Core Stratigraphy and Paleotemperature Estimates to Characterize Last Interglacial Tropical Pacific Climate Variability and El Nino Southern Oscillation During MIS 5e

年际气候变率以El Niño南方涛动（ENSO）为主。ENSO表现为热带太平洋海面温度的变化，它影响着全球的自然和人类系统。ENSO事件是否会在未来变得更强尚不清楚，部分原因是控制ENSO的过程尚未完全了解。利用赤道东太平洋海洋沉积物的地球化学代理证据可以重建过去的ENSO活动。最后一个温暖气候期，被称为海洋同位素阶段5e (MIS 5e)，发生在约119,000-126,000年前。因此，来自MIS 5e的东太平洋沉积物记录了之前温暖状态下的ENSO行为。本研究将利用有孔虫壳化学对赤道东太平洋沉积物岩心的MIS 5e沉积物进行表征。这些新记录将为沉积物岩心提供可靠的年代控制。然后可以将该岩心的数据与其他地点的古气候数据进行比较。这项研究将通过有意义的本科生研究机会，支持扩大STEM和地球科学参与的推广工作。本科生研究助理将参与项目的所有阶段。地球化学分析将成为本科生暑期工作坊的重要组成部分。这将使学生对现代分析技术有宝贵的经验。由于我们对控制热带太平洋变率的机制的理解尚不完整，ENSO对大气中二氧化碳升高的响应行为尚未得到很好的约束。以往暖期，特别是末次间冰期（MIS 5e） ENSO的重建是有限的。这样的重建可以在没有现代二氧化碳强迫的情况下，测试ENSO与不断变化的气候背景条件、轨道强迫和季节变化的关系。东赤道太平洋冷舌区是ENSO的活动中心，但具有足够物质、分辨率和特征的沉积物岩心稀少。本研究将利用地表和地下有孔虫生成稳定同位素和微量元素地层学，以识别和表征赤道东太平洋沉积物岩心中的MIS 5e沉积物。生成从末次冰期极大期到MIS 5e的长期地表和地下地层学，将使沉积物的组成、积累速率和分辨率得以表征，从而能够利用有孔虫地球化学代用物对热带太平洋变动性进行未来的高分辨率分析，并允许测试ENSO控制的关键假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Inter-annual climate variability is dominated by the El Niño Southern Oscillation (ENSO). ENSO is expressed as changes in tropical Pacific sea surface temperatures, and it impacts natural and human systems across the globe. Whether ENSO events will become stronger in the future is unclear, in part because the processes that control ENSO are not fully understood. Past ENSO activity can be reconstructed using geochemical proxy evidence from ocean sediments from the eastern equatorial Pacific. The last warm climate period, known as Marine Isotope Stage 5e (MIS 5e), occurred ~119,000-126,000 years ago. Thus, Eastern Pacific sediments from MIS 5e record ENSO behavior during a previous warm state. This research will characterize MIS 5e sediments in an eastern equatorial Pacific sediment core using the shell chemistry of foraminifera. These new records will provide reliable age control for the sediment core. The data from this core can then be compared with paleoclimate data from other locations. The study will support outreach efforts to broaden participation in STEM and in the geosciences through meaningful undergraduate research opportunities. Undergraduate research assistants will be involved in all phases of the project. The geochemical analyses will be a key component of a summer workshop for undergraduates. This will give the students valuable experience on modern analytical techniques. ENSO’s behavior in response to elevated atmospheric carbon dioxide is not well constrained as our understanding of the mechanisms controlling tropical Pacific variability is incomplete. Reconstructions of ENSO during previous warm periods, and in particular the last interglacial (MIS 5e) are limited. Such reconstructions would enable testing of ENSO’s relationship with changing climate background conditions, orbital forcing, and seasonal changes in the absence of modern carbon dioxide forcing. The eastern equatorial Pacific cold tongue region is a center-of-action for ENSO, but sediment cores with adequate material, resolution, and characteristic are sparse. This research will generate a stable isotope and trace elemental stratigraphy using surface and subsurface foraminifera to identify and characterize MIS 5e sediments in an eastern equatorial Pacific sediment core. Generation of a long-term surface and subsurface stratigraphy spanning the last glacial maximum to MIS 5e will allow the sediments to be characterized for composition, accumulation rates and resolution, enabling future, high-resolution analysis of tropical Pacific variability using foraminiferal geochemical proxies, and allow for testing of key hypotheses of ENSO control.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.