Todd A. Anderson J.K. Bohlke Baohua Gu Paul B. Hatzinger Stanley J. Mroczkowski Balaji Rao Neil C. Sturchio W. Andrew Jackson Nubia Estrada 2021 <div id="abstracts" class="Abstracts u-font-serif"><div id="ab005" class="abstract author" lang="en"><div id="as005"><p id="sp0005"><span>Natural&nbsp;perchlorate&nbsp;(ClO</span>₄⁻<span>) exists in many places on Earth, in lunar&nbsp;regolith,&nbsp;meteorites, and on the surface of Mars. Terrestrial natural ClO</span>₄⁻<span>&nbsp;has widely variable Cl and O stable&nbsp;isotopic compositions&nbsp;(δ</span>³⁷Cl, δ¹⁸O, Δ¹⁷O). The δ¹⁸O and Δ¹⁷O values of ClO₄⁻<span>&nbsp;</span>from the most hyper-arid locations co-vary. ClO₄⁻<span>&nbsp;</span>from less arid areas has relatively little<span>&nbsp;</span>¹⁷O excess and poor Δ¹⁷O-δ¹⁸O correlation. ClO₄⁻<span>&nbsp;</span>from the Atacama Desert has unusually low δ³⁷Cl (&lt;−10‰) and exhibits a positive correlation between δ³⁷Cl and δ¹⁸O, while the δ³⁷Cl of ClO₄⁻<span>&nbsp;</span>from all other locations varies between −5 and +7‰ with no δ³⁷Cl-δ¹⁸O covariation. To evaluate the impact of different precursors (ClO_x) and reaction pathways on the isotopic composition of ClO₄⁻, we measured the isotopic composition of ClO₄⁻<span>&nbsp;</span>produced in the laboratory by UV or O₃<span>&nbsp;</span>mediated aqueous oxidation of Cl⁻, OCl⁻, ClO₂⁻, and ClO₂° as well as O₃<span>&nbsp;</span>mediated oxidation of dry NaCl. ClO_x<span>&nbsp;</span>oxidation in aqueous or dry systems enriched in O₃<span>&nbsp;</span>produced ClO₄⁻<span>&nbsp;</span>with Δ¹⁷O values that generally increased with the number of O atoms required and included evidence that the site-specific<span>&nbsp;</span>¹⁷O anomaly in O₃<span>&nbsp;</span>was preferentially transferred to ClO₄⁻. Based on the inferred number of O atoms sourced from O₃, and known Cl and O reaction pathways, it appears that ClO₂° and ClO₃* were required intermediates in the production of ClO₄⁻<span>&nbsp;</span>in the O₃<span>&nbsp;</span>experiments. ClO_x<span>&nbsp;</span>aqueous oxidation by UV irradiation produced ClO₄⁻<span>&nbsp;</span>with a large range of δ¹⁸O values and little or no<span>&nbsp;</span>¹⁷O anomaly. ClO₃⁻<span>&nbsp;</span>was produced to a much greater extent than ClO₄⁻<span>&nbsp;</span>in all experiments except dry oxidation of NaCl by O₃. The isotopic composition of ClO₃⁻<span>&nbsp;</span>was distinct from that of ClO₄⁻<span>&nbsp;</span>produced from the same initial reactants. Combined results of O₃<span>&nbsp;</span>and UV mediated reactions largely bracketed the range of natural ClO₄⁻<span>&nbsp;</span>δ¹⁸O and Δ¹⁷O values as well as δ³⁷Cl values of non-Atacama natural samples, but no conditions produced the low δ³⁷Cl values of Atacama ClO₄⁻. Our results indicate that variation in production mechanisms, possibly combined with isotopically variable precursors, could be responsible for much of the observed isotopic variation in natural ClO₄⁻<span>&nbsp;</span>and ClO₃⁻.</p></div></div></div> application/pdf 10.1016/j.gca.2021.06.039 en Elsevier Origin of the isotopic composition of natural perchlorate: Experimental results for the impact of reaction pathway and initial ClOx reactant article