Moisture availability and productivity at Lake Nakuru, Kenya leading into the African Humid Period

Lake Nakuru, a lake with the one of the highest primary production rates in the world, is an eastern African soda lake that contains important records of environmental change since the Late Pleistocene. As a closed basin at one of the highest points of the East African Rift System, Lake Nakuru shows significant changes in lake level from annual to millennial timescales even during times of minor precipitation change. Various studies have focused on Lake Nakuru in part due to abundant archaeological sites within the surrounding basin. Despite research attention focused on Nakuru's record related to rift-wide environmental reconstructions across the East African Rift System, little focus has been made on its own unique sedimentary record. Here we present a new multi-proxy record from the upper ∼11.5 m of two duplicate 17-m drill cores from Lake Nakuru. Using lithological, diatom, total nitrogen, total carbon, total organic carbon, and micro-x-ray fluorescence data with a multi-annual to decadal time resolution, we provide insights into lake depth and hydroclimatic changes of the past 35,000 years. The available age model indicates recurring anoxic phases based on μ-XRF and lithological data coeval with low diatom species richness and abundant Thalassiosira rudolfi ∼35, ∼25.5 to 24.5, and 19.5 to 17.5 ka. T. rudolfi therefore acts as an indicator of highly productive and/or deeper waters with limited mixing rather than of higher conductivity/pH, strictly due to increased evaporation within the basin. This indicates the challenge of T. rudolfi's use within highly alkaline soda lakes like Lake Nakuru. Other lake phases evident through this record include dry, shallow conditions from 24.5 to 19.5 ka, alkaline conditions from 17.5 to 15.4 ka, and a variable deepening phase from 15.4 to 13.6 ka followed by a more stable deep phase from 13.6 to 12.6 ka. We propose that hydroclimate changes at Lake Nakuru during this time, including presumed wet, anoxic phases, may be related to high and low latitude teleconnections in sea surface temperatures and moisture availability over the Late Pleistocene.