Elsevier

Geochimica et Cosmochimica Acta

Volume 67, Issue 4, 15 February 2003, Pages 693-708
Geochimica et Cosmochimica Acta

One hundred fifty–year record of lead isotopes in Antarctic snow from Coats Land

https://doi.org/10.1016/S0016-7037(02)01136-5Get rights and content

Abstract

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period ∼1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 m and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Pb concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1.208 for 206Pb/207Pb ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Pb reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the ∼1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica.

Introduction

During the last decades, various investigations have confirmed the advantages of the use of Pb isotope systematics to probe the changing anthropogenic vs. natural origins of this toxic heavy metal in well-preserved snow and ice archives of atmospheric constituents (Rosman, 2001). Most investigations, however, have been devoted to the Greenland icecap (see, e.g., Rosman et al 1993, Rosman et al 1994a, Rosman et al 1997, Rosman et al 1998a, Boyle et al 1994, Sherrell et al 2000; high-altitude alpine regions have been investigated more recently (Rosman et al., 2000).

On the other hand, there are very few reliable measurements of Pb isotopes in remote Antarctic snow and ice. The first were carried out by Rosman and coworkers, who determined Pb isotopes in four surface snow blocks, collected in 1983 to 1984 along a transect from the coastal station Dumont d’Urville to a site 433 km inland and at the geographic South Pole, and in a single sample of ancient ice dated from 7.5 kyr BP obtained at Dome C (72°39′S, 124°10′E) (Rosman et al., 1994b). The results supported earlier geochemical evidence of Pb pollution (Boutron and Patterson, 1987) and pointed to South America as a likely source of the anthropogenic Pb in Antarctic snow dated from the 1980s.

A second series of measurements by Rosman and coworkers provided preliminary evidence of Pb isotope variations in selected snow/ice cores DE08 (66°43′S, 113°12′E) and DSS (66°46′S, 112°48′E) drilled at the sites on Law Dome (Rosman et al., 1998b). Nine sections were dated 1843 to 1940, one was dated from 946 BC, and the last was ice dated from at least ∼110 kyr. These analyses proved extremely demanding because of the low Pb concentrations encountered (∼0.1 pg/g). Despite the fact that sophisticated procedures were used to decontaminate the core sections (Candelone et al., 1994) and highly developed thermal ionization mass spectrometry (TIMS) procedures (Chisholm et al., 1995) were employed, there was evidence that a number of samples were contaminated (Rosman et al., 1998b). Also at these concentrations, both the accuracy of the concentrations and the isotopic composition were highly sensitive to the value used to correct for Pb contamination introduced during the decontamination process. This problem has been subsequently addressed by Vallelonga et al. (2002), resulting in improved accuracy of the data at these low concentrations.

Rosman et al. (1999) have also reported measurements of Pb isotopes on 22.6-kyr-old ice from Dome C, i.e., ice dated from the cold terminal stage of the last ice age (Last Glacial Maximum). This Pb is less radiogenic than that found in Holocene ice but is similar to the pelagic sediments found near southern South America and volcanic rocks from Central Chile (Rosman et al., 1999).

Recently, Matsumoto and Hinkley (2001) reported Pb isotopes and heavy metal concentrations in nine ice samples dated between 1.3 kyr and 73 kyr BP from Taylor Dome (77°48′S, 158°43′E; 2374-m altitude), a near coastal Antarctic site at the western edge of the Ross Sea. They found that rock and soil dust and sea salt accounted for only a few percent of Pb present in most samples and that the Pb deposition rate to the ice was approximately matched by the output rate to the atmosphere by quiescent (nonexplosive) degassing of volcanoes worldwide. The isotopic composition of Pb in the ice was found to be similar to those of a suite of ocean island volcanoes, mostly in the Southern Hemisphere. Although pollution issues were not addressed, the depositional fluxes of metals were considered to be appropriate in modern times.

We present here comprehensive data on Pb isotopes, Pb and Ba in Antarctic snow dated 1840 to 1990. They were obtained by analyzing pit and core samples collected at a remote location in Coats Land (Planchon et al., 2001), Antarctica. Pb isotopes, Pb, and Ba were determined by TIMS, taking advantage of improvements reported by Vallelonga et al. (2002). These new data provide a clearer picture of the changing occurrence of natural and anthropogenic Pb at one of the most remote locations on our planet.

Section snippets

Sampling locations

The main sampling location (Site A) was at 77°34′S, 25°22′W in Coats Land, Antarctica. This site is of interest because it is situated in a sector of Antarctica that faces the southern Atlantic Ocean (Fig. 1a). It is adjacent to the Weddell Sea. It was then ideally situated to assess the changing natural and anthropogenic Pb inputs from South America and various subantarctic islands of the Atlantic Ocean. The site (Fig. 1b) was at 1420 m altitude, 200 km from the nearest permanent scientific

Results and discussion

Table 1 gives the results for the two snow pits (years 1920 to 1990). Table 2 shows the data for the snow core (years 1834 to 1920). These data represent the most comprehensive record of the impact of anthropogenic Pb on Antarctica that has previously been reported.

