Trace metal signatures in continental sedimentary systems: Isotope constraints, biogeochemistry, and potential as a paleoclimatic tracer

智力上的优点。这项拟议的工作将解决关于导致钼、铀和钒从水生系统中移除的生物地球化学相互作用以及在有机物分解过程中发生的钼同位素分馏的假说。我们的研究地点坦噶尼喀湖是一个古老的裂谷湖，由富氧的上层水柱和硫化物深水组成。在这两个水域下面都有沉积矿床的存在，为量化金属溶解度的变化和检验与金属沉淀有关的同位素分馏预测提供了一个令人兴奋和及时的机会。我们的工作是在两个假设的指导下进行的，这两个假设预测了金属积累速度和碳循环之间的密切联系。这些假设预测了钼同位素的不同行为，这取决于上覆水是否存在硫化物。(1)在上覆水柱不含硫化物的地区，我们假设沉积物中微量元素的积累和钼同位素组成与有机碳的循环密切耦合。(2)当沉积物浸泡在富硫化物的水中时，我们假设微量元素的丰度对有机碳循环很敏感，但钼的同位素值是不变的。虽然我们使用这些假设作为我们研究的指导，但我们确实预计目标元素将对有机碳循环和水柱硫化物浓度表现出一系列的敏感性。目标元素已经提供了潜在的生物地球化学示踪剂，这项提议为解决有关其环境化学的重要问题提供了一个令人兴奋的机会。钼同位素还保留了在地质时期作为氧和硫化物有效性示踪剂的潜力，这一提议将使我们能够研究水柱硫化物的存在如何影响钼同位素行为。最后，非洲五大湖港有丰富的气候历史记录，可以追溯到中新世。我们在这里提供的是校准一套沉积示踪剂的机会，这些示踪剂最终可以对生物地球化学过程提供强有力的见解，不仅在坦噶尼喀山，而且在其他沉积系统中也是如此。坦噶尼喀湖是东非人民的宝贵资源。该湖拥有地球上相当大一部分淡水，为几个国家的经济提供了宝贵的渔业资源。从广义上讲，这项提议为解决与湖泊碳动态如何应对过去气候变化相关的问题提供了工具。作为这项提议的一部分，麦克马努斯将在2006年夏天参加Nyanza项目。Nyanza项目是一个本科生/研究生实地研究项目，提供了在大陆裂谷研究古气候学和地质学的机会，裂谷孕育着世界上最古老的湖泊之一。作为该项目的参与者，McManus将参与培训美国和非洲学生，我们计划让一名非洲学生和两名美国学生参与我们的实地研究。我们还将在资助的第二年资助一名俄亥俄州立大学的本科生。本科生对PI的研究计划做出了重大贡献，导致在主要会议上发表了摘要，在大学范围内的学生研究计划中发表了摘要，并与人合著了两篇手稿。我们学院正开始邀请我们学院的学生参与研究，我们计划在短期内启动一个REU项目。我们预计，这些项目中的一名学生也将参与拟议中的研究。最后，这项提案将为一名博士后研究助理(Chris Siebert)提供支持。

Intellectual merit. The proposed work will address hypotheses regarding thebiogeochemical interactions that lead to the removal of molybdenum, uranium, andvanadium from aquatic systems and the fractionation of Mo isotopes that occurs duringorganic matter decomposition. Our study site, Lake Tanganyika, is an ancient rift lake thathas an oxygenated upper water column and sulfidic deep waters. The existence ofsedimentary deposits underlying both these waters offers an exciting and timely opportunityto quantify changes in metal solubility and to test predictions regarding isotope fractionationassociated with metal precipitation. Our work is guided by two hypotheses that predict aclose link between metal accumulation rate and carbon cycling. These hypotheses predictdifferent behavior for Mo isotopes depending on whether or not the overlying water hassulfide present. (1) In regions where the overlying water column is absent of sulfide, wehypothesize that trace element accumulation in the sediments and Mo isotope compositionsare closely coupled to the cycling of organic carbon. (2) Where sediments are bathed withsulfide-rich water, we hypothesize that trace element enrichments remain sensitive to theorganic carbon cycling but Mo isotope values are invariant. Although we use thesehypotheses as a guide for our research, we do expect that the targeted elements will exhibit arange of sensitivities to organic carbon cycling and water column sulfide concentrations.Broader impacts I: Scientific value. The targeted elements already offer potential asbiogeochemical tracers, and this proposal represents an exciting opportunity to addressimportant issues regarding their environmental chemistry. Molybdenum isotopes alsoretain potential as a tracer for the availability of oxygen and sulfide through geologic time,and this proposal will allow us to examine how the presence of water column sulfideinfluences Mo isotope behavior. Finally, the African Great Lakes harbor rich records ofclimate history extending back to the Miocene. What we offer here is an opportunity tocalibrate a suite of sedimentary tracers that could ultimately provide powerful insights onbiogeochemical process, not only in Tanganyika, but in other sedimentary systems as well.Broader impacts II: Human impacts and opportunities for education. LakeTanganyika is a valuable resource to the East African people. The lake contains asignificant fraction of the Earth's fresh water and supplies the economies of several nationswith a valuable fisheries resource. In a broad sense, this proposal offers tools foraddressing questions related to how the lake's carbon dynamics have responded to pastchanges in climate. As part of this proposal, McManus will be participating in the Nyanzaproject during the summer of 2006. The Nyanza Project is an undergraduate/graduate fieldresearch program that offers opportunities to study paleoclimatology and geology in acontinental rift cradling one of the world's oldest lakes. As a participant in the programMcManus will be engaged in training both U.S. and African students, and we plan onhaving one African student and two U.S. students working on our field research. We willalso support an OSU undergraduate during our second year of funding. Undergraduatestudents have contributed significantly to the PI's research program resulting in abstractsdelivered at major conferences, university-wide student research programs, and coauthorshipon two manuscripts. Our college is beginning to engage students from our university'shonors college in research and we are planning on initiating an REU program in the nearterm. We anticipate having a student from one of these programs participating in theproposed research as well. Finally, this proposal will provide support for a postdoctoralresearch associate (Chris Siebert).