High precision TIMS measurements of stable Sr isotopes (δ88/86Sr) of standards with different matrices and depth bound seawater samples from the Bay of Bengal using a new 87Sr-84Sr double-spike

Ganguly, S and Chakrabarti, R (2022) High precision TIMS measurements of stable Sr isotopes (δ88/86Sr) of standards with different matrices and depth bound seawater samples from the Bay of Bengal using a new 87Sr-84Sr double-spike. In: Journal of Analytical Atomic Spectrometry, 37 (10). pp. 1961-1971.

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Abstract

We report high precision stable Sr isotopic data (δ88/86Sr) using an 87Sr-84Sr double spike TIMS technique for a variety of standards with different matrices (carbonate, silicate, seawater, and pure Sr). The composition of the double spike used in the present study, determined using a total evaporation technique using TIMS, is significantly different from other Sr double spike solutions reported in the literature; it is less expensive as the compositions of the 84Sr (carbonate) and 87Sr (metal) single spikes are slightly less pure compared to those reported in the literature. Despite the lesser purity of the single spikes, the long-term external reproducibility of δ88/86Sr values, based on multiple analyses of a variety of standards with different matrices, is better than ±0.035‰ which is comparable to, if not better than, previous studies. We demonstrate that the δ88/86Sr values are not affected by the nature of the loading filament (Ta versus zone refined Re) or the amount of Sr loaded on the filament (500 ng, 1 μg, 2 μg). Additionally, the δ88/86Sr values do not vary over a wide range of spike/sample ratios, consistent with our modelling calculations. We report δ88/86Sr values relative to the NIST SRM987 standard for an ICPMS Sr standard (0.101 ± 0.033‰, 2SD, n = 22), NASS-6 seawater (0.387 ± 0.034‰, 2SD, n = 4), JCp-1 coral carbonate (0.196 ± 0.006‰, 2SD, n = 2), JCt-1 clam shell (0.252 ± 0.004‰, 2SD, n = 2), BCR-2 basalt (0.264 ± 0.003‰, 2SD, n = 2), and SRM987 (0 ± 0.023‰, 2SD, n = 26) standards. Finally, we report δ88/86Sr values of depth bound samples from the Bay of Bengal for the first time. The δ88/86Sr values range from 0.373 to 0.411‰ with an average of 0.388 ± 0.025‰ (2SD, n = 10), which overlaps with δ88/86Sr values of global oceans. Our results demonstrate that despite variations in 87Sr/86Sr in the Bay of Bengal, where radiogenic 87Sr/86Sr at 100-120 m depth is explained by submarine groundwater discharge, the δ88/86Sr values are invariant and the average δ88/86Sr of the Bay of Bengal overlaps with global seawater data.

Item Type:	Journal Article
Publication:	Journal of Analytical Atomic Spectrometry
Publisher:	Royal Society of Chemistry
Additional Information:	The copyright for this article belongs to Royal Society of Chemistry.
Keywords:	Binary alloys; Carbonation; Isotopes; Mass spectrometers; Silicates; Sodium compounds, Bay of Bengal; High-precision; Isotopic data; matrix; Measurements of; Model calculations; Reproducibilities; Seawater samples; Stable Sr isotopes; Value-based, Seawater
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences Division of Interdisciplinary Sciences > Interdisciplinary Centre for Water Research
Date Deposited:	03 Jan 2023 12:07
Last Modified:	03 Jan 2023 12:07
URI:	https://eprints.iisc.ac.in/id/eprint/78676

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