Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

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Palaeogeography, Palaeoclimatology, Palaeoecology

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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 are restricted to a single al., 2011-this issue). major river drainage in the catchment, volcanogenic sediments C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 5

Fig. 2. Bedrock geology and fault map of the Lake Malawi Rift (from Lyons, 2009). entering the lake are mainly limited to the northern basin of Lake older, with volcanism initiating prior to 30 ma, whereas much of the Malawi. western branch of the system may be late Miocene or younger; the The East African rift is separated into the magmatically active initiation of rifting is observed to be progressively younger from north eastern branch, which is comprised of the Ethiopian, Turkana, Kenya, to south (e.g., Ebinger and Sleep, 1998; Tiercelin and Lezzar, 2002). In and Gregory Rifts, and the largely amagmatic western branch, the 1980s, geophysical studies from the Great Lakes of East Africa led dominated by large freshwater lakes. Numerous studies undertaken to the recognition of the pronounced segmentation and cross- throughout the rift system reveal that the Ethiopian system is much sectional asymmetry of rift systems, and the importance of 6 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

Fig. 3. Perspective view of the Malawi rift generated using NASA software, illustrating pronounced rift valley segmentation. Dashed lines denote main rift segments.

lithospheric thermomechanical properties in the rifting process the basin, have played critical roles in determining the sediment (Morley, 1988; Rosendahl, 1987). In particular, seismic reflection pathways into the most deeply subsided parts of the basins. The studies in Lakes Tanganyika and Malawi led to the observation of current morphometry of these two deep basins, with very steep pronounced cross-rift asymmetry and consistent rift segment dimen- margins on at least one side, gives rise to significant down-slope sions along the full axis of the system (Fig. 3). For instance the Lake sediment transport systems, facilitating gravity flows, and especially Malawi rift is comprised of three main linked half-graben basins, turbidity flows, over broad areas of the basin (e.g. Ng'ang'a, 1993; which alternate in polarity along axis (Specht and Rosendahl, 1989) Scholz, 1995; Soreghan et al., 1999). (Figs. 2 and 3). This pattern is observed along the 2000 km-long western branch of the rift, and discrete segments are also observed 3. Climate and hydrology along the Tanganyika, Kivu, Edward, and Albert Rift zones (Ebinger, 1989; Rosendahl, 1987)(Fig. 1). In Lake Malawi, deep-basin As in most areas of the tropics, seasonal climate variability in the subsidence is accommodated by slip on a few primary border faults, Malawi rift valley is dominated by changes in precipitation rather which in the north basin is observed on the northeastern margin, on than temperature, and in East Africa rainfall is strongly influenced by the western margin in the central basin, and on the east side of the the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), lake in the case of the South Basin (Fig. 2). The coastlines of the border north and south of the equator (Fig. 1). Convection associated with fault margins are characterized by high mountains in the central and the passage of the ITCZ gives rise to heavy rains on the landscape. The north basins, which comprise the footwall (e.g. Wheeler and Karson, region around the Malawi Rift is dominated during the austral 1989). These mountains commonly rise 1000–1500 m above the summer by a single rainy season that extends from ~December to adjacent lake surface, and define bold, unforgiving shorelines (e.g. March, although in some years it begins in October and extends Figs. 1 and 3). Along the length of the western branch of the rift, each through early May. Rainfall within the rift also varies by elevation and half-graben basin averages 80–200 km in length, and 30–60 km latitude, with higher terrain generally wetter, the southwest coast across, and the most deeply subsided points within each basin are receiving as little as 80 cm/yr, and areas to the north of the lake commonly observed adjacent to the border fault and the zone of averaging more than 200 cm/yr (Malawi Department of Surveys, maximum footwall uplift (Ebinger et al., 2002). 1983). Moisture is derived from both the Atlantic and Indian Oceans, Studies of individual border fault systems reveal evidence for although East African rainfall variability has been shown to be broadly dextral oblique-slip deformation along the Livingstone Mountains linked to sea surface temperatures of the Indian Ocean (e.g. Cane et al., border fault and the Rukwa Border Fault (Wheeler and Karson, 1989), 1994; Goddard and Graham, 1999; Marchant et al., 2007). Sedimen- as well as in southern Lake Tanganyika (Klerkx et al., 1998). Similar tation in Lake Malawi is markedly influenced by the seasonal cycle, outcrop-scale studies have not been carried out on the central basin with most terrigenous material introduced into the lake margins border fault system in Lake Malawi, but studies of intrabasinal fault during the intense rainy season. During the austral winters, strong structures observed in seismic reflection data also suggest some prevailing winds from the south set up an oscillation of the internal amount of oblique-slip deformation in that area (Mortimer et al., stratification in the lake (Patterson and Kachinjika, 1995) resulting in 2007; Scott et al., 1994; Specht and Rosendahl, 1989). Detailed pronounced upwelling and algal blooms, particularly at the north and observations of border fault structures in the central basin of Lake south ends. This seasonal cycle results in annually laminated Malawi show that several main border fault strands accommodate sedimentary couplets deposited in many areas of the basin (Pilskaln, subsidence there (Soreghan et al., 1999), each of which likely evolved 2004; Pilskaln and Johnson, 1991). from the propagation or coalescence of several much smaller faults Modern Lake Malawi is hydrologically open. Seven large river early in the history of the rift (e.g. Schlische, 1995; Mortimer et al., systems comprise 70% of the lake's catchment area (Bootsma and 2007). Intrabasinal faults within the northern and central basins of Hecky, 1999; Wells et al., 1994), and the Shire River is the lake's sole Lake Malawi are secondary features relative to the main border faults, outlet. Although there is nearly continuous outflow from the Shire at least in terms of total displacement (Specht and Rosendahl, 1989). River, ~90% of the annual water loss is via evaporation (Drayton, However in several localities these basement-involved fault systems 1984). This condition is very different from most high-latitude lake produce relief on the modern lake floor, and for much of the history of basins, and results in seasonal fluctuations in water level of 1–2m. C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 7

The lake's tenuous outlet discharge was interrupted during historical 1989). These data provide information on the distribution of the main times (Owen et al., 1990a,b), and probably frequently in the recent half-graben basins, as well as on the geometry of intrabasinal fault geological past. Modeling studies of past lake levels have helped families (e.g. Mortimer et al., 2007). Some of these structures generate quantify the response in this highly sensitive system, which is delicately 10s of meters of relief on the lake floor (e.g. Scott et al., 1991), and balanced between precipitation and evaporation (e.g. Lyons et al., 2010; therefore impact down-slope sediment transport processes into the Owen et al., 1990a,b), and where lake level drops of several hundred basin, as well as the final position of associated deposits. High-density meters can occur in a few thousand years or less. grids of high-resolution seismic reflection data were acquired using small airguns as the seismic source, and these grids, nested within the 4. Significance for paleoenvironmental reconstruction sparsely spaced multichannel seismic reflection data, were most suitable for locating the drill sites (Lyons et al., 2011-this issue) Long-term records of tropical climatic change, and especially the (Fig. 4). timing and rate of dramatic changes in climate relative to the modern The Lake Malawi sediment record is a proven, high-sensitivity climatology described above, are essential for understanding global archive of subtle shifts in climate (Finney and Johnson, 1991; Johnson scale climate shifts. Much of the incident solar radiation striking the et al., 2002; Owen et al., 1990a,b). Sediment core and geophysical data earth hits the tropics and subtropics, and the resultant heat energy is offer abundant evidence for repeated episodes of profound hydrologic exported to the high latitudes by the oceans, and to a lesser extent by drawdown of the lake, and marked lateral shifts of the lake shoreline the atmosphere. Sediment records from the offshore of North Africa over distances of many tens of kilometers (e.g. Finney and Johnson, show that African climate responds to insolation change on orbital 1991; Scholz and Rosendahl, 1988). Part of the evidence for these (Milankovitch) time scales (deMenocal et al., 2000). Those far-field major lake level shifts comes from major unconformities that are records are important for providing low-resolution information about observed on the shoaling, or flexural margins of half-graben basins in past climate of the tropical continents, but determining spatial and Lake Malawi (e.g. Scholz and Rosendahl, 1988). Accordingly, a key temporal variability of past regional climate requires new records criteria for site selection for the drilling program included localities from the continental interiors themselves. The new drill cores from where the seismic data indicated that the stratigraphic section was Lake Malawi sample an important region of the Southern Hemisphere relatively complete, with no major time gaps. Because of the continental tropics on a scale of decades to centuries, which has not ubiquitous unconformities around the basin margins, the recovery been previously sampled, other than from short cores, low-resolution of a long and continuous stratigraphic section required drilling near data sets, or through studies of punctuated sedimentary sequences the basin center in water depths N500 m (Fig. 1). preserved in outcrops. Particularly lacking are records from the Seasonal wind variations and pronounced upwelling of nutrient- Southern Hemisphere continental tropics that are suitable for direct rich deep waters at the north end of the lake during the austral winter comparison to longer marine records. help preserve heightened signals of paleoclimate change in the form Key science issues addressed by this project include 1) determining of laminated sediments (e.g. Johnson et al., 2002; Pilskaln, 2004). the direction, magnitude and timing of effective moisture, wind, and temperature change on a millennial scale, during the past several glacial– interglacial cycles; 2) assessing if observed climate shifts coincide with SST variability in the tropical oceans, or perhaps more closely with changes in North Atlantic thermohaline circulation; 3) constraining the lake level history of Malawi, and comparing it to records of methane concentration in the polar ice cores (interpreted to be a globally averaged measure of tropical moisture on the continents); 4) determining if the observed evidence for abrupt climate change in Lake Malawi and other parts of East Africa coincides with known events from other regions on Earth, such as Heinrich or Dansgaard–Oeschger events; and, 5) assessing if the climate of this Southern Hemisphere site responded only to changes in low latitude precessional insolation (23, 19 kyr) or also to high-latitude ice volume (100 kyr and 41 kyr) forcing in the Pleistocene. All these issues are helpful in constraining the environmental back- ground to early modern human evolution and migration, and to understanding species evolution in lakes.

