Did the North Atlantic Ocean play a role driving Green Sahara conditions during the Late Pliocene and Early Pleistocene?

North Africa is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in North Africa and are implicated in both the major Sahelian drought of the late 20^th century and extreme droughts associated with the Heinrich events of the last glacial period.

 

To better understand how African hydroclimate responds to SST variability across a range of climate states, we reconstruct changes in the ocean and atmosphere through the transition from the Pliocene epoch (when atmospheric CO₂ levels were comparable to present) into the cooler Pleistocene. We present data from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our dust accumulation and X-ray fluorescence core scan data record repeated shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa. The amplitude of these humid events is modulated by both global climate state and variability in solar insolation, with three unusually long intervals of low dust emissions (each lasting ca. 100 kyr) occurring at times when insolation variability was weak. We also present new paired alkenone-derived SST estimates and multi-species planktonic foraminiferal isotope records from 3.5–2.3 Myr ago to explore the role of North Atlantic dynamics in driving African hydroclimate variability. Our records help to develop the environmental framework needed to assess evolutionary outcomes on land and improve our understanding of the mechanisms driving precipitation variability in North Africa.