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.

海洋的深海区域，在水深约1000米以下，是世界海洋的最大部分。人们最初认为这个地区是一片平静的、几乎停滞不前的水层，但这种看法已经被用能够承受深海中普遍存在的高压和腐蚀性条件的仪器所做的观察所推翻。特别是，在强烈和变化的表面洋流下的深海盆地，见证了近底高速和沉积物再悬浮的事件，导致海底附近形成了富含颗粒的层，称为底栖nepheloid层（bnl）。雾状指。Nepheloid指的是希腊语中的“云”，事实上，bnl在受到干扰时在视觉上是多云的。虽然这些被称为“底栖风暴”的现象在大约40年前就被发现了，但它们是如何形成的仍然是个谜。在这个项目中，一个详细的海洋环流和沉积物运输的计算机模型将被应用于研究北大西洋西部海底风暴的两种机制的可行性。一种可能的机制是，墨西哥湾流的不稳定性，导致了曲流、环流和漩涡，从而产生了底栖风暴。另一种可能的机制是大气扰动的通过，如热带风暴和飓风产生了它们。这两种机制都被假定为在整个水柱中产生向下的能量转移，并导致底栖风暴，这是一个将大气、海洋和海底沉积物联系起来的过程。通过详细的模式模拟，并与底栖风暴留下的沉积物的观测结果进行比较，该项目将促进对底栖风暴和bnl起源的了解。此外，由于这些沉积物被科学家用来研究海洋的古气候，这项工作将为海洋动力学对这一主要地质档案的影响提供评估。这项工作还将有助于评估沉积物再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GEOTRACES的目标。该项目涉及一名博士后研究员（PDI）和两名本科生（USs），将产生更广泛的影响。所有的结果将通过创建一个网站和将为这个项目开发的计算机代码存档在nsf资助的官方软件注册表中与公众共享。这些代码将从一个开源平台生成，并将附有一份“操作”文档，以供更广泛的公众访问。该项目将应用海洋环流和沉积物运输的漩涡解析模型，探索墨西哥湾流曲流、环流和漩涡以及大气扰动对北大西洋西部深海精细沉积物运动的影响。工作计划将分三步进行。(1)将配置一个现有的海洋环流和沉积物输运模式来代表北大西洋西部两个不同的区域。以新斯科舍省隆起为中心的一个相对较小的区域，那里的底栖风暴已被特别详细地记录下来，将用于产生局部但详细的（亚中尺度）沉积物运输模拟。一个更大的区域将用于在北大西洋西部强烈的中尺度涡旋场中产生不太详细但盆地尺度的沉积物输运模拟。(2)利用该模式进行不同大气条件和泥沙特征的数值试验。(3)模型结果将与从水文汇编、野外项目和卫星测高中收集的物理观测结果，与从重力、化学和光学测量中获得的颗粒浓度分布，以及从海底系绳仪器获得的流速和水浊度时间序列进行比较。通过这些比较，该项目将评估各种动力现象——深层气旋、地形罗斯比波和内波——重新分配海底沉积物和产生底栖风暴的潜力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。