5. Basin framework and site selection

Studies of the sediments of the large lakes of east Africa have shown that the stratigraphy and the depositional framework of these basins are complex (Scholz et al., 1990; Tiercelin et al., 1992). Half- graben sub-basins comprise the large rift-lakes, and their steep faulted margins are prone to gravity flows, mass wasting events, and the construction of major sublacustrine fan complexes that can extend across the floors of the basins for several 10s of kilometers (e.g. Soreghan et al., 1999; Tiercelin et al., 1992). Zones of enhanced turbidite accumulation are problematic for reconstructing detailed records of past climatic and limnological conditions, and accordingly it was imperative during the Lake Malawi drilling project to site the Fig. 4. Representative seismic reflection data from Lake Malawi. A) Regional drilling locations away from areas where turbidites and other gravity multichannel seismic reflection profile showing full sedimentary section, pre-rift basement, and location of scientific drill core. B) High-resolution single-channel airgun flow deposits have accumulated. seismic profile showing ancient progradational delta in ~−200 of water off of the The basin scale structure of the rift was assessed through regional Songwe River. See Lyons et al., for full treatment of the basin framework seismic multichannel seismic reflection studies (e.g. Specht and Rosendahl, reflection data. 8 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

Because of this sensitivity, a high-priority for drilling Lake Malawi also except every few days. The riparian countries of Malawi, Tanzania and included acquiring a high-resolution record of the past ~100 ka at the Mozambique have limited infrastructure and manufacturing, so most northern end of the lake. equipment and supplies required for the drilling operation were Tropical lakes are known to accumulate sediments enriched in procured from outside of Africa. The project chartered the 160′ fuel organic matter, due to high biological productivity in the surface waters, barge Viphya from Malawi Lake Services to serve as a drilling platform and to enhance preservation of organic remains in the anoxic zone that (Fig. 5). The Viphya was redesigned (Lengeek Engineering Ltd., persists in deeper waters. Accordingly, over long spans of geological Halifax) to accommodate the 100 ton geotechnical drilling rig time (N2 million years), such sediments are prone to organic matter (Seacore Ltd., Cornwall), accommodations, galley, toilet/shower, and diagenesis and thermogenic maturation, and can generate significant workshop containers, drilling moon pool, and portable dynamic and even economic accumulations of hydrocarbons, for example as in positioning system, which was used to maintain the position of the Lake Albert, Uganda (Smith and Rose, 2002). Scientificdrillingsystems drilling barge for the duration of each hole (Fig. 5). A dynamic such as those used by the Integrated Ocean Drilling Program (IODP) drill positioning system with Nautronix© controllers was purchased by ship JOIDES Resolution, and the Lake Malawi ScientificDrillingProject DOSECC Inc. for the project. DOSECC drilling tools initially designed generally do not return circulating drilling fluids to the drilling vessel, for the GLAD 800 drilling system were deployed within a 5″ API drill and accordingly are not suitable for drilling into formations with string on loan from the IODP. Engineering and planning required overpressurized zones, or strata containing oil or gas. Accordingly, it was about three years of effort prior to drilling. Barge refit work was imperative to only drill in areas of Lake Malawi with no evidence or completed in the ship yard in Monkey Bay, Malawi, and the final potential for hydrocarbon accumulation. This was achieved by carefully mobilization of the Seacore drill rig aboard the Viphya was completed examining high-resolution and deep-basin multichannel and single- on the jetty in the port of Chipoka, Malawi. channel seismic reflection data for signs of seismic amplitude anomalies Mobilization for field operations began in December 2004 with sea that might suggest subsurface gas or fluids. The proposed drill sites were trials of the portable dynamic positioning system, and preparations also positioned to avoid any potential hydrocarbon traps, such as are for the drilling effort continued into February 2005. Drilling ensued in commonly found on structural anticlines or on the crests of tilted fault late February 2005, after extensive testing and modification of blocks. equipment. The drilling operations required a team of 26 people on Drill Site 1 was chosen to achieve the primary science objective of a the drilling barge Viphya, including nine drillers, and a team of about long-term and continuous record of climate change in the Southern thirty people onshore and on support boats as logistical support staff. Hemisphere tropics of East Africa (Figs. 1 and 4). The drill site is The shore-based team also carried out extensive outreach efforts, situated in the central basin, southeast of the deep depocenter. visiting many Malawian secondary schools and government offices Continuous hemipelagic sediments comprise the stratigraphic section (Fig. 5)(http://malawidrilling.syr.edu/photos/Outreach%20Program/ of this area (Fig. 4). These sediments accumulated at this site because index.html). Technical challenges early in the field operations of its isolation from the main down-slope transport pathways present included initial difficulty tuning the dynamic positioning system, on the western and northeastern margins of the basin, and because of and the operation of the DOSECC tools within the API drill string, but its relatively deep water. Additionally, no erosional unconformities are these operational issues were ultimately overcome by the resourceful observed at this locality. Details of the drill site and cores recovered are staff of engineers and technicians. Routine drilling operations began presented in Table 1. Drill Site 2 was selected to recover a high- on 9 March 2005, and continued for ten days at deep drill Site 1, resolution signal of upwelling, river sediment discharge, and aeolian located at a water depth of approximately 592 m in the central basin processes known from the northern end of the lake. The drill site was of Lake Malawi. Following the completion of four holes to a maximum positioned in an area of hemipelagic sediment deposition, and the total sub-bottom depth of 380 m (Table 1), the Viphya proceeded to the projected depth of the cores at this site was 40 m (Figs. 1 and 4). northern site and completed three holes at that locality.

6. Drilling engineering and field operations 7. Methods of sediment drill core analyses Lake Malawi is landlocked and there are no navigable waterways between the lake and ports on the Indian Ocean coast of East Africa. 7.1. Logging, core processing and initial core descriptions Shipping and port operations exist on the lakeshore, but because fi much of the lake is bounded by faulted coastlines with rocky Logging in the eld of Site 1 holes included down-hole gamma headlands and escarpments, there are only a few sheltered harbors logging following drilling, and whole core logging using a GEOTEK along the full 560 km-length of the lake. Because of the size of the lake multisensory track logging system at a shore-based site. Measure- fi and the distance between these drill sites and the shoreline and ments made with the eld GEOTEK instrument included GRAPE sheltered harbors, it was necessary to organize a drilling operation density (gamma ray attenuation porosity evaluator), magnetic capable of running 24 hours per day from a stand-alone drilling susceptibility, and P-wave velocity. Following the completion of the vessel, without the need to refuel, resupply, or shift crews to shore, drilling program, all cores were shipped to the National Lacustrine Core Repository (LacCore) in Minneapolis, Minnesota. Replicate whole core GEOTEK logging was then carried out at high-resolution on all cores recovered from sites 1 and 2 (Table 1). Natural gamma Table 1 logging of whole cores was also carried out at the LacCore facility. Core locations and core details. Following logging, cores were split and described according to Hole Latitude Longitude Water depth Total depth standard paleolimnological procedures (Schnurrenberger et al., (mblf) 2003). Immediately following splitting, cores were scraped clean 1A 11 17.6387 S 34 26.2331 E 592 47.6 and high-resolution color scans were acquired of each core, using a 1B 11 17.6814 S 34 26.1793 E 592 380.7 DMT CoreScan digital linescan camera or a Geotek Geoscan-III digital 1C 11 17.6575 S 34 26.1462 E 592 89.9a 1D 11 17.6183 S 34 26.1469 E 592 21.0 linescan camera. Smear slides were made at selected intervals and 2A 10 01.0597 S 34 11.1607 E 359 41.1 examined in parallel with the completion of the visual core 2B 10 01.0567 S 34 11.1527 E 359 40.1 descriptions. Discrete subsamples of core were acquired for other 2C 10 01.0532 S 34 11.2067 E 359 37.0 analyses at this time. Following the splitting, description and sub- a Corrected for initial over-penetration by 6.51 m. sampling work, cores were scanned in an ITRAX core scanner at the C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 9

Fig. 5. Photographs of the drilling barge on Lake Malawi (A,C,D), and (B) outreach effort by drilling team scientific staff.

