The Riverine Fluxes of Rhenium and Molybdenum to the Ocean

peucker - ehrenbrinkin智力价值：该提案中提出的数据挑战了传统观点，即河口中铼的保守行为。铼和钼定义了放射性成因的Re-Os和稳定的Mo同位素体系，具有重要的基础和应用科学应用。这两种元素被认为在含氧水生环境中表现出保守的行为。它们在海水中的溶解浓度较高（Re: 40 pM; Mo: 105 nM），而平均河水浓度较低（Re: 2 pM; Mo: 5 nM），因此在海水中停留时间较长。这两种元素都对氧化还原敏感，并在还原性沉积物中积累。它们在氧化风化过程中很容易从沉积物中被动员起来，可以作为古沉积有机质氧化的指示物。保守Re行为的概念受到我们在哈德逊河河口盐度剖面中发现的明显的非保守Re浓度剖面的挑战。预测的~60 pM淡水浓度超过公认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检测到类似的高Re浓度，但这些浓度被解释为反映了人为污染（燃煤）。该计划有三个目标：1)在哈德逊河河口沿盐度梯度进行Re（和Mo）浓度调查，以确定非保守Re剖面是否是一个稳态特征。两个巡航将在非常不同的水流阶段进行，以确定这一特征是由自然过程还是人为污染造成的。2)与佛朗哥·马尔坎托尼奥教授（杜兰大学）合作，将在密西西比河河口研究Re（和Mo）的行为。此外，将分析密西西比河主要支流一年、两周的Re和Mo浓度时间序列，以及三个月的Re和Mo浓度时间序列，以确定高Re输入的来源区域。3)对世界平均河流Re和Mo通量的估算将进行修正。这将通过协作研究组成部分来实现，协作研究的基础是使用标准的、低成本的和经过充分测试的采样/过滤工具包，这些工具包将发送给世界各地的合作者，并分析（由合作者）存放在世卫组织和其他地方的存档河水样本。更广泛的意义：限制Re和Mo的河流通量对于使用放射性成因的Re- os和稳定的Mo同位素系统作为有机物循环的指标至关重要。现代河流系统中潜在的广泛的Re污染可能表明一个泄漏的工业再循环或其他人为来源。使用标准化样品包的目的是测试这种方法是否提供了一种经济的方法来改善“难以污染”元素的全球河流通量，如氧化离子Re、Mo和u。如果成功，这种方法将在未来作为一种结合教育和研究的工具，让科学教师及其学生参与地球化学研究。该项目将支持研究助理Tracy Abbruzzese和MIT/WHOI联合项目学生Christian Miller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.