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

GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany, e-mail: kristen{at}gfz-potsdam.de

A. Fuhrmann

GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany Present address: Saudi Aramco, Dhahran 31311, Saudi Arabia, e-mail: a.fuhrmann{at}hotmail.com

J. Thorpe

formerly at Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, Great Britain, e-mail: jo_thorpe{at}yahoo.com

U. Röhl

Center for Marine Environmental Sciences (MARUM), Universität Bremen, Leobener Strasse, 28359 Bremen, Germany, e-mail: uroehl{at}marum.de

H. Wilkes

GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany, e-mail: wilkes{at}gfz-potsdam.de

H. Oberhänsli

GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany, e-mail: oberh{at}gfz-potsdam.de

Sediments from Lake Tswaing (25°24'30'' S, 28°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-eval 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 (~23 Ka) on African subtropical climate. This influence weakens during the last glacial period (~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.