Collaborative Research: Lagrangian transport and patchiness of buoyant material in estuarine systems

了解河口系统中物质运输的过程是河口物理基础研究的核心，也是这些重要的社会经济和高度人为影响系统的管理实践的核心。浮力物质，如漂浮碎片、海洋生物、石油和微塑料，可能在这些运输过程中聚集和滞留在河口，或分散并排放到沿海海洋。强辐合的表层水流穿过河口，将浮力物质组织成横向狭窄的近地表斑块，这些斑块可能沿着河口延伸几公里。移动这些斑块的当地洋流可能与潮汐和横向平均洋流有很大的不同，而潮汐和横向平均洋流通常用于估计河口运输特征。这个项目的主要目标是对比材料在一个框架中的传输，这个框架被称为拉格朗日框架，与一个基于固定点参考框架或欧拉框架的框架。通常物质的拉格朗日轨迹不同于从欧拉平均流中推断出来的轨迹。经典的例子来自表面波，其中一点的平均速度（欧拉）将为零，但由于斯托克斯漂移或斯托克斯速度，与波包含流振荡的粒子将在波传播方向上具有平均速度。该项目将调查河口斯托克斯运输的重要性。项目研究假设：(1)与潮汐流幅值和相结构相关的Stokes输运对浮力物质在顺槽和跨槽方向的输运都有显著贡献。(2)受河口侧向环流的影响，浮力物质呈斑块状组织。(3)浮力物质斑块基本上是由时空局域流输送的，这些局域流在河口间变化很大。(4)特拉华湾海洋垃圾的时空分布是拉格朗日河口输运的特征标志。该项目将利用建模和观测来解决河口浮力物质的运输问题。这项研究将有助于解决与海洋污染、气体交换和渔业有关的实际问题。pi与资源经理和政策制定者有密切的工作关系，他们将与他们沟通相关的新理解。该项目将培养研究生和本科生，pi和学生都将参加公共宣传活动。本项目将研究河口中浮力物质的运输，特别是特拉华河口，包括其在河口内的聚集，以及由此产生的浮力物质斑块对其通过河口运输的影响。这些假设将通过采用原始概念模型以及观察和模拟的综合研究计划来解决。研究目标包括：(1)评估和推进三维河口环流的理想线性和弱非线性模型，确定控制二次环流的关键因素，如水深、潮汐、科里奥利力和斜压性。(2)将理想模型与现有的野外观测结合起来，利用渐近Stokes漂移分析，建立和评估河口环流的拉格朗日框架，对比欧拉方法和拉格朗日方法之间的根本差异。(3)开展特拉华河口水动力模拟与野外观测相结合，了解潮小泉和高低河流量变化。(4)将拉格朗日框架应用于模拟和观测结果，以及最近的海洋垃圾观测，揭示拉格朗日主要输运特征和改进的河口输运估计。通过探索和发展拉格朗日框架，该项目将从根本上推进我们对河口输运过程的物理理解。这项工作将改变目前河口物质运输的范式，包括新的横向运输过程，从而推进目前对河口浮力示踪剂动力学的概念理解，并将有助于解决实际的现实世界问题。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。

Understanding processes that transport material in estuarine systems is central to fundamental studies of estuarine physics as well as to management practices in these socioeconomically important and highly anthropogenically impacted systems. Buoyant material, such as floating debris, marine organisms, oil and microplastics may be aggregated and trapped within estuaries or dispersed and discharged to the coastal ocean by these transport processes. Strong convergent surface flows across the estuary organize buoyant material into laterally narrow near-surface patches that may extend up to a few kilometers along the estuary. Local currents that move these patches may substantially differ from tidally and laterally averaged currents, which are often used to estimate estuarine transport characteristics. A major objective of this project is to contrast the transport of material in a frame work that follows the flow, known as the Lagrangian framework, with one based on a fixed point reference frame, or the Eulerian framework. Often the Lagrangian trajectories of material differ from those inferred from the Eulerian mean flows. The classic example stems from surface waves where the average velocity at a point (Eulerian) will be zero but a particle oscillating with the wave included flow will have an average velocity in the direction of wave propagation, due to the Stokes drift or Stokes velocity. This project will investigate the importance of Stokes transport in estuaries. The project research hypotheses are: (1) Stokes transport associated with amplitude and phase structure of tidal flows contribute significantly to the transport of buoyant material in both the along-channel and cross- channel directions. (2) Buoyant material organizes in surface patches due to the lateral estuarine circulations. (3) Patches of buoyant material are fundamentally transported by spatiotemporally localized currents that vary substantially across the estuary. (4) The observed spatiotemporal distributions of marine debris in Delaware Bay are a characteristic signature of Lagrangian estuarine transport. The project will use both modeling and observations to address transport of buoyant material in estuaries. This research will help solve practical real world problems related to marine pollution, gas exchange and fisheries. The PIs have close working relationships with resource managers and policy makers with whom they will communicate relevant new understanding. The project will train graduate and undergraduate students, and both PIs and students will participate in public outreach events. This project will examine transport of buoyant material in estuaries, specifically the Delaware Estuary, including its aggregation within estuaries, and the effects of resulting patchiness of buoyant material on its transport through the estuary. The hypotheses will be addressed through an integrated research program that employs original concept models as well as observations and simulations. Research objectives include: (1) Assess and advance idealized linear and weakly-nonlinear models of the three-dimensional estuarine circulations to determine key factors that control secondary circulations, such as bathymetry, tides, Coriolis force, and baroclinicity. (2) Develop and evaluate a Lagrangian framework for the estuarine circulation based on the integration of the idealized models with existing field observations and an asymptotic Stokes drift analysis to contrast fundamental differences between the Eulerian and Lagrangian approaches. (3) Conduct and integrate hydrodynamic simulations and field observations of the Delaware Estuary to understand tidal neap-spring and high-low river discharge variability. (4) Apply the Lagrangian framework to simulation and observation results, as well as recent marine debris observations, to reveal principal Lagrangian transport characteristics and improved estuarine transport estimates. By exploring and developing a Lagrangian framework this project would fundamentally advance our understanding of the physics of estuarine transport processes. This work will transform the current paradigm of estuarine material transport to include new lateral transport processes, thereby advancing the current conceptual understanding of buoyant tracer dynamics in an estuary, and will contribute to solving practical real world problems.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.