Paleoclimate Variability Recorded in Varved Sediments of Lake Malawi, Tropical Africa

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Abstract ATM-9709291 University of Minnesota Johnson, Thomas C. Title: Paleoclimate Variability Recorded in Varved Sediments of Lake Malawi, Tropical Africa The award supports the collection of sediment cores from four sites in northern Lake Malawi, to establish a robust, high-solution record of past climate change that spans the entire Holocene. The cores will be dated by Pb-210, AMS C-14, and varve counts. The sediments will be analyzed for weight per cent biogenic silica and for light and dark layer thickness of the varves. Biogenic silica abundance is believed to reflect primary productivity, which is a function of upwelling intensity, related to wind strength and seasonal cooling. The light layers in the varve couplets are diatom ooze, also reflecting primary productivity during the dry windy season (June - August). The dark layers consist of terrigenous silts and clays with admixtures of diatoms. These reflect the intensity of river runoff during the rainy season in the austral summer (Dec. - March). The varve thickness records (light layer, combined) will be subjected to evolutionary spectral analysis, paying particular attention to ENSO-scale variability through the Holocene. Pilot studies on the sediments will include redox-sensitive elemental analysis, organic matter isotopic composition, and diatom assemblage composition. This research will be in collaboration with the Malawi Global Environment Facility (GEF) program funded by the World Bank, which will provide ship time, logistical support in the country, and Pb-210 analyses of the sediments. This will be a collaborative effort with scientists from Malawi, Canada and Norway. This paleoclimatological investigation on Lake Malawi will be conducted as part of the International Decade for the East African Lakes (IDEAL). IDEAL is a multi-disciplinary, multinational program of research and training on the large lakes of East Africa.