Large Lakes Observatory at the University of Minnesota-Duluth for after step-wise increasing alternating field demagnetization steps major and minor element abundances. were done on U-channel samples using a 2-G Enterprises automated U-channel magnetometer system located at the University of Rhode Island. These data were used to construct composite estimated relative 7.2. Age dating paleointensity cores (NRM/ARM) for Lake Malawi drill sites 1 and 2 using the “Splicer” software program developed by the Ocean Drilling The upper parts of all cores were age-dated using radiocarbon Program. Splicer builds composite sections by using an optimized accelerator mass spectrometry at the Accelerator Mass Spectrometry cross-correlation approach. Multiple parameters are used simulta- Laboratory at the University of Arizona. Previous studies of Late- neously to achieve the optimal match, and fills core gaps while Pleistocene and Holocene cores from Lake Malawi have demonstrated avoiding stretching or compressing the depth scale. The data sets used the efficacy of dating of organic-rich bulk samples (Johnson et al., in Splicer were the GRAPE density, susceptibility, NRM20/ARM20mT, 2002), and accordingly all radiocarbon subsamples analyzed from the and characteristic Inclination. Holes A and B were composited for Site drilling project cores at sites 1 and 2 were bulk sediment samples. 2, whereas holes C and D were composited for Site 1. Samples for radiocarbon dating were acquired at 50 cm intervals in the uppermost parts of each hole. Because modern Lake Malawi waters are undersaturated with respect to calcium carbonate, and the 7.3. Paleoclimate indicators catchment contains limited amounts of carbonate bedrock, no reservoir corrections were made to radiocarbon dates. The resulting A primary paleoclimate objective of the Lake Malawi Drilling Project is 14C ages were calibrated using the Cologne Radiocarbon Calibration to assess a long-term record of effective moisture and lake level in the and Radiocarbon Research Package (CAL-PAL) (Weninger et al., 2005). catchment. A variety of fundamental observations contribute to our Subsamples deeper in the cores were dated using Optically understanding of these key measures of past climatic conditions. Primary Stimulated Luminescence (OSL), and in the case of MAL-1C, also among these are the lithostratigraphy of the core, and the sequence paleomagnetic inclination and paleointensity. Paleointensity was stratigraphy of the basin surrounding the drill sites. Lithostratigraphic determined using the ratio of natural remnant magnetization to observations were completed as part of the Initial Core Descriptions anhysteretic remnant magnetization (NRM/ARM) (a measure of completed at the University of Minnesota, and lithology was further magnetic field intensity), and 10Be, and 10Be/9Be in core Mal-1C, quantified through analyses of color data extracted from core images, as were correlated to a previously published paleointensity record from well as through analyses of physical properties measured on cores. Details the Somali Basin (McHargue et al., 2011-this issue; Meynadier et al., of the seismic stratigraphy and basin framework of the Lake Malawi 1992). Magnetic measurements of anhysteretic remanent magnetiza- section are presented in Lyons et al. (2011-this issue) and the details of tion (ARM) and natural remanent magnetization (NRM) before and the lithostratigraphy and smear slide character of the key lithologies are 10 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 presented in Scholz et al. (2011-this issue).Keygeochemicalmeasuresof (e.g. Castañeda et al., 2011-this issue) and pollen transport (Beuning the core (e.g., total organic carbon, total organic nitrogen, Ca abundance, et al., 2011-this issue). and δ13C of organic matter) that contribute to our understanding of past limnological conditions are presented in Scholz et al. (2011-this issue). 8. Results Elemental analyses of sediments using scanning X-ray fluorescence methods have been presented in Brown et al. (2007), Brown (2011-this 8.1. Age dating issue) and Scholz et al. (2011-this issue). A record of past lake productivity from records of biogenic silica is presented by Johnson et al. (2011-this A summary of 14C, paleointensity, OSL and inclination age dates is issue). Records of landscape moisture from pollen records are presented presented in Table 2. In the interval 0–52 ka the radiocarbon ages in Beuning et al. (2011-this issue), and a high-resolution perspective of were used to define the age–depth relationship, and a 3-term water column geochemistry from diatom records is presented in Stone et polynomial curve was used to characterize this interval. For the al. (2011-this issue). Studies of ostracod assemblages are particularly interval 52–145 ka a linear regression was used based upon helpful in constraining lake levels, CaCO3 saturation and water column paleointensity, inclination, and two OSL-based ages (Fig. 6)(Scholz dynamics in the system (e.g. Cohen et al., 2007; Park and Cohen, 2011-this et al., 2007). Because the Mal-1C core initially over-penetrated to a issue). An analysis of the faunal remains of fish and the possible impact of depth of 6.5 m, we used dates from an adjacent piston core (M98-13P) major hydrologic changes on fish paleoecology is presented in Reinthal et to provide the age–depth relationship in the upper 6.5 m of the al. (2011-this issue). sediment section at this site. Records of past temperature from lake sediments have been recovered in the past using chironomid remains, but molecular methods 8.2. Sequence stratigraphic framework using tetra ethers (TEX86) can now quantify paleotemperatures in tropical lakes as well, where chironomid-based methods are not useful Basin-scale multichannel seismic profiles provide the regional for paleotemperature analysis (Powers et al., 2005; Tierney et al., 2008). and deep stratigraphic context for evaluating dense grids of single- In this volume, Powers et al. (2011-this issue) demonstrate further channel high-resolution seismic reflection data that are tied to the refinement of this method, presenting results of TEX86 analyses of drill cores and the detailed paleoclimate measurements (Fig. 4) samples from short cores from northern Lake Malawi spanning the past (Lyons et al., 2011-this issue). Important elements of the strati- 700 years. In a parallel study from the same short core, Castañeda et al. graphic section observed in high-resolution seismic reflection data (2011-this issue) describe biomarker evidence for recent changes in include stacked progradational deposits, clearly identified as deltaic primary productivity from the same 700 year record. Woltering et al. deposits associated with much lower stages of Lake Malawi (e.g.

(2011-this issue) present a 74,000 year Tex86 record from Lake Malawi Lyons et al., 2011-this issue; Scholz, 1995)(Fig. 4). Other evidence of sediments, subsampled from Malawi core 2A. stratigraphic variability in the high-resolution Lake Malawi seismic Another key set of parameters describing past climate in the records includes packages of facies couplets, which alternate continental interior comes from analyses of past wind regimes. The between high-amplitude and continuous seismic facies and discon- seasonal wind pattern associated with the migration of the ITCZ is an tinuous and low-amplitude facies (see Lyons et al., 2011-this issue). important aspect of the regional climate dynamics. In Lake Malawi These variations are observed in the seismic data at the same scale of changes in past wind regimes are assessed from sediment cores variation as the profound changes in lithology observed in the through studies of windblown material (e.g. Brown et al., 2007), sediment drill cores. The firm linkage of the drill core and seismic upwelling as seen in laminated sediments signals of lake productivity observations is provided through a detailed evaluation of the drill

Table 2 Age Data for Lake Malawi Drilling Project Hole 1C.

Hole Depth below lake floor Type of date Lab number 14C age ±Error Calendar age ±Error (kyr BP) (kyr BP)

Lake Malawi 1C/13P 0.555 14C AA34424 875 45 0.816 0.067 Lake Malawi 1C/13P 1.7 14C AA34425 1830 45 1.772 0.05 Lake Malawi 1C/13P 3.705 14C AA34426 3845 55 4.273 0.095 Lake Malawi 1C/13P 5.46 14C AA34427 6235 55 7.141 0.09 Lake Malawi 1C 6.705 14C AA71824 9649 52 11.009 0.138 Lake Malawi 1C 7.5075 14C AA71820 10,635 59 12.628 0.079 Lake Malawi 1C 7.9 14C AA34428 11,425 75 13.329 0.145 Lake Malawi 1C 8.5075 14C AA71821 12,392 62 14.565 0.313 Lake Malawi 1C 9.4565 14C AA65692 15,196 92 18.451 0.222 Lake Malawi 1C 9.5565 14C AA71823 15,507 95 18.799 0.18 Lake Malawi 1C 10.5455 14C AA65008 18,000 110 21.528 0.47 Lake Malawi 1C 11.5235 14C AA71822 20,070 120 23.973 0.267 Lake Malawi 1C 12.4575 14C AA65693 21,990 150 26.59 0.427 Lake Malawi 1C 14.0895 14C AA65694 26,230 240 30.89 0.214 Lake Malawi 1C 15.806 14C AA65009 31,040 440 36.139 0.423 Lake Malawi 1C 21.053 14C AA65010 46,900 2800 50.457 3.243 Lake Malawi 1C 17.5 Paleointensity 39 Lake Malawi 1C 21 Paleointensity 53 Lake Malawi 1C 32 Paleointensity 67 Lake Malawi 1C 39.5 Paleointensity 80 Lake Malawi 1C 46 Paleointensity 83 Lake Malawi 1C 72.5 Paleointensity 114.5 15 Lake Malawi 1C 84.5 Paleointensity 135 Lake Malawi 1C 67.25 Inclination 122.5 7 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 11

Fig. 6. A) Age–depth relationship for Site 1C drill hole. See text and Table 2 for details of geochronology. B) Paleointensity profiles correlating sites 1 and 2 with the Somalia Basin record of Meynadier et al. (1992), core 85–674. 12 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

