Targeted equatorial Pacific foraminifera-bound N isotope measurements: implications for a rare record of nutrient dynamics and the El Nino-Southern Oscillation

厄尔尼诺-南方涛动（ENSO）是全球气候变异的最大来源，对世界各地的地表温度和降水有着深远的影响。该项目旨在检验初步结果，这些结果表明，厄尔尼诺/南方涛动对过去在上一个地质时期（上新世）温室气体浓度的变化没有反应，当时的二氧化碳水平被认为与今天相似。这些发现对未来的ENSO行为具有重要意义，因此，本项目试图通过额外的高质量测量来彻底审查初步结果。该研究包括培训和指导加州尔湾大学的本科生在基本的实验室技能和科学交流，并支持一个早期的职业科学家没有以前的NSF support.This研究旨在了解如何ENSO响应温室气体强迫的变化，通过检查ENSO变化在上新世，最后一次pCO 2水平被认为是类似于现代。现代赤道太平洋硝酸盐消费的变化与ENSO有关，基于这种关系，利用散装沉积物的氮同位素特征构建了一个500万年的硝酸盐消费记录。这些结果表明，长期赤道太平洋硝酸盐消费的变化并没有响应温室气体浓度的变化，在过去的5百万年，并意味着长期ENSO变化也是不敏感的温室气体辐射强迫。受资助的研究旨在通过测量来自相同沉积物样本的南极有孔虫的氮同位素特征来确定这些大量沉积物结果的保真度，这些结果可以被成岩作用叠加。这些“有孔虫约束”的签名应较少受到沉积后的蚀变，从而更强大的代理过去的硝酸盐利用。这些结果将解决两个问题：（1）什么是赤道太平洋散装沉积物氮同位素的保真度？(2)在过去的500万年里，赤道太平洋的硝酸盐消费是如何演变的？

The El Niño-Southern Oscillation (ENSO) is the largest source of global climate variability and has a profound influence on surface temperatures and precipitation around the world. This project seeks to test preliminary results that suggest that ENSO did not respond to past changes in greenhouse gas concentrations during the last geological period (the Pliocene) when carbon dioxide levels are thought to have been similar to today's. These findings have important implications for future ENSO behavior and, consequently, this project seeks to thoroughly scrutinize the preliminary results with additional high quality measurements. The research involves training and mentoring of University of California, Irvine undergraduate students in fundamental laboratory skills and scientific communication, and supports an early career scientist with no prior NSF support.This research seeks to understand how ENSO responds to changes in greenhouse gas forcing by examining ENSO variability during the Pliocene, the last time pCO2 levels are thought to have been similar to modern. Modern equatorial Pacific nitrate consumption variability has been linked to ENSO and, based on this relationship, a 5 million year long record of nitrate consumption was constructed using nitrogen isotope signature of bulk sediments. These results suggest that long-term equatorial Pacific nitrate consumption variability did not respond to changes in greenhouse gas concentrations over the past 5 million years, and imply that long-term ENSO variability is also insensitive to greenhouse gas radiative forcing. The funded research seeks to determine the fidelity of these bulk sediment results, which can be overprinted by diagenetic effects, by measuring the nitrogen isotope signature of planktic foraminifera from the same sediment samples. These "foraminifer-bound" signatures should be less subject to post-depositional alteration and thus a more robust proxy for past nitrate utilization. These results will address two questions: (1) what is the fidelity of equatorial Pacific bulk sediment nitrogen isotopes? (2) how did equatorial Pacific nitrate consumption evolve over the past 5 million years?