25,000 YEARS OF MOISTURE VARIABILITY BASED ON DIATOM CONDUCTIVITY RECONSTRUCTION AT LAKE NAKURU, CENTRAL KENYA RIFT

Lake Nakuru in Kenya, located south of the equator on the East African Plateau, is one of many modern, shallow saline lakes in the East African Rift System (EARS). Despite modern saline lake conditions throughout the EARS, during the African Humid Period (AHP) 15,000 to 5,000 years ago, many of these lakes were instead deep, freshwater lakes due to a change in Earth’s precession causing increased moisture throughout the region. This sensitive reaction to even moderate moisture changes classifies these lakes as “amplifier lakes,” but beyond the existence of such lakes during the AHP, little is known about them, particularly in relation to their transitional speed in and out of wet phases and their internal stability/instability throughout the AHP. To address these uncertainties, we present a high-resolution conductivity record for the last 25,000 years based on diatom identification and the application of a North/East African diatom transfer function. 153 samples were retrieved from the upper 8 m of two duplicate, 17 m drill cores taken by the Lake Naivasha Coring Project in 2004. The chronology of the cores is based on 11 AMS ¹⁴C ages measured on charcoal and 2 ⁴⁰Ar/³⁹Ar ages from separate tephra layers. This record will be compared with other proxy records from the cores to reconstruct moisture changes over the past 25,000 years. Beyond providing a new high-resolution record of paleolimnological changes at Lake Nakuru, this study will contribute to knowledge regarding the impact of moisture changes both during and along the transitions of dry-wet-dry cycles on the amplifier lake systems of the EARS. Furthermore, the new record will resolve a regional data gap of the synchronicity of lake level changes and its associated impact on past humans and their migrations.