Conclusion

We have presented here the first comprehensive data on changes in Pb isotopic ratios in Antarctic snow since the mid-19th century obtained from a site in the Atlantic sector (Weddell Sea) in Antarctica. It will now be interesting to obtain similar time series from other selected sites in Antarctica, especially in the Ross Sea sector, which is another important location of deep-water formation of the World Ocean, and in the Indian Ocean sector that faces Australia. Also, it will be necessary to

Acknowledgements

This research was supported in France by the Institut Universitaire de France, the Ministère de l’Environnement et de l’Aménagement du Territoire, the Agence de l’Environnement et de la Maîtrise de l’Energie, the Institut National des Sciences de l’Univers, and the University Joseph Fourier of Grenoble. In Australia, it was supported by a research grants from the Australian Research Council (A39938047) and the Antarctic Science Advisory Committee (No. 1092) in the Glaciology Sections. In the

References (60)

  • T.K. Hinkley et al.

    Metal emissions from Kilauea, and a suggested revision of the estimated worldwide metal output by quiescent degassing of volcanoes

    Earth Planet. Sci. Lett

    (1999)
  • M.J. Hole et al.

    Trace-element and isotopic characteristic of small-degree melts of the asthenosphereEvidence from the alkalic basalts of the Antarctic Peninsula

    Chem. Geol

    (1993)
  • A. Matsumoto et al.

    Trace metal suites in Antarctic pre-industrial ice are consistent with emissions from quiescent degassing of volcanoes worldwide

    Earth Planet. Sci. Lett

    (2001)
  • A. Ng et al.

    Natural concentrations of lead in ancient Arctic and Antarctic ice

    Geochim. Cosmochim. Acta

    (1981)
  • J.O. Nriagu

    The rise and fall of leaded gasoline

    Sci. Total Environ

    (1990)
  • C.C. Patterson et al.

    Review of data on eolian fluxes of industrial and natural lead to lands and seas in remote regions on a global scale

    Mar. Chem

    (1987)
  • F.A.M. Planchon et al.

    Ultrasensitive determination of heavy metals at the sub-picogram per gram level in ultraclean Antarctic snow samples by Inductively Coupled Plasma Sector Field Mass Spectrometry

    Anal. Chim. Acta

    (2001)
  • A. Rocholl et al.

    Geochemical evolution of rift magmas by progressive tapping of a stratified mantle source beneath the Ross Sea Rift, Northern Victoria Land

    Earth Planet. Sci. Lett

    (1995)
  • K.J.R. Rosman

    Natural isotopic variations in lead in polar snow and ice as indicators of source regions

  • K.J.R. Rosman et al.

    Isotopic evidence to account for changes in the concentrations of lead in Greenland snow between 1960 and 1988

    Geochim. Cosmochim. Acta

    (1994)
  • K.J.R. Rosman et al.

    Seasonal variations in the origin of lead in snow at Dye 3, Greenland

    Earth Planet. Sci. Lett

    (1998)
  • K.J.R. Rosman et al.

    A two century record of lead isotopes in high altitude alpine snow and ice

    Earth Planet. Sci. Lett

    (2000)
  • E.D. Suttie et al.

    Preconcentration method for electrothermal atomic absorption spectrometric analysis for heavy metals in Antarctic snow at sub-ng/kg

    Anal. Chim. Acta

    (1992)
  • E.D. Suttie et al.

    The local deposition of heavy metal emissions from point sources in Antarctica

    Atmos. Environ

    (1993)
  • P. Vallelonga et al.

    Recent advances in measurement of Pb isotopes in Polar ice and snow at sub-picogram per gram concentrations using thermal ionisation mass spectrometry

    Anal. Chim. Acta

    (2002)
  • E.W. Wolff et al.

    Antarctic snow record of cadmium, copper and zinc content during the twentieth century

    Atmos. Environ

    (1999)
  • K.K. Andersen et al.

    Atmospheric dust under glacial and interglacial conditions

    Geophys. Res. Lett

    (1998)
  • C. Barbante et al.

    Recent decrease in the lead concentration of the Antarctic snow

    Int. J. Environ. Anal. Chem

    (1997)
  • C. Barbante et al.

    Sources and origins of aerosols reaching Antarctica as revealed by lead concentration profiles in shallow snow

    Ann. Glaciol

    (1998)
  • I. Basile et al.

    Patagonian origin of glacial dust deposited in East Antarctica (Vostok and Dome C) during glacial stages 2, 4 and 6

    Earth Planet. Sci. Lett

    (1997)
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