Abstract
Terrestrial fossil pollen records are frequently used to reveal the response of vegetation to changes in both regional and global climate. Here we present a fossil pollen record from sediment cores extracted from Lake Bosumtwi (West Africa). This record covers the last c. 520 thousand years (ka) and represents the longest terrestrial pollen record from Africa published to date. The fossil pollen assemblages reveal dynamic vegetation change which can be broadly characterized as indicative of shifts between savannah and forest. Savannah formations are heavily dominated by grass (Poaceae) pollen (>55%) typically associated with Cyperaceae, Chenopodiaceae–Amaranthaceae and Caryophyllaceae. Forest formations are palynologically more diverse than the savannah, with the key taxa occurring in multiple forest zones being Moraceae, Celtis, Uapaca, Macaranga and Trema. The fossil pollen data indicate that over the last c. 520 ka the vegetation of lowland tropical West Africa has mainly been savannah; however six periods of forest expansion are evident which most likely correspond to global interglacial periods. A comparison of the forest assemblage composition within each interglacial suggests that the Holocene (11–0 ka) forest occurred under the wettest climate, while the forest which occurred at the time of Marine Isotope Stage 7 probably occurred under the driest climate.
Highlights
Today West Africa contains highly diverse grasslands and forests (Myers et al, 2000) which play an important role in the global carbon cycle (Lewis et al, 2009) and climate systems (Wang and Eltahir, 2000)
In this paper we present the first fossil pollen data from the landmark Lake Bosumtwi sediment core to provide an overview of tropical West African vegetation change during the last c. 520 ka
To place the Lake Bosumtwi sediments in a wider regional context and gain a broader picture of West African vegetation during previous interglacials we present a comparison of our findings with terrestrial and marine records from the region, covering at least one glacial to interglacial transition
Summary
Today West Africa contains highly diverse grasslands and forests (Myers et al, 2000) which play an important role in the global carbon cycle (Lewis et al, 2009) and climate systems (Wang and Eltahir, 2000). The distribution and composition of tropical West African vegetation is strongly linked to the prevailing climate (Holdridge et al, 1971). Over the coming decades regional climate models suggest that temperatures will increase and precipitation regimes, such as the West African Monsoon, will alter (Christensen et al, 2007). The response of vegetation to the projected climate change remains uncertain. One way in which we can improve our understanding of the relationship between vegetation and climate is to examine fossil vegetation records which span periods of global climate change of a comparable magnitude. The most recent period of time which spans a similar magnitude climate fluctuation to those projected for the future is the last
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