An assessment of natural and anthropogenic influences on atmospheric fluoride deposition in central Tibetan Plateau during 1951–2008 A.D. using the Zangser Kangri ice core

Abstract

Fluoride contamination poses great threat to ecosystems and human health, and has caused widespread concern. Large gaps in knowledge still exist regarding the distribution, sources of fluoride and the influence of atmospheric transport on its dispersal, particularly at high altitudes because of a lack of data due to geographic constraints. Tibetan ice cores are a natural archive for chemical depositions from the atmosphere, and can be used to reconstruct past variations of atmospheric fluoride in remote environment. In this study, we investigate the trends, sources and controlling factor of atmospheric fluoride during 1951–2008 AD using high-resolution chemical deposition records derived from the Zangser Kangri (ZK) ice core, central Tibetan Plateau (TP). Our data shows that the concentration peaks of F− coincide with those of typical crustal species (e.g., Ca2+, Mg2+), indicating that variation of F− in the ZK ice core is largely driven by dust activities, and dust emission from soil is the primarily natural source of F−. F− sources and transport pathways were further investigated by using the empirical orthogonal function (EOF) analysis, excess (Ex) concentration, in combination with airmass backward trajectory analysis. Ex F− in the ZK ice core record could be attributed to anthropogenic emissions, and its significant increase since 1990 was likely related to increased industrial and agricultural activities in the northwestern Indian peninsula. In addition, the strength of the South Asian monsoon is also a key factor in the transport of anthropogenic fluoride to the ZK glacier. This study provides valuable data for understanding the past atmospheric fluoride budget in the central TP.