Press Release: August 31, 2007 - African climate change and early humans

Introduction

The Lake Malawi Drilling Project recently completed a scientific drilling campaign on Lake Malawi, recovering a series of continuous sediment cores for paleoclimate studies. Lake Malawi is situated at the southern end of the East African Rift Valley, and has long been recognized as an outstanding laboratory and archive for the study of tropical paleoclimatology, extensional tectonics, and evolutionary biology. Along with Lake Tanganyika, Lake Malawi holds the promise of a high-resolution paleoclimate record of unparalleled antiquity in the continental tropics. Lake Malawi is one of the world's largest, deepest (maximum water depth of 700 m), and oldest lakes (>7ma?), and is the largest lake in the southern hemisphere (9º-14ºS) after Lake Tanganyika.

Bathymetric map of Lake Malawi with locations of two 2005 drill sites.  Small
images to right are seismic reflection profiles acquired over the two core sites.
Bathymetric contour interval is 100 m.  Drilling operations mobilized from
Chipoka, and the project was resupplied from the ports of Nkhata Bay and
Chilumba. 
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The dynamically-positioned drilling barge Viphya, departing port.  Lake Malawi is 
one of the world's largest and deepest lakes, and along with Lake Tanganyika 
contains more than 80% of the surface freshwater on the African continent.   
New drill core evidence shows that the 700 m-deep lake was reduced by more 
than 500 m prior to 75,000 years ago, indicating periods of severe aridity. 
Image courtesy of M.R. Talbot, Department of Earth Sciences, University of Bergen.
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Key Scientific Objectives

* Our top scientific objective is to chronicle a continuous, high-resolution (annual-decadal) record of past climates in the continental tropics over the Bruhnes epoch, and to determine if tropical African climate responded to changes in low-latitude precessional insolation (23-19 kyr) or to high-latitude ice volume (100 kyr and 41 kyr) forcing, in the last part of the Pleistocene.

* We will assess the phasing of lake level changes in Lake Malawi during this time,and determine if Malawi responded to Southern Hemisphere insolation forcing,as is suggested in late-Pleistocene and Holocene records.

* From the high-resolution Lake Malawi drill core records we will determine if high-frequency climate variations (analogous to Dansgaard-Oeschger or Heinrich events) are superimposed on glacial-interglacial timescale variations in the form of wet/dry cycles.

* The continuous Lake Malawi record will allow us to establish how interannual African climate variability has changed in association with longer-term climate variations.

* We will determine the long-term evolution of tropical East African climate, and assess the postulated shift in the dominant Milankovitch frequency, from the present day 100 kyr dominance to 41 kyr dominance to 21 kyr dominance, as is observed in the marine record.

The project will profoundly impact other fields, including extensional basin evolution and neotectonics, evolutionary biology, and the environmental background to human origins.

 
Aerial view of the 160' drilling barge on Lake Malawi in 2005, where 26 members 
of the drill team, science team, and ships crew lived for six weeks.
Image courtesy of I. Castaneda, University of Minnesota. 
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Members of the science team await the next sample on the crowded rig floor. 
Image courtesy of C.A. Scholz, Department of Earth Sciences, Syracuse University. 
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Finely-laminated, diatom-rich silty-clay, deposited during lake highstands.
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Image courtesy of the Lake Malawi Drilling Project.

Grey, carbonate-rich mottled clay deposited during severe lowstands and megadroughts.
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Image courtesy of the Lake Malawi Drilling Project.

Scientific Drilling Completed on Lake Malawi – March 2005

• Scientific drilling on Lake Malawi was recently completed, following two months of extraordinary efforts on the part of the field team.

• More than 623 m of core was recovered at two sites (92% recovery), and in seven holes.   We triple-cored our high-resolution site, which extends back ~100kyr, double cored our deep site covering the past ~200 kyr, and single-cored the deep site to 380 m, perhaps 1.5 million years in age at the bottom. 

• Sample material recovered included a variety of laminated and homogenous algal-rich mud (dominantly clay) in zones of alternating dry-dense/ and soft, high-water content material; cemented siltstone; volcanic ash horizons; and fine-grained well-sorted sands at the base of holes at both sites.

• The successful outcome of this very difficult and risky drilling project was accomplished through tight teamwork and the extraordinary efforts of the scientific team, General Contractor, University of Rhode Island, the ADPS drilling barge Captain and marine crew, the Seacore drill crew, DOSECC field rep, the Malawi Geological Survey, Lengeek Vessel Engineering marine architects and engineers, and the many project support staff, including the caterers and onshore logistics support group, Malawi Lake Services and the crews of the three support vessels.  In all more than 80 individuals actively contributed to the operational phase of the program.

• We extend a special “thank you” to the government and people of Malawi, for permission to conduct this research.

Science team member briefs a group of secondary school students on rig operations.  
Image courtesy of C.A. Scholz, Department of Earth Sciences, Syracuse University 
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Science team member shows an example of a lake sediment core to a group of  
Malawian secondary school students.  
Image courtesy of I. Castaneda, University of Minnesota. 
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Waterspout near drilling barge Viphya at conclusion of drilling operation, along with 
hatch of like flies.
Image courtesy of C.A. Scholz, Department of Earth Sciences, Syracuse, University.
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