Fig. 7. Paleoclimate proxy records from sites 1 and 2 in Lake Malawi. From left to right: lithology; normalized core imagery (Scholz et al., 2011-this issue); red values (extracted from imagery); saturated bulk density (from GRAPE, or Gamma Ray Attenuation Porosity Evaluator); total organic carbon (TOC); Principal Component 1 from diatom and other palaeoecological analyses (PC-1) (Stone et al., 2011-this issue); total pollen accumulation rate (PAR) (Beuning et al., 2011-this issue); Lake Malawi TEX86 (Site 2) (Woltering et al., 2011-this issue); Ostracode concentration (Cohen et al., 2007; Park and Cohen, 2011-this issue). core velocity and density parameters, which were used to generate a about every 15–20 m below about 32 m in the core (~60 ka) (Fig. 7). synthetic seismogram for the drill core (Lyons et al., 2011-this issue). Detailed results of bulk organic matter analyses are presented in the The detailed stratigraphic framework built-out from the sediment study of Scholz et al. (2011-this issue) which describes the drill cores allows us to further constrain the history of water level proportions of terrestrial and aquatic organic matter deposited into variation in the basin over the past 145 kyr. Lake Malawi over the past 145,000 years. Paleoecological records provide a wealth of information on water 8.3. Paleoclimate inferences column conditions over the length of the core (Figs. 7 and 9). Stone et al. (2011-this issue) reconstruct a record of lake level and Sediment lithology in the Malawi Drilling Project 1C drill core paleolimnology from principle component analyses of diatom paleo- shows considerable variability, as initially characterized by visual ecology and sieved fossil and mineral residues (Figs. 7, 9, and 10). examination of the split sediment cores (Fig. 7). The quantification of Many of the key components of the early fossil diatom record observed lithology was then completed using sediment physical properties, in Hole 1C sediments are in general not observed in the open waters of core imagery, and geochemical methods. the central basin today. The diatom record over the past 60,000 years Sediment density was quantified at high-resolution in the at the deep central basin site is reflective of dilute, deep waters, and sediment cores using the GEOTEK logging system, and these data dysaerobic bottom conditions, similar to the modern system and combined with color (RGB) data extracted from core images show comparable to what has been described for the lake for the Holocene, pronounced variability, especially at depths in the core below 28 m Last Glacial Maximum, and deglacial intervals. Prior to 70 ka however, depth (~60 ka). In the zone between the base of the core at ~90 m the diatom records as well as ancillary fossil and minerogenic residues sub-bottom (145 ka) and 32 m there are marked and cyclical changes suggest that this area and the lake in general was much shallower, from low-density dark-brown homogeneous and laminated mud, to alkaline and at least mildly saline. During intervals described by Scholz high bulk density, grey, massive and mottled mud (Figs. 7 and 8). Bulk et al. (2007) and Cohen et al. (2007) as megadroughts, species are organic matter measurements show that the low-density sections are dominated by Aulacoseira taxa that are today mainly found in the characterized by high values of organic carbon, whereas the high- southern shallow basin of the lake. The dominance of saline/alkaline density zones are characterized by very low values of TOC, but plankton such as Aulacoseira ambigua during these megadrought significant enrichment in calcium carbonate, as measured by Ca intervals suggests a shallower closed basin, which would have had abundance in scanning XRF data (Fig. 8). Analyses of bulk organic drastically different mixing processes and nutrient inputs relative to matter and major elements (using high-resolution XRF core scanning) the modern system (Stone et al., 2011-this issue). also permit the quantification of lithologic variations. At deep-water A study of ostracod assemblages from Hole 1C shows occurrences Site 1C in the central basin, total organic carbon shows an inverse of seven genera, and these varying assemblages, in combination with relationship with Ca abundance, and at depth this alternation occurs other taphonomic variables such as valve breakage, and carbonate and C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 13

less than 3000 grains/cm2/yr, with a switch to dominantly grass pollen (Beuning et al., 2011-this issue). Coincident with severe drought intervals, total charcoal abundance was also dramatically reduced (e.g. Cohen et al., 2007), implying a dry land climate with very limited fuel available for brushfires. According to Beuning et al. (2011-this issue) such pollen spectra are indicative of climate regimes with b800 mm/ year rainfall availability. Following this severe megadrought interval, woodland taxa rose significantly, suggesting an increase in average rainfall in the catchment to 1100–1200 mm/year. The interval 75–30 ka was an interval of instability and variability in the pollen records, with a significant peak in Pollen Accumulation Rate (PAR) (Fig. 7) and Podocarpus centered around 60 ka (Beuning et al., 2011-this issue), and then a gradual decline in total pollen production. The interval 30– 15 ka is characterized by relatively low PAR, and stands in contrast to other areas of East Africa to the north which show a more dramatic response to presumably Last Glacial Maximum conditions. Lithostratigraphy and sequence stratigraphy, elemental and bulk organic matter chemostratigraphy, and paleoecological analyses, especially of diatoms and ostracods provide detailed constraints on the history of lake level and effective moisture in the catchment over the past 145,000 years. Pollen records are particularly indicative of conditions of catchment vegetation during this interval. Other key records of past climate change in the basin include measures of

surface water temperatures as derived from the TEX86 paleotherm- ometer, based on Crenarchaeota picoplankton (Woltering et al., 2011- this issue). Reinthal et al. analyzed remains of fish scales, bones and teeth, and their δ13C isotopic values of fish bones, all of which provide insights to the presence of inshore versus pelagic faunas at the drill site over the past 145,000 years (Fig. 9).

Fig. 8. Core images from Hole 1C. A) Well-laminated, organic-rich mud from upper 9. Synthesis of Malawi lake levels and climate variability of the section of hole, typical of lake high stand deposits. B) Massive, dense grey-blue mud past 145,000 years from middle part of hole typical of lake lowstand deposits that accumulated during megadrought intervals. Lake Malawi climate variability over the past 145 ka is best separated into two main intervals, pre- and post-60,000 years before present (Fig. 10). From 145 to 60 ka we observe evidence for oxidized coatings provide additional constraints on lake levels and remarkable variability in lake levels, mixing regime, and trophic paleolimnological conditions over the past 145,000 years (Park and state, which, given the size and latitudinal extent of the Malawi Cohen, 2011-this issue)(Figs. 8–10). Few ostracod occurrences are catchment, likely reflect continental scale variability in the climate noted in the upper ~30 m of core at the deep site, suggesting a system. During the last 60 ka, the lake appears to have behaved much stratified lake during this time, and indicating that the deep site was like the modern water body, with only minor variations in water continuously bathed by anoxic bottom waters for the past volume and water depth (e.g. within a few percent of modern values), ~50,000 years (Cohen et al., 2007; Park and Cohen, 2011-this issue). and nothing as extreme as in earlier times. A Limnocythere-dominated shallow, saline/alkaline assemblage (133– 130 ka) and a deeper water Cypridopsine assemblage (118–90 ka) 9.1. Paleohydrology and paleoclimate variability 145–60 ka that lived in waters 10s to 100s meters deep are observed during two older intervals (Fig. 9 and 10). The latter assemblage also dominated 9.1.1. 135–145 ka during lake level transitions at 136–133 ka, 129–128 ka and 86–63 ka Lithological, paleoecological and geochemical indicators from this (Park and Cohen, 2011-this issue). Notably monospecific assemblages interval of the core (Fig. 10) suggest a lake system considerably different of Limnocythere spp. are typical of littoral environments in highly from modern, but representing relatively deep-water conditions at this alkaline and saline African lakes such as Lake Turkana (Cohen et al., site. Diatom assemblages indicate that Site 1 (presently nearly 600 m 1983, 2007). These Limnocythere assemblages are also characterized depth) had a setting comparable to the intermediate to deeper waters of by high adult/juvenile ratios, limited decalcification, carbonate coat- the modern lake. Organic-rich sediments, with measurable but low ings, and valve abrasion, indicating shallow water and calcium carbonate content suggest a deep, stratified lake environment in this carbonate supersaturated conditions (Cohen et al., 2007; Park and locality, and maximum water depths on the order of 350–550 m. As the Cohen, 2011-this issue)(Fig. 9). oldest section in Hole 1C, below major unconformities, we are unable to Pollen profilesacquiredfromHole1Crevealahistoryofsignificant directly tie this interval to shoreline indicators observed in seismic and sometimes rapid changes in catchment vegetation over the past reflection data; accordingly there is great uncertainty for the lake level 145,000 years (Beuning et al., 2011-this issue). The most dramatic estimate for this interval. excursions from the modern catchment floral assemblage are observed between 135 and 127 ka, and from 110 to105 ka, when production and 9.1.2. 124–135 ka abundance of Podocarpus increased and abundances of as high as 38% Sediments deposited during this interval are characterized as are observed. This indicates a dramatic expansion of montane forests to massive and dense, light-grey, carbonate-rich mud, with low TOC much lower elevations, and implies a cooler and drier climate during values. Bulk organic matter geochemical data suggest a mixture of these intervals. The latter interval of severe droughts extended further, algal and C3-pathway organic matter accumulating in the basin and at and during the period 105–90 ka total pollen accumulation dropped to the drill site during this interval (Scholz et al., 2011-this issue). 14 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

Fig. 9. Images of key core constituents. A) Mica-rich siliciclastic sample. Q — quartz; M — muscovite; Ch — chlorite; Bt — biotite (photo courtesy M.R. Talbot). B) Charred graminoid epidermis (photo courtesy M.R. Talbot) C) Common diatom from Hole 1C (Stephanodiscus muelleri — see Stone et al., 2011-this issue). D) ostracode valve: right valve of Cypridopsine sp. R from MAL05-1C-24E3 361 58.1–59.1 cm (see Park and Cohen, 2011-this issue). E) Phytolith from an unidentified plant (photo courtesy M.R. Talbot) F) Fish vertebrae from sample 5-H-2 (93.4–94.4 cm), 20.19 mblf, approximately 48,000 years old (see Reinthal et al., 2011-this issue).

