High-sensitivity measurements of strontium isotopes in polar ice

doi:10.1016/S0003-2670(02)00720-1

Analytica Chimica Acta

Volume 469, Issue 2, 3 October 2002, Pages 225-233

https://doi.org/10.1016/S0003-2670(02)00720-1 Get rights and content

Abstract

Techniques have been developed to measure the isotopic composition and concentration of Sr at sub-nanogram per gram levels in polar snow and ice samples. A $^{84} Sr$ spike was used to determine Sr concentrations on a single sample aliquot of a few millilitre. Microlitre scale columns of Sr-Spec resin were used to purify Sr samples. Thermal ionisation mass spectrometry (TIMS) was used to measure the Sr isotopic ratios. A single TIMS measurement of the Sr sample yielded both isotopic composition and concentration after deconvolution of spike and sample spectra. This allows isotopic variations in Sr to be used to identify source regions of crustal dust. Early Holocene and last glacial maximum ice core samples from both Antarctica and Greenland were analysed to demonstrate the applicability of the technique. Sr isotopes were analysed in ∼20 g sized samples of Antarctic early Holocene ice where the concentration was only ∼31 pg g⁻¹. This represents an improvement of two orders of magnitude in sample consumption over previous studies allowing for a much higher time resolution in the analysis of polar ice cores.

Introduction

Strontium is used extensively for geochronology and isotope geochemistry [1]. Both take advantage of the enhancement of the $^{87} Sr$ abundance in rocks from the radioactive decay of $^{87} Rb$ (half life: ∼5×10¹⁰ years). Measurements involve the precise determination of the $^{87} Sr$ / $^{86} Sr$ ratio as well as Sr and Rb concentrations by isotope dilution mass spectrometry (IDMS) [2]. Recently, however, there has been a resurgence of interest in using Sr as an isotopic tracer in environmental studies. For instance, Sr and Pb isotopes have been used to determine the sources of particulate and dissolved matter in a river in flood [3], while Sr isotope systematics allowed the origin of groundwaters from granitoids in France to be deciphered [4]. Sr together with Nd isotopic ratios have been used to show that continental dust deposited in ice at Vostok and Dome C sites in east Antarctica during the colder glacial stages is of Patagonian origin [5], [6]. Also, the probable origin of dust deposited at Summit, Greenland in 23–26 ky BP ice was found to be east Asia [7]. However, these studies have required relatively large volumes of ice core and integrated ∼1000–2000 years per sample (5.5 m of ice core) [5], 500–4000 years per sample (∼8 kg ice) [6] and 20–100 years per sample (0.6–2 m of ice core) [7]. These large sample sizes run counter to the demand by analysts, the expense of obtaining ice cores and their scientific value. They also obscure any short time-scale events.

In this paper, we present techniques developed to analyse the isotopic composition of picogram quantities of Sr in continental glacier and polar ice cores. In these samples the concentrations are relatively low (usually <1 ng g⁻¹) and only small quantities of ice (often <30 g) are usually available for analysis. Consequently, the contributions of Sr inadvertently introduced during sample processing can significantly alter the isotopic composition and concentration of the sample. Here, we describe techniques that were developed to reliably measure the isotopic composition of Sr in these samples.

Section snippets

Samples

The applicability of the technique is shown by analysing a variety of samples from different locations and containing a wide range of Sr concentrations.

Standards, blanks and quality controls

Table 1 shows the results of repeated measurements of various samples used to verify the accuracy of the procedures. The $^{87} Sr$ / $^{86} Sr$ ratio of SRM 987 was found to be 0.71027±0.00002 which is the same within experimental uncertainty as our Johnson–Matthey Specpure (JMC $^{87} Sr$ / $^{86} Sr =0.71028±0.00002$ ). Since the source of SRM 987 and Johnson–Matthey Sr were the same some 20 years ago this is not surprising [24].

