Browsing by Autor "C.F. Boutron"

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    Changes in the occurrence of heavy metals in the tropical atmosphere during the past 22,000 years as recorded in Bolivian ice core
    (Springer Science+Business Media, 2003) Sungmin Hong; J. K. Park; Lonnie G. Thompson; C.F. Boutron; Christophe Ferrari; Bruno Franco; Laurence Maurice
    Nine sections from the Sajama ice core recovered from the summit of an extinct Andean volcano in Bolivia were analysed for various heavy metals to assess anthropogenic changes in the tropical upper troposphere over South America. These samples include two sections dating from 14100 to 19200 years BP, corresponding to the Last Glacial Stage (LGS), one section dating from 2800 years BP (the late Holocene), and six sections dating from AD 790 to 1988. The preliminary data, combined with data reported elsewhere, demonstrate that the heavy metal concentrations since the late Holocene are higher than in the period from the LGS to the early Holocene. The enrichment factors calculated by normalizing for crustal abundance using the metal/Al ratio in the mean upper continental crust indicate that a significant input of heavy metals attributed to anthropogenic contributions has occurred since the beginning of the 19th century for Pb and from the last century for Cd, Cu, and Zn.
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    Pb and Sr isotopes from an ice-core provides evidence for changing atmospheric conditions at the Sajama icecap, South America
    (Springer Science+Business Media, 2003) K. J.R. Roman; Sang-Bum Hong; G. Bulion; Laurie J. Burn; C.F. Boutron; Christophe Ferrari; Lonnie G. Thompson; Laurence Maurice; Bernard Francou
    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.