OCE-PRF: Biomediated corrosion of methane-derived authigenic carbonates in the deep ocean and its implications for carbon fluxes from methane seeps

这个研究项目调查了通过生物过程释放回海水中的碳量，这些生物过程溶解了海洋甲烷渗漏形成的碳酸盐岩结构。在整个世界的海洋中，甲烷从俯冲带的海底沉积物和海底下埋藏的古老有机物质中上升。大部分甲烷在进入海洋或大气之前，会被独特的微生物和化学活动消耗掉。在这个“甲烷圈”中，海底附近的软沉积物在溶解或从下面渗出的气态碳沉淀成固体碳酸盐时形成岩石。这些岩石为深海生物栖息和储存碳提供了坚硬的表面，否则会导致海洋和大气中二氧化碳的增加。碳酸盐岩在其表面及周围发生了复杂的生物地球化学反应，当其周围水体酸含量增加时，碳酸盐岩会溶解回海水中。如果不考虑碳酸盐的这种溶解，那么在与人为气候变化相关的时间尺度上，从海底到达大气的碳量就不能完全量化。本研究将资助两名本科生，并提供地理信息系统方面的培训；图像处理软件；数据库管理;以及同行评审的手稿开发和出版。除了对加州大学洛杉矶分校的本科生进行培训外，研究人员还与阿拉斯加本土科学与工程项目和南加州海洋学院（SoCalSeas）合作，后者是由南加州两年制和四年制大学的教师组成的网络，旨在搭建海洋学教育的桥梁。该项目的结果将以各种媒体内容的形式传播给公众和学术团体，包括加州大学洛杉矶分校科学多元化领导中心，旨在为深海科学及相关领域的参与提供信息和激励。例如，这个项目中的海底地图将被改编成高中、社区学院和大学课堂教学的GIS练习。虽然美国国家科学基金会资助的METHANOSPHERE项目旨在重新定义深海甲烷渗漏对底栖生态系统的影响，但生物介导的碳酸盐腐蚀的作用尚未得到解决。本研究旨在通过u系列年代测定碳酸盐的年代，直接评估与腐蚀驱动的甲烷自生碳酸盐溶解相关的碳损失随时间的变化；用活微生物接种碳酸盐进行孵育，以确定与不同微生物腐蚀过程相关的碳通量；扫描电子显微镜定量碳酸盐表面腐蚀并确定其来源；以及地球化学模型，将这些结果与相关的甲烷圈项目结果结合起来，计算在标准深海条件下生物介导的碳酸盐腐蚀随时间的碳损失。甲烷圈站点将允许在高氧水平与低光合食物输入（阿留申群岛）和低氧水平与高生产力条件（加利福尼亚州）的代表性条件下比较甲烷衍生的自生碳酸盐腐蚀。将计算这些地点与碳酸盐腐蚀有关的碳通量，并将其与负责估计与给定环境和腐蚀过程有关的通量的生物体联系起来。本研究的目标是产生1.)南加州边缘地带渗漏的侵蚀物质平衡，包括实验数据、海底照相图和基材图。2 .阿留申边缘渗漏的侵蚀物质平衡，包括实验数据、海底显微摄影和基材图；甲烷衍生自生碳酸盐腐蚀模式识别指南（包括两个站点的数据）。研究人员正在通过船上和实验室的孵化和分析来测量、取样和表征碳酸盐，以实现这些目标。这项研究的见解将在每年至少一次的国际会议上提出；并在加州大学洛杉矶分校的新生课程“甲烷是另一个温室问题”和本科生/研究生课程“水生地球微生物学”中担任客座讲师，该课程针对非stem学生。由于甲烷渗漏和残余碳酸盐在大陆边缘广泛分布，通过渗漏碳酸盐的碳循环可能是全球海底甲烷预算的重要组成部分，其量化对于估算甲烷衍生碳的长期埋藏至关重要。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。

This research fellowship investigates the amount of carbon released back into seawater by biological processes that dissolve the carbonate rock structures formed at oceanic methane seeps. Throughout the worlds’ oceans, methane rises through seafloor sediments from subduction zones and old organic material buried below the seafloor. Most of this methane is consumed by unique microbial and chemical activity before it can reach the ocean or atmosphere. Within this “methanosphere”, rocks form in the soft sediments near the seafloor when dissolved or gaseous carbon seeping up from below precipitates as solid carbonate. These rocks provide a hard surface for deep-sea organisms to inhabit and store carbon that would otherwise contribute to increased carbon dioxide in the ocean and atmosphere. Carbonate will dissolve back into seawater when the acid content of surrounding waters increases, which can be caused by the complicated biogeochemical reactions occurring on and around the carbonate rocks. Without accounting for this dissolution of carbonate, the amount of carbon that reaches the atmosphere from the subseafloor on timescales relevant to anthropogenic climate change cannot be fully quantified. This research will support two undergraduates and provide training in Geographic Information Systems; image processing software; database management; and peer-reviewed manuscript development and publication. In addition to training for undergraduate students at UCLA, the investigators are collaborating with the Alaska Native Science and Engineering Program and SoCalSeas, the Southern California network of teachers from 2-year and 4-year colleges designed to bridge education in oceanography. Results of the project will be disseminated to public and academic groups, including the Center of Diverse Leadership in Sciences at UCLA, as a variety of media content for a range of learning styles designed to inform and inspire participation in deep-sea science and related fields. For example, the seafloor maps from this project will be adapted to GIS exercises for high school, community college, and university classroom instruction.While the NSF-funded METHANOSPHERE project aims to redefine the footprint of deep ocean methane seepage for benthic ecosystems, the role of biomediated carbonate corrosion is not addressed. This study aims to directly evaluate the carbon loss over time associated with corrosion-driven dissolution of methane derived authigenic carbonate through U-series chronology to date carbonates; incubation of carbonates inoculated with living microbes to determine the carbon flux associated with different microbiological corrosion processes; scanning electron microscopy to quantify carbonate surface corrosion and identify its source; and geochemical modeling that combines these results with the relevant METHANOSPHERE project results to calculate the carbon loss over time from biomediated carbonate corrosion under canonical deep ocean conditions. The METHANOSPHERE sites will allow the comparison of methane derived authigenic carbonate corrosion under the representative conditions of higher oxygen levels with lower photosynthetic food input (Aleutian) and lower oxygen with higher productivity conditions (California). Carbon fluxes associated with carbonate corrosion at these sites will be calculated and related to the organisms responsible to estimate a flux associated with a given environment and corrosion process. The goals of this study are to produce 1.) An erosion mass balance of the Southern California Borderlands Seep, including experimental data, seafloor photomosaics, and substrate maps, 2.) An erosion mass balance of the Aleutian Margin Seep including experimental data, seafloor photomosaics and substrate maps, and 3.) A methane derived authigenic carbonate corrosion pattern identification guide (including data from both sites). The investigators are addressing these goals by surveying, sampling, and characterizing carbonates through shipboard and laboratory incubations and analyses. Insights from the study will be presented at least once annually at an international conference; and as a guest lecture in the UCLA Freshman class "Methane the other greenhouse problem”, which targets non-STEM students, and the undergraduate/graduate course "Aquatic Geomicrobiology". As methane seeps and relic carbonates are widespread along the continental margins, carbon cycling through seep carbonates is likely a substantial component of the global subseafloor methane budget and its quantification is crucial to estimate long-term burial of methane-derived carbon.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.