HR: 09:15h
AN: PP21A-06    [PDF]
TI: ITCZ Position Over East Africa Since the Late Glacial: The Lake Malawi Record
AU: * Brown, E T
EM: etbrown@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota, Duluth, MN 55812 United States
AU: Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota, Duluth, MN 55812 United States
AB: Varved sediments of the north basin of Lake Malawi, the southernmost of the East African Rift lakes, have yielded records of past climate conditions for a range of temporal scales. Profiles of biogenic silica and Nb:Ti spanning nearly 25,000 years in Malawi may be compared with the Cariaco Basin high-resolution records of Haug et al. (2001). During the past 1000 years Nb:Ti and biogenic silica track one another in Malawi sediments, as observed for the Late Glacial (Johnson et al., 2002). These signals are interpreted as a reflection of the intensity or frequency of north winds over the basin. Such winds carry Nb-rich volcaniclastic sediments into the lake and promote upwelling, favorable to diatom productivity. Johnson et al. (2002) attributed the greater frequency of north winds over the Malawi basin during "cold" episodes such as the Younger Dryas to southward shifts in the Intertropical Convergence Zone (ITCZ). Haug et al. (2001) have suggested that southward migration of the ITCZ over South America as such times caused decreased rainfall and delivery of terrigenous clastics rich in Fe and Ti to the Cariaco basin. During the Late Glacial, the trends in the African and South American records are remarkably similar. In addition, they both show evidence for the ITCZ being positioned more to the north during the Medieval Warm Period, more to the south during the Little Ice Age, and subsequently returning to the north. Both records also exhibit greater variability during the LIA, with distinct southerly ITCZ excursions. Twentieth Century climate records indicate that episodes of enhanced north winds over Malawi were dry over the Orinoco basin, suggesting that the mechanism of teleconnection developed from sedimentary evidence for 100 to 10,000 years timescales may also play a role in the modern climate.
DE: 1845 Limnology
DE: 3344 Paleoclimatology
DE: 9305 Africa
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting