Coupled carbonate dissolution and authigenic clay formation in the bioturbated zone

海洋沉积物中发生的化学反应在全球地球化学循环（包括碳循环）中起着重要作用。了解这些反应是预测海洋对气候变化等持续扰动的反应的关键。该项目将结合联合收割机现场测量、受控实验室实验和建模，以增加对穴居生物和地球化学反应造成的沉积物混合的相互作用的理解，以及它们如何影响海洋的碳和碱度平衡。该项目为研究生和本科生提供实地工作、实验程序、使用先进的分析设备、定量数据分析和数值建模技术方面的培训。教育目标是鼓励科学发现，同时培养创造力，促进批判性思维能力，提高解决问题的能力，并鼓励下一代科学家的发展，能够解决社会面临的许多环境挑战。该项目的总体目标是推进我们的概念性理解和预测性定量建模的氧化还原和酸碱反应的复杂模式的生物扰动带内的地球化学过程的影响。在含氧水体下的大陆边缘沉积物中，还原代谢产物如铵、铁（II）、锰（II）和黄铁矿的再氧化导致强酸的产生。特别是沉积黄铁矿的氧化作用可以驱动碳酸盐溶解和硅酸盐自生作用。碳酸盐和硅酸盐反应的最终耦合仍然知之甚少，并且可能产生或消耗碳酸盐碱度。这些反应集中在好氧区和缺氧区之间的边界。生物扰动沉积物中的缺氧-缺氧环带和环带相互作用模式反映了灌溉洞穴结构的形成、缩放和停留时间以及摄食和流动性活动，这动态地暴露了缺氧沉积物，促进了再氧化和缺氧-缺氧振荡。如初步实验所示，这些过程不仅导致碳酸盐的不饱和和增强的溶解，而且还可能促进正向（产生碱度）和反向（消耗碱度）硅酸盐风化反应。拟议的研究将利用现场测量，控制实验室实验操作和几何模拟，2-D成像传感器和理论建模的综合方法，以解决如何复杂，动态的生物运输反应几何结构，导致生物扰动活动，介导耦合氧化还原反应与碳酸盐溶解和粘土自生，并影响净底栖碱度通量。这项新的研究将进一步限制因素控制净沉积物之间的沉积物-水碱度通量的岩性存款和上覆水，从而海洋acidization.This奖项的模型反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Chemical reactions that occur in ocean sediments play an important role in global geochemical cycles, including the carbon cycle. Understanding these reactions is key to predicting the response of the ocean to ongoing disturbances like climate change. This project will combine field measurements, controlled laboratory experiments, and modeling to increase understanding of the interplay of sediment mixing by burrowing organisms and geochemical reactions, and how they affect the ocean’s carbon and alkalinity balance. The project provides for the training of graduate and undergraduate students in field work, experimental procedures, the use of sophisticated state-of-the-art analytical equipment, quantitative data analysis, and numerical modeling techniques. The educational goals are to encourage scientific discovery while fostering creativity, promote critical-thinking skills, enhance problem solving skills, and to encourage the development of the next generation of scientists to be able to address the many environmental challenges facing society. The general objectives of the project are to advance our conceptual understanding and predictive quantitative modeling of the impacts of complex patterns of oxidation-reduction and acid-base reactions on biogeochemical processes within the bioturbated zone. In continental margin deposits underlying oxygenated water, the reoxidation of reduced metabolic products such as ammonium, iron (II), manganese (II) and pyrite results in strong acid production. Sedimentary pyrite oxidation in particular can drive carbonate dissolution and silicate authigenesis. The resulting coupling of carbonate and silicate reactions remains poorly known, and may produce or consume carbonate alkalinity. These reactions are focused at boundaries between oxic and anoxic zones. Oxic-anoxic zonation and zonal interaction patterns in bioturbated deposits reflect the formation, scaling, and residence times of irrigated burrow structures as well as feeding and mobility activity, which dynamically exposes anoxic sediment and promotes reoxidation and oxic-anoxic oscillations. As shown by initial experiments, these processes result not only in undersaturation of carbonates and enhanced dissolution, but may also promote forward (alkalinity producing) and reverse (alkalinity consuming) silicate weathering reactions. The proposed research will utilize a combined approach of field measurements, controlled laboratory experimental manipulations and geometric mimics, 2-D imaging sensors, and theoretical modeling, to address how complex, dynamic biogenic transport-reaction geometries that result from bioturbation activities, mediate coupled redox reactions associated with carbonate dissolution and clay authigenesis, and affect net benthic alkalinity fluxes. This novel research will further constrain factors controlling net sediment-water alkalinity fluxes between lithogenic deposits and overlying water, and thus models of ocean acidification.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.