Late Quaternary behavior of the East African monsoon and the importance of the Congo Air Boundary |
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| Authors: | Jessica E Tierney James M Russell Jaap S Sinninghe Damsté Yongsong Huang Dirk Verschuren |
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| Institution: | 1. Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, USA;2. Brown University Department of Geological Sciences, Box #1846, Providence RI 02912, USA;3. Faculty of Geosciences, Utrecht University, PO Box 80021, 3508 TA Utrecht, The Netherlands;4. Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands;5. Limnology Unit, Department of Biology, Ghent University, Ledeganckstraat 35, 9000 Gent, Belgium;1. School of Geography and Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK;2. Long Term Ecology Laboratory, Department of Zoology, University of Oxford, UK;3. Department of Environmental and Geographical Science, University of Cape Town, South Africa;1. Department of Meteorology and Centre for Past Climate Change, University of Reading, RG6 6BB, UK;2. Environmental Change Institute, University of Oxford, OX1 3QY, UK;1. MARUM – Center for Marine Environmental Sciences, University of Bremen, D-28359 Bremen, Germany;2. Alfred Wegener Institute for Polar and Marine Research, Am Alten Hafen 26, D-27568 Bremerhaven, Germany;1. Brown University, Department of Geological Sciences, 324 Brook St., Box 1846, Providence, RI 02912, United States;2. Department of Geography, College of Science, Swansea University, Singleton Park, Swansea SA32 7QD, United Kingdom;3. NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands;4. University of Utrecht, Department of Geosciences, PO Box 80.021, 3508 TA Utrecht, The Netherlands;1. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;2. Department of Earth and Environmental Sciences, Columbia University, New York, NY 10025, USA;3. Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA;4. Royal Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands;5. MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany;6. Department of Environmental Studies, Macalester College, St. Paul, MN 55105, USA |
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| Abstract: | Both Atlantic and Indian Ocean climate dynamics exert influence over tropical African hydroclimate, producing complex patterns of convergence and precipitation. To isolate the Indian Ocean influence on African paleohydrology, we analyzed the deuterium/hydrogen ratio of higher plant leaf waxes (δDwax) in a 25 000-year sediment record from Lake Challa (3° S, 38° E) in the easternmost area of the African tropics. Whereas both the seismic record of inferred lake level fluctuations and the Branched and Isoprenoidal Tetraether (BIT) index proxy record changes in hydrology within the Challa basin, δDwax, as a proxy for the isotopic composition of precipitation (δDP) is interpreted as a tracer of large-scale atmospheric circulation that integrates the history of the moisture transported to the Lake Challa area. Specifically, based on modern-day isotope–rainfall relationships, we argue that Lake Challa δDwax reflects the intensity of East African monsoon circulation. The three hydrological proxy records show generally similar trends for the last 25 000 years, but there are important differences between them, primarily during the middle Holocene. We interpret this deviation of δDwax from local hydrological history as a decoupling of East African monsoon intensity – which heavily influences the isotopes of precipitation in East Africa today – from rainfall amount in the Challa basin. In combination, the hydrological proxy data from Lake Challa singularly highlight zonal gradients in tropical African climate that occur over a variety of timescales, suggesting that the Congo Air Boundary plays a fundamental role in controlling hydroclimate in the African tropics. |
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