Late Pleistocene to Holocene Multi-proxy Paleoenvironmental and Paleoclimatic Reconstruction of the Makgadikgadi Basin, Central Kalahari, Botswana

The Makgadikgadi Basin (MKB), in the central Kalahari Basin of northeastern Botswana, currently consists of a wide complex playa lake system, a relic of the Paleolake Makgadikgadi. Reconstructing the Quaternary depositional, environmental, and climatic history of the lacustrine-playa system has great significance for revealing the basin's evolution. However, its sedimentary record remains largely unexplored due to methodological challenges. In this study, four sediment cores, up to 1.6 m deep, were collected along a generally E-W transect from the western to central parts of the Ntwetwe pan, MKB.  Our multi-proxy record, including sedimentology, chronology, ostracod-based biostratigraphy, and clumped (∆₄₇) isotope geochemistry from these cores, reveals three complex hydroclimatic sequences that refine the environmental and climatic evolution of the MKB for the past 29 cal ka BP. The computed Bayesian age depth model and preliminary clumped isotope analysis on ostracod valves suggest the late Pleistocene (~29-19.5 cal ka BP) hypersaline-saline phase occurred under relatively low temperature conditions (∆₄₇-T = ~18.5-21°C), aligning with global glacial cooling and supporting interpretations of severe aridity in the Kalahari during the Last Glacial Maximum. The shift to a freshwater ostracod assemblage by ~5.2 cal ka BP partly corresponds to the termination of the African Humid Period (AHP), with a mean temperature (∆₄₇-T) of ~16.8°C. However, our record reveals significant complexity during the Late Holocene. The dominance of brackish water assemblage from ~4-1.6 cal ka BP suggests a prolonged transitional phase toward aridity, consistent with the broad trend of ITCZ retreat. Most notably, the late Holocene (~1.6-1 cal ka BP) assemblage, indicating a mix of brackish and freshwater taxa alongside extreme and warmer temperatures (∆₄₇-T = ~28.5°C). This implies a period of complex hydrological variability, potentially driven by increased summer rainfall variability or episodic flood inflow. Consequently, the Late Pleistocene and Middle Holocene data align with regional patterns, while the Late Holocene sequence particularly highlights the current extreme climate in the region, suggesting ostracod growth under extreme ephemeral playa lake conditions.