Collaborative Research: Photodegradation of Dissolved Organic Matter and its Contribution to Surface Water CO2 fluxes and the Carbon Cycle in a River Dominated Ocean Margin

海洋边缘是陆地-海洋-空气界面上的高度动态系统，它们在这些储存库中的全球碳通量中扮演着不成比例的大角色。河流控制的边缘接收到大量的陆源溶解有机物(DOM)及其发色组分(CDOM)，这些物质具有高度的光活性，似乎在很大程度上被边缘表层水域中的二氧化碳重新矿化。尽管在以河流为主的边缘地区，光化学过程的重要性得到了公认，但地表水二氧化碳通量中光化学过程的整体意义仍然不确定。在这个项目中，南卡罗来纳大学哥伦比亚分校和佐治亚大学的研究人员将对墨西哥湾北部边缘表层水中光化学和耦合光化学-微生物碳(包括CO2和CO)通量和陆源DOM和CDOM的清除进行区域尺度的估计。这个大洋边缘接受了来自密西西比河水系的陆源DOM(3Tg Cyr-1)和CDOM的主要贡献。具体目标包括测定光产生二氧化碳和一氧化碳的表观量子产率(AQY)，光化学去除DOC，以及光化学-微生物耦合去除DOC。实验确定的AQY将与现场测量、卫星图像和建模相结合，以提供对研究区域光化学介导的碳通量的时间综合、区域尺度的评估。该项目将包括改进遥感算法和开发区域尺度的海洋边缘碳循环模型。一旦开发出这种方法，就可以用来在其他以河流为主的海洋边缘提供类似的评估。在海上，该项目将利用一艘机遇船，并与目前资助的一项研究相结合，该研究调查墨西哥湾北部边缘的总二氧化碳通量和生物过程。这种项目的协调将提供一个前所未有的机会，以了解在一个以河流为主的主要边缘地区控制大气-海洋二氧化碳通量的基本物理、生物和光化学过程。更广泛的影响：北美碳计划和海洋碳与气候变化计划已经确定，测量海洋边缘的碳通量(特别是CO2和CO)并确定推动这些通量的基本因素具有重要意义。该项目将提供对北美大陆以河流为主的一个主要边缘地区表层水中光化学和光化学-微生物耦合碳通量的区域估计。该项目将为每个机构的一名研究生提供培训、经验和支持。这两位主要研究人员都教授本科生和研究生课程，涵盖碳循环的各个方面，从这个项目收集的数据将作为这些课程的具体例子。这种将来自积极研究项目的信息融入课堂的方法已被证明对提高学生对科学的兴趣非常有效，并鼓励本科生参与研究。

Ocean margins are highly dynamic systems at the land-sea-air interfaces, and they play a disproportionately large role in global carbon fluxes among these reservoirs. River dominated margins receive large quantities of terrigenous dissolved organic matter (DOM) and its chromophoric component (CDOM) that is highly photoreactive and appears to be largely remineralized to CO2 in margin surface waters. Despite the recognized importance of photochemical processes in river dominated margins, the overall significance of photochemistry in surface water CO2 fluxes remains uncertain. In this project, researchers at the University of South Carolina at Columbia and the University of Georgia will develop regional-scale estimates of photochemical and coupled photochemical-microbial carbon (including CO2 and CO) fluxes and removal of terrigenous DOM and CDOM in surface waters of the northern Gulf of Mexico margin. This ocean margin receives major contributions of terrigenous DOM (3 Tg C yr-1) and CDOM from the Mississippi River system. Specific objectives include determination of apparent quantum yields (AQY) for the photoproduction of CO2 and CO, the photochemical removal of DOC, and the coupled photochemical-microbial removal of DOC. Experimentally determined AQYs will be used in combination with field measurements, satellite imagery, and modeling to provide temporally-integrated, regional-scale assessments of photochemically-mediated carbon fluxes in the study region. The project will include improvement of remote-sensing algorithms and the development of regional-scale models for ocean margin carbon cycling. Once developed, this approach can be utilized to provide similar assessments in other river dominated ocean margins. At sea, the project will utilize a ship of opportunity and integrate with a currently funded study investigating total CO2-fluxes and biological processes in the northern Gulf of Mexico margin. This coordination of projects will provide an unprecedented opportunity for understanding the fundamental physical, biological, and photochemical processes controlling air-sea CO2 fluxes in a major river dominated margin. Broader Impacts: Measuring carbon fluxes (specifically CO2 and CO) in ocean margins and identifying the fundamental factors driving these fluxes have been identified as of great importance by the North American Carbon Program and Ocean Carbon and Climate Change programs. This project will provide regional estimates of photochemical and coupled photochemical-microbial carbon fluxes in surface waters of one of the major river dominated margins of the North American continent. This project will provide training, experience and support for a graduate student at each institution. Both principal investigators teach undergraduate and graduate classes that cover various aspects of the carbon cycle, and data collected from this project will be used as specific examples in these classes. This approach of incorporating information from active research programs into the classroom has proven to be very effective for increasing student interest in science and has encouraged undergraduate participation in research.