Transport mechanism and paleoclimatic significance of terrigenous silt deposited in varved sediments of an African rift lake

We analyzed a varved sequence of sediment from a 350-m depth in the north basin of Lake Malawi, East Africa, for the size distribution of the sortable silt fraction (10-64 μm). Mean size of the sortable silt (SS) varies measurably in sediments spanning the past 650 yr and covaries with the mass accumulation rate of terrigenous silt and clay (TMAR) over much of the interval. Most of the silt and clay is delivered to the offshore basin in benthic nepheloid plumes of unknown duration and frequency. TMAR appears to be related to annual rainfall (which is related to the North Atlantic Oscillation) because it roughly tracks the historical record of lake level that extends back to 1860. SS should be related to density or thickness of underflow, thus related to resuspension intensity or river flood loading. It also tracks lake level and regional wind strength as determined by National Center for Environmental Prediction (NCEP) Reanalysis.