T134 Phanerozoic Paleoenvironmental Evolution of Africa II

Monday, 19 October 2009
1:30 PM - 5:30 PM
Portland Ballroom 255

VEGETATION AND CLIMATE OF LAKE MALAWI, SOUTHEAST AFRICA DURING THE LAST DEGLACIATION

Paper number: T134-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

Cores from Lake Malawi, drilled in March 2005 as part of the Lake Malawi Drilling Project, provide a continuous continental record of southeast African regional climate from the Middle Pleistocene to present. Pollen analyses from the northern basin site (Mal-2A) provide a high-resolution record of the influence of the African Monsoon on vegetation in south-east Africa during the Pleistocene/Holocene transition (~18,000-9000 cal yrs BP) including the Younger Dryas interval (YD), a period of widespread aridity in the region. Recent studies of local vegetation from lowland sites have reported contrasting rainfall signals and abrupt changes in seasonality during the YD. Located just south of the Rungwe Volcanic Highlands and at the current southernmost limit of the Intertropical Convergence Zone (ITCZ), Lake Malawi provides a regional record to track vegetation changes and provides a comparison with other records of local forest maintenance during the YD.

In agreement with studies showing a gradual increase in temperature and humidity at the end of the LGM, the Mal-2A pollen record shows gradual decline of afromontane vegetation likely enhanced by migration of these taxa to higher altitudes. Around 14.5ka, afromontane vegetation is replaced by semi-deciduous forest and, more gradually, Zambezian woodland until the beginning of the YD. At ~13ka, through a series of forest transitions, drier, more open formations are gradually established. Though semi-deciduous forest taxa are still present in the catchment during the YD, this drought intolerant forest type is likely restricted to areas of favorable edaphic conditions along permanent waterways. The establishment of savannah and Zambezian woodland follows a stepwise decrease in temperature and reinforcement of southeasterly tradewinds resulting in a more pronounced dry season at ~11.8ka. The establishment of the driest, most open vegetation type is coincident with the lake lowstand following the YD.