Drivers of ecosystem and climate change in tropical West Africa over the past ∼540 000 years

Charlotte S Miller,David B Kemp,Angela L Coe,Iain Gilmour,William D Gosling

doi:10.1002/jqs.2893

Charlotte S Miller, David B Kemp + Show 3 more

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https://doi.org/10.1002/jqs.2893

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Abstract

ABSTRACTA paucity of empirical non‐marine data means that uncertainty surrounds the impact of climate change on terrestrial ecosystems in tropical regions beyond the last glacial period. The sedimentary fill of the Bosumtwi impact crater (Ghana) provides the longest continuous Quaternary terrestrial archive of environmental change in West Africa, spanning the last ∼1.08 million years. Here we explore the drivers of change in ecosystem and climate in tropical West Africa for the past ∼540 000 years using pollen analysis and the nitrogen isotope composition of bulk organic matter preserved in sediments from Lake Bosumtwi. Variations in grass pollen abundance (0−99%) indicate transitions between grassland and forest. Coeval variations in the nitrogen isotopic composition of organic matter indicate that intervals of grassland expansion coincided with minimum lake levels and low regional moisture availability. The observed changes responded to orbitally paced global climate variations on both glacial–interglacial and shorter timescales. Importantly, the magnitude of ecosystem change revealed by our data exceeds that previously determined from marine records, demonstrating for the first time the high sensitivity of tropical lowland ecosystems to Quaternary climate change.

Highlights

Understanding the relationship between tropical ecosystems and climate in Africa is of critical importance because of the continent’s sensitivity to global climate change (IPCC, 2013), the region’s high ecological value (Myers et al, 2000) and its role in hominid evolution
The highly biodiverse tropical West African region is regarded as being vulnerable to impacts from a rapidly growing human population (Lambin et al, 2003), and naturally driven periodic multi-decadal drought (Shanahan et al, 2009)
Quaternary records of environmental change in West Africa can provide vital insights into how ecosystems may respond to future climate change because of the comparable magnitude of Quaternary temperature changes (Gosling and Holden, 2011) with those predicted in the coming years (IPCC, 2013)

Summary

Introduction

Understanding the relationship between tropical ecosystems and climate in Africa is of critical importance because of the continent’s sensitivity to global climate change (IPCC, 2013), the region’s high ecological value (Myers et al, 2000) and its role in hominid evolution (deMenocal, 2004). Water currents (Hooghiemstra et al, 2006) and (iii) typically low pollen concentrations that may dampen the true variance of terrestrial vegetation change (Dupont, 2011). The sedimentary fill of the Lake Bosumtwi impact crater (Ghana, West Africa; 6 ̊300N, 1 ̊250W; Fig. 1) has yielded the longest Quaternary terrestrial archive of African vegetation to date, spanning the last c 540 ka (Miller and Gosling, 2014).

Results

Conclusion