Meaghan Brundrett J.K. Bohlke Paul B. Hatzinger Stanley J. Mroczkowski Neil C. Sturchio W Andrew Jackson 2021 <div id="abstracts" class="Abstracts u-font-serif"><div id="abs0010" class="abstract author" lang="en"><div id="abssec0010"><p id="abspara0010">Natural chlorate (ClO₃⁻) is widely distributed in terrestrial and extraterrestrial environments. To improve understanding of the origins and distribution of ClO₃⁻, we developed and tested methods to determine the multi-dimensional isotopic compositions (δ¹⁸O, Δ¹⁷O, δ³⁷Cl,<span>&nbsp;</span>³⁶Cl/Cl) of ClO₃⁻<span>&nbsp;</span>and then applied the methods to samples of natural nitrate-rich caliche-type salt deposits in the Atacama Desert, Chile, and Death Valley, USA. Tests with reagents and artificial mixed samples indicate stable-isotope ratios were minimally affected by the purification processes. Chlorate extracted from Atacama samples had δ¹⁸O&nbsp;=&nbsp;+7.0 to&nbsp;+11.1‰, Δ¹⁷O&nbsp;=&nbsp;+5.7 to&nbsp;+6.4‰, δ³⁷Cl&nbsp;=&nbsp;−1.4 to&nbsp;+1.3‰, and<span>&nbsp;</span>³⁶Cl/Cl&nbsp;=&nbsp;48&nbsp;×&nbsp;10⁻¹⁵<span>&nbsp;</span>to 104&nbsp;×&nbsp;10⁻¹⁵. Chlorate from Death Valley samples had δ¹⁸O&nbsp;=&nbsp;−6.9 to&nbsp;+1.6‰, Δ¹⁷O&nbsp;=&nbsp;+0.4 to&nbsp;+2.6‰, δ³⁷Cl&nbsp;=&nbsp;+0.8 to&nbsp;+1.0‰, and<span>&nbsp;</span>³⁶Cl/Cl&nbsp;=&nbsp;14&nbsp;×&nbsp;10⁻¹⁵<span>&nbsp;</span>to 44&nbsp;×&nbsp;10⁻¹⁵. Positive Δ¹⁷O values of natural ClO₃⁻<span>&nbsp;</span>indicate that its production involved reaction with O₃, while its Cl isotopic composition is consistent with a tropospheric or near-surface source of Cl. The Δ¹⁷O and δ¹⁸O values of natural ClO₃⁻<span>&nbsp;</span>are positively correlated, as are those of ClO₄⁻<span>&nbsp;</span>and NO₃⁻<span>&nbsp;</span>from the same localities, possibly indicating variation in the relative contributions of O₃<span>&nbsp;</span>as a source of O in the formation of the oxyanions. Additional isotopic analyses of ClO₃⁻<span>&nbsp;</span>could provide stronger constraints on its production mechanisms and/or post-formational alterations, with applications for environmental forensics, global biogeochemical cycling of Cl, and the origins of oxyanions detected on Mars.</p></div></div></div> application/pdf 10.1016/j.chemosphere.2021.129586 en Elsevier Isotopic composition of natural and synthetic chlorate (δ18O, Δ17O, δ37Cl, 36Cl/Cl): Methods and initial results article