Late Quaternary relative humidity changes from Mt. Kilimanjaro, based on a coupled 2H-18O biomarker paleohygrometer approach

The combined usage of δ2Hn-alkanes and δ18Osugars allowed us to reconstruct δ2H/δ18O of source water utilized by plants in the study area, which is directly linked to local precipitation. The results of this reconstruction caution against a straightforward interpretation of δ2Hleaf-wax and δ18Osugars records as proxies for isotopic composition of local precipitation because variable and primarily RH-dependent isotopic evaporative enrichment of leaf water can mask changes of δ2Hprec/δ18Oprec in the past. The biomarker-based δ2H/δ18Osource-water records derived for the Maundi site revealed a discernible link with the reconstructed RHD record; lower RHD values were generally observed during periods characterized by more negative δ2H/δ18Osource-water values, indicating a reverse relationship with the expected precipitation amount. This indicates that the empirical relationship between amount of rainfall and its isotopic composition, observed nowadays on monthly timescale in the East African region, might not be valid on millennial time scale.