Deep-sea sediment redistribution induced by a meandering Gulf Stream

蜿蜒的墨西哥湾流引起的深海沉积物重新分布

• 批准号: 1949536
• 负责人: Olivier Marchal
• 金额: $ 68.26万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-04-01 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1949536&HistoricalAwards=false
• 关键词: Deep; sea; sediment; redistribution; induced

The abyssal region of the ocean, below a water depth of about 1000 m, is the largest portion of the world's oceans. The original perception of this region as a quiet, almost stagnant, layer of water has been overthrown by observations made with instruments that can withstand the high pressures and corrosive conditions that prevail in the deep sea. In particular, deep oceanic basins underlying strong and variable surface currents witness episodes of high near-bottom velocities and sediment resuspension, leading to the formation of particle-rich layers near the seafloor that are called benthic nepheloid layers (BNLs). Nepheloid refers. Nepheloid refers to the Greek word for "cloud" and indeed BNLs are visually cloudy when disturbed. Although these episodes, called “benthic storms”, have been discovered about 40 years ago, how they form remains a mystery. In this project, a detailed computer model of ocean circulation and sediment transport will be applied to study the plausibility of two mechanisms responsible for benthic storms in the western North Atlantic. One possible mechanism is that the instability of the Gulf Stream, leading to meanders, rings, and eddies generates the benthic storms. The other possible mechanism is that the passage of atmospheric disturbances, such as tropical storms and hurricanes generates them. Both mechanisms have been postulated to produce a downward transfer of energy throughout the water column and to lead to benthic storms, a process that links the atmosphere, the ocean, and the seafloor sediment. Through detailed model simulations and comparison with observations of the sediment left by benthic storms, the project will advance the understanding of the origin of benthic storms and BNLs. Moreover, because such sediments are used by scientists for studying the paleoclimate of the oceans, the work will provide an assessment of the effect of ocean dynamics on this major geologic archive. The work will also help to evaluate the impact of sediment resuspension on the distribution of particles in the oceans, such as those targeted by the ongoing international oceanographic program GEOTRACES. The project will have a broader impact by involving a Post-Doctoral Investigator (PDI) and two Undergraduate Students (USs). All of the results will be shared with the public by creating a web site and by archiving the computer codes developed for this project at an official NSF-funded software registry. The codes will be produced from an open source platform and will be accompanied by a “how-to” document for broader public accessibility.The project will apply an eddy-resolving model of ocean circulation and sediment transport to explore the effects of Gulf Stream meanders, rings, and eddies, as well as the effects of atmospheric disturbances, on the movement of fine sediments at abyssal depths in the western North Atlantic. The work plan will be in three steps. (1) An existing model of ocean circulation and sediment transport will be configured to represent two different domains in the western North Atlantic. A relatively small domain centered on the Nova Scotia Rise where benthic storms have been particularly well documented will be used to produce local but detailed (submesoscale) simulations of sediment transport. A larger domain will be used to produce less detailed but basin-scale simulations of sediment transport in the intense mesoscale eddy field that characterizes the western North Atlantic. (2) Numerical experiments will be conducted with the model for varying atmospheric conditions and sediment characteristics. (3) Model results will be compared to physical observations collected from hydrographic compilations, field programs, and satellite altimetry, to distributions of particle concentration derived from gravimetric, chemical, and optical measurements, and to time series of current velocity and water turbidity obtained from bottom-tethered instruments. From these comparisons, the project will assess the potential of various dynamical phenomena – deep cyclones, topographic Rossby waves, and internal waves – to redistribute sediments on the seafloor and produce benthic storms.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.

海洋深处的深渊区域（大约1000 m）是世界海洋中最大的部分。该地区的原始感知是一种安静的，几乎停滞的水层，这是通过使用可以承受高压和腐蚀性的仪器进行的观察到的，这些仪器在深海中占据了高压力和腐蚀条件。尤其是，强大和可变的表面电流的深海低音见证了高近底速度和沉积物的发作，导致在海底附近形成富含粒子的层，这些层被称为底栖肾上腺层（BNLS）。肾上非转介。肾上非引用“云”的希腊语，实际上BNL在受影响时视觉上是云。尽管大约40年前发现了这些称为“底栖风暴”的情节，但它们的形成方式仍然是一个谜。在该项目中，将采用详细的海洋循环和沉积物运输计算机模型来研究北大西洋西部底栖风暴的两种机制的合理性。一种可能的机制是，墨西哥湾流的不稳定性，导致蜿蜒，环和涡流产生底栖风暴。另一个可能的机制是，大气灾害的通过，例如热带风暴和飓风。两种机制都已张贴，可以在整个水柱中产生能量下降，并导致底栖风暴，这是将大气，海洋和海底沉积物连接起来的过程。通过详细的模型模拟以及与底栖风暴留下的沉积物的观察，该项目将提高人们对底栖风暴和BNL的起源的理解。此外，由于科学家使用了这样的沉积物来研究海洋的古气候，因此该工作将评估海洋动力学对这个主要地质档案的影响。这项工作还将有助于评估沉积物重新悬浮对海洋中颗粒分布的影响，例如正在进行的国际海洋学计划地理位置的目标。该项目将通过涉及博士后调查员（PDI）和两名本科生（US）产生更大的影响。所有结果将通过创建网站并在NSF官方资助的软件注册表中为该项目开发的计算机代码与公众共享。 The codes will be produced from an open source platform and will be accompanied by a “how-to” document for broader public accessibility.The project will apply an eddy-resolving model of ocean circulation and sediment transport to explore the effects of Gulf Stream menders, rings, and eddies, as well as the effects of atmospheric disasters, on the movement of fine sediments at abyssal depths in the western North Atlantic.工作计划将分为三个步骤。 （1）现有的海洋循环和沉积物运输模型将配置为代表北大西洋西部的两个不同领域。一个相对较小的领域以新斯科舍省的崛起为中心，底栖风暴尤其有充分的文献记载，将用于生成局部但详细的（subbseScale）沉积物运输模拟。一个较大的域将用于产生较少详细的，但盆地尺度模拟对北大西洋西部的强烈中尺度涡流中的沉积物传输模拟。 （2）将使用模型进行数值实验，以实现不同的大气条件和沉积物特征。 （3）将将模型结果与从水文汇编，现场程序和卫星高度计收集的物理观察结果，与粒度，化学和光学测量结果得出的颗粒浓度的分布，以及从底部旋转器获得的当前速度和水浊度的时间序列。从这些比较中，该项目将评估各种动态现象的潜力 - 深旋风，地形罗斯比波浪和内部波动 - 重新分配在海底上的沉积物并产生底栖风暴。这奖反映了NSF的法定任务，并认为通过基金会的知识优点和广泛的影响，通过评估通过评估来获得珍贵的支持。