Changes in atmospheric Pb for last 800 years recorded in the remote high altitude Mt. Everest ice core: the isotopic evidences for Pb enrichment over the Himalayas responding to anthropogenic emissio

Abstract

1. Introduction During recent decades, the snow and ice cores recovered from Polar regions and high altitude mountain glaciers in the mi latitude have revealed the changes in atmospheric Pb responding to anthropogenic emissions. Recetly, reliable measurements of Pb isotope ratios in snow and ice cores recovered from Polar Regions and European Alps provided identification of natural and anthropogenic sources for atmospheric Pb over corresponding regions. In Asian glaciers, however, limited snow and ice core records of Pb are available despite Asia becomes the largest emission source for worldwide atmospheric Pb. the only ice core record of Pb long enough to allow comparison between present and pre industrial period is presented in our previous research which shows the enrichment of Pb due to the leaded gasoline consumption, fossil fuel combustion, and non-ferrous metal production in India from the 1970s. In this research, we present the records of Pb isotope ratios in the high altitude Mt. Everest ice core. they are the first records of historical changes in Pb isotope ratios recovered from Asian mountain glaciers. These records provide isotopic evidences fo natural and anthropogenic for atmospheric Pb over last 800 years.

2. Sampling and analysis In 2002, two ice cores - 108.8 (ER-a) and 95.8 m (ER-b) in length, respectively - were recovered from East Rongbuk glaciers located on the northeast side of Mt. Everest. The ER-a ice core was dated primarily by counting annual cycles of del 18 O and ions back to 1594 AD at 98m and calibrated with large volcanic events through Bi peaks. Below 98m, flow model was used because annual cycles were absent due to layer thinning. The Pb isotope ratios in the ice cores were measured using thermal Ionization Mass Spectrometer. The analytical procedures were described in Vallelonga et al. (2002).

3. Result and discussion The Pb isotope ratios are relatively constant from 1205 AD to the 1960s ranged from 1.191 (2.483) to 1.214