Introduction

Key Scientific Objectives

• Our top scientific objective is to obtain 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.
  
  

Site Selection and Drilling Strategy

Seismic site survey data is in hand for all the proposed drill sites.


• The top priority site is situated in the central basin, southeast of the deepest part of the lake. It is here that seismic reflection site survey data indicate the best prospects for continuous cores of hemipelagic sediment. Such a depositional setting, in an area with no major stratigraphic hiatuses, offers the best chance to recover a continuous section of high-quality paleoclimate proxy records back through the Bruhnes-Matayama boundary. A core through this site will allow us to construct a detailed chronostratigraphy, and be a basis for correlations between other sites that may contain punctuated paleoclimate records.
• A site in the southern part of the lake (13ºS) will allow us to record a southern hemisphere tropical signal, as well as nearshore facies that developed during lake lowstands.
• We intend to recover a series of cores along a northern basin "offset drilling transect" that will allow us to extend the stratigraphic record far back into the Pliocene or perhaps Miocene. In addition, a northern basin site is most likely to recover a section of finely laminated or varved sediments.