Investigating climate changes in East Africa during MIS5 using GDGTs from Lake Challa

Abstract

Determining past continental climate variability is important for understanding Earth´s climate system, testing climate models and projections of anthropogenic climate change, and developing an environmental context for human evolution. Here I present a precipitation and temperature reconstruction for Eastern Equatorial Africa during the period 140 to 70 ka based on the relative abundances of lipid biomarkers (GDGTs) preserved in Lake Challa. This study confirms the occurrence of extended periods of severe aridity in tropical African during the last interglacial, termed African Megadroughts. The warmest temperatures during this interval occurred around 135 ka, and temperature recorded at Lake Challa shows similar trend to marine and ice core isotope records. Further, this study examines the presence of the so called H-Shaped GDGTs or GMGTs in Lake Challa and other East African lakes. In the East African lakes, there is a general trend of greater relative abundance of GMGTs in lakes with higher mean annual air temperature (MAAT). This thesis presents three new indices (Ratio 1, Ratio 2 and IRbrGMGT), based on the relative abundances of branched GMGTs in East African lake sediments, which show a strong correlation to MAAT. Using these indices to estimate past temperature changes at Lake Challa produces variable results.