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包括碳循环在内的全球地球化学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干扰的反应的关键。该项目将结合实地测量、受控实验室实验和建模，以加深对穴居生物和地球化学反应对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、尖端分析设备的使用、定量数据分析和数值模拟技术方面的培训。教育目标是鼓励科学发现，同时培养创造力，培养批判性思维技能，提高解决问题的能力，并鼓励下一代科学家的发展，以应对社会面临的许多环境挑战。该项目的总体目标是推进我们对生物扰动区内复杂氧化还原和酸碱反应模式对生物地球化学过程影响的概念理解和预测定量建模。在含氧水下的大陆边缘沉积物中，还原性代谢产物如铵、铁（II）、锰（II）和黄铁矿的再氧化产生强酸。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。由此产生的碳酸盐和硅酸盐反应的耦合仍然知之甚少，并且可能产生或消耗碳酸盐碱度。这些反应集中在有氧区和无氧区之间的边界上。生物扰动沉积物中的氧-缺氧分带和分带相互作用模式反映了灌溉穴居结构的形成、结垢、停留时间以及取食和流动活动，动态地暴露了缺氧沉积物，促进了再氧化和氧-缺氧振荡。初步实验表明，这些过程不仅导致碳酸盐欠饱和和溶解增强，而且可能促进正向（产碱）和反向（消碱）硅酸盐风化反应。拟议的研究将利用现场测量、受控实验室实验操作、几何模拟、二维成像传感器和理论建模相结合的方法，来解决由生物扰动活动引起的复杂、动态的生物运输-反应几何形状，介导与碳酸盐溶解和粘土自生相关的耦合氧化还原反应，并影响净底栖碱度通量。这项新研究将进一步限制控制岩质沉积物和上覆水之间净沉积物-水碱度通量的因素，从而确定海洋酸化模型。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。

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.