Diatom assemblages indicate a period of highly variable lake level, and 92 ka, based in part on the dominance of shallow-water Aulacoseira several other paleoecological indicators suggest saline and alkaline species diatoms (Stone et al., 2011-this issue). The presence of conditions. Lake levels are interpreted to be severely reduced during carbonate nodules in this interval, along with sediment textures this time, perhaps 550 m or more below modern levels. This estimate resembling gleyed paleosols, even indicates the possibility of subaerial is further constrained by a stratigraphic tie to a set of prograding exposure at this site during this time period. A stratigraphic tie is also clinoform reflections observed in the North Basin (Lyons et al., this made to a major lowstand delta clinoform package observed in high- issue), which provides an indication of shoreline position. resolution seismic reflection data in the north basin of the lake. Taken together, all these indicators suggest a major low lake stage and where 9.1.3. 117–124 ka water volumes were reduced to ~2% of the modern levels. Charcoal This interval is characterized by several indicators suggesting abundances during this interval are also dramatically reduced, intermediate to high lake levels, including organic-rich laminated- indicating limited vegetation in the catchment and possibly a semi- homogenous mud with low CaCO3 content. Vivianite crystals are desert environment in the lowland areas. observed in the wet-sieved fraction (Cohen et al., 2007), indicating stratification and bottom water anoxia. We estimate that water depths 9.1.5. 85–71 ka were relatively deep at drill Site 1 during this time, and probably This interval is characterized by fluctuating lake levels, which are 0–200 m below modern levels. Because there are no definitive mainly much higher than those of the megadroughts centered at ~100 stratigraphic ties to seismically-identified shoreline indicators, there is and 130 ka. A spike in ostracod and calcium carbonate abundance at considerably greater uncertainty for our paleowater depth estimates 75 ka is tied stratigraphically to another deltaic deposit identified at during this period. The water column was undersaturated with respect −350 m below modern lake level (e.g. Lyons et al., 2011-this issue). to calcium carbonate, suggesting hydrologically open conditions during Abundant uncoated juvenile cypridopsine ostracods indicate some- this interval, and water depths comparable to modern conditions. what deeper water and less calcium carbonate-rich conditions during this time relative to the megadrought interval. Some intervals of this 9.1.4. 85–117 ka zone are dominated by carbonate-poor, organic-rich sediments with This period is marked by a very severe lake level drawdown to levels evidence of vivianite, suggesting that there were periods when the of at least 500–550 m below that of the modern lake. Sediment lithology lake was deeper and stratified. consists of blue-grey, mostly massive carbonate-rich mud, with an interval of medium-fine sand. Diatom assemblages indicate elevated 9.1.6. 61–72 ka salinity in this interval, and Limnocythere ostracods, and carbonate The sediments deposited between ~61 and 72 ka are more coated grains support the interpretation of littoral conditions at the core regularly laminated and darker in color than the overlying sediments site during this interval. The most severe low lake stage occurred ~109– and display some of the highest TOC values of any material recovered C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 15

Fig. 10. Summary of key paleoclimate indicators and other tropical climate information. A) Mean insolation at the start of the single rainy season in the Malawi catchment (1 October–1 December, 10°S). B) Interpreted Lake Malawi water levels over the past 145,000 years (blue) and orbital eccentricity (dotted black). Lake level interpretation developed from synthesis of sediment core paleoclimate indicators with observations from seismic reflection records (e.g. Lyons et al., 2011-this issue). Note prolonged intervals of extremely low lake levels centered at 130 and 100 kyr BP. Intervals 1–8 are described in detail in the text. C) Ostracod abundance. Site one modern water depths=592 m, and waters below ~250 m are anoxic. Accordingly Late-Pleistocene section is devoid of any benthic invertebrates. Single * indicates core intervals dominated by profundal ostracod taxa; double ** indicates core intervals dominated by littoral zone ostracod taxa when lake shoreline was very close to drill site. D) Total organic carbon (weight %). Intervals of elevated TOC are commonly finely-laminated, and indicative of intervals of high lake level, water column stratification, and bottom water anoxia. E) Principal component (PC-1) of diatoms and other paleoecological indicators (from Stone et al., 2011-this issue). Elevated PC-1 indicates periods when the lake was alkaline, saline to mildly saline, with much lower water levels. F) Ca abundance from scanning X-ray fluorescence. Peaks in elevated Ca indicate periods of Ca saturation in the water column. Vertical grey bars indicate periods of severe low lake levels, marked aridity and prolonged drought in the Lake Malawi catchment. These occur during times of high eccentricity, when the system responded to extremes in orbital precession. Periods of severe aridity are broadly, although not perfectly aligned with diminished mean insolation at the start of the rainy season in the Malawi catchment. See text for further discussion. in Hole 1C, generally indicating high productivity, and stratification series of major lowstand delta deposits observed at 200 m below with bottom water anoxia. Because this interval follows a period of modern lake level, and adjacent to many of the modern river systems much lower lake levels (see above), the highly varying organic matter in the lake (Lyons et al., 2011-this issue). enrichment may also in part be due to the fertilization effects of remobilized material following the earlier low lake stages (e.g. Talbot 9.2. Paleohydrology and paleoclimate variability 60–0ka et al., 2006). This interval is also marked by the last significant occurrence of carbonate in the section, indicating a brief, ~2000-year Following the period of severely fluctuating lake levels and climate period of carbonate saturation in the water column, centered at about changes between 145,000 and 60,000 years ago, the lake rose to much 13 62 ka. It is the youngest of the high CaCO3–high δ C and low C/N–low higher levels, and the amplitude of environmental change was much TOC periods described above, and is stratigraphically correlated to a diminished compared to the earlier period. Although lake levels are 16 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 relatively high for the duration of the period 0–60 ka, the frequency of observed in 1) the diatom record from the north basin generated by shifts in wind regimes and water column dynamics is very rapid (e.g. F. Gasse, which shows evidence for lower lake levels from the LGM Brown et al., 2007), and paleoclimate variations are observed to occur until about 16 ka (Johnson et al., 2002), and 2) in high-resolution on time frames of hundreds years. These high-frequency changes are seismic reflection data documented by Lyons et al. (2011-this issue), well-constrained, as the age-dating of this interval is far more precise where a paleo-delta of the Dwangwa river is interpreted as evidence than that developed for earlier intervals. of a comparatively minor −100 m drop in lake level. Although there appears to be comparatively limited change in effective moisture in 9.2.1. 60–32 ka the Lake Malawi catchment when northern tropical East African sites Lake levels during this interval are generally high, with subtle clearly experienced significant impacts at the LGM, there are variability as observed on the sediment core diatom record (Stone discernable shifts in temperature of about 3–4 °C, determined from et al., 2011-this issue). Ostracods are lacking through virtually the TEX86 analyses (Powers et al., 2005). Shifts in wind strength and entire interval, but occasional occurrences of diatoms that tolerate prevailing direction are interpreted through variability in airborne elevated alkalinity suggest fluctuating levels, however briefly. dust contributions to the lake (Brown et al., 2007), and in north basin upwelling, as seen in biogenic silica profiles (Johnson et al., 2002, 9.2.2. 31–16 ka 2011-this issue). Responses similar to those observed in the Lake Stone et al. (2011-this issue) observe over this interval a gradual Malawi drill cores are also observed in Lake Tanganyika, in a transition to diatom assemblages that bear strong resemblance to the 90,000 year-old condensed section recovered from the Kavala Island modern flora, with increasing concentrations of vivianite suggesting a Ridge (Burnett et al., 2011-this issue). The Lake Tanganyika surface stable water column and bottom water anoxia. water temperature response as measured by the TEX86 paleotherm- Water levels were within 100 m of the modern levels for the entire ometer is somewhat stronger, with a N5 °C change over the past interval, and at the deep site in the central basin relatively consistent 60,000 years (Tierney et al., 2008) compared to ~3–4° in Lake Malawi lithologic and chemostratigraphic proxy records are observed. There (Woltering et al., 2011-this issue). Tierney et al. (2008) suggested that is some evidence of fluctuating lake levels in the seismic reflection the more pronounced Lake Tanganyika signal may imply a north-to- data from the Dwangwa delta, suggesting lake level lowering of south gradient in the effectiveness of Northern Hemisphere climate ~100 m around the time of the LGM. However the environmental forcing during the LGM. Paleoecological climate proxy records from conditions at the Site 1 drill site were relatively insensitive to water the LGM, including pollen (Beuning et al., 2011-this issue) and level variability of this magnitude. diatoms (Stone et al., 2011-this issue) also yield no pronounced LGM Paleoclimate indicators at Site 2 near the northern tip of the lake signals in the Lake Malawi drill cores. reveal subtle climate signals that are more pronounced than at Site 1. The record from Lake Malawi drill cores from the last 60,000 years Core Site 2 is more sensitive to climate shifts which are detectable due suggests a tropical environment broadly comparable to the rift valley to its proximity to volcanic terrane north of the lake, and to changes in today. The lower elevations were predominantly woodland with lake upwelling behavior in this part of the lake basin. Brown et al. some grassland areas, and afromontane forests dominated the very (2007) report on millennial-scale variability in bulk elemental ratios highest elevations. Abrupt, millennial-scale changes are clearly of Zr:Ti, which reflects windblown volcanogenic dust from the documented during this time interval, but the primary variability Rungwe Volcano. This millennial-scale structure of the lake sediment was in wind intensity and direction, and lake water column dynamics record bears strong resemblance to signatures of rapid climate change and the amplitude of change of effective moisture and temperature observed from the Greenland and Antarctic ice cores, and demon- were damped in comparison. At various times prior to 60,000 years strates strong teleconnections with high-latitude processes. Interest- before present however, climate was dramatically different, and ingly the thermal structure of the lake over this time interval does not megadroughts prevailed, producing cool, dry semi-desert landscapes show that same type of abrupt response (Woltering et al., 2011-this with markedly reduced rainfall. The evidence for these extreme shifts issue), although their TEX86 data set indicates a general trend in the hydrological regime is documented in many sediment core consistent with that observed in Lake Tanganyika (Tierney et al., climate proxy records from the drill cores, as well as in geophysical 2008) that, on an orbital time scale, tracks Northern Hemisphere data sets from the basin. Full records of paleotemperature from core summer insolation over the past 60 ka. 1C await further analytical work (Johnson and Berke, 2009), but

results of TEX86 analyses from Site 2 in the north basin (Woltering et 10. Discussion and on-going research al., 2011-this issue) hint at pronounced variability in period before 60,0000 years before present. The largest temperature variability

