Collaborative Research: A revised Plio-Pleistocene view of the effect of climate on North Pacific oxygenation from foraminifera-bound nitrogen isotopes

像大多数陆地生物一样，海洋生物，如浮游动物，鱼类和海洋哺乳动物，需要氧气来分解食物并产生能量。然而，在海洋的三个不同区域，存在由于细菌而耗尽氧气的深度（大约200至500米）。这些被称为缺氧区（ODZs），其中最大的发生在热带北太平洋东部。臭氧消耗区限制了海洋生物的栖息地和活动，包括人类赖以生存的渔业。它们还影响海洋中重要营养物质的可获得性和循环。对这些营养物质的影响会影响海洋的生物生产力和不同种类浮游植物的普遍性。最后，臭氧消耗区可能会影响海洋与大气的温室气体（二氧化碳和一氧化二氮）交换。这些气体可以改变地球的气候。研究表明，臭氧消耗区在上个世纪已经扩大，可能是由于持续的全球变暖。然而，气候模式对未来臭氧破坏区范围的预测产生了不确定的结果。重建过去的ODZ变化将明确ODZ范围的主要控制措施，提高预测未来变化的能力。在该项目中，将在深海沉积物芯中测量浮游生物化石壁中捕获的氮的化学成分，以重建热带北太平洋东部臭氧破坏区过去的变化。这些数据将与过去的气候和海洋特性进行比较，以表明这些特性中哪一个对臭氧消耗区的控制最强。在普林斯顿，从事这项研究的团队将为初中和高中STEM教师举办一个关于气候和海洋的研讨会。这将是向公众传达结果的多种机会之一。马萨诸塞州波士顿大学的研究小组将支持本科生的有偿研究机会。马萨诸塞州波士顿大学是一所少数民族服务机构，第一代和佩尔助学金获得者学生的比例很高。这些学生将与普林斯顿大学的研究团队密切合作，学习和应用尖端的地球化学分析技术。海洋臭氧消耗区及其随时间的变化值得我们以多种身份予以关注：作为海洋和大气环流的监测者;作为海洋地球化学通量的热点;作为主要的海洋次环境和对海洋物种的限制;以及作为海洋生物碳泵的反映。沉积物氮（N）同位素已被用于重建过去的变化，通过其对水柱反硝化作用的敏感性，这增加了供应到地表沃茨的硝酸盐的15 N/14 N（δ 15 N）。大量沉积氮的δ 15 N（δ 15 Nbulk）在这一研究中得到了广泛的应用，得出了更新世冰期与ODZ收缩有关的一般结论。然而，δ 15 N bulk可能被海底成岩作用和外源N输入的变化所叠加。为了避免这些潜在的偏差，现在可以测量结合在浮游有孔虫壳内并受到其保护的少量有机质的δ 15 N（有孔虫结合δ 15 N，或FB-δ 15 N）。赤道东太平洋的FB-δ 15 N数据和热带北太平洋东部（ETNP）的新试点数据与以前基于δ 15 N块体的推断不同，即ODZ范围存在强烈的冰期/间冰期对比。为了检验先前的推断，并提供对ETNP反硝化作用和ODZ范围过去变化的新见解，将在ETNP的大洋钻探计划1241站点生成FB-δ 15 N记录。在过去的3.3 Ma中，将分析4个300-500 kyr的时间窗，每个时间窗的亚轨道（~3 kyr）分辨率。对ETNP ODZ历史的重建将为这一关键区域的古气候数据集增加一个关键的地球化学成分，从而深入了解（1）对热带太平洋上层海洋环流的控制，包括风场和温度场，（2）这些物理参数对气候驱动变化的地球化学响应，以及（3）对海洋生物状况和生物分布的影响-该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

Like most life on land, life in the ocean such as zooplankton, fish, and marine mammals require oxygen to break down their food and generate energy. However, in three different regions of the ocean, there are depths (from roughly 200 to 500 m) where the oxygen has been exhausted due to bacteria. These are known as the oxygen-deficient zones (ODZs), with the largest of these occurring in the eastern tropical North Pacific. The ODZs restrict the habitats and movements of ocean life, including fisheries on which humans rely. They also affect the availability and cycling of important nutrients in the ocean. The impact on these nutrients can affect the ocean’s biological productivity and the prevalence of different types of phytoplankton. Finally, the ODZs may affect the ocean’s exchange of greenhouse gases (both carbon dioxide and nitrous oxide) with the atmosphere. These gases can alter Earth’s climate. Studies have suggested that the ODZs have expanded over the last century, possibly due to ongoing global warming. However, climate model predictions of the ODZ extent in the future yield an uncertain picture. Reconstructing ODZ changes in the past will clarify the main controls on ODZ extent, improving the ability to predict future changes. In this project, the chemical composition of nitrogen trapped in the wall of fossil plankton will be measured in a deep-sea sediment core to reconstruct past changes in the ODZ of the eastern tropical North Pacific. The data will be compared with climate and ocean properties in the past, indicating which of these properties most strongly controls the ODZs. At Princeton, the team pursuing this research will lead a workshop on climate and the ocean for middle and high school STEM teachers. This will be one of multiple opportunities to communicate the results to the public. The research team at University of Massachusetts Boston will support paid research opportunities for undergraduate students. University of Massachusetts Boston is a minority-serving institution with a high proportion of both first-generation and Pell grant recipient students. These students will learn and apply cutting-edge geochemical analysis techniques in close collaboration with the research team at Princeton University. The ocean’s ODZs and their changes over time deserve our attention in multiple capacities: as monitors of ocean and atmospheric circulation; as hotspots of biogeochemical fluxes; as major ocean sub-environments and constraints on ocean species; and as reflections of the ocean’s biological carbon pump. Sedimentary nitrogen (N) isotopes have been used to reconstruct past changes in the ODZs through their sensitivity to water column denitrification, which increases the 15N/14N (δ15N) of the nitrate supplied to surface waters. The δ15N of bulk sedimentary N (δ15Nbulk) has been applied extensively in this effort, leading to the general conclusion that the Pleistocene ice ages have been associated with ODZ contraction. However, δ15Nbulk may be overprinted by variations in seafloor diagenesis and exogenous N inputs. To avoid these potential biases, it is now possible to measure the δ15N of the small quantity of organic matter bound within and protected by planktonic foraminifera shells (foraminifera-bound δ15N, or FB-δ15N). Recent FB-δ15N data from the eastern equatorial Pacific and new pilot data from the eastern tropical North Pacific (ETNP) argue against previous δ15Nbulk-based inferences of a strong ice age/interglacial contrast in ODZ extent. To test prior inferences and provide new insight into past variations in ETNP denitrification and ODZ extent, a FB-δ15N record will be generated at Ocean Drilling Program Site 1241 in the ETNP. Four time-windows of 300-500 kyr will be analyzed over the last 3.3 Ma, each at suborbital (~3 kyr) resolution. The reconstruction of the history of the ETNP ODZ will add a key biogeochemical component to the paleoclimate data sets from this key region, yielding insights into (1) the controls on tropical Pacific upper ocean circulation, which include the wind and temperature fields, (2) the biogeochemical responses to climate-driven changes in these physical parameters, and (3) the consequences for the biological conditions of the ocean and the distribution of biologically-stored excess CO2 in the ocean interior.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.