Pb and Sr isotopes from an ice-core provides evidence for changing atmospheric conditions at the Sajama icecap, South America

Abstract

Measurements of Pb and Sr isotopes and Pb, Sr, Ba and Rb concentrations in ice-core samples from the Sajama icecap in Bolivia were made to investigate the changing environmental conditions in the region over the past 22 ky.. The Pb isotopic measurements indicate there has been a significant change in the 206 Pb/ 207 Pb ratio in the ice by 1700 AD which can be attributed to human activity. This change was also accompanied by increasing Pb/Ba ratios that reach ∼10 times natural values by the beginning of the 20 th century, confirming an increase of anthropogenic Pb levels. Sr and Rb concentrations are highly enhanced in 3 ky and 0.5 ky BP ice relative to the upper-crustal rock indicating a different origin for a significant proportion of the dust in these samples. Likely sources of this dust are dry lake beds that occur on the Altiplano as a result of changing climatic conditions. This dust adds to the background level of dust accumulating on the Sajama icecap.