10.1. Paleoclimate record of the past 145,000 years observed in the Site 2 TEX86 records of Woltering et al. (2011-this issue) is between 80,000 and 60,000 years ago, coincident with the The response of tropical Africa to high-latitude cooling at the Last highest variability in indicators of lake level and effective moisture. Glacial Maximum is well-documented in many sites in east Africa, and Hydrological variability in Lake Malawi over the past 145,000 years the very limited hydrological response in Lake Malawi during this is characterized by high-amplitude variability on a 10–20 kyr cycle prior time is somewhat surprising. Surface temperatures were lower by to about 70,000 years ago (Lyons, 2009), and relatively high lake levels several degrees (Bard et al., 1997; Gasse, 2000; Stute and Talma, with subtle millennial-scale climate shifts from 60,000 years until the 1998), effective moisture was reduced, and water levels were lower in present (Fig. 10). This transition has been interpreted as due to a many large lakes of tropical Africa, including Lake Victoria, which was relaxation of eccentricity modulation of precessional forcing of tropical desiccated (Johnson et al., 1996); Lake Tanganyika, which was ~250 m African climate (Scholz et al., 2007). During intervals of increased lower (Gasse et al., 1989); Lake Albert, which was hydrologically- insolation, atmospheric convection and tropical convergence are closed and possibly desiccated (Beuning et al., 1997); and Lake enhanced, which leads to an increase in precipitation (e.g. Deino et al., Edward (−37 m, McGlue et al., 2006)(Fig. 1). However in past studies 2006; Kutzbach and Street-Perrott, 1985). Scholz et al. (2007) referred of Lake Malawi sediment cores, the paleohydrological response during to a climate model focused on tropical precipitation to assess the role of the LGM has proven equivocal or relatively muted, and a similar result orbital precession versus zonal and meridional heating gradients as is observed in the new Lake Malawi scientific drill cores. Finney and drivers of local hydrological cycles (e.g. Clement et al., 2004). When Johnson (1991) reported a low lake stage in the early Holocene based precessional forcing is weak during intervals of low eccentricity, such as on analyses of sediment cores from the southern basin. Evidence for a during the period 0–60,000 years before present, global teleconnections lower lake stage in Lake Malawi within the past ~20,000 years is may be enhanced, and high-latitude influences on tropical climate may C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 17 prevail (Chiang et al., 2003). The megadrought intervals interpreted work will also be required in order to fully constrain and quantify past from our records correspond to zones of elevated Ca and diminished climate boundary conditions in the continental tropics. TOC, which generally occur during insolation minima (Fig. 10). We interpret the interval between 145 and ~60 kyr ago as a period of enhanced precession-scale variability in the hydrologic cycle, dominat- Acknowledgements ed by periods of extreme drought conditions, due primarily to a peak in orbital eccentricity which enhanced the amplitude of precession Many individuals and organizations contributed to the successful fi (Fig. 10). Similar signals are observed in many other tropical and planning and execution of the eld program, as well as the analyses and subtropical sites in Africa, including marine cores from both the Atlantic support for analytical phases of the project. Especially, we thank the and Indian Oceans, outcroppings of lacustrine sediments deposited people and government of Malawi for permission to conduct this during lake highstands in the Central Kenya Rift (Trauth et al., 2003; research, and in particular the Geological Survey of Malawi for local Deino et al., 2006; Kingston et al., 2007), as well as in the Pretoria Salt assistance and participation. Numerous individuals from key contrac- Pan in South Africa (Partridge et al., 1993), although the phasing of wet tors worked tirelessly in order to complete the program, including the and dry intervals varies latitudinally between different parts of the following: Lengeek Vessel Engineering; ADPS dynamic positioning and African continent. The intensification of the African monsoon at ship's crew; the drilling team from Seacore Ltd; DOSECC, and LacCore for approximately precessional-scale intervals has been documented at a assistance with core analysis and archiving. We thank the US-NSF Earth number of sites (Rossignol-Strick, 1985; McDougall et al., 2005; Trauth System History and Paleoclimate programs, and the International fi fi et al., 2003) and records that are located close to the equator show Continental Scienti c Drilling program for nancial support. evidence of wet climates every ~11 kyr, corresponding to the half- precessional cycle (e.g. Bergner et al., 2003; Short et al., 1991; Trauth et References al., 2003, 2007). It is possible that some paleoclimate proxy signatures from the Malawi cores also show this half-precessional signature Bard, E., Rostek, F., Sonsogni, C., 1997. Interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry. Nature 385, 707–710. (Fig. 10). Bergner, A.G.N., Trauth, M.H., Bookhagen, B., 2003. Paleoprecipitation estimates for the The dramatic rise in water level in Lake Malawi as well as in other Lake Naivasha basin (Kenya) during the last 175 k.y. using a lake-balance model. lakes in Africa after 70 kyr ago (Scholz et al., 2007) is evidence for Global and Planetary Change 36, 117–136. increased effective moisture across a wide swath of the African Beuning, K.R.M., Talbot, M.R., Kelts, K., Livingstone, D.A., 1997. A revised 30,000-year paleoclimatic and paleohydrologic history of Lake Albert, East Africa. Palaeogeo- tropics. This effect is most dramatically observed in extant lakes (e.g. graphy, Palaeoclimatology, Palaeoecology 136, 259–279. Moernaut et al., 2010), as the discontinuous records preserved at Beuning, K.R.M., Zimmerman, K.A., Ivory, J.J., Cohen, A.S., 2011. Vegetation response to – outcrop localities generally do not preserve the full climate response. glacial interglacial climate variability near Lake Malawi in the southern African tropics. Palaeogeography, Palaeoclimatology, Palaeoecology 303, 81–92 (this issue). The relaxation in eccentricity explains the diminished precession- Bootsma, H.A., Hecky, R.E., 1999. Water Quality Report. Lake Malawi/Nyasa Biodiversity scale climate variability since 70,000 years ago, but it does not account Conservation Project, Senga Bay, Malawi. for the long-term shift to overall higher lake level. A possible Brown, E.T., 2011. Lake Malawi's response to “megadrought” terminations: sedimentary records of flooding, weathering and erosion. Palaeogeography, Palaeoclimatology, explanation for this phenomenon comes from climate modeling Palaeoecology 303, 120–125 (this issue). results. Clement et al. (2004) suggest that the southward shift of the Brown, E.T., Johnson, T.C., Scholz, C.A., Cohen, A.S., King, J.W., 2007. Abrupt change in austral summer Hadley cell during the LGM produced an increase in tropical African climate linked to the bipolar seesaw over the past 55,000 years. Geophysical Research Letters 34, 20702–20707. latitudinal temperature gradients, which led to dry intervals at Burnett, A.P., Soreghan, M.J., Scholz, C.A., Brown, E.T., 2011e. Tropical East African equatorial and northern tropicallatitudes,butanincreasein climate change and its relation to global climate: a record from Lake Tanganyika, precipitation in the Southern Hemisphere, including in the Lake Tropical East Africa, over the past 90+kyr. Palaeogeography, Palaeoclimatology, Palaeoecology 303, 155–167 (this issue). Malawi catchment. Accordingly the onset of glacial conditions in the Cane, M.A., Eshel, G., Buckland, R.W., 1994. Nature 370, 204–205. Northern Hemisphere over the past 70 ka may have produced a Castañeda, I.S., Werne, J.P, Johnson, T.C., Oberem, L.P., 2011. Organic geochemical similar effect, resulting in higher lake levels. The climate modeling records from Lake Malawi (East Africa) of the last 700 years, part II: Biomarker studies support the idea that the high-eccentricity interval from evidence for recent changes in primary productivity. Palaeogeography, Palaeocli- matology, Palaeoecology 303, 140–154 (this issue). ~145–70 kyr ago is responsible for generating the high precession- Chiang, J.C.H., Biasutti, M., Battisti, D.S., 2003. Sensitivity of the Atlantic Intertropical scale variability in Malawi lake levels in that time frame especially. Convergence Zone to Last Glacial Maximum boundary conditions. Paleoceano- These results combined with observations from a number of other graphy 18. doi:10.1029/2003PA000916. Clement, A.C., Hall, A., Broccoli, A.J., 2004. The importance of precessional signals in the sites suggest a mode switch to high-latitude forcing and overall tropical climate. Climate Dynamics 22, 327–341. wetter, more stable conditions around 70 kyr ago. The severity of the Cohen, A.S., Dussinger, R., Richardson, J., 1983. Lacustrine paleochemical interpretations observed lowstands, especially those centered at ~100 and ~135 kyr based on Eastern and Southern African ostracodes. Palaeogeography, Palaeoclima- tology, Palaeoecology 43, 129–151. B.P. during the period of enhanced eccentricity, strongly suggest a Cohen, A.S., Stone, J., Beuning, K., Park, L., Reinthal, P., Dettman, D., Scholz, C.A., Johnson, precessional control on tropical African climate during this interval, T., King, J.W., Talbot, M., Brown, E., Ivory, S., 2007. Ecological Consequences of Early when glacial influence was relatively minor. Late–Pleistocene Megadroughts in Tropical Africa. Proceedings of the National Academy of Sciences 104, 16422–16427. Crossley, R., 1984. Controls of sedimentation in the Malawi Rift Valley, Central Africa. 10.2. Further research Sedimentary Geology 40, 33–50. Daly, M.C., Chorowicz, J., Fairhead, J.D., 1989. Rift basin evolution in Africa: the influence of reactivated steep basement shear zones. Geological Society, London, Special The sediment drill cores collected from Lake Malawi in 2005 will Publications — Inversion in Other Geological Environments 44, 309–334. no doubt undergo extensive additional analyses in the years to come. de Martonne, E., 1897. Die Hydrographie des oberen Nilbeckers. Z. Ges. Erdkd 32, 315. Among the key records yet to be generated are the detailed records of Deino, A.L., Kingston, J.D., Glen, J.M., Edgar, R.K., Hill, A., 2006. Precessional forcing of paleotemperature from TEX , detailed biomarker studies that assess lacustrine sedimentation in the late Cenozoic Chemeron Basin, Central Kenya Rift, 86 and calibration of the Gauss/Matuyama boundary. Earth and Planetary Science the origin of organic matter in the lake and catchment, high- Letters 247, 41–60. resolution records of vegetation change in the basin from pollen deMenocal, P.B., Ortiz, J., Guilderson, T., Adkins, J., Sarnthein, M., Baker, L., Yarusinsky, studies, and much longer records of past climate from core 1B, which M., 2000. Abrupt onset and termination of the African Humid Period: rapid climate responses to gradual insolation forcing. Quaternary Science Reviews 19, 347–361. extended more than 380 m below the bottom of the lake at Site 1. Dixey, F., 1926. The Nyasaland section of the Great Rift Valley. The Geographical Journal Ultimately scientific drill core records from other sites around the 68, 117–137. African continent will be required in order to fully characterize Drayton, R.S., 1984. Variations in the level of Lake Malawi. Hydrological Sciences 29, 1–12. Quaternary climate changes in the region, but in parallel with these Ebinger, C.J., 1989. Tectonic development of the western branch of the East African rift observational studies, global and regional-scale climate modeling system. GSA Bulletin 101, 885–903. 18 C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19

