Due to their potential to support chemolithotrophic life, relic hydrothermal systems on Mars are a key target for astrobiological exploration. We analysed water and sediments at six geothermal pools from the rhyolitic Kerlingarfjöll and basaltic Kverkfjöll volcanoes in Iceland, to investigate the localised controls on the habitability of these systems in terms of microbial community function. Our results show that host lithology plays a minor role in pool geochemistry and authigenic mineralogy, with the system geochemistry primarily controlled by deep volcanic processes. We find that by dictating pool water pH and redox conditions, deep volcanic processes are the primary control on microbial community structure and function, with water input from the proximal glacier acting as a secondary control by regulating pool temperatures. Kerlingarfjöll pools have reduced, circum-neutral CO₂-rich waters with authigenic calcite-, pyrite- and kaolinite-bearing sediments. The dominant metabolisms inferred from community profiles obtained by 16S rRNA gene sequencing are methanogenesis, respiration of sulphate and sulphur (S⁰) oxidation. In contrast, Kverkfjöll pools have oxidised, acidic (pH < 3) waters with high concentrations of SO₄^2- and high argillic alteration, resulting in Al-phyllosilicate-rich sediments. The prevailing metabolisms here are iron oxidation, sulphur oxidation and nitrification. Where analogous ice-fed hydrothermal systems existed on early Mars, similar volcanic processes would likely have controlled localised metabolic potential and thus habitability. Moreover, such systems offer several habitability advantages, including a localised source of metabolic redox pairs for chemolithotrophic microorganisms and accessible trace metals. Similar pools could have provided transient environments for life on Mars; when paired with surface or near-surface ice, these habitability niches could have persisted into the Amazonian. Additionally, they offer a confined site for biosignature formation and deposition that lends itself well to in situ robotic exploration.

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火山对类似火星热液环境微生物宜居性的控制

由于它们具有支持化能生物的潜力，火星上的遗迹热液系统是天体生物学探索的关键目标。我们分析了冰岛流纹岩 Kerlingarfjöll 和玄武岩 Kverkfjöll 火山的六个地热池中的水和沉积物，以研究微生物群落功能对这些系统宜居性的局部控制。我们的结果表明，宿主岩性在池地球化学和自生矿物学中起次要作用，系统地球化学主要受深部火山过程控制。我们发现，通过决定池水 pH 值和氧化还原条件，深部火山过程是微生物群落结构和功能的主要控制因素，来自近端冰川的水输入通过调节池温度作为辅助控制。₂富含自生方解石、黄铁矿和高岭石沉积物的水域。从通过 16S rRNA 基因测序获得的群落概况推断出的主要代谢是产甲烷、硫酸盐呼吸和硫 (S ⁰ ) 氧化。相比之下，Kverkfjöll 池具有氧化性、酸性（pH < 3）水和高浓度 SO ₄ ^2-和高泥质蚀变，导致富含铝页硅酸盐的沉积物。这里主要的代谢是铁氧化、硫氧化和硝化。在早期火星上存在类似的冰源热液系统的地方，类似的火山过程可能控制了局部代谢潜力，从而控制了宜居性。此外，这样的系统提供了几个宜居优势，包括化能微生物和可接近的痕量金属的代谢氧化还原对的局部来源。类似的水池可以为火星上的生命提供短暂的环境；当与地表或近地表冰相结合时，这些宜居生态位可能会持续到亚马逊河中。此外，它们为生物特征的形成和沉积提供了一个封闭的场所，非常适合原位机器人探索。