Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Scientific drilling in the Great Rift Valley: The 2005 Lake Malawi Scientific Drilling Project — An overview of the past 145,000 years of climate variability in Southern Hemisphere East Africa C.A. Scholz a,⁎, A.S. Cohen b, T.C. Johnson c, J. King d, M.R. Talbot e, E.T. Brown c a Department of Earth Sciences, Syracuse University, Syracuse NY, 13244, USA b Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA c Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, USA d Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA e Department of Earth Science, University of Bergen, N-5007 Bergen, Norway article info abstract Article history: The recovery of detailed and continuous paleoclimate records from the interior of the African continent has Received 18 March 2010 long been of interest for understanding climate dynamics of the tropics, and also for constraining the Received in revised form 17 October 2010 environmental backdrop to the evolution and spread of early Homo sapiens. In 2005 an international team of Accepted 20 October 2010 scientists collected a series of scientific drill cores from Lake Malawi, the first long and continuous, high- Available online 9 November 2010 fidelity records of tropical climate change from interior East Africa. The paleoclimate records, which include lithostratigraphic, geochemical, geophysical and paleobiological observations documented in this special Keywords: 3 Lake Malawi issue of Palaeo , indicate an interval of high-amplitude climate variability between 145,000 and ~60,000 years East African rift ago, when several severe arid intervals reduced Lake Malawi's volume by more than 95%. These intervals of Paleoclimatology pronounced tropical African aridity in the early Late Pleistocene around Lake Malawi were much more severe Scientific drilling than the Last Glacial Maximum (LGM), a well-documented period of drought in equatorial and Northern Lake level change Hemisphere tropical east Africa. After 70,000 years ago climate shifted to more humid conditions and lake levels rose. During this latter interval however, wind patterns shifted rapidly, and perhaps synchronously with high-latitude shifts and changes in thermohaline circulation. This transition to wetter, more stable conditions coincided with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Malawi and Tanganyika contain more than 80% of the surface water found on the African continent, and are a critical resource for riparian In 2005 an international team of scientists set out to recover a long populations. Pioneering geophysical studies undertaken by B.R. and continuous record of past climatic changes from the African Rosendahl and colleagues in the 1980s proved the remarkable interior, through scientific drilling and sampling of the sediments of antiquity of these lakes through reconnaissance geophysical studies Lake Malawi. Lake Malawi is one of the largest, deepest and oldest (e.g. Rosendahl, 1987), and following those studies proposals rapidly lakes in the world, and as one of the Great Lakes of Africa, is emerged for scientific drilling in the deep lake waters of Africa's Great considered among the natural wonders of the world. Also referred to Rift Valley (Lewin, 1981). as Lake Nyasa, it is situated at the southern end of the western branch Initial scientific exploration of the Great Rift Valley ensued shortly of the East African Rift System (EARS), between ~9° and ~14° South after the European settlement, with seminal publications by Suess latitude (Fig. 1). Malawi and the other great lakes of the region (1891), de Martonne (1897) and Gregory (1896) proposing that (Tanganyika, Victoria, Edward, Albert, Kivu and Turkana) are famous either tensile forces or active (vertical) motions were responsible for for their large numbers of fish and invertebrate species (in particular producing the distinctive, block-fault topography of East Africa. These the cichlid fishes) (e.g. Verheyen et al., 2003). Taken together Lakes early studies (Oldham, 1922; Suess, 1891) contributed significantly to emerging concepts of continental drift and plate tectonics. The remarkable depths, evident antiquity, and peculiar faunas of the ⁎ Corresponding author. Department of Earth Sciences, 204 Heroy Geology Great Lakes instigated numerous scholarly publications and debate Laboratory, Syracuse University, Syracuse, NY 13244, USA. Tel.: +1 315 443 4673; fax: +1 315 443 3363. (e.g. “The Tanganyika Problem”—Moore, 1903) at the start of the E-mail address: [email protected] (C.A. Scholz). 