Determining aqueous sulfate sources in terrestrial cold environments can provide an insight into the surface hydrological conditions and sulfur cycle on Mars. In this study, we analyzed sulfur and oxygen isotope compositions of secondary sulfate salts (e.g., gypsum, thenardite) in the surficial sediments and soils of the McMurdo Dry Valleys (MDV), Antarctica to determine contributions of sulfate from bedrock chemical weathering and atmospheric deposition under persistent dry polar conditions. The sulfate showed wider variation of δ³⁴S (+15.8‰ to +32.5‰) compared to smaller ranges of δ¹⁸O (−8.9‰ to −4.1‰). In contrast, the δ³⁴S of bedrock sulfide showed significantly lower and consistent values across the studied area (−0.6‰ to +3.3‰). Based on the δ³⁴S trends, sulfide weathering may contribute up to 20–50% of secondary sulfate salts in the MDV. While the remaining 50–80% of sulfate inputs may originate from atmospheric deposition (e.g., sea aerosols, dimethulsulfide oxidation), the subglacial brines derived by relicts of seawater and/or lake/pond water influenced by microbial sulfate reduction could also be important sulfate endmembers particularly in the Antarctic lowland thaw zones. Additional field observations of frost, ponding water, and thin gypsum crusts on the terrestrial gypsum dunes at White Sands supports reactivity of gypsum on the surface of these dunes during cold winter conditions. Combined with our improved geochemical model of the sulfur cycle for cold Antarctic settings, we propose that transient liquid water or frost was available in near-surface environments at the time of gypsum formation in the north polar region on Mars. Ice and/or water interaction with basaltic sand of the basal unit (paleo-erg) would have enhanced leaching of sulfate from both sulfide oxidation and atmospheric deposition and resulted in formation of secondary gypsum salts.

中文翻译：

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评估寒冷条件下的硫酸盐来源，作为火星周极沙丘中硫酸盐来源的地球化学替代物

确定陆地寒冷环境中的含水硫酸盐来源可以洞悉火星的地表水文条件和硫循环。在这项研究中，我们分析了南极麦克默多干旱谷（MDV）表层沉积物和土壤中的次生硫酸盐（例如石膏，芒硝）的硫和氧同位素组成，以确定基岩化学风化和大气沉积中硫酸盐的贡献在持续干燥的极地条件下。硫酸显示δ的较宽变化³⁴ S（+ 15.8‰至+ 32.5‰）相比的较小范围δ ¹⁸ O（-8.9‰至-4.1‰）。与此相反，δ ³⁴基岩硫化物第表明显著低且一致的值跨越研究区（-0.6‰至+ 3.3‰）。基于δ³⁴从趋势上看，硫化物风化可能占MDV中次级硫酸盐的20％至50％。尽管其余50-80％的硫酸盐输入可能来自大气沉积（例如，海洋气溶胶，二甲基硫醚氧化），但受微生物硫酸盐还原影响的海水和/或湖泊/池塘水的残渣所产生的冰下盐水也可能是重要的硫酸盐。最终成员，特别是在南极低地解冻区。在白沙的陆上石膏沙丘上的霜冻，积水和薄石膏结皮的其他现场观察结果证明，在寒冷的冬季条件下，这些沙丘表面的石膏具有反应性。结合我们改良的南极寒冷环境中硫循环的地球化学模型，我们建议在火星北极地区的石膏形成时，在近地表环境中可获得短暂的液态水或霜冻。冰和/或水与基础单元（古生物）的玄武质砂的相互作用将增强硫化物氧化和大气沉积中硫酸盐的浸出，并导致形成次生石膏盐。