Geochemical and sedimentological data in a continuous 60,000-year sediment core record from the Kalya horst region of central Lake Tanganyika provide a detailed history of paleoclimate-mediated weathering and overflow events from upstream Lake Kivu. Univariate (elemental profiles), bivariate (elemental ratios) and multivariate analyses of chemical trends show variations between the dry Late Pleistocene (32-18 ka cal yr BP) and the wetter conditions that both preceded and post-date that interval. This record places important new constraints on the timing of aridity in East Africa during the high-latitude Last Glacial Maximum (LGM) based on significant decreases in magnetic susceptibility and soluble cation concentrations coinciding with biogenic silica. Elemental indicators in the oldest portion of the sedimentary record (60-50 ka cal yr BP) characterize this interval as a comparatively wet period, similar to modern conditions. Our record demonstrates that the ensuing transition toward arid conditions in tropical Africa during high-latitude glaciation was a two staged event with intermediate levels of aridity occurring from 50-32 ka cal yr BP followed by intense aridity from 32-18 ka cal yr BP. The initiation of inflow from upstream Lake Kivu into Lake Tanganyika is evidenced at 10.6 ka cal yr BP through its influence on both elemental profiles (Mg, Ca) and through its effect on 87Sr/86Sr. Increases in elemental (Mg, Ca, Sr) concentrations coincide with the timing of the Lake Kivu overflow. Metal geochemistry suggests that the overflow from Lake Kivu into Lake Tanganyika may have ceased between 8 and 6 ka cal yr BP, suggesting a period of Middle Holocene aridity in East Africa.
Bibliographical noteFunding Information:
We gratefully acknowledge support from the US NSF (The Nyanza Project, ATM#0223920 and BIO#0383765 with support from the Office of International Science and Engineering), ChevronTexaco scholarships, ISPE (Institute for the Study of Planet Earth, University of Arizona) graduate student travel grant. We would like to thank the University of Dar es Salaam for permitting, TAFIRI-Kigoma Station for logistical support, and the Limnological Research Center at the University of Minnesota, Minneapolis. We thank Dr. Jon Chorover and Mary Kay Amistadi in the Dept. of Soil, Water and Environmental Sciences at the University Arizona for ICP-MS analyses, and Jeremy Weiss, Jessica Conroy, and Devin Gaugler at the University of Arizona for laboratory assistance. We thank J. Ruiz at the University of Arizona for support and access to the W.M. Keck Foundation analytical facility. We thank Jean-Pierre Rehault and Jacques Begot of UMR-CNRS-UBD 6538, France for the use of their IUEM-based sparker seismic unit. This project would not have been possible without the help of the M/V Maman Benita crew and the 2004 Nyanza Project participants, and especially Christine Gans and Winston Wheeler. We would also like to thank two anonymous reviewers for their time and thoughtful comments.
Copyright 2018 Elsevier B.V., All rights reserved.
- Lake Tanganyika
- Last Glacial Maximum
- Late Pleistocene paleoclimate
- Rift lakes