East African lake evidence for Pliocene millennial-scale climate variability

M A Maslin,J D Kingston,A W Mackay,K E Wilson,A L Deino,M J Leng,R K Edgar

doi:10.1130/g35915.1

Abstract

Late Cenozoic climate history in Africa was punctuated by episodes of variability, characterized by the appearance and disappearance of large freshwater lakes within the East African Rift Valley. In the Baringo-Bogoria basin, a well-dated sequence of diatomites and fluviolacustrine sediments documents the precessionally forced cycling of an extensive lake system between 2.70 Ma and 2.55 Ma. One diatomite unit was studied, using the oxygen isotope composition of diatom silica combined with X-ray fluorescence spectrometry and taxonomic assemblage changes, to explore the nature of climate variability during this interval. Data reveal a rapid onset and gradual decline of deepwater lake conditions, which exhibit millennial-scale cyclicity of ∼1400–1700 yr, similar to late Quaternary Dansgaard-Oeschger events. These cycles are thought to reflect enhanced precipitation coincident with increased monsoonal strength, suggesting the existence of a teleconnection between the high latitudes and East Africa during this period. Such climatic variability could have affected faunal and floral evolution at the time.

Highlights

Cenozoic aridification and emergence of grassland habitats in East Africa were punctuated by periods of enhanced climate variability, coincident with global climate transitions (Trauth et al, 2005)
These have been linked with precessionally driven ecosystem variability (Magill et al, 2013) and precipitation changes that resulted in the periodic appearance and disappearance of freshwater lakes within the East African Rift Valley (Deino et al, 2006; Ashley, 2007; Kingston et al, 2007)
Its onset is marked by a sharp contact with underlying fluvial sediments, and the upper 150 cm are characterized by a transition from a relatively pure (~95% diatoms) laminated diatomite to diatomaceous clay (~60% diatoms)

Summary

Introduction

Cenozoic aridification and emergence of grassland habitats in East Africa were punctuated by periods of enhanced climate variability, coincident with global climate transitions (Trauth et al, 2005). These have been linked with precessionally driven ecosystem variability (Magill et al, 2013) and precipitation changes that resulted in the periodic appearance and disappearance of freshwater lakes within the East African Rift Valley (Deino et al, 2006; Ashley, 2007; Kingston et al, 2007). The modern East Africa climate is driven by interactions between atmospheric convergence zones and regional factors (e.g., topography, coastal currents, and sea-surface temperature fluctuations), resulting in complex and locally variable climatic regimes. Questions remain about how these large-scale patterns have changed in the past

Results

Discussion

Conclusion