Chemical Characterization of Saline Lake and Playa Salts in Qaidam Basin: Implications for Climates of Planet Earth and Mars

Abstract

<p>Salt aerosol from saline lakes and playas has been recognized to affect climate in the global scale, but the understandings of the chemical and physical natures of these salts are still limited due to their complex chemical composition. The Qaidam Basin, one of the largest and driest deserts on Earth, is composed of many saline lakes and is regarded as a good terrestrial analogue for Mars due to similar environment conditions and elementary composition(Xiao et al., 2017). The study on the chemical characteristics of salts from Qaidam Basin is helpful to explore their influences on climate and reveal the physical and chemical factors affecting the paleoclimate of both Planet Earth and Mars.</p><p> </p><p>In this study, four types of salt samples (brines, crystalized brines, lakebed salts and crust salts) collected at and near four saline lakes (Chaka, Keke, Qarhan and Mang’ai) in the Qaidam Basin are studied for their physicochemical characteristics. The common cations (Na<sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup> and Ca<sup>2+</sup>) and anions (Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, and NO<sub>3</sub><sup>−</sup>) are determined by ion chromatography (IC), and the elemental compositions are measured by energy dispersive X-ray fluorescence (EDXRF) spectrometry. The chemical composition results are analyzed by positive matrix factorization (PMF)(Paatero and Tapper, 1994). The pH of sample brines and solutions are measured, and the governing factors are discussed.</p><p> </p><p>The common elements detected by XRF and IC have excellent consistency. Notably, the crystalized brines exhibit similar ionic compositions with brines, suggesting that the crystalized brines well reflect the complex mineral composition of brines and evaporative crystallization can be used for brine preservation. However, the natural solid salts (lakebed salts and crust salts) present obvious composition differences. Mg<sub>2</sub><sup>+</sup> and SO<sub>4</sub><sup>2-</sup> are primarily found in brines, while the natural solid salts are dominated by NaCl and KCl. The pH of the brines and salt solutions are found to correlate to Mg<sup>2+</sup> concentrations and potentially affected by ambient CO<sub>2</sub> uptake. The electrical conductivities of sample solutions are not linearly scaled by the dilution factors, indicating that balanced reactions and buffer systems exist in the salt textures. Three interpretable factors are identified by the PMF analysis, and the differences of sample types and sampling sites are clearly reflected by the three factors. The lakebed salts (except for the QH lakebed salt) presented excellently correlation with the crust salts, and the crystalized salts are greatly correlated with the brines. This study improves the understandings of the physiochemical features of saline lake and playa salts in Qaidam Basin, and the roles that surface salts potentially play in the climate systems of both Planet Earth and Mars are discussed.</p><p> </p><p><strong>Reference</strong></p><p>Paatero, P., and Tapper, U., Environmetrics, 5, 111-126, <strong>1994</strong>.</p><p>Xiao, L., Wang, J., Dang, Y., et al., Earth-Sci Rev, 164, 84-101, <strong>2017</strong>.</p>