Decoupled hydroclimate dynamics in eastern Africa as revealed by the Sr isotope record of paleolake Chew Bahir

Reconstructing eastern African hydroclimate requires distinguishing changes in regional moisture supply from the local hydrological response of individual basins, yet these components are often difficult to separate in paleoclimate records. Here, we evaluate 87 Sr/ 86 Sr ratios as a tracer of water provenance and hydrological connectivity in the Chew Bahir basin (southern Ethiopian Rift) using a multi-core dataset of biogenic and authigenic materials spanning the past 40 ka. The results demonstrate that 87 Sr/ 86 Sr provides a robust proxy for basin-wide lake-water composition, largely independent of substrate type. Moreover, it reliably reflects changes in water provenance, including contributions from the Ethiopian Highlands. Comparison with elemental proxies (K content) reveals similar temporal variability in water provenance and local hydrological conditions during the late Pleistocene and the onset of the Holocene, followed by a progressive divergence beginning at ∼9.8 ka. While potassium (K) records increasing aridity that becomes particularly pronounced after ∼6 ka, 87 Sr/ 86 Sr indicates continued hydrological connectivity with the Ethiopian Highlands despite an increasingly negative local precipitation–evaporation (P–E) balance in the Chew Bahir lowlands. Sr isotope mass-balance sensitivity analysis shows that water quantity alone cannot reproduce the lowest Holocene 87 Sr/ 86 Sr values, requiring a shift in surface-water provenance and/or source-water composition. This decoupling likely reflects contrasting hydrological responses between the highlands and the lowlands during the warmer Holocene. Placed in a broader climatic context, the record indicates that eastern African hydroclimate was influenced by forcing mechanisms operating across different spatial and temporal scales. Local hydrological balance closely followed precessional variability, whereas the Sr isotope record showed a stronger association with glacial–interglacial climate boundary conditions. These findings demonstrate the potential of Sr isotopes for reconstructing water provenance and show that combining tracers of water provenance and local hydrological balance provides a process-based framework for disentangling the eastern African hydrological cycle.