HR: 1330h
AN: PP22A-1197    [PDF]
TI: Tropical African climate variability during the last glacial/interglacial transition: the molecular record from Lake Malawi
AU: * Casta\~{n}eda, I S
EM: cast0150@tc.umn.edu
AF: Large Lakes Observatory, University of Minnesota, Duluth, 10 University Dr, 109 RLB, Duluth, MN 55812 United States
AU: Werne, J P
EM: jwerne@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota, Duluth, 10 University Dr, 109 RLB, Duluth, MN 55812 United States
AU: Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota, Duluth, 10 University Dr, 109 RLB, Duluth, MN 55812 United States
AB: In general, information regarding tropical African climate variability is relatively limited, especially in comparison with high-latitude studies. Unlike the high-latitudes where climate change is often expressed by fluctuations in temperature, low-latitude climate change is often expressed as variability in zonal circulation, which can result in hydrological fluctuations. Lake Malawi, situated in low-latitude tropical Africa (9-14$\deg$ S), contains a continuous and high-resolution sedimentary record of the past 22ka BP and is anoxic below 250m, which enhances preservation of organic matter (OM). For these reasons, L. Malawi is an excellent location to examine the response of low-latitude African climate to global climate change. The climate of Malawi is strongly influenced by the position and seasonal migration of the ITCZ. During the rainy season from November to March, the ITCZ is positioned over L. Malawi (12-13$\deg$ S) and the dominant winds are weak and northerly. Between April and May the ITCZ moves northward towards the equator and strong southerly winds prevail (Jury \& Mwafulirwa, 2002). Previous studies of L. Malawi have shown responses to global climatic events, such as the Younger Dryas. Additionally, studies have demonstrated the response of L. Malawi to local or regional events, such as variability in the ITCZ. Based on BSi MAR, diatom, phosphorus, and trace metal data, Johnson et al. (2002) proposed that at times more frequent or stronger northerly winds promoted upwelling in the northern basin of L. Malawi, and suggested more southerly migrations of the ITCZ (reaching latitudes of $>$13\deg S) as the cause of these increased winds. Additionally, a recent study of L. Malawi based on multiple bulk geochemical proxies provides evidence for both southward and northward displacements of the ITCZ during the past 23ka BP (Filippi and Talbot, submitted). In this study the molecular biomarker record of L. Malawi is examined. Previous studies of Lake Malawi have been based on bulk geochemical parameters, which are indicators of the type of OM preserved in sediments. These studies indicate that variations in primary productivity likely have occurred during the past 22ka BP, however, these bulk geochemical analyses have also yielded ambiguous results and have failed to adequately distinguish terrestrially and aquatically derived OM. Presently, the algal community of L. Malawi is dominated by four major groups: diatoms, cyanobacteria, dynoflagellates, and green algae, with diatoms being the major contributor to primary productivity. Each of these algal groups has characteristic biomarkers, therefore, from the molecular record we will examine primary production as a whole within L. Malawi. Molecular reconstructions will provide information on the response of the L. Malawi algal community to hydrological variations, which may be linked global climate events or to smaller regional events, such as fluctuations in position and intensity ITCZ.
DE: 1055 Organic geochemistry
DE: 1620 Climate dynamics (3309)
DE: 3344 Paleoclimatology
DE: 4239 Limnology
DE: 9305 Africa
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting