Contributions of abiotic and biotic processes on travertine deposition are still not well-understood due to technical difficulties, despite that the travertines draw attention as analogues for ancient microbial carbonates and oil reservoirs. To evaluate their contributions, this study examined eight hot springs in Japan. Water chemistry analyses showed common downstream trends: a decrease in CO₂ concentration and increases in CO₃²⁻ concentration and pH. Mineralogical analysis showed that the constituent minerals of travertines at six hot springs were both calcite and aragonite, while one was just calcite and another only aragonite. Microscopic observations of travertine surfaces indicated the dominance of cyanobacteria secreting extracellular polymeric substances without a detectable amount of carboxyl groups. Small particles were sometimes entangled/covered by these cyanobacteria. Microelectrode measurements showed the occurrence of abiotic CaCO₃ precipitation and photosynthetic induction/inhibition of CaCO₃ precipitation, the extent of which was different at each site. By integrating these results, the contributions of abiotic and biotic processes were evaluated. Cyanobacteria inhabiting travertine surfaces were generally not calcified regardless of an ambient high CaCO₃ saturation state; instead, they contributed to creating pore spaces and trap/bind suspended particles. Downstream CO₂ degassing increased the CaCO₃ saturation state by shifting carbonate chemical equilibrium and caused abiotic CaCO₃ precipitation. Suspended particles trapped by cyanobacteria increased the surface area for crystal growth to further accelerate precipitation. The contribution of photosynthesis-induced CaCO₃ precipitation was low because of several factors, including variable cyanobacteria populations and photosynthetic inhibition of CaCO₃ precipitation. The average contributions of photosynthesis-induced CaCO₃ precipitation, Ca²⁺ adsorption and abiotic precipitation in the eight hot springs were 16%, 3% and 81%, respectively, indicating predominance of the abiotic process for travertine deposition. Mineralogical composition of travertines significantly correlated with concentrations of SO₄²⁻ and Mg²⁺, much more than with Mg/Ca ratio and water temperature, suggesting their importance for controlling CaCO₃ polymorphs in travertines.

中文翻译：

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控制石灰华沉积的非生物和生物过程：来自日本八个温泉的见解

尽管石灰华作为古代微生物碳酸盐和油藏的类似物引起了人们的关注，但由于技术困难，非生物和生物过程对石灰华沉积的贡献仍未得到充分理解。为了评估他们的贡献，本研究考察了日本的八个温泉。水化学分析显示了共同的下游趋势：CO ₂浓度下降和 CO ₃ ^2−增加浓度和 pH 值。矿物学分析表明，6个温泉钙华的组成矿物均为方解石和文石，1个为方解石，1个为文石。钙华表面的显微镜观察表明，蓝藻主要分泌细胞外聚合物，但没有可检测到的羧基量。小颗粒有时会被这些蓝藻缠住/覆盖。微电极测量显示非生物 CaCO _{3沉淀的发生和 CaCO 3}的光合作用诱导/抑制降水量，每个地点的降水量不同。通过整合这些结果，评估了非生物和生物过程的贡献。无论环境中的高 CaCO ₃饱和状态如何，栖息在石灰华表面的蓝藻通常不会钙化；相反，它们有助于创造孔隙空间和捕获/结合悬浮颗粒。下游CO ₂脱气通过改变碳酸盐化学平衡增加了CaCO ₃饱和状态并导致非生物CaCO ₃沉淀。蓝藻捕获的悬浮颗粒增加了晶体生长的表面积，以进一步加速沉淀。光合作用诱导的CaCO _3的贡献由于多种因素，包括可变的蓝藻种群和CaCO ₃沉淀的光合作用抑制，降水量较低。8个温泉中光合作用诱导的CaCO ₃沉淀、Ca ^{2+吸附和非生物沉淀的平均贡献分别为16%、3%和81%，表明钙华沉积的非生物过程占优势。}_{石灰华的矿物学成分与 SO 4} ²⁻和 Mg ²⁺的浓度显着相关，远大于 Mg/Ca 比和水温，表明它们对于控制石灰华中CaCO _{3多晶型物的重要性。}