High resolution multi-proxy analyses document Mid to Late-Holocene environmental change in arid Marsabit County, northern Kenya, East Africa

Abstract

Pastoralism was first established in East Africa in the arid lowlands adjacent to Lake Turkana, northern Kenya, ~4800 years ago. Currently, there are limited palaeoecological records documenting the environmental conditions at the time of this transition, especially for areas east of Lake Turkana. To address this knowledge gap, sedimentary cores were recovered from the Chalbi Basin, Marsabit County, Kenya. These document a detailed environmental history of this arid region derived from evidence from pollen, plant and insect macrofossils, chemical analysis and diatoms, since the end of the Mid-Holocene ~5200 years BP. The high resolution analysis indicates the presence of variable freshwater and saline lake conditions later transitioning to a wetland. Diatom composition from the basin indicates that the water body varied widely in conductivity between ~200 and >20,000 μS cm⁻¹ and 7.5–11.5 pH. The palaeolake and wetlands occasionally exceeded diatom tolerance limits and may have intermittently desiccated. The microfossil record shows that there was a broad trend towards more arid conditions at the end of the Mid-Holocene after ~4650 BP, interrupted by short intermittent wetter conditions, reflecting changes across the wider ecosystem. During the past 3300 years, the wetland changed from more terrestrial conditions with relatively abundant gallery tree taxa (Acalypha, Syzygium and Phoenix) to a Cyperaceae-dominated margin, and more consistent shallow water conditions. Fires were infrequent at the site, with the largest charcoal concentrations observed at 310 cm (3100 cal BP); thereafter, the magnitude of peak charcoal decreased and signs of fire are absent in the most recent sediments.