Abstract：
Covered by vast eolian landforms, gravel deposits, and playas, the worldwide typical evaporite deposit land, Qaidam Basin, in northwestern China is analogous to early Mars when the aridification process had lasted for millions of years since the end of a wetter climate. This study aims to investigate the chemical and isotopic characteristics of waters in an evaporite-rich environment, as well as the habitable conditions therein, that have undergone a transformation similar to early Mars. In May 2023, a total of 26 water samples were collected across the representative central axis of a longitudinal aridity gradient in the Qaidam Basin, including categories of meteoric water, freshwater, standing water accumulated after precipitation, salty lacustrine water, and hypersaline brines to inspect compounds made up of carbon, nitrogen, phosphorus, sulfur, halogen, and metallic elements. As evaporation intensified, the salt types transformed from HCO3-Ca·Na to Cl·SO4-Na or ClMg. The dominance of carbonate will gradually be replaced by sulfate and chloride, leaving much more dilute and less detectable contents. The presence of trace ClO4-, ClO3-, ClO2-, and BrO3- was confirmed in a few of the sampled Qaidam waters, indicating the preservation of oxyhalides in waters within an arid region and possibly the presence of relevant microbial enzymes. The isotopes of water, carbonaceous, and nitrogenous compounds provide valuable references for either abiogenic or biogenic signatures. With undetectable amount, phosphorus was found to be the limiting nutrient in evaporative aquatic environments but not necessarily antibiosignatures. Overall, these results suggest that the paleo-lacustrine environments on Mars are more likely to preserve biosignatures if they feature the dominance of carbonate minerals, bioavailable nitrate, phosphorus, and organic carbon, the presence of thermodynamically unstable oxyhalides, and isotope ratios that point to the involvement of biological activity.
摘要：
被广阔的风积地貌覆盖，砾石矿床,和playas,全球典型的蒸发岩矿床，柴达木盆地,在中国西北部，类似于火星早期，自潮湿气候结束以来，干旱化过程持续了数百万年。本研究旨在研究富含蒸发岩的环境中水域的化学和同位素特征，以及其中的可居住条件，经历了类似于早期火星的转变。2023年5月，沿柴达木盆地纵向干旱梯度的代表性中轴共采集了26个水样，包括大气水的种类，淡水,沉淀后积水，咸咸的湖水，和高盐盐水来检查由碳组成的化合物，氮，磷，硫磺,卤素,和金属元素。随着蒸发加剧，盐类型从HCO3-Ca·Na转化为Cl·SO4-Na或ClMg。碳酸盐的优势将逐渐被硫酸盐和氯化物取代，留下更多的稀释和更少的可检测的内容。微量ClO4-的存在，ClO3-,ClO2-,在柴达木的一些采样水域中确认了BrO3-，表明干旱地区水域中卤氧化物的保存以及可能存在的相关微生物酶。水的同位素，含碳的,和含氮化合物为非生物或生物特征提供了有价值的参考。检测不到的数量，发现磷是蒸发水生环境中的限制性营养素，但不一定是抗生素。总的来说,这些结果表明，如果火星上的古湖相环境具有碳酸盐矿物的优势，它们更有可能保留生物特征，生物可利用硝酸盐，磷，有机碳,热力学不稳定的卤氧化物的存在，和同位素比率表明生物活性的参与。
