A High-Resolution Paleoclimate Record Spanning the Past 25,000 Years in Southern East Africa

Abstract

High-resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern Lake Malawi provide a climate signal for this part of tropical Africa spanning the past 25,000 years. The biogenic silica mass accumulation rate was low during the relatively dry late Pleistocene, when the river flux of silica to the lake was suppressed. Millennial-scale fluctuations, due to upwelling intensity, in the late Pleistocene climate of the Lake Malawi basin appear to have been closely linked to the Northern Hemisphere climate until 11 thousand years ago. Relatively cold conditions in the Northern Hemisphere coincided with more frequent north winds over the Malawi basin, perhaps resulting from a more southward migration of the Intertropical Convergence Zone.

An abrupt change in the African monsoon at the end of the Younger Dryas

“…In addition to local effects, and the possibility that there are real differences in the timing of the events discussed here, there are significant uncertainties associated with dating several of the archives. In large, deep lakes there may be a measurable but poorly constrained reservoir age, and reworked organic matter (OM) can affect age determinations from sediments in all types of water bodies [Cohen et al, 1997;Barry et al, 2002;Russell et al, 2003]. In marine cores the principal uncertainties are reservoir age, particularly from areas of upwelling [e.g., Kim et al, 2002;Farmer et al, 2005], and differences in the 14 C age yielded by different proxies from the same stratigraphic level [Mollenhauer et al, 2003;Farmer et al, 2005].…”

“…Variations in either of these may in turn lead to changes in the flux and preservation of autochthonous biogenic material at the lake floor. Fossil diatom assemblages, biogenic silica (BSi) accumulation rates, and the amount and composition of sedimentary OM have previously been used to infer past changes in the wind-driven mixing of lakes in both West and East Africa [Haberyan and Hecky, 1987;Talbot and Johannessen, 1992;Talbot and Laerdal, 2000;Talbot, 2001;Gasse et al, 2002;Johnson et al, 2002Johnson et al, , 2004Filippi and Talbot, 2005]. Data from Lakes Malawi and Tanganyika, East Africa, and Lake Bosumtwi, West Africa, document a major change in the mixing regime of these water bodies at the end of the Younger Dryas.…”

“…Lake Malawi [7] Three cores, M98-1P, -2P and -3P, have been studied in detail [Filippi and Talbot, 2005]. Core chronology is based upon 6 accelerator mass spectrometric dates from 1P, 8 from 2P, and 3 from 3P; additional correlation between the cores is provided by tephras and other distinctive marker beds [Barry et al, 2002]. To reduce high-frequency noise, data from the three cores has been stacked [Paillard et al, 1996].…”

Forcing of wet phases in southeast Africa over the past 17,000 years

“…Climate changes reconstructed from Lake Malawi, the southernmost of the East African Great Lakes and located within the Zambezi catchment, point to arid conditions and strong northerly wind anomalies during Northern Hemisphere cold events such as the Younger Dryas (YD) 2,3 . It has been inferred that these periods represent southward shifts of the ITCZ 2,3,6 .…”

“…It has been inferred that these periods represent southward shifts of the ITCZ 2,3,6 . Dry conditions during the YD and Heinrich Stadial 1 (HS1) in Lake Tanganyika, located closer to the equator in East Africa, were interpreted to have been caused by lowered Indian Ocean SST 4 .…”