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)是全球气候变率的最大来源，对世界各地的地表温度和降水有深远的影响。这个项目试图测试的初步结果表明，在上一个地质时期(上新世)，当二氧化碳水平被认为与今天的水平相似时，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行为具有重要的影响，因此，该项目试图通过额外的高质量测量来彻底审查初步结果。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，并支持一名没有NSF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，上一次二氧化碳水平被认为与现代类似。现代赤道太平洋硝酸盐消耗量的变化与ENSO有关，根据这种关系，利用大宗沉积物的氮同位素特征，建立了长达500万年的硝酸盐消耗量记录。这些结果表明，赤道太平洋硝酸盐的长期消耗变化对过去500万年来温室气体浓度的变化没有响应，这意味着ENSO的长期变化对温室气体辐射强迫也不敏感。这项受资助的研究试图通过测量来自相同沉积物样本的浮游有孔虫的氮同位素特征，来确定这些大宗沉积物结果的保真度，这些结果可能会受到成岩作用的影响。这些“受有孔虫限制的”特征应较少受到沉积后改变的影响，因此是过去硝酸盐利用的更可靠的替代物。这些结果将解决两个问题：(1)赤道太平洋大宗沉积物氮同位素的保真度是多少？(2)过去500万年来赤道太平洋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?