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

合作研究：气候对北太平洋氧合作用有孔虫结合氮同位素影响的修正上古-更新世观点

• 批准号: 2303549
• 负责人: Jesse Farmer
• 金额: $ 14.1万
• 依托单位: University of Massachusetts Boston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2303549&HistoricalAwards=false
• 关键词: Collaborative; Research; revised; Plio; Pleistocene

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.

与陆地上的大多数生物一样，浮游动物、鱼类和海洋哺乳动物等海洋生物也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，存在深度（大约 200 至 500 m）。 ），其中氧气因细菌而耗尽，这些区域被称为缺氧区（ODZ），其中最大的缺氧区位于热带北太平洋东部，这些区域限制了海洋生物的栖息地和活动。它们还影响海洋中重要营养物质的可用性和循环。对这些营养物质的影响会影响海洋的生物生产力和不同类型浮游植物的分布。最后，ODZ 可能会影响海洋的交换。大气中的温室气体（二氧化碳和一氧化二氮）可能会改变地球的气候。研究表明，ODZ 可能由于持续的全球变暖而扩大。未来 ODZ 范围的模型预测会产生不确定的图像 重建过去 ODZ 的变化将阐明 ODZ 范围的主要控制因素，提高预测墙壁中氮的化学成分的能力。将在深海沉积物核心中测量浮游生物化石的数量，以重建热带北太平洋东部ODZ的过去强烈变化。这些数据将与过去的气候和海洋特性进行比较，表明这些特性中哪一个最能控制海洋。在普林斯顿大学，开展这项研究的团队将为初高中 STEM 教师举办一次有关气候和海洋的研讨会，这将是马萨诸塞大学波士顿分校的研究团队向公众传达研究结果的众多机会之一。马萨诸塞大学波士顿分校是一所为少数族裔服务的机构，第一代学生和佩尔助学金获得者比例很高，这些学生将与他们密切合作学习和应用尖端的地球化学分析技术。普林斯顿大学的研究团队。海洋的 ODZ 及其随时间的变化在多种方面值得我们关注：作为海洋和大气环流的监测器；作为生物地球化学通量的热点；作为主要的海洋子环境和对海洋物种的限制；以及作为海洋生物碳泵的反映。沉积氮 (N) 同位素已被用来重建 ODZ 过去的变化，因为它们对水柱反硝化作用敏感，从而增加了 15N/14N提供给地表水的硝酸盐的 δ15N (δ15Nbulk) 在这项工作中得到了广泛应用，得出了更新世冰河时代与 ODZ 收缩有关的普遍结论。为了避免这些潜在的偏差，现在可以测量少量的 δ15N。浮游有孔虫壳内结合并受其保护的有机物（有孔虫结合的 δ15N，或 FB-δ15N）最近来自赤道东部太平洋的 FB-δ15N 数据和来自热带北太平洋东部（ETNP）的新试点数据与之前的 δ15Nbulk 数据相矛盾。基于 ODZ 范围内强烈冰河时代/间冰期对比的推论，以测试先前的推论并为过去的变化提供新的见解。 ETNP 反硝化和 ODZ 范围，将在 ETNP 海洋钻探计划站点 1241 生成 FB-δ15N 记录，将在过去 3.3 Ma 中分析 300-500 kyr 的四个时间窗口，每个时间窗口位于亚轨道（~3 kyr）。 ETNP ODZ 历史的重建将为古气候数据集添加一个关键的生物地球化学成分。关键区域，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）对气候驱动的这些物理参数变化的生物地球化学响应，以及（3）对热带太平洋上层海洋环流的影响该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。