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

Abstract

Paleoclimate investigations of the peat deposits in the Nilgiri Plateau, an important paleoclimate archive of India, are mainly restricted to the carbon isotope composition ((δ13C) 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 (δDC28 and δ13CC28, respectively) and demonstrate that the peatland leaf wax hydrogen isotopes provide a sensitive record of past hydrology. The decoupling of δ13CC28 and δD of vegetation-corrected rain during the Holocene indicate that δD of the leaf wax compounds mainly respond to past hydrological variability whereas δ13C variations might reflect the temperature-controlled variability of C3 and C4 vegetation. Conforming with the other paleoclimate records from the region, the δDC28 variations showed a reducing precipitation trend since the early Holocene. However, a large amplitude of reconstructed δD of rain (~44‰) during the Holocene indicated changes in the moisture source and trajectory could be an additional factor contributing to the orbital-scale δD variability of proxies from the Indian region.