Hydrological changes in southern Africa over the last 200 Ka as recorded in lake sediments from the Tswaing impact crater

Sediments from Lake Tswaing (25 degrees 24'30" S, 28 degrees 04'59" E) document hydrological changes in southern Africa over the last 200 Ka. Using high-resolution XRF- scanning, basic geochemistry (TIC, TOC, TN), organic petrology and rock-evil pyrolysis, we identify intervals of decreased carbonate precipitation, increased detrital input, decreased salinity and decreased autochthonous (algal and bacterial) organic matter content that represent periods of less stable water column stratification and increased rainfall. Between 200 and 80 Ka BP, these intervals appear to be contemporaneous with local summer insolation maxima, indicating a strong influence of precessional variability (similar to 23 Ka) on African subtropical climate. This influence weakens during the last glacial period (similar to 80 to 10 Ka BP), when humid intervals at 73 to 68 Ka, 54 to 50 Ka, 37 to 35 Ka and 15 to 10 Ka BP are largely out of phase with insolation changes, and presumably reflect southward displacement of the ITCZ (Inter Tropical Convergence Zone) and/or changes in ocean circulation.