Collaborative Research: Reconstructing Mean State and ENSO Variability in the Eastern Equatorial Pacific under Glacial Forcing: A Combined Geochemical and Organic Proxy Approach

厄尔尼诺/南方涛动（ENSO）现象是地球气候系统中最大的自然年际信号，对全球气候产生广泛影响，影响到全世界数百万人。最近的一系列研究预测，随着地球气候继续变暖，极端厄尔尼诺和拉尼娜现象的频率将增加。为了让气候科学家预测ENSO将如何演变以应对全球变暖，有必要准确、全面地记录该系统在过去是如何自然变化的，特别是在过去的突然变暖事件中。 然而，关于热带太平洋气候过去的变化以及厄尔尼诺/南方涛动变化如何与上一个冰河时代的千年尺度变暖事件相关联，仍然存在很大的不确定性。因此，本项目将利用从加拉帕戈斯群岛附近采集的沉积物岩心中获得的无机和有机地球化学代用指标，重建过去65 000年来多个极端气候事件中东赤道太平洋气候变化和厄尔尼诺/南方涛动变率的综合记录。 这项研究的结果将有助于预测厄尔尼诺/南方涛动在下一个世纪将如何变化，并大大改进今后的减缓努力。 该项目的成果也将被纳入多个教育和公共宣传计划在两个老自治领大学和佛罗里达大学。 在ODU，首席研究员将指导一名博士后研究员，他将监督一个本科生研究项目。这项研究概述了迄今为止最全面的研究，评估了EEP平均状态和ENSO如何在海洋同位素第3阶段（MIS 3）的Dansgaard-Oeschger（D-O）循环中变化。 这些突发性气候事件的规模、持续时间和数量使其成为测试该系统在不久的将来将如何演变的理想自然实验。通过在一项研究中利用多代理方法的独特组合，该项目将从3万至6万5千年的EEP中的8个时间片生成地表和地下温度、温跃层温度变化、上层水柱水文和上升流变化的记录。这些目标将通过使用2010年"梅尔维尔号"考察船MV 1014巡航期间从冷舌EEP上升流区域中心回收的高沉降率岩心来实现。在热带太平洋对厄尔尼诺/南方涛动敏感的区域中，该核心的沉积速率是最高的，约为10.5厘米/千年，可以解决千年尺度的气候事件。该项目将使用有孔虫稳定同位素和微量金属地球化学相结合，以重建跨MIS 3的EEP平均状态的长期变化。 接下来，将选择8个跨越MIS 3气候极端事件（D-O interstadials，stadials和Heinrich事件）的时间片进行进一步分析。对于每个时间段，将使用从单壳有孔虫Mg/Ca分析得出的温跃层温度变化来确定ENSO变率。 此外，上升流强度和营养变化的特点是由二醇指数和长链二醇指数。总之，这种多代理方法将允许最完整地描述EEP如何在MIS 3的千年尺度气候事件中变化，并将为ENSO如何与过去的极端气候状态相关提供关键的见解。 这项研究还将为气候建模者提供模拟未来气候变化所需的关键信息。

The El Niño/Southern Oscillation (ENSO) phenomenon is the largest natural interannual signal in the Earth's climate system and has widespread effects on global climate that impact millions of people worldwide. A series of recent research studies predict an increase in the frequency of extreme El Niño and La Niña events as Earth's climate continues to warm. In order for climate scientists to forecast how ENSO will evolve in response to global warming, it is necessary to have accurate, comprehensive records of how the system has naturally changed in the past, especially across past abrupt warming events. Nevertheless, there remains significant uncertainty about past changes in tropical Pacific climate and how ENSO variability relates to the millennial-scale warming events of the last ice age. Therefore, this project will use both inorganic and organic geochemical proxies from a sediment core recovered from near the Galapagos Islands to reconstruct a comprehensive record of Eastern Equatorial Pacific (EEP) climate change and ENSO variability across multiple extreme climate events over the last 65,000 years. Results generated from this research will aid in the prediction of how ENSO will change over the next century and greatly improve future mitigation efforts.  Results of the project will also be integrated into multiple educational and public outreach programs at both Old Dominion University and the University of Florida. At ODU, the lead investigator will mentor a postdoctoral researcher who will supervise an undergraduate research project. This research outlines the most comprehensive study to date evaluating how the EEP mean state and ENSO varied across the Dansgaard-Oeschger (D-O) cycles of Marine Isotope Stage 3 (MIS 3). The magnitude, duration, and number of these abrupt climate events make them the ideal natural experiment to test how the system will evolve in the near future. By utilizing a unique combination of multi-proxy methods together in a single study, this project will generate records of surface and subsurface temperature, thermocline temperature variance, upper-water column hydrography and upwelling variability from eight time slices in the EEP between 30 to 65 kyr. These objectives will be achieved by using a high-sedimentation rate core recovered from the heart of the cold-tongue EEP upwelling region during R/V Melville cruise MV1014 in 2010. Sedimentation rates in this core are among the highest in ENSO-sensitive regions of the tropical Pacific, ~10.5 cm/kyr, allowing for the resolution of millennial-scale climate events. The project will use a combination of foraminiferal stable isotope and trace metal geochemistry to reconstruct long-term changes in the EEP mean state across MIS 3. Next, 8 time slices spanning the extremes of MIS 3 climate (D-O interstadials, stadials and Heinrich Events) will be selected for further analyses. For each time slice, ENSO variability will be determined using thermocline temperature variance derived from single shell foraminiferal Mg/Ca analyses. In addition, upwelling intensity and nutrient variability will be characterized by the Diol Index and the Long Chain Diol Index. Together, this multi-proxy approach will allow for the most complete characterization of how the EEP varied across millennial-scale climate events of MIS 3 and will provide critical insight into how ENSO is related to extreme climate states of the past. This study will also provide climate modelers with critical information needed to simulate future climate change.