The Riverine Fluxes of Rhenium and Molybdenum to the Ocean

EAR-0519387PEUCKER-EHRENBRINK智慧价值：这项提案中提出的数据挑战了传统观点，即河口地区Re的保守行为。Re和Mo定义了具有重要基础科学和应用科学应用的放射性成因Re-Os和稳定的Mo同位素体系。这两种元素都被认为在有毒的水环境中表现出保守的行为。它们的特点是在海水中的停留时间较长，这是由于海水中的溶解浓度相对较高(Re：40 pm；Mo：105 nm)和低平均浓度(Re：2 pm；Mo：5 nM)所致。这两种元素都对氧化还原反应敏感，并在还原沉积物中积累。在氧化风化过程中，它们很容易从这种沉积物中被活化，并可用作旧沉积有机质氧化的指示物。我们在哈德逊河口盐度剖面发现了明显的非保守Re浓度剖面，挑战了保守Re行为的概念。预计的淡水浓度约为60 PM，超过了可接受的世界平均河流浓度30倍。密西西比河淡水中~90 Pm的高Re浓度表明哈德逊河中的高Re浓度也不例外。虽然在20世纪90年代初，在流入黑海的河流中也检测到了类似的高Re浓度，但这些浓度被解释为反映了人为污染(燃煤)。这一建议有三个目标：1)将沿着哈德逊河河口的盐度梯度进行Re(和Mo)浓度的调查，以确定非保守的Re剖面是否是一个稳定的特征。将在非常不同的流动阶段进行两次巡航，以确定这一特征是由自然过程还是人为污染造成的2)与杜兰大学的Franco Marcantonio教授合作。将在密西西比河河口研究Re(和Mo)的行为。此外，将对密西西比州主要支流长达一年、每两周一次的Re和Mo浓度时间序列以及每三个月一次的Re和Mo浓度时间序列进行分析，以确定高Re输入的源区。3)将修订世界平均河流Re和Mo通量的估计。这将通过一个合作研究部分实现，该部分的基础是使用标准化、低成本和经过良好测试的采样/过滤工具包，将其发送给世界各地的合作者，以及(合作者)对世界卫生组织和其他地方存储的存档河水样本进行分析。广泛的影响：限制河流中Re和Mo的通量对于使用放射性成因Re-Os和稳定的Mo同位素系统作为有机物质循环的指示器至关重要。现代河流系统潜在的广泛再污染可能表明工业循环的泄漏或另一个人为来源。使用标准化样品盒旨在测试这种方法是否提供了一种经济的方法来改善全球河流中“难污染”元素的通量，如Re、Mo和U。如果成功，这种方法将在未来被用作教育和研究的结合工具，让科学教师和他们的学生参与到地球化学研究中来。该项目将支持研究助理特蕾西·阿布鲁泽斯和麻省理工学院/世界卫生组织联合项目学生克里斯蒂安·米勒的科学教育。

EAR-0519387PEUCKER-EHRENBRINKIntellectual Merit: Data presented in this proposal challenge the conventional view of conservative behavior of rhenium in estuaries. Rhenium and molybdenum define the radiogenic Re-Os and the stable Mo isotope systems that have important basic and applied science applications. Both elements are thought to exhibit conservative behavior in oxic aquatic environments. They are characterized by long residence times in seawater that result from relatively high dissolved concentrations in seawater (Re: 40 pM; Mo: 105 nM) and low averageriverine concentrations (Re: 2 pM; Mo: 5 nM). Both elements are redox-sensitive and accumulate in reducing sediments. They are easily mobilized from such sediments during oxic weathering and can be used as indicators of oxidation of old sedimentary organic matter.The notion of conservative Re behavior is challenged by our finding of a pronounced nonconservative Re concentration profile in the Hudson River Estuary salinity profile. The projected freshwater concentration of ~60 pM exceeds the accepted world-average river concentration 30-fold. High Re concentrations of ~90 pM in fresh Mississippi River water indicate that the high Re concentrations in the Hudson River are no exception. Though similarly high Re concentrations were detected in the early 1990s in rivers draining into the Black Sea, these concentrations were interpreted as reflecting anthropogenic contamination (coal burning).This proposal has three goals:1) Surveys of Re (and Mo) concentrations will be conducted along the salinity gradient in theHudson River estuary to determine whether the non-conservative Re profile is a steady-state feature. Two cruises will be conducted at very different flow stages to determine whether this feature is caused by a natural process or by anthropogenic contamination.2) In collaboration with Prof. Franco Marcantonio (Tulane Univ.) the behavior of Re (and Mo) will be studied in the Mississippi River estuary. In addition, a year-long, bi-weekly time series of Re and Mo concentrations as well as a tri-monthly time series of Re and Mo concentrations in major Mississippi tributaries will be analyzed to identify source regions of high Re input.3) Estimates of world-average riverine Re and Mo fluxes will be revised. This will be achieved through a collaborative research component that is based on the use of standardized, low-cost and well-tested sampling/filtration kits to be sent to collaborators world-wide, as well as the analyses of archived river water samples stored at WHOI and elsewhere (by collaborators).Broader Implications: Constraining riverine fluxes of Re and Mo is critical for using the radiogenic Re-Os and stable Mo isotope systems as indicators of organic-matter cycling. The potentially wide-spread Re contamination of modern river systems may indicate a leaky industrial Re cycle or another anthropogenic source. The use of standardized sample kits aims at testing whether this method provides an economical way of improving global riverine fluxes for "hard to contaminate" elements, such as oxyanions Re, Mo, and U. If successful, this method will be used in the future as a combined educational and research tool for involving science teachers and their pupils in geochemical research. The project will support the scientific education of Research Assistant Tracy Abbruzzese and MIT/WHOI Joint Program student Christian Miller.