CAREER: Do microbes form caves? Sulfide oxidation and limestone corrosion in sulfuric acid caves

职业：微生物会形成洞穴吗？

• 批准号: 2239710
• 负责人: Daniel Jones
• 金额: $ 90.89万
• 依托单位: New Mexico Institute of Mining and Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-15 至 2028-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2239710&HistoricalAwards=false
• 关键词: CAREER; Do; microbes; form; caves

Some of the world’s largest and most spectacular limestone caves, including Carlsbad Cavern and Lechuguilla Cave in New Mexico, were created by sulfuric acid. These caves form where groundwaters carrying dissolved hydrogen sulfide are exposed to oxygen, usually at or near the cave water table. Hydrogen sulfide is unstable in the presence of oxygen, and it rapidly reacts to form sulfuric acid and other sulfur compounds that dissolve limestone and precipitate new minerals. And because of the abundant chemical energy from hydrogen sulfide, chemosynthetic microorganisms thrive at the water table and speed up sulfide oxidation, producing what might be the fastest known rates of cave enlargement. This project will use an interdisciplinary combination of microbiology, geochemistry, and modeling to determine where, how, and how fast limestone dissolves in these caves, and how specifically microorganisms contribute to bedrock corrosion. Results from this research will show us how microorganisms form caves, but also how they contribute to similar carbonate weathering processes that occur across other more widespread but less accessible subsurface environments. Carbonate mineral weathering by strong acids is an important source of carbon dioxide to the atmosphere, but sulfuric acid weathering is not well understood in the terrestrial subsurface, especially in areas with limestone and other carbonate bedrock. Sulfuric acid caves are windows through which we can directly access and study these extensive but otherwise hidden processes of subterranean carbonate weathering, gas flux, and mineral formation. And, caves are exceptional platforms for science communication. This project will take advantage of the excitement of caves to create new educational opportunities through course-based research, K-12 teacher education, and science communication activities. In actively-forming sulfuric acid caves, substantial limestone corrosion and void development can occur above the water table, where springs and streams degas hydrogen sulfide to the cave atmosphere. However, the overall impact of this degassing-driven processes is not well understood, and we don’t know the contribution of vadose corrosion for sulfuric acid cave formation, or how microorganisms affect karst development above the water table. This project will therefore combine geochemical and molecular analyses with speleogenetic modeling to address three questions: (1) Do microorganisms speed up sulfide oxidation and limestone dissolution above the water table, and can these rates explain observed cave morphologies? (2) How do microorganisms affect subaerial carbonate dissolution, both during the active phase of sulfuric acid corrosion but also throughout the long lifetime of the caves? (3) What is the impact of gas emissions from sulfuric acid karst for climate and carbon cycling? The team will address these questions by combining direct measurements of limestone dissolution and biological sulfide oxidation kinetics with metatranscriptomics and other community analyses to directly link microbial activity with cave formation both close to and far from the sulfidic aquifer. They will use air flow and speleogenetic modeling to relate these measurements to cave morphologies and gas flux. And they will explore how these processes change in ancient sulfuric acid caves that no longer have a sulfide source. Parts of Questions 2 and 3 will be addressed through course-based research that emphasizes biodiscovery, Earth systems, and science communication. This CAREER award is co-funded by the Geobiology and Low-Temperature Geochemistry Program and the Education and Human Resources Program in the NSF Division of Earth Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

一些世界上最大、最壮观的石灰岩洞穴，包括新墨西哥州的卡尔斯巴德洞穴和勒丘吉拉洞穴，都是由硫酸形成的。这些洞穴是在地下水携带溶解的硫化氢暴露于氧气的地方形成的，通常在洞穴地下水位或附近。硫化氢在氧气的存在下是不稳定的，它会迅速反应形成硫酸和其他含硫化合物，从而溶解石灰石并沉淀新的矿物质。由于硫化氢中含有丰富的化学能，化学合成微生物在地下水位繁殖，加速硫化物氧化，产生可能是已知最快的洞穴扩大速度。该项目将使用微生物学、地球化学和建模的跨学科组合来确定石灰岩在这些洞穴中的溶解位置、方式和速度，以及微生物对基岩腐蚀的具体影响。这项研究的结果将向我们展示微生物如何形成洞穴，以及它们如何促成类似的碳酸盐风化过程，这些过程发生在其他更广泛但不易进入的地下环境中。碳酸盐矿物在强酸作用下的风化作用是大气中二氧化碳的重要来源，但在陆地地下，特别是在石灰岩和其他碳酸盐基岩地区，对硫酸风化作用的了解还不是很清楚。硫酸洞穴是一扇窗户，通过它我们可以直接进入和研究这些广泛但隐藏的地下碳酸盐风化、气体通量和矿物形成过程。洞穴是科学交流的绝佳平台。该项目将利用洞穴的兴奋感，通过课程研究、K-12教师教育和科学交流活动创造新的教育机会。在活跃形成的硫酸洞穴中，大量的石灰石腐蚀和空洞的形成可能发生在地下水位以上，在那里，泉水和溪流将硫化氢气体释放到洞穴大气中。然而，这种脱气驱动过程的整体影响尚不清楚，我们不知道水蒸气腐蚀对硫酸洞穴形成的贡献，也不知道微生物如何影响地下水位以上的喀斯特发育。因此，该项目将结合地球化学和分子分析与洞穴成因模型来解决三个问题：(1)微生物是否加速了硫化物氧化和石灰岩在地下水位以上的溶解，这些速率是否可以解释观察到的洞穴形态？(2)无论是在硫酸腐蚀的活性阶段，还是在洞穴的整个生命周期中，微生物是如何影响地面碳酸盐溶解的？(3)硫酸岩溶气体排放对气候和碳循环的影响是什么？该团队将通过结合石灰岩溶解和生物硫化物氧化动力学的直接测量，以及亚转录组学和其他群落分析来解决这些问题，从而直接将微生物活动与靠近或远离硫化物含水层的洞穴形成联系起来。他们将使用气流和洞穴成因模型将这些测量结果与洞穴形态和气体通量联系起来。他们将探索这些过程在不再有硫化物来源的古代硫酸洞穴中是如何变化的。问题2和问题3的部分将通过强调生物发现、地球系统和科学传播的课程研究来解决。该奖项由美国国家科学基金会地球科学部的地球生物学和低温地球化学项目以及教育和人力资源项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。