Ebinger, C.J., Sleep, N.H., 1998. Cenozoic magmatism throughout east Africa resulting Owen, R.B., Crossley, R., Johnson, T.C., Tweddle, D., Kornfield, I., Davison, S., Eccles, D.H., from impact of a single plume. Nature 385, 788–791. Engstrom, D.E., 1990a. Major low lake levels of Lake Malawi and their implications Ebinger, C.J., Deino, A.L., Drake, R.E., Tesha, A.L., 1989. Chronology of volcanism and rift for speciation rates in cichlid fishes. Proceedings of the Royal Society of London, basin propagation: Rungwe Volcanic Province, East Africa. J. Geophys. Res. 94, Series B, Biological Sciences B240, 519–553. 15,785–15,803. Owen, R.B., Crossley, R., Johnson, T.C., Tweddle, D., Kornfield, I., Davison, S., Eccles, D.H., Ebinger, C., Petit, C., Burov, E., 2002. Causes and consequences of the lithospheric Engstrom, D.E., 1990b. Major low lake levels of Lake Malawi and their implications extension: the ups and downs of continental rifts. In: Renaut, R.W., Ashley, G. for speciation rates in cichlid fishes. Proceedings of the Royal Society of London. (Eds.), Sedimentation in Continental Rifts: SEPM Special Publication, 73, pp. 11–23. Series B, Biological Sciences B 240, 519–553. Finney, B.P., Johnson, T.C., 1991. Sedimentation in Lake Malawi (East Africa) during the Park, L.E., Cohen, A.S., 2011. Paleoecological response of ostracods to Early–Late past 10,000 years: a continuous paleoclimate record from the southern tropics. Pleistocene lake level changes in Lake Malawi, East Africa. Palaeogeography, Palaeogeography, Palaeoclimatology, Palaeoecology 85, 351–366. Palaeoclimatology, Palaeoecology 303, 71–80 (this issue). Furman, T., 1995. Melting of metasomatized subcontinental lithosphere: undersatu- Partridge, T.C., Kerr, S.J., Metcalfe, S.E., Scott, L., Talma, A.S., Vogel, J.C., 1993. The Pretoria rated mafic lavas from Rungwe, Tanzania. Contributions to Mineralogy and Saltpan: a 200,000 year Southern African lacustrine sequence. Palaeogeography, Petrology 122, 97–115. Palaeoclimatology, Palaeoecology 101, 317–337. Gasse, F., 2000. Hydrological changes in the African tropics since the Last Glacial Patterson, G., Kachinjika, O., 1995. Limnology and phytoplankton ecology. In: Menz, A. Maximum. Quaternary Science Reviews 19, 189–211. (Ed.), Natural Resources Inst., Chatham, UK, pp. 1–67. Gasse, F., Lédée, V., Massault, M., Fontes, J.-C., 1989. Water-level fluctuations of Lake Pilskaln, C.H., 2004. Seasonal and interannual particle export in an African rift valley Tanganyika in phase with oceanic changes during the last glaciation and lake: a 5-year record from Lake Malawi, southern East Africa. Limnology and deglaciation. Nature 342, 57–59. Oceanography 49, 964–977. Goddard, L., Graham, N.E., 1999. Importance of the Indian Ocean for simulating rainfall Pilskaln, C.H., Johnson, T.C., 1991. Seasonal signals in Lake Malawi sediments. anomalies over eastern and southern Africa. Journal of Geophysical Research 104, Limnology and Oceanography 36, 544–557. 19099–19116. Powers, L.A., Johnson, T.C., Werne, J.P., Castañeda, I.S., 2005. Large temperature Gregory, J.W., 1896. The Great Rift Valley. John Murray, London. variability in the southern African tropics since the Last Glacial Maximum. Harkin, D.A., 1960. The Rungwe Volcanics at the Northern End of Lake Nyasa. Printer, Geophysical Research Letters 32, L08706. doi:10.1029/2004GL022014. Tanzania Govt. Powers, L.A., Werner, J.B., Castañeda, I.S., Johnson, T.C., Hopmans, E.C., Sinninghe Damstéc, J.S., Johnson, T.C., Berke, M.A., 2009. A 150,000-year record of temperature from Lake Schouten, S., 2011. Organic geochemical records of environmental variability in Lake

