^1,2Longye Du, ^1,3Xiaoxiao Yu, ⁴Yiliang Li, ¹Xiao Wu, ¹Lin Gong, ¹Gangjian Wei, ¹Qiang Wang, ^1,5Mang Lin
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.019]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²University of Chinese Academy of Sciences, Beijing 100049, China
³College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
⁴Department of Earth and Planetary Sciences, the University of Hong Kong, Hong Kong Special Administrative Region of China
⁵Center for Advanced Planetary Science (CAPS), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

A primary objective of Mars sample return missions is the detection and characterization of potential biosignatures. Sulfates, among the most abundant hydrated minerals on Mars, represent promising targets for such investigation. Terrestrial studies have shown that gypsum can preserve life-associated organic matter and that its δ34S signatures provide key evidence for microbial sulfate reduction as early as ∼ 3.5 billion years ago. This study analyzes quadruple sulfur (δ34S, Δ33S, Δ36S) and triple oxygen (δ18O, Δ́17O) isotopes in gypsum from three strong evaporation basins on the Qinghai-Tibet Plateau, where sulfate deposition is extensive but surface environments are only marginally habitable due to severe limitations in water, soil development, and nutrient availability. We focus on the Qaidam Basin as a Mars analog environment and place it in context through comparison with a higher-elevation region (Shuanghu) and a magmatic rock-dominated region (Yushu). Together with isotopic mixing models, an open-system steady-state sulfur cycle model, and triple-oxygen isotope oxidation pathway calculations, our quadruple sulfur and triple oxygen isotope measurements reveal that the studied gypsum deposits preserve distinct isotopic biosignatures. In particular, the isotopic compositions of the samples reflect microbial sulfur disproportionation and cryptic sulfur cycling, both of which extend beyond widespread microbial sulfate reduction, demonstrating how sulfur can be internally recycled and energetically utilized to sustain life in Mars-analog environments. This integrated isotopic approach significantly advances our capability to decipher sulfur cycling in extreme terrestrial environments, including Mars analog systems, and provides critical methodology for interpreting potential biosignatures in returned Martian samples.