Career: Geochemistry of Redox-Sensitive Elements and Osmium and Uranium Isotopes in Large Pristine Rivers

大陆风化是全球地球化学循环的一个重要组成部分，也是大气二氧化碳水平的最重要决定因素之一，因此在地质时间尺度上也是气候的决定因素。有机碳的风化是二氧化碳的重要来源；硅酸盐的风化是二氧化碳的汇。PI研究的长期目标是了解目前各种原始环境中大陆风化的机制和程度，然后使用合适的替代物将结果投射到地质过去。在这项工作中，表征不同化学元素的行为作为风化环境的函数是重要的。PI建议研究大型原始河流中表现出来的富含有机碳的还原沉积物的风化作用。这项建议描述了一种综合方法，使用氧化还原敏感的氧阴离子形成元素(Re，Mo，V，U)和与它们密切相关的Os同位素系统(187Os/188Os)。这些元素在还原沉积物中富含，并在经历快速氧化风化时以可溶氧阴离子的形式释放。拟议的研究活动包括三个部分：实地工作、仪器分析和数据解释。野外工作将在中国西部、西藏东部和越南北部进行，这些地区受到喜马拉雅碰撞的影响，但对其河流地球化学了解甚少。这将是与中国和越南科学家成功合作的延续。西北大学的一名研究生和来自越南的中国访问学者将参加这三项活动。在本科生水平上，这项研究将被整合到国际地球物理研究所正在开发的地球化学分析方法课程中，以加强西北大学的跨学科环境科学计划。这项工作将提供对氧化还原敏感元素和Os同位素行为的基本理解，这反过来对破译地球古环境也很重要。另一个好处是记录了长江上游目前的风化状况，这对中国科学家试图监测三峡大坝的影响和表层土壤侵蚀正成为一个严重问题非常重要。此外，在未开发的源头和受农业影响的中国和越南河流的下游之间也可以进行明确的比较。

0134966HudContinental weathering is an important component of global geochemical cycles and is one of the most significant determinants of the atmospheric CO2 levels, and hence climate, on geologic time scales. Weathering of organic carbon is an important source of CO2; weathering of silicates a sink. The long-term goal of the PI's research is to understand the mechanisms and magnitudes of continental weathering in various pristine environments at present and to then project the results into the geologic past using suitable proxies. In this endeavor, characterizing the behavior of different chemical elements as a function of weathering environment is important. The PI proposes to study weathering of organic carbon rich reducing sediments as manifested in large pristine rivers. This proposal describes an integrative approach using redox-sensitive, oxyanion-forming elements (Re, Mo, V, U) and the Os isotopic system (187Os/188Os) intimately related to them. These elements are enriched in reducing sediments and are released as soluble oxyanions when they undergo fast oxidative weathering. The proposed research activities consist of three parts: field work, instrumental analyses and data interpretation. Field work will be carried out in western China, eastern Tibet, and northern Vietnam, areas affected by the Himalayan collision but whose fluvial geochemistry is poorly understood. This will be a continuation of the successful collaboration with scientists in China and Vietnam. A graduate student at Northwestern University and visiting scholars from China/Vietnam will be involved in all three activities. At undergraduate students level, this research will be integrated into the Analytical Methods in Geochemistry course that the PI is developing to strengthen the interdisciplinary Environmental Science Program at Northwestern University.This work will provide fundamental understanding of the behavior of redox-sensitive elements and Os isotopes, which is in turn important in deciphering the paleo-environments of the Earth. Additional benefit is documenting the present weathering regime of the Upper Yangtze, which is important for the Chinese scientists in their attempt to monitor the effect of the Three Gorges Dam and erosion of top soil that is becoming a serious problem. Also, a clear comparison can be made between the undeveloped headwaters and the agriculturally impacted lower reaches of the Chinese and Vietnamese rivers.