The procedural blank for the sample purification was 14±2 pg Sr with an $^{87} Sr$ / $^{86} Sr$ ratio of

Conclusion

Here we have presented a technique that permits small volumes of polar ice to be analysed for Sr concentration and isotopic composition. This opens the way to studies of the EH, where Sr concentrations are relatively low, and where seasonal and other short term variations with smaller periods of snow accumulation must be analysed. It is now possible to measure Sr isotopic composition and concentration in snow and ice cores from ancient to modern times. Because the sample sizes described in this

Acknowledgements

We thank Paul Vallelonga, Jean-Pierre Candelone, Sungmin Hong and Katja Van de Velde for decontaminating the samples analysed in this study. We also thank colleagues and students of the TIMS Laboratory in the John de Laeter Centre for Mass Spectrometry (JdLCMS) at Curtin University for their helpful discussion. JdLCMS is supported by the Australian Research Council and the Antarctic Science Advisory Committee. In France, the work was supported by the Institut Universitaire de France, the

References (24)

J.-M Luck et al.
Chem. Geol.
(1998)
P Negrel et al.
Chem. Geol.
(2001)
F.E Grousset et al.
Earth Planet. Sci. Lett.
(1992)
I Basile et al.
Earth Planet. Sci. Lett.
(1997)
K.J.R Rosman et al.
Earth Planet. Sci. Lett.
(2000)
S Hong et al.
Atm. Environ.
(1997)
S Hong et al.
Earth Planet. Sci. Lett.
(1996)
A Ng et al.
Geochim. Cosmochim. Acta
(1981)
J.-P Candelone et al.
Anal. Chim. Acta
(1994)
C Pin et al.
Anal. Chim. Acta
(1994)

J.L Birck

Chem. Geol.

(1986)

R.H Steiger et al.

Earth Planet. Sci. Lett.

(1977)

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New techniques which allow small amounts of Sr to be reliably analysed [G.R. Burton, V.I. Morgan, C.F. Boutron, K.J.R. Rosman, High-sensitivity measurements of strontium isotopes in polar ice, Anal. Chim. Acta 469 (2002) 225–233] by TIMS (Thermal Ionisation Mass Spectrometry) have been used to measure the isotopic composition of Sr and the concentration of Rb and Sr at sub-nanogram per gram levels in a Mt Blanc snow and ice core. This two century time series of Sr isotopes is the first to be reported in an Alpine glacier. The Sr and Rb concentrations range from 3 ng/g to 20 pg/g and 1 ng/g to 10 pg/g, respectively, with higher concentrations evident in more recent times. This trend is consistent with that reported previously for other metals such as Cd, Cu and Zn [K. Van de Velde, C. Barbante, G. Cozzi, I. Moret, T. Bellomi, C. Ferrari, C. Boutron, Changes in the occurrence of silver, gold, platinum, palladium and rhodium in Mont Blanc ice and snow since the 18th century, Atmos. Environ. 34 (2000) 3117–3127; K. Van de Velde, C. Boutron, C. Ferrari, T. Bellomi, C. Barbante, S. Rudnev, M. Bolshov, Seasonal variations of heavy metals in the 1960s Alpine ice: sources versus meteorological factors, Earth Planet. Sci. Lett. 164 (1998) 521–533; K.J.R. Rosman, C. Ly, K. Van de Velde, C.F. Boutron, A two century record of lead isotopes in high altitude Alpine snow and ice, Earth Planet. Sci. Lett. 176 (2000) 413–424]. The ⁸⁷Sr/⁸⁶Sr ratios vary between 0.7020 and 0.7176 and display relatively larger variations in recent times which have been attributed to seasonal variations made evident by the increased sampling resolution available at shallower depths. No change with time is evident in this ratio which has a mean value of ∼ 0.712 and is similar to Glacial ice at Summit Greenland, suggesting that aerosols reaching Mt Blanc represent the same mixture of sources. Also, anthropogenic sources would appear to have the same isotopic ratio. The presence of Saharan dust in some samples is confirmed here by their strontium isotopic ratios.

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High-sensitivity measurements of strontium isotopes in polar ice

Abstract

Introduction

Section snippets

Samples

Standards, blanks and quality controls

Conclusion

Acknowledgements

Chem. Geol.

Chem. Geol.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Atm. Environ.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

Chem. Geol.

Earth Planet. Sci. Lett.