20th century. The remarkable hydrological variability of Lake Malawi 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.10.030 4 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 Fig. 1. A) Regional digital elevation model of east Africa generated using the GTOPO data set, showing locations of major lakes. Inset shows maximum January and July position of the intertropical convergence zone (ITCZ). B) High-resolution digital elevation model (SRTM data set) and bathymetry of the Lake Malawi Rift and catchment. Numbers indicate locations of two drill sites. over geologic time was also described in early records, as observed 2. Geological background through raised beaches and lacustrine sequences especially on the north shore of the lake (Dixey, 1926). The importance of the African The first reports of the geology of the Lake Malawi (Nyasa) region Great Lakes for understanding climatic changes in the Pleistocene has date from the early part of the 20th century (e.g. Dixey, 1926) and been noted for decades (Livingstone, 1965). provide details of the basement rocks and sedimentary sequences The early seismic imaging and sediment sampling studies in Lake surrounding the basin. Much of the catchment of the lake is underlain Malawi established that the basin's thick accumulations of fine-grained, by Precambrian and early Paleozoic crystalline rocks associated with and commonly laminated sediments contain a rich and unique record of Pan-African mobile belts (Daly et al., 1989)(Fig. 2). The metamorphic climatic, evolutionary and tectonic change in tropical east Africa, which basement of the area is composed of greenschist–amphibolite grade warranted deep sampling through extensive coring and scientific rocks, and is affiliated with granites and syenites emplaced during the drilling (e.g. Crossley, 1984; Rosendahl and Livingstone, 1983). Ubendian and Irumide orogenies. This crystalline rock terrane Following extensive basin framework and short core sampling studies underlies many of the largest river drainages which empty into Lake (e.g. Owen and Crossley, 1989; Scholz et al., 1990; Scott et al., 1991), an Malawi, and it is the source of most of the detrital siliciclastic material international collaboration of scientists organized a scientific drilling observed in deep-water Lake Malawi sediment cores. program in March and April 2005. This special issue of Palaeogeography, On the western side of the North Basin are sedimentary sequences Palaeoclimatology, Palaeoecology is devoted to the results of detailed of widely varying age (Fig. 2). Permo-Triassic Karoo sandstone, shale studies from Lake Malawi and affiliated sites, covering the time interval and coal-bearing intervals 2–3 km in thickness are observed to extend of the middle–Late Pleistocene through Holocene, mainly focusing on across Malawi and western Tanzania near the Ruhuhu River (e.g. analyses and results from the 2005 scientific drill core 1C, as well as cores Kreuser, 1990; Yemane et al., 1989). Terrestrial sedimentary from Site 2. These papers include a review of basin framework (Lyons et sequences of Cretaceous age bearing vertebrate fossils are also al., 2011-this issue), and studies of lithostratigraphy and geochemistry observed outcropping on the northwest shore of the lake (e.g. Roberts (e.g. Brown, 2011-this issue; Johnson et al., 2011-this issue; McHargue et et al., 2004). These are overlain by Neogene and Quaternary al., 2011-this issue; Scholz et al., 2011-this issue; Woltering et al., 2011- sediments, including fossiliferous limestones. Less than 40 km north this issue) and paleobiology (Beuning et al., 2011-this issue; Park and of the northern shoreline of the lake is the Rungwe volcanic complex, Cohen, 2011-this issue; Reinthal et al., 2011-this issue; Stone et al., 2011- composed primarily of basalt and nephelinite (e.g. Furman, 1995; this issue) from cores from holes 1C, 2A and 2B. Companion studies from Harkin, 1960), which is one of the three late-Cenozoic volcanic centers other sediment cores from Lakes Malawi and Tanganyika and spanning located in the western branch of the EARS (Ebinger, 1989)(Fig. 2). the late Pleistocene and Holocene are also presented in this volume (e.g. Dating of these volcanic rocks suggest an initiation of rifting in the late Burnett et al., 2011-this issue; Castañeda et al., 2011-this issue; Powers et Miocene (Ebinger et al., 1989). Because these