# Fundamentally unchanged northwestern African rainfall regimes across the Plio-Pleistocene transition

## TL;DR

This study shows that summer rainfall in northwestern Africa remained stable during a major climate shift 3 million years ago.

## Contribution

The study provides new evidence that summer monsoons in northwestern Africa were not affected by global cooling at the Pliocene-Pleistocene boundary.

## Key findings

- Rainfall regimes in northwestern Africa were stable from 3.5 to 2.5 million years ago.
- Summer rainfall responded to 21,000-year insolation cycles, not global cooling.
- Summer rains and winter winds were driven by different climate forcings.

## Abstract

Northern African climate is characterized by strongly contrasting wet summers and dry winters. Dust exported by the northeasterly trade (Harmattan) winds creates marine sedimentary records that have been long interpreted to show that northern African climate became drier and more variable across the Pliocene-Pleistocene boundary [2.58 million years ago (Ma)], when global climate cooled and high-latitude glacial-interglacial cycles intensified. However, questions about the impact of summer rainfall on winter dust fluxes and thus the history of the African summer monsoons remain. We present a leaf wax hydrogen isotope record from offshore northwestern Africa that demonstrates that rainfall regimes remained stable and varied solely in response to 21,000-year cycles in summer insolation from 3.5 to 2.5 Ma. We infer that the summer rains and winter winds respond to different climate forcings, with summer rainfall driven by solar radiation over the northern African landmass and the winter trades affected by high-latitude climate and meridional temperature gradients.

The northern African summer monsoon was unaffected by global cooling at the end of the Pliocene 3 million years ago.