Stable δ¹³C isotope analysis at hot and cold springs suggests that rapid degassing overprints carbon isotopic biosignatures even when microbial activity produces biogenic textures in the minerals. Mineral precipitation and potential biosignature preservation are evaluated at a cold spring system in Ten Mile Graben, Utah, USA, with scanning electron microscopy, X-ray diffraction, and stable carbon isotopes. Putative biogenic mineral habits such as aragonite microspheres and botryoids, and biologic materials (EPS and diatom tests) are abundant in modern mats, but the δ¹³C values are between +2‰ and +7.8‰, consistent with rapid CO₂ degassing reported by other researchers. Multiple factors, however, influence isotopic signatures of mineral precipitates in this spring system, including rapid degassing, preferential microbial uptake of light carbon isotopes via multiple carboxylation pathways, hydrocarbon-charged fluid, and other inherited isotopic signatures in the fluid, particularly from dissolution of older limestones; therefore, it is not likely that this narrow range of isotopic ratios definitively shows an abiotic signature. A fossil vent preserves biogenic mineral habits, but not microbial body fossils. This study highlights the need for novel biosignature detection methods—and an understanding of what an abiotic signature definitively is—as we prepare for sample caching of carbonate rocks by the Mars2020 mission and future sample return.

中文翻译：

---

美国犹他州冷泉系统中的稳定同位素分馏：火星样本选择的见解

冷热泉的稳定 δ ¹³ C 同位素分析表明，即使微生物活动在矿物质中产生生物结构，快速脱气也会叠加碳同位素生物特征。在美国犹他州十英里地堑的冷泉系统中，利用扫描电子显微镜、X 射线衍射和稳定碳同位素对矿物沉淀和潜在的生物印记保存进行了评估。假定的生物矿物习性，例如文石微球和类葡萄石，以及生物材料（EPS 和硅藻测试）在现代垫子中很丰富，但 δ ¹³ C 值在 +2‰ 和 +7.8‰ 之间，与快速 CO ₂一致其他研究人员报告的脱气。然而，有多种因素会影响这个泉水系统中矿物沉淀的同位素特征，包括快速脱气、微生物通过多种羧化途径优先吸收轻碳同位素、带碳氢化合物的流体和流体中的其他遗传同位素特征，特别是来自较旧的石灰岩；因此，这种窄范围的同位素比率不太可能明确显示出非生物特征。化石喷口保留了生物矿物习性，但不保留微生物体化石。这项研究强调了对新型生物特征检测方法的需求——以及对非生物特征的明确理解——因为我们准备通过 Mars2020 任务和未来的样品返回来缓存碳酸盐岩的样品。