CAREER: The Role of Sulfur in Regulating the Marine Carbon Cycle: Implications for Understanding Oceanic Anoxic Events

智力优势：海洋缺氧事件（OAE）记录了有机碳埋藏的显着增加，并以海洋碳酸盐和有机碳（C）的正偏移为标志。虽然人们普遍认为，这些事件是由地表沃茨内初级生产力的增强所驱动的，但支撑OAE开始、维持和终止的细节仍然不明确。这项工作将揭示硫（S）同位素研究的潜力，以阐明海洋沉积物中硫酸盐浓度变化对磷酸盐（PO 4）再生的作用，并将对理解C循环的行为产生深远的影响，因此气候，特别是在深时间记录中。这是因为在地球历史的大部分时间里，海洋硫酸盐水平一直很低。该提案的目的是调查硫在低硫酸盐海洋中调节海洋碳循环中的作用。将检验以下假设：鉴于海洋硫酸盐浓度低的平均背景，海水硫酸盐水平的增加可能会促进磷（P）的再循环，从而提高海洋表层沃茨的初级生产，从而引发大范围的海洋缺氧。因为地球上大部分地区的海水硫酸盐浓度都很低？根据历史，过去硫酸盐水平的大幅波动可能在调节古代海洋中的碳循环方面发挥了关键作用。为了验证这一假设，该提案详细介绍了一项具有三个基本主题的研究，每个主题都将与西北大学教育与社会政策学院的STEM教育伙伴关系办公室（OSEP）开发的教育推广工作相结合。这些主题包括：（1）低硫酸盐、永久缺氧湖泊（Lake McCarrons，MN）中S同位素系统学以及硫酸盐水平波动与磷循环之间的联系;（2）海水硫酸盐、沉积黄铁矿的S同位素组成以及两次海洋缺氧事件之前、期间和之后的两个阶段（Δ 34 S）之间的差异。早白垩世的OAE 1a事件和晚泥盆世的弗拉斯期-法门期事件;（3）利用硫同位素建立与储层相关的物质平衡模型。这个项目的结果将改善社区？S和P循环在低硫酸盐系统的理解，建立<$34S硫酸盐-黄铁矿的两个时间段，标志着广泛缺氧（早白垩世和晚泥盆世），并帮助确定一套复杂的反馈，海洋氧化还原和地球化学循环的C，S，P，和Fe在地球上的低硫酸盐海洋？更广泛的影响：该项目将为两名研究生提供实地研究技术和分析同位素地球化学方面的培训，并有助于了解C、S、P和Fe的地球化学循环的控制及其与地球系统氧化还原状态的关系。该项目的影响超出了科学界，通过外联努力扩大到公立高中。外展工作的总体目标是给高中生带来做真实的科学的兴奋和挑战。该提案要求提供资金，每年夏天招募一名当地高中科学教师参加研究。这位教师将合作开发实验室活动，通过NSF资助的iLab网络（ilabcentral.org）为高中生提供研究经验，该网络允许学生和教育工作者使用远程实验设备通过Web进行实验。一旦iLab实验通过测试，通过与最初的高中，然后与OSEP合作伙伴学校在该地区的发展，他们将提供给任何高中教师与网络浏览器。为了解决地球科学中代表性不足的群体的问题，与EXCITE项目建立了合作伙伴关系，该项目将西北大学？美国的人才发展中心与当地学校，以确定科学倾向的少数民族学生，并支持他们通过高中获得数学和科学技能。星期六与项目EXCITE学生和他们的家长的丰富课程正在进行中，重点是关键的地球科学概念（地震，海啸，气候变化）和地球和行星科学的职业选择。该提案寻求资金，以支持EXCITE的高中学生担任实验室助理，以提高当地学生及其家庭对地球科学机会的认识。

Intellectual Merit: Oceanic anoxic events (OAE) record significant increases in organic carbon burial and are marked by positive excursions in both marine carbonate and organic carbon (C). While it is widely held that these events were driven by enhanced primary production within surface waters, the details underpinning the initiation, maintenance and termination of OAEs remain equivocal. This work will reveal the potential of sulfur (S) isotope studies to illuminate the role of changing sulfate concentrations on phosphate (PO4) regeneration in marine sediments and will have far-reaching implications for understanding the behavior of the C cycle, and therefore climate, especially in the deep time record. This is because marine sulfate levels have been low for much of Earth history. The objective of this proposal is to investigate the role sulfur plays in regulating the marine carbon cycle in low sulfate oceans. The following hypothesis will be tested: given an average background of low marine sulfate concentrations, an increase in seawater sulfate levels may trigger widespread oceanic anoxia by facilitating enhanced phosphorus (P) recycling and thus higher primary production within marine surface waters. Because seawater sulfate concentrations have been low for most of Earth?s history, substantial fluctuations in sulfate levels in the past may have played a key role in regulating C cycling in ancient oceans. In order to test this hypothesis, this proposal details a study with three fundamental themes, each of which will be integrated with an educational outreach effort developed through the Office of STEM Education Partnerships (OSEP) in the School of Education and Social Policy at Northwestern University. The themes include: (1) S isotope systematics and the link between fluctuating sulfate levels and P recycling in a low sulfate, permanently anoxic lake (Lake McCarrons, MN), (2) the S isotope composition of seawater sulfate, sedimentary pyrite and difference between the two phases (Ä34S) before, during and after two oceanic anoxic events?OAE1a in the Early Cretaceous and the Frasnian-Famennian event in the Late Devonian, and (3) reservoir dependent mass balance modeling using S isotopes. The results from this project will improve the community?s understanding of S and P cycling in low sulfate systems, establish Ä34Ssulfate-pyrite for two time periods marked by widespread anoxia (the Early Cretaceous and the Late Devonian), and help to ascertain the complex set of feedbacks that link ocean redox and the geochemical cycles of C, S, P, and Fe in the low sulfate oceans of Earth?s past.Broader Impacts: This project will provide training to two graduate students in field research techniques and analytical isotope geochemistry and make contributions to understanding controls on biogeochemical cycles of C, S, P and Fe and their relationship to the redox state of the Earth system. Impacts of this project extend beyond the scientific community via an outreach effort to public high schools. The overall goal of the outreach effort is to bring the excitement and challenge of doing real science to high school students. This proposal requests funds to recruit a local high school science teacher to participate in research each summer. This teacher will collaborate to develop laboratory activities to provide high school students with research experiences through the NSF-funded iLab Network (ilabcentral.org), which allows students and educators to use remote experimental apparatus to carry out experiments via the Web. Once the iLab experiments have been tested, through development with the initial high school and then with OSEP partner schools in the area, they will be made available to any high school teacher with a web browser. To address the problem of underrepresented groups in Earth Science, a partnership has been initiated with Project EXCITE, a program that links Northwestern?s Center for Talent Development with local schools to identify scientifically inclined minority students and support their acquisition of math and science skills through high school. Saturday enrichment sessions with Project EXCITE students and their parents are ongoing, focusing on key Earth science concepts (earthquakes, tsunamis, climate change) and career options in Earth and Planetary Sciences. This proposal seeks funds to support high school students from EXCITE as lab assistants to increase awareness of opportunities in Earth science for local students and their families.