Fossil Coral Radiocarbon Records of Equatorial Pacific Upwelling over the Last Millennium

摘要（Cobb - 0452920）智力价值：这项研究由佐治亚理工学院的一名教师和学生资助，探讨了海洋环流在过去一千年中塑造热带太平洋气候变化的作用。这项工作的理由是，每隔两到七年，被称为厄尔尼诺-南方涛动（ENSO）的气候振荡就会导致热带太平洋的海面温度上升，从而显著改变世界许多地区的温度和降水模式。尽管卫星提供了最近的ENSO变率，但由于对控制热带太平洋气候变率的复杂大气和海洋相互作用了解不足，对热带太平洋气候变化的短期和长期预测都受到限制。从长寿的珊瑚中收集到的过去热带太平洋气候变化的记录，为全球气候系统的这一关键组成部分提供了几个世纪以来的视角，指导了理论和预测模型的发展。事实上，最近对热带太平洋珊瑚化石的研究表明，在过去的一千年里，热带太平洋的气候变化范围惊人地大——这种变化目前缺乏一个机制上的解释，但无疑为未来的气候变化提供了线索。这项受资助的研究包括通过测量在过去1000年里生长的中部热带太平洋珊瑚中的放射性碳，生成按季节到百年时间尺度的赤道太平洋上升流的月度分辨率、年代准确的记录，放射性碳被用来记录海洋垂直混合的强度。样本来自Line岛链（特别是Palmyra和Christmas Islands）的化石和现代珊瑚。本项目将免费收集额外的样本。将对样品进行岩石学和地球化学筛选以确定成岩作用。大多数样品已经用U-Th测定了年代，并对其进行了18O的分析，以确定时间和海面温度的控制，这项研究的结果将为上层海洋环流和热带太平洋气候变率之间的反馈提供急需的约束，这两者在预测未来人为气候变化方面都具有很大的不确定性。本研究中分析的珊瑚放射性碳数据将作为海洋环流模型的地面真相，并有助于改进垂直混合的参数化，目前这种参数化受到现有仪器数据的限制很差。更广泛的影响：本研究的更广泛影响包括将结果整合到佐治亚理工学院的研究生水平的同位素地球化学课程中。此外，两名本科生研究人员参与了这项工作，该研究将构成一名女研究生的博士论文研究。这项研究支持了一名没有获得NSF支持的女教师，并在NSF ADVANCE机构（佐治亚理工学院和加州大学欧文分校）的两名女教师之间建立了宝贵的合作和指导关系。这些数据将立即应用于海洋环流模式和海洋-大气耦合模式，这些模式对热带太平洋垂直混合的参数化需要用长时间、高分辨率的代理记录进行测试。

ABSTRACT (Cobb - 0452920)Intellectual Merit: This research, which supports a faculty member and student at the Georgia Institute of Technology, probes the role that ocean circulation plays in shaping tropical Pacific climate variability over the last millennium. Justification for the work comes from the fact that every two to seven years, the climate oscillation known as the El Nino-Southern Oscillation (ENSO) causes sea-surface temperatures to rise in the tropical Pacific ocean, significantly altering temperature and precipitation patterns in many areas of the world. Despite the recent ENSO variability afforded by satellites, both short and long-term predictions of tropical Pacific climate change are limited by poor understanding of the complex atmospheric and oceanic interactions that govern tropical Pacific climate variability. Records of past tropical Pacific climate variability, gleaned from long-lived corals, provide centuries-long perspectives on this key component of the global climate system, guiding the development of both theory and predictive models. In fact, recent work on a collection of fossil corals from the tropical Pacific has revealed a surprisingly large range of tropical Pacific climate variability during the last millennium - variability that currently lacks a mechanistic explanation, yet undoubtedly holds clues as to future climate change. The funded research involves generating monthly-resolved, well-dated records of equatorial Pacific upwelling on seasonal to centennial timescales by measuring radiocarbon in central tropical Pacific corals that grew during the last 1,000 years, with radiocarbon being used to document the strength of vertical mixing in the ocean. Samples come from fossil and modern corals from the Line Island Chain (Palmyra and Christmas Islands, in particular). Additional samples will be collected at no cost to this program. Samples will be screened petrographically and geochemically for diagenesis. Most samples have already been dated with U-Th and analyzed for 18O to determine chronological and sea surface temperature controls Results of this research will deliver much-needed constraints on the feedback between upper ocean circulation and tropical Pacific climate variability, both of which represent large uncertainties in predictions of future anthropogenic climate change. The coral radiocarbon data analyzed in this study will serve as ground-truthing for ocean circulation models and help improve parameterizations of vertical mixing, which is presently poorly constrained by available instrumental data.Broader impacts: Broader impacts of this research include the integration of results into a graduate-level Isotope Geochemistry course at Georgia Tech. In addition, two undergraduate research fellows are involved in this work and the research will constitute the PhD dissertation research of a female graduate student. The research supports a female faculty member with no prior NSF support and fosters a valuable collaboration and mentoring relationship between two female faculty at NSF ADVANCE institutions (Georgia Tech and UC-Irvine). The data will have immediate application in ocean general circulation models and coupled ocean-atmosphere models, whose parameterizations of vertical mixing in the tropical Pacific require testing with long, high-resolution proxy records.