HR: 1340h
AN: PP13A-0579    [Abstracts]
TI: An Equatorial Harmonic of the Holocene 1500 Year Cycle: Cyclic Geochemical Variability in Lake Edward, Uganda-Congo
AU: * Russell, J M
EM: russ0154@umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, 110 RLB, Duluth, MN 55812-2496 United States
AU: Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, 110 RLB, Duluth, MN 55812-2496 United States
AB: The "1500-year cycle" in the late Pleistocene and Holocene climate of the North Atlantic is well-documented. Several studies from subtropical sites in the Atlantic have shown a relatively direct relationship between millennial-scale climate events in the northern subtropics and the North Atlantic that may be explained by latitudinal shifts in the Intertropical Convergence Zone. In contrast, the effects of this millennial-scale variability on equatorial and south tropical latitudes are poorly constrained. The large East African rift lakes span 5o N to 14o S and combine high climatic sensitivity characteristic of closed basin lakes with high sedimentation rates, making them ideal for high-resolution paleoclimate analysis. Analyses of the stable isotopic and chemical composition of calcite in Lake Edward, situated on the equator at the eastern edge of the Congo basin, have documented a ~725 year cycle in the lake's water balance during the mid- to late Holocene. By filtering the 725-year period in Lake Edward and the Holocene1500 year period in the North Atlantic, we show that drought in equatorial Africa occurs during both the cold and warm phases of the North Atlantic's 1500 year cycle. This relationship can be explained by either latitudinal displacement of the ITCZ away from its equatorial mean position, resulting in equatorial drought, or by changes in rainfall intensity along the ITCZ. Our results per se cannot explain the causes of millennial-scale global climate variability. However, the 725-year cycle present in equatorial African climate has also been recognized in marine records from the Indian Ocean and South China Seas, suggesting teleconnections between millennial-scale climate variability in African rainfall and the Indo-Pacific, and hence, the heart of the ENSO system. This suggests that the tropics at the very least could serve an important role in transmitting, if not causing, millennial-scale climate change. Regardless, our results highlight the importance of understanding how regional climate systems respond to global climate perturbations, and further demonstrate that the 1,500-year climate cycle is felt at equatorial latitudes during at least the Holocene.
DE: 3344 Paleoclimatology
DE: 1833 Hydroclimatology
DE: 1845 Limnology
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting