Mid-Pliocene glaciation preceded by a 0.5-million-year North African humid period

Past North African humid periods caused expanded vegetation over the Sahara,
due to northward tropical African rainbelt displacement, opening migration
pathways for hominins. Commonly, these precession-timed humid periods
ended within 15,000 years due to rainbelt retreat. During North African
humid periods, eastern Mediterranean organic-rich layers called sapropels
were deposited at least since 8 Myr. Here we combine climate modelling
with palaeoclimate proxy data to show that weakened sapropel preservation
during the 5.3–3.3 Myr period resulted from nutrient runoff limitation
associated with enhanced North African vegetation cover due to a persistently
more northward-located African monsoon front, relative to the mid-Pliocene
(3.3–3.0 Myr, when glacial intensity increased). Moreover, sapropel absence
within the 3.8–3.3 Myr period coincided with maximum monsoon runoff and
extensively humid, vegetated conditions throughout North Africa. Our model
results indicate that this 0.5-Myr-long pan-North African humid period ended
at ~3.3 Myr because of southward monsoon front displacement with Northern
Hemisphere glacial intensification. The 3.8–3.3 Myr humid period coincided
with the earliest known evidence for hominin coexistence over eastern and
central North Africa. We posit that persistent green corridors during this humid
phase facilitated early hominin connectivity and migration, expanding their
habitat range over the wider North African territory.