Holocene precipitation hydrogen isotopic values on Nilgiri Plateau (southern India) suggest a combined effect of precipitation amount and transport paths

Paleoclimate investigations of the peat deposits in the Nilgiri Plateau, an important paleoclimate archive of India, are mainly restricted to the carbon isotope composition ((delta C-13) of plant-derived materials and pollen studies. However, it is unclear whether these proxies reflect past variability in temperature or hydrology. Here, we report the hydrogen and carbon isotopic variability of n-alkanoic acid of chain length 28 (delta D-C28 and delta C-13(C28), respectively) and demonstrate that the peatland leaf wax hydrogen isotopes provide a sensitive record of past hydrology. The decoupling of delta C-13(C28) and delta D of vegetation-corrected rain during the Holocene indicate that delta D of the leaf wax compounds mainly respond to past hydrological variability whereas delta C-13 variations might reflect the temperature-controlled variability of C3 and C4 vegetation. Conforming with the other paleoclimate records from the region, the delta D-C28 variations showed a reducing precipitation trend since the early Holocene. However, a large amplitude of reconstructed dD of rain (similar to 44%) during the Holocene indicated changes in the moisture source and trajectory could be an additional factor contributing to the orbital-scale dD variability of proxies from the Indian region.