Lead isotopes in snow and ice as an indicator of past changes to the Antarctic environment
Entry ID:
ASAC_966
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Summary
Abstract:
From the abstracts of the referenced papers: Techniques for Pb measurements have reached the stage where Antarctic ice with sub-picogram per gram concentrations can be reliably analysed for isotopic composition. Here, particular attention has been given to measuring the quantity of Pb added during the decontamination and sample storage stages of the sample preparation process because of their ... impact on accuracy at low concentrations. These stages, including the use of a stainless steel chisel for the decontamination, contributed ~5.2pg to the total sample analysed, amounting to a concentration increase of ~13fg per gram, which is significantly less than expected. Consequently the corrections to the isotopic ratios and concentration were also smaller. Other contributions to the blank, such as Pb fallout onto critical working areas in the HEPA-filtered laboratories, were also relatively small as was the amount of Pb leached from preconditioned perfluoroalkoxy (PFA) beakers during sample processing. The ion source contributed typically 89 plus or minus 19 fg to the blank. Although this was relatively large, its influence depended upon the amount of Pb available for analysis and it had the greatest impact when small volumes of samples with a very low concentration were analysed. A 15 months investigation of the leaching characteristics of Pb from a low-density polyethylene (LDPE) samplestorage bottle showed 11 fg per cm per cm per day was released immediately following the initial 2 months cleaning process, but this decreased to immeasurable values after a further 3 months of cleaning.
Lead isotopic compositions and Pb and Ba concentrations have been measured in ice cores from Law Dome, East Antarctica, covering the past 6500 years. 'Natural' background concentrations of Pb (~0.4 pg/g) and Ba (~1.3 pg/g) are observed until 1884 AD, after which increased Pb concentrations and lowered 206Pb/207Pb ratios indicate the influence of anthropogenic Pb. The isotopic composition of 'natural' Pb varies within the range 206Pb/207Pb=1.20-1.25 and 208Pb/207Pb=2.46-2.50, with an average rock and soil dust Pb contribution of 8-12%. A major pollution event is observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration four-fold and changing 206Pb/207Pb ratios in the ice to ~1.12. Based on Pb isotopic systematics and Pb emission statistics, this is attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia. Anthropogenic Pb inputs are at their greatest from ~1900 to ~1910 and from ~1960 to ~1980. During the 20th Century, Ba concentrations are consistently higher than 'natural' levels and are attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation.
The fields in this dataset are:
Veneer
Mass
Pb
Concentration
206Pb/207Pb 
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Description:
Download point for the data
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Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
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N: -66.0
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S: -66.0
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E: 110.0
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W: 110.0
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Temporal Coverage
Start Date:
1996-09-30
Stop Date:
1998-03-31
Paleo Temporal Coverage
Paleo Start Date:
7500 YBP
Paleo Stop Date:
0 YBP
Chrono Unit:
Quality
Values provided in temporal coverage are approximate only.
Access Constraints
The data are available for download from the url given below.
PDF copies of the referenced papers are also included in the download file.
Data Set Progress
COMPLETE
Distribution
Distribution Media:
HTTP
Distribution Size:
5851 kb
Distribution Format:
excel, word, pdf
Fees:
free
Personnel
Role:
INVESTIGATOR
Role:
TECHNICAL CONTACT
Role:
DIF AUTHOR
Phone:
+61 8 9266 7542
Fax:
+61 8 9266 2377
Email:
k.rosman at curtin.edu.au
Contact Address:
Department of Applied Physics
GPO Box U 1987
Curtin University
City:
Perth
Province or State:
Western Australia
Postal Code:
6845
Country:
Australia
Publications/References
Vallelonga, P., Van de Velde, K., Candelone, J.P., Ly, C., Rosman, K.J.R., Boutron, C.F., Morgan, V.I., and Mackey, D.J. (2002) Recent advances in measurement of Pb isotopes in polar ice and snow at sub-picogram per gram concentrations using thermal ionisation mass spectrometry. Analytica Chimica Acta, 453, 1-12.
Vallelonga, P., Van de Velde, K., Candelone, J.P., Morgan, V.I., Boutron, C.F. and Rosman, K.J.R. (2002) The lead pollution history of Law Dome, Antarctica, from isotopic measurements on ice cores: 1500 AD to 1989 AD. Earth Planet. Sci. Lett, 204, 291-306.
Creation and Review Dates
DIF Creation Date:
2000-08-08
Last DIF Revision Date:
2008-04-10
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