THE LAKE MALAWI CLIMATE RECORD: LINKS TO SOUTH AMERICA

We have extracted high resolution records of past climate conditions from varved sediments accumulating near 10^o S in the north basin of Lake Malawi, the southernmost of the East African Rift lakes. Here we compare profiles of biogenic silica and Nb:Ti spanning nearly 25,000 years in Malawi with the Cariaco Basin high-resolution record of Haug et al. (2001), which is based primarily on sedimentary profiles of Fe and Ti. 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 have been 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.