Organic carbon burial in Mediterranean sapropels intensified during Green Sahara Periods since 3.2 Myr ago

Dark organic-rich layers (sapropels) have accumulated in Mediterranean sediments since the Miocene due to deep-sea dysoxia and enhanced carbon burial at times of intensified North African run-off during Green Sahara Periods (GSPs). The existence of orbital precession-dominated Saharan aridity/humidity cycles is well known, but lack of long-term, high-resolution records hinders understanding of their relationship with environmental evolution. Here we present continuous, high-resolution geochemical and environmental magnetic records for the Eastern Mediterranean spanning the past 5.2 million years, which reveal that organic burial intensified 3.2 Myr ago. We deduce that fluvial terrigenous sediment inputs during GSPs doubled abruptly at this time, whereas monsoon run-off intensity remained relatively constant. We hypothesize that increased sediment mobilization resulted from an abrupt non-linear North African landscape response associated with a major increase in arid:humid contrasts between GSPs and intervening dry periods. The timing strongly suggests a link to the onset of intensified northern hemisphere glaciation. Mediterranean sediment records spanning the last five million years suggest an abrupt increase in carbon burial and terrigenous accumulation coincided with enhanced fluvial sediment mobilisation in North Africa during orbitally-driven Green Sahara Periods.

Automated summary

Dark organic-rich layers have accumulated in Mediterranean sediments since the Miocene. Through studying high-resolution geochemical and environmental magnetic records, it is found that organic burial intensified 3.2 million years ago, possibly due to a sudden nonlinear change in the environment of North Africa. This finding is of great significance for understanding environmental evolution.