A Lagrangian approach to quantifying isopycnal dispersion and the role of mixing in the Eastern North Atlantic Oxygen Minimum Zone

量化北大西洋东部最低氧气区等密度分散和混合作用的拉格朗日方法

• 批准号: 1736985
• 负责人: Jaime Palter
• 金额: $ 29.1万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736985&HistoricalAwards=false
• 关键词: Lagrangian; approach; quantifying; isopycnal; dispersion

In the ocean interior, microbial respiration creates a layer of low oxygen waters that is inhospitable to many marine organisms. This layer is most severely oxygen-depleted along the eastern margins of every tropical and subtropical basin, in the so-called Oxygen Minimum Zone (OMZs). OMZs which are dynamically isolated from the oxygenated surface layers play a role in ocean biogeochemistry and ecosystem structure that is disproportionate to their size. For instance, OMZs control the global nitrogen cycle, as they are the principal locations where bio-available nitrogen is removed from the ocean. Such nitrogen removal is accompanied by the production of carbon dioxide, providing a source of the greenhouse gas to the atmosphere. The OMZs also influence the distribution of large pelagic fish Moreover, OMZs are predicted to expand under global warming, an effect that is already evident in observational records and strongest in the Atlantic Ocean. This project focuses on understanding of these critical regions by describing the dynamics and quantify the rates that govern isopycnal dispersion and mixing in the tropics using a high resolution Lagrangian set data collected under previous NSF funding. This research is expected to advance conceptual models of the processes controlling oxygen concentrations in the OMZs and their representation in ocean circulation models. A graduate student will be trained in modern oceanographic analysis techniques and the results from the project will be incorporated in the classroom. Visits to middle school classrooms through the Rhode Island Teacher At Sea program will discuss oceanographic topics each spring by incorporating discussions on ocean hypoxia and how acoustic methods are used to observe circulation.Ocean circulation models do not accurately simulate the intensity of the ocean's OMZs, a persistent problem that is hypothesized to be linked to their representation of isopycnal mixing. A quantification and process-level understanding of such mixing has been historically challenged by the scarcity of high-quality data collected in these regions. From 2003-2005, NSF supported the Lagrangian Isopycnal Dispersion Experiment (LIDEX) to overcome these challenges. The LIDEX data, which included Lagrangian trajectories from the deployment of 92 isopycnal RAFOS floats at the edge of the Atlantic OMZ, are poised to address the problem of isopycnal mixing in the tropics. The LIDEX floats were successfully ballasted to drift on two different density surfaces and released in clusters at five locations near the western edge of the Atlantic OMZ. The resulting trajectories represent among the most accurate oceanic observations of Lagrangian particles to date. All floats carried temperature sensors and half were equipped with oxygen sensors. 62 floats were tracked continuously four times a day for 5 months, and 49 floats completed a 15-month mission with only one short gap. Synthesis of these data can provide valuable insight into mixing in this region, and ultimately help improve predictions of the fate of OMZs. The following three critical questions will be addressed:1. What are the processes and rates of dispersion on isopycnal surfaces from several kilometers to hundreds of kilometers?2. How does the diffusivity calculated from the float dispersion compare with other attempts to quantify mixing, and what does this comparison tell us about the flux of oxygen into the OMZ?3. Do the representations of subgridscale turbulence in coarse resolution ocean general circulation models prevent them from successfully simulating OMZ intensity?

在海洋内部，微生物的呼吸作用产生了一层低氧水域，这是许多海洋生物不适合居住的。这一层在每个热带和亚热带盆地的东部边缘，即所谓的氧最小带（OMZs），是最严重的缺氧层。动态分离于含氧表层的omz在海洋生物地球化学和生态系统结构中发挥着与其大小不成比例的作用。例如，海洋保护区控制着全球氮循环，因为它们是从海洋中去除生物可利用氮的主要场所。这种氮的去除伴随着二氧化碳的产生，为大气提供了温室气体的来源。此外，据预测，在全球变暖的情况下，表层海洋区还会扩大，这一影响在观测记录中已经很明显，在大西洋最为明显。这个项目的重点是通过描述动力学和量化控制热带等压扩散和混合的速率来理解这些关键区域，使用以前在NSF资助下收集的高分辨率拉格朗日集数据。这项研究预计将提出控制omz中氧浓度过程的概念模型及其在海洋环流模式中的表示。研究生将接受现代海洋分析技术的培训，项目结果将纳入课堂。每年春天，通过罗德岛州的海上教师计划访问中学教室，讨论海洋学主题，包括讨论海洋缺氧和如何使用声学方法观察环流。海洋环流模型不能准确地模拟海洋omz的强度，这是一个长期存在的问题，据推测与它们对等环流混合的表现有关。由于在这些地区收集的高质量数据稀缺，对这种混合的量化和过程级理解一直受到历史挑战。2003-2005年，美国国家科学基金会资助了拉格朗日等尺度色散实验（LIDEX）来克服这些挑战。LIDEX的数据包括在大西洋OMZ边缘部署的92个等环流RAFOS浮标的拉格朗日轨迹，准备解决热带地区等环流混合的问题。LIDEX浮标成功地在两个不同密度的表面上漂流，并在大西洋OMZ西部边缘附近的五个地点集中释放。由此产生的轨迹代表了迄今为止对拉格朗日粒子最精确的海洋观测。所有的浮标都装有温度传感器，其中一半配备了氧气传感器。62个浮标每天连续跟踪4次，持续5个月，49个浮标完成了15个月的任务，只有一次短暂的间隙。综合这些数据可以为该地区的混合提供有价值的见解，并最终有助于改进对omz命运的预测。将解决以下三个关键问题：在几公里到几百公里的等平表面上，色散的过程和速率是什么？从浮子分散计算的扩散率与其他量化混合的尝试相比如何，这种比较告诉我们氧气进入OMZ的通量是什么？在粗分辨率海洋环流模式中，亚网格尺度湍流的表征是否会阻止它们成功地模拟OMZ强度？

项目成果

Isopycnal Mixing in the North Atlantic Oxygen Minimum Zone Revealed by RAFOS Floats

RAFOS 浮标揭示北大西洋氧气最低区的等密度混合

• DOI: 10.1029/2019jc015148
• 发表时间: 2019
• 期刊: Journal of Geophysical Research: Oceans
• 作者: Rudnickas, Jr., Donald;Palter, Jaime;Hebert, David;Rossby, H. Thomas
• 通讯作者: Rossby, H. Thomas

On Rates of Isopycnal Dispersion at the Submesoscale

关于亚介尺度的等密度色散速率

• DOI: 10.1029/2021gl093526
• 发表时间: 2021
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Rossby, T.;Omand, M.;Palter, J.;Hebert, D.
• 通讯作者: Hebert, D.

The Sensitivity of Future Ocean Oxygen to Changes in Ocean Circulation

未来海洋氧气对海洋环流变化的敏感性

• DOI: 10.1002/2017gb005777
• 发表时间: 2018
• 期刊: Global Biogeochemical Cycles
• 影响因子: 5.2
• 作者: Palter, Jaime B.;Trossman, David S.
• 通讯作者: Trossman, David S.