HR: 14:25h
AN: PP13C-04    [Abstracts]
TI: Linking the North Atlantic Oscillation to Rainfall Over Northern Lake Malawi
AU: * Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, Duluth, MN 55812 United States
AU: Powers, L A
EM: lindsaypowers@gmail.com
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, Duluth, MN 55812 United States
AU: Werne, J P
EM: jwerne@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, Duluth, MN 55812 United States
AU: Brown, E T
EM: etbrown@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, Duluth, MN 55812 United States
AU: Castaneda, I
EM: cast0150@tc.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Drive, Duluth, MN 55812 United States
AU: Schouten, S
EM: schouten@nios.nl
AF: Department of Marine Biogeochemistry and Toxicology, Netherlands Institute for Sea Research, Den Burg, 1790 AB Netherlands
AU: Sinninghe-Damste, J
EM: sinninghe-damste@nios.nl
AF: Department of Marine Biogeochemistry and Toxicology, Netherlands Institute for Sea Research, Den Burg, 1790 AB Netherlands
AB: Piston and multi-cores recovered from the north basin of Lake Malawi in 1998 by the International Decade for the East African Lakes (IDEAL) have provided a rich history of climate variability spanning the past 25,000 years. As we now begin to analyze the cores recovered by the Malawi Drilling Project in early 2005, we are considering the relationships among sedimentary signals of temperature (TEX86), northerly winds associated with a southward excursion of the Inter-Tropical Convergence Zone (per cent biogenic silica), and rainfall (terrigenous mass accumulation rate) in the well dated 1998 cores. A high-resolution record of the past 800 years suggests that rainfall in this region (10 - 12§ S, 30 - 35§ E) was relatively low during the Little Ice Age, when northerly winds were more prevalent, attributed to a more southerly position of the ITCZ during austral summers. The TEX86 signal of lake (surface?) temperature ranged mostly between 24 and 26§C during this period, with the coldest temperature of about 22§C around AD1680 and the warmest temperature, exceeding 27§C, in the youngest sediment sample. The cooler water temperatures coincide with periods of highest diatom productivity, consistent with the latter being due to relatively intense upwelling associated with the northerly winds. Our observation of low rainfall during periods of more southerly migration of the ITCZ is consistent with the results of McHugh and Rogers (2001), who linked rainfall in southeastern Africa to the North Atlantic Oscillation (NAO). During years of weak NAO, equatorial westerly transport of Atlantic moisture across Africa during austral summer is relatively intense, causing high rainfall in the East African Rift between the equator and 16§ S. Conversely, when the NAO is positive, rainfall is higher south of 15§ S than north of this latitude, which is consistent with a southward migration of the ITCZ. McHugh, M. J. and J. C. Rogers (2001). "North Atlantic Oscillation influence on precipitation variability around the southeast African convergence zone." Journal of Climate 14: 3631-3642.
DE: 0458 Limnology (1845, 4239, 4942)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1051 Sedimentary geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005