Rare Earth Elements As Geochemical Tracers of Paleoenvironments in Tropical Montane Peat, Western Ghats, India

Mineral dust, especially from the Middle-East, has been known to affect monsoon circulation in India, a country whose economy is heavily contingent on the timely arrival of the monsoon. Reconstruction of dust circulation in the past and its relationship to the monsoon has never been attempted in India although inorganic geochemical proxies from peat have been used in various parts of the world. Finding suitable peat archives to use inorganic geochemical proxies in the largely tropical and sub-tropical Indian environments is a challenge. Montane peat in the Sandynallah valley in the southern Western Ghats, peninsular India, is one of the oldest in the world (>50 ka) and has been shown to record continuous climatic and vegetation changes of at least 30,000 yrs of the past. We explored the usefulness of inorganic geochemical proxies for the first time here to reconstruct dust circulation. Inorganic geochemical analysis was carried out on acid digested peat samples analyzed using Inductively Coupled Plasma-Mass Spectrometry and Optical Emission Spectroscopy at EcoLab, Toulouse. We see that the major (e.g., Al, Fe, Mn, K, Na, Mg, Ca) and commonly used trace (Cu, Zn, Pb) elements do not show many significant trends for paleoenvironmental interpretation. Preliminary analyses indicate that lithogenic elements Ti and Zr have high correlation through time. In this study, we used scaled Rare Earth Element (REE) concentrations and Zr as a reference to calculate enrichment factors (REE EFs) and found that the Lanthanide series showed promise for identifying potential sources of atmospheric dust. We find strong enrichments in some sections of the last glacial (the strongest enrichment is observed at ~30 ka), indicative of environmental conditions that supported increased dust input, possibly related to the higher dust circulations in the glacial periods as evidenced by ice core studies. We report for the first time inorganic geochemical proxies from peat in India and propose that the lanthanide group could be established as a useful proxy for atmospheric dust sources in tropical montane peat.