Deep-sea sediment redistribution induced by a meandering Gulf Stream

海洋的深海区域，在水深约1000米以下，是世界上最大的海洋部分。人们最初认为该地区是一个安静的、几乎停滞的水层，但通过使用能够承受深海中普遍存在的高压和腐蚀性条件的仪器进行的观测，这种看法已经被推翻。特别是，在强烈和多变的表面流之下的深海盆地经历了高近底速度和沉积物再悬浮的时期，导致在海底附近形成富含颗粒物的层，这些层被称为海底云状层。类星云指的是。Nephelid指的是希腊语中的“云”，事实上，BNL在受到干扰时视觉上是多云的。虽然这些被称为“海底风暴”的事件在大约40年前就已被发现，但它们是如何形成的仍然是一个谜。在这个项目中，一个详细的海洋环流和沉积物输送的计算机模型将被用来研究导致北大西洋西部海底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，导致曲折、环状和涡流，产生了海底风暴。另一种可能的机制是，热带风暴和飓风等大气扰动的通过产生了它们。这两种机制都被假设为在整个水柱中产生向下的能量转移，并导致海底风暴，这是一个连接大气、海洋和海底沉积物的过程。通过详细的模型模拟和与海底风暴留下的沉积物观测的比较，该项目将促进对海底风暴和BNL起源的理解。此外，由于这些沉积物被科学家用于研究海洋的古气候，这项工作将评估海洋动力学对这一主要地质档案的影响。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所针对的颗粒。该项目将产生更广泛的影响，涉及一名博士后研究员(PDI)和两名本科生(USS)。所有成果将通过创建一个网站并将为该项目开发的计算机代码存档在国家科学基金会资助的官方软件登记处与公众共享。这些代码将由一个开放源代码平台生成，并将伴随着一份更广泛的公众可及文件。该项目将应用海洋环流和沉积物输送的涡旋解析模型，以探索墨西哥湾流曲折、环状和涡流的影响，以及大气扰动对北大西洋西部深海细小沉积物运动的影响。工作计划将分三步走。(1)现有的海洋环流和沉积物输送模型将被配置为代表北大西洋西部的两个不同领域。以新斯科舍省隆起为中心的一个相对较小的区域，在那里海底风暴被特别好地记录下来，将被用来产生局部但详细的(亚中尺度)沉积物输送模拟。一个更大的区域将被用来对北大西洋西部的强烈中尺度涡场中的沉积物输送进行不太详细的但盆地规模的模拟。(2)利用该模式进行了不同大气条件和泥沙特性的数值试验。(3)模型结果将与从水文汇编、野外程序和卫星测高收集的物理观测结果进行比较，与由重力、化学和光学测量得出的颗粒浓度分布进行比较，并与从底部系泊仪器获得的水流速度和水的浑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Rossby波和内波--在海底重新分配沉积物并产生海底风暴的潜力。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.