. However, there are major discrepancies between different types of proxy data and between these reconstructions and those generated by numerical models as to the spatial and temporal occurrence of humid events and to the seasonality of the rainfall responsible. Two major contributing problems concern (i) the incontinuous nature of palaeo records from terrestrial archives (palaeolake sediments and stalagmites) and (ii) the challenges of attribution associated with records from marine sediment cores. Here, we report geochemical and stable isotope data from the Arabian Sea to reconstruct past environmental changes in a multi-proxy approach, which will help us to understand the relationship between palaeoclimate change and hominid evolution, reveal how the West Asian monsoon responded to a period of increased global warmth and furthermore, provide a reliable data set for model simulations in the future.