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

El Niño-Southern涛动（ENSO）是全球气候变率的最大来源，对全球地表温度和降水有着深远的影响。该项目旨在测试初步结果，该结果表明，在上一个地质时期（上新世），当二氧化碳水平被认为与今天相似时，ENSO没有对过去温室气体浓度的变化做出反应。这些发现对未来的ENSO行为具有重要意义，因此，该项目旨在通过额外的高质量测量彻底审查初步结果。这项研究包括对加州大学欧文分校的本科生进行基本实验室技能和科学交流方面的培训和指导，并支持一位没有获得美国国家科学基金会支持的早期职业科学家。这项研究试图通过检查上新世期间的ENSO变化来了解ENSO如何响应温室气体强迫的变化，上新世是二氧化碳分压水平被认为与现代相似的最后一个时期。现代赤道太平洋硝酸盐消耗变化与ENSO有关，基于这种关系，利用大块沉积物的氮同位素特征构建了500万年的硝酸盐消耗记录。这些结果表明，过去500万年赤道太平洋硝酸盐消耗的长期变率不响应温室气体浓度的变化，并暗示长期ENSO变率对温室气体辐射强迫也不敏感。这项资助的研究旨在通过测量来自同一沉积物样本的浮游有孔虫的氮同位素特征，来确定这些大块沉积物结果的保真度，这些结果可能被成岩作用叠加。这些“有孔虫束缚”的特征应该较少受到沉积后蚀变的影响，因此是过去硝酸盐利用的更可靠的代表。这些结果将解决两个问题：(1)赤道太平洋大块沉积物氮同位素的保真度如何？(2)在过去的500万年里，赤道太平洋的硝酸盐消耗是如何演变的？

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?