Malawi, East Africa. Eos Trans. AGU 90 (52) Fall Meet. Suppl., Abstract PP14A-05. Malawi during the last 700 years, part I: The Tex86 Temperature Record. Palaeogeo- Johnson, T.C., Scholz, C.A., Talbot, M.R., Kelts, K., Ricketts, R., Ngobi, G., Beuning, K., graphy, Palaeoclimatology, Palaeoecology 303, 133–139 (this issue). Ssemmanda, I., McGill, J.A., 1996. Late Pleistocene desiccation of Lake Victoria and Reinthal, P., Cohen, A.S., Dettman, D.L., 2011. Fish fossils as paleo-indicators of rapid evolution of cichlid fishes. Science 273, 1091–1093. ichthyofauna composition and climatic change in Lake Malawi, Africa. Palaeogeo- Johnson, T.C., Brown, E.T., McManus, J., Barry, S., Barker, P., Gasse, F., 2002. A high- graphy, Palaeoclimatology, Palaeoecology 303, 126–132 (this issue). resolution paleoclimate record spanning the past 25,000 years in southern East Roberts, E.M., O'Connor, P.M., Gottfried, M.D., Stevens, N., Kapalimad, S., Ngasalad, S., Africa. Science 296, 113–116. 2004. Revised stratigraphy and age of the Red Sandstone Group in the Rukwa Rift Johnson, T.C., Brown, E.T., Shi, J., 2011. Biogenic silica deposition in Lake Malawi, East Basin, Tanzania. Cretaceous Research 25, 749–759. Africa over the past 150, 000 years, Palaeo-3. Palaeogeography, Palaeoclimatology, Rosendahl, B.R., 1987. Architecture of continental rifts with special reference to East Palaeoecology 303, 103–109 (this issue). Africa. In: Wetherill, G.W. (Ed.), Ann. Rev. Earth Planet. Sci., 15, pp. 445–503. Kingston, J.D., Deino, A.L., Edgar, R.K., Hill, A., 2007. Astronomically forced climate Rosendahl, B.R., Livingstone, D.A., 1983. Rift Lakes of East Africa: New Seismic Data and change in the Kenyan Rift Valley 2.7–2.55 Ma: implications for the evolution of Implications for Future Research. , pp. 14–19. early hominin ecosystems. Journal of Human Evolution 53, 487–503. Rossignol-Strick, M., 1985. Mediterranean Quaternary sapropels, an immediate Klerkx, J., Theunissen, K., Delvaux, D., 1998. Persistent fault controlled basin formation response of the African monsoon to variation of insolation. Palaeogeography, since the Proterozoic along the Western Branch of the East African Rift. Journal of Palaeoclimatology, Palaeoecology 49, 237–263. African Earth Sciences 26, 347–361. Schlische, R.W., 1995. Geometry and origin of fault-related folds in extensional settings. Kreuser, T., 1990. Depositional evolution of Permo-Triassic Karoo basins in Tanzania with AAPG Bulletin 79, 1661–1678. reference to their economic potential. Journal of African Earth Sciences 10, 151–167. Schnurrenberger, D., Russell, J., Kelts, K., 2003. Classification of lacustrine sediments Kutzbach, J.E., Street-Perrott, A., 1985. Milankovitch forcing of fluctuations in the level based on sedimentary components. Journal of Paleolimnology 29, 141–154. of tropical lakes from 18 to 0 kyr BP. Nature 317, 130–134. Scholz, C.A., 1995. Deltas of the Lake Malawi Rift, East Africa: seismic expression and Lewin, R., 1981. Lake bottoms linked with human origins. Science 211, 564–566. exploration implications. AAPG Bulletin 79, 1679–1697. Livingstone, D.A., 1965. Sedimentation and the history of water level change in Lake Scholz, C.A., Rosendahl, B.R., 1988. Low lake stands in Lakes Malawi and Tanganyika, Tanganyika. Limnology and Oceanography 10, 249–280. East Africa, delineated with multifold seismic data. Science 240, 1645–1648. Lyons, R.P., 2009. Stratigraphic and hydrologic responses to tropical climate variability: Scholz, C.A., Rosendahl, B.R., Scott, D.L., 1990. Development of coarse-grained facies in scientific drilling in Lake Malawi, East Africa. Syracuse University. 228 pp. lacustrine rift systems: examples from East Africa. Geology 18, 140–144. Lyons, R.P., Scholz, C.A., Buoniconti, M.R., Martin, M.R., 2011. Late Quaternary stratigraphic Scholz, C.A., Johnson, T.C., Cohen, A.S., King, J.W., Peck, J., Overpeck, J.T., Talbot, M.R., analysis of the Lake Malawi Rift, East Africa: an integration of drill-core and seismic- Brown, E.T., Kalindekafe, L., Amoako, P.Y.O., Lyons, R.P., Shanahan, T.M., Castaneda, I.S., reflection data. Palaeogeography, Palaeoclimatology, Palaeoecology 303, 20–37 Heil, C.W., Forman, S.L., McHargue, L.R., Beuning, K.R., Gomez, J., Pierson, J., 2007. East (this issue). African megadroughts between 135–75 kyr ago and bearing on early-modern human Lyons, R.P., Kroll, C.N., Scholz, C.A., 2010. An energy-balance hydrologic model for the origins. Proceedings of the National Academy of Sciences 104, 16416–16421. Lake Malawi Rift Basin, East Africa. Global and Planetary Change 75, 83–97. Scholz, C.A., Talbot, M.R., Brown, E.T., Lyons, R.P., 2011. Lithostratigraphy, Malawi Department of Surveys, 1983. National Atlas of Malawi, Blantyre. physical properties and organic matter variability in Lake Malawi Drillcore Marchant, R., Mumbi, C., Behera, S., Yamagata, T., 2007. The Indian Ocean dipole — the sediments over the past 145, 000 years. Palaeogeography, Palaeoclimatology, unsung driver of climatic variability in East Africa. Afr. J. Ecol. 45, 4–16. Palaeoecology 303, 38–50 (this issue). McDougall, I., Brown, F.H., Fleagle, J.G., 2005. Stratigraphic placement and age of Scott, D.L., Ng'ang'a, P., Johnson, T.C., Rosendahl, B.R., 1991. High-resolution acoustic modern humans from Kibish, Ethiopia. Nature 433, 733–736. character of Lake Malawi (Nyasa), east Africa and its relationship to sedimentary McGlue, M.M., Scholz, C.A., Karp, T., Lezzar, K.E., Ongodia, B., 2006. Facies architecture of processes. In: Anadon, P., Cabrera, L., Kelts, K. (Eds.), Lacustrine Facies Analysis. Sp. flexural margin lowstand delta deposits in Lake Edward, East African Rift: constraints Pub. of IAS, Blackwell, Oxford, pp. 129–146. from seismic reflection imaging. Journal of Sedimentary Research 76, 942–958. Scott, D.L., Braun, J., Etheridge, M.A., 1994. Dip analysis as a tool for estimating McHargue, L.R., Jull, T., Cohen, A., 2011. Measurement of 10Be from Lake Malawi (Africa) regional kinematics in extensional terranes. Journal of Structural Geology 16, drill core sediments and implications for geochronology. Palaeogeography, 393–401. Palaeoclimatology, Palaeoecology 303, 110–119 (this issue). Short, D.A., Mengel, J.G., Crowley, T.J., Hyde, W.T., North, G.R., 1991. Filtering of Meynadier, L., Valet, J.-P., Weeks, T., Shackleton, N.J., Hagee, V.L., 1992. Relative Milankovitch cycles by Earth's geography. Quaternary Research 35, 157–173. geomagnetic intensity of the field during the last 140 ka. Earth and Planetary Smith, B., Rose, J., 2002. Uganda's Albert graben due first serious exploration test. Oil & Science Letters 114, 39–57. Gas Journal 100, 42–48. Moernaut, J., Verschuren, D., Charlet, F., Kristen, I., Fagot, M., DeBatist, M., 2010. The Soreghan, M.J., Scholz, C.A., Wells, J.T., 1999. Coarse-grained deep-water sedimentation seismic–stratigraphic record of lake-level fluctuations in Lake Challa: hydrological along a border fault margin of Lake Malawi, Africa: seismic stratigraphic analysis. stability and change in equatorial East Africa over the last 140 kyr. Earth and Journal of Sedimentary Research 69, 832–846. Planetary Science Letters 290, 214–223. Specht, T.D., Rosendahl, B.R., 1989. Architecture of the Lake Malawi Rift, East Africa. Moore, J.E.S., 1903. The “Tanganyika Problem”. The Geographical Journal. The Royal Journal of African Earth Sciences 8, 355–382. Geographical Society (with the Institute of British Geographers). Stone, J.R., Westover, K.S., Cohen, A.S., 2011. Late Pleistocene paleohydrography and Morley, C.K., 1988. Variable extension in Lake Tanganyika. Tectonics 7, 785–801. diatom paleoecology of the central basin of Lake Malawi, Africa. Palaeogeography, Mortimer, E., Paton, D., Scholz, C.A., Strecker, M., Blisniuk, P., 2007. Orthogonal to Palaeoclimatology, Palaeoecology 303, 51–70 (this issue). oblique rifting: effect of rift basin orientation in the evolution of the North Basin, Stute, M., Talma, S., 1998. Glacial temperatures and moisture transport regimes Malawi Rift, East Africa. Basin Research 19, 393–407. reconstructed from noble gas and δ18O, Stampriet aquifer, Namibia. Isotope Ng'ang'a, P., 1993. Deltaic sedimentation in a lacustrine environment Lake Malawi, Techniques in the Study of Past and Current Environmental Changes in the Africa. Journal of African Earth Sciences 16, 253–264. Hydrosphere and the Atmosphere: Proceedings of Vienna Symposium 1997, IAEA, Oldham, R.D., 1922. The African Rift Valleys. The Geographical Journal 59, 151. Vienna, SM-349/53, pp. 307–328. Owen, B., Crossley, R., 1989. Rift structures and facies distributions in Lake Malawi. Suess, E., 1891. Die Brueche de ostlichen Afrikas, Denkschr. Akad, Wiss, Wien 553, Journal of African Earth Sciences 8, 415–427. 1–580. C.A. Scholz et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 3–19 19

Talbot, M., Jensen, N., Laerdal, T., Filippi, M., 2006. Geochemical responses to a major Verheyen, E., Salzburger, W., Snoeks, J., Meyer, A., 2003. Origin of the superflock of transgression in giant African Lakes. J. Paleolimnol. 35, 467–489. cichlid fishes from Lake Victoria, East Africa. Science 300, 325–329. Tiercelin, J.-J., Lezzar, K.E., 2002. A 300 million years history of rift lakes in Central and Wells, J.T., Scholz, C.A., Johnson, T.C., 1994. Highstand deltas of Lake Malawi, East Africa: East Africa: an updated broad review. In: Odada, E.O., Olago, D.O. (Eds.), The East environments of deposition and processes of sedimentation. In: Lomando, A.J., African Great Lakes: Limnology, Paleolimnology and Biodiversity. Kluwer, Schreiber, B.C., Harris, P.M. (Eds.), Lacustrine Reservoirs and Depositional Systems: Dordrecht, pp. 3–60. SEPM Core Workshop No. 19, pp. 1–35. Tiercelin, J.J., Soreghan, M., Cohen, A.S., Lezzar, K.E., Bouroullec, J.L., 1992. Sedimentation Weninger, B., Jöris, O., Danzeglocke, U., 2005. CalPal-2007. Cologne Radiocarbon in large rift lakes: example from the middle Pleistocene—modern deposits of the Calibration & Palaeoclimate Research Package. http://www.calpal.de/.accessed2005. Tanganyika Trough, East African Rift system. Bull. Centres Rech. Explor.-Prod. Elf Wheeler, W., Karson, J.A., 1989. Structure and kinematics of the Livingstone Mountains Aquitaine 16, 83–111. border fault zone, Nyasa (Malawi) Rift, southwestern Tanzania. Journal of African Tierney, J.E., Russell, J.M., Huang, Y., Sinninghe Damsté, J.S., Hopmans, E.C., Cohen, A.S., Earth Sciences 8, 393–413. 2008. Northern Hemisphere controls on Tropical Southeast Africa climate during Woltering, M., Johnson, T.C., Werne, J.P., Schouten, S., Sinninghe Damsté, J.S., 2011. Late

the past 60,000 years. Science 322, 252–255. Pleistocene temperature history of Southeast Africa: a Tex86 temperature record Trauth, M.H., Deino, A., Bergner, A.G.N., Strecker, M.R., 2003. Earth Planet. Sci. Lett. 206, from Lake Malawi. Palaeogeography, Palaeoclimatology, Palaeoecology 303, 297–313. 93–102 (this issue). Trauth, M.H., Maslin, M.A., Deino, A., Strecker, M.R., Bergner, A.G.N., Dühnforth, M., Yemane, K., Siegenthaler, C., Kelts, K., 1989. Lacustrine environment during Lower 2007. High- and low-latitude forcing of Plio-Pleistocene African climate and human Beaufort (Upper Permian) Karoo deposition in northern Malawi. Palaeogeography, evolution. Journal of Human Evolution 53, 475–486. Palaeoclimatology, Palaeoecology 70, 165–178.