A Br Isotopic Study of Australian Arid Playa Lakes and halophyte vegetation as a monitor of Br transport

Abstract:

Bromine possesses a chemistry broadly comparable to that of Cl and F, however its heavier mass and lower abundance results in slightly different behaviours in geochemical cycling. For example it is disproportionately enriched in sea water with respect to Cl. Br can be considered to be a “hydrophile” element, and hence its behaviour is in governed by that of water. It possesses two isotopes ⁷⁹Br (50.686%) and ⁸¹Br (49.314%).

This study has developed new chemical extraction, and most significantly, new mass spectrometric protocols for Br isotopes on silicates, evaporites and waters using N-TIMS methodologies. Existing CF-IRMS methodologies offer internal precision of ~0.3‰ (1SD, [1]), whereas N-TIMS measurements of laboratory HBr and seawater standards produce external reproducibility of <0.07‰ (1SD) over an 18 month period with internal precision typically <0.06‰ (1SD) on single analyses.

This study presents the first high precision, N-TIMS isotopic data on playa lake evaporites, recording a >5‰ variation in solar system ⁸¹Br/⁷⁹Br. Also presented is data from the analysis of the halophylic saltbush (sp Atriplex) adjacent to the lakes to constrain biological fractionation of Br isotopes. Variations of ~4‰ are observed between the lakes with a comparable shift for the leaves of the saltbush.

[1] Shouaker-Stash et al., Anal. Chem, 77; p4027-4033, 2005.