Green Sahara Periods in a warmer world: a proxy-based reconstruction of the last 11 Myr

The Sahara is a vast, bare, intensely arid, dust exporting landscape today. Yet, in the early Holocene, the Sahara was green; a well-vegetated landscape crosscut by a network of rivers and lakes, populated by hippopotamuses, other megafauna and our early ancestors. Strong evidence also exists for multiple earlier Green Sahara Periods (GSPs), with their occurrence paced by variability in solar insolation. However, terrestrial climate archives used to provide direct evidence of past humid conditions are often plagued with intervals of erosion and/or non-deposition, while sapropels (organic-rich sediment layers in the Mediterranean Sea) only provide an indirect record of North African climate. Here, we explore how the expression of GSPs has changed across a range of global climate states, including warmer intervals than today, with new, detailed records of terrigenous inputs to North Atlantic deep-sea sediments situated underneath the Saharan dust plume. We document a long and sustained history of astronomically-paced oscillations between distinctly humid and arid conditions from at least 11 million years ago, with three distinct phases in the sensitivity of the relationship between astronomical forcing and African hydroclimate identified. Our data provide a new framework for assessing evolutionary outcomes on land, including implications for our hominid ancestors.