Collaborative Research: Mixing of river water into the coastal ocean and the role and structure of the outer edge of the discharge

合作研究：河水混入沿海海洋以及排放外缘的作用和结构

• 批准号: 1756599
• 负责人: Daniel MacDonald
• 金额: $ 56.76万
• 依托单位: University of Massachusetts, Dartmouth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-15 至 2023-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756599&HistoricalAwards=false
• 关键词: Collaborative; Research; Mixing; river; water

As river waters enter the coastal ocean they mix with the saltier sea water. This process starts at the seaward boundary of the river discharge (plume) and it affects circulation and flow near the river mouth and throughout the adjacent coastal region. Although the area where this river-ocean interface occurs represents a small region of the ocean, it is very important to ocean mixing and is often poorly resolved in circulation models used to predict environmental conditions in coastal regions. As part of this investigation the researchers will carry out field measurements and utilize numerical models to define variability in the structure of the seaward boundary of the freshwater discharge, and the mixing that occurs there. These processes will be examined for different river discharge and tidal conditions. In addition, this study will assess how much of an ebbing riverine outflow is cycled through the seaward boundary and evaluate the overall importance of this region to mixing the total river discharge to a near-ocean salinity. The outcomes from this work will reveal the details of the physical processes taking place at the riverine-ocean interface and improve the predictive capabilities of large-scale models. In addition, the advances gained from this study will ultimately allow better prediction of the fate and transport of pollutants, nutrients and water masses in the ocean. During the period of this project three graduate student will supported contributing to building scientific capacity.The frontal region of a river plume is the seaward boundary that separates a buoyant coastal discharge from ambient ocean water. Oceanic fronts of all scales act as significant energy sinks over several orders of magnitude through mechanisms that are poorly understood. Although significant efforts have advanced knowledge of plume dynamics over the last several decades, fundamental gaps still exist in our understanding of frontal evolution, and the role of the front in establishing the dynamics in the interior of the plume and in the overall plume mixing budget. The objective of this proposal is to understand the evolution and significance of frontal processes across a range of scales, from small scale propagating discharge fronts to intermediate scale shelf fronts bounding an ebb pulse, and to identify the mechanisms controlling the evolution of a front from engineering scales to geostrophic scales. Our hypothesis is that the relative importance of frontal mixing to overall mixing in the plume is controlled by the ratio of a frontal length scale representing water mass interaction with the front, to the overall plume length scale, and diminishes as the plume front evolves, due to diminishing connectivity between the plume front and the source through the ebb tide. We hypothesize that mechanisms of diminishing connectivity include both weakening of barotropic gradients through the plume as well as Coriolis effects as the plume becomes geostrophic. This work will be pursued using 21st century current, hydrography and microstructure measurements in the plume front and core to assess mixing using various techniques, as well as hydrostatic and non-hydrostatic realistic and idealized numerical models. The field effort is focused on the mid-sized Merrimack and Connecticut rivers, which are well studied and provide an ideal setting to observe frontal evolution in regions with and without strong tidal currents. Results from the field study will allow calibration and validation of models, which can then be used to understand similar frontal processes across a wide swath of parameter space.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.

当河水沃茨进入沿海时，它们与较咸的海水混合。这一过程始于河流排放（羽流）的向海边界，影响河口附近和整个邻近沿海地区的环流和流动。 虽然这一河流-海洋界面发生的区域代表了海洋的一个小区域，但它对海洋混合非常重要，并且在用于预测沿海地区环境条件的环流模型中往往解决不好。作为这项调查的一部分，研究人员将进行实地测量，并利用数值模型来确定淡水排放的向海边界结构的变化，以及那里发生的混合。 这些过程将在不同的河流流量和潮汐条件下进行检查。 此外，这项研究将评估有多少退潮的河流流出是通过向海边界循环，并评估该地区的整体重要性，以混合总河流排放到近海洋盐度。 这项工作的结果将揭示在河流-海洋界面发生的物理过程的细节，并提高大规模模型的预测能力。 此外，这项研究取得的进展最终将使人们能够更好地预测污染物、营养物质和水体在海洋中的命运和迁移。在本项目期间，将支助三名研究生为建设科学能力作出贡献。河流羽流的前沿区域是将有浮力的沿海排放物与周围海水分开的向海边界。 各种规模的海洋锋通过人们知之甚少的机制，在几个数量级上充当重要的能量汇。 虽然在过去的几十年里，我们已经做出了重大努力来提高对羽流动力学的认识，但在我们对锋面演变的理解以及锋面在羽流内部和整个羽流混合预算中的作用方面仍然存在根本性的差距。这个建议的目的是了解的演变和意义的锋面过程跨越一系列的尺度，从小规模的传播放电前的中间规模的货架前界定的落潮脉冲，并确定控制的机制，从工程尺度的演变前地转尺度。我们的假设是，锋面混合的相对重要性，在羽流中的整体混合控制的比例的锋面长度尺度代表与前面的水团相互作用，整体羽流长度尺度，并减少作为羽流前端的演变，由于减少羽流前端和源之间的连接通过退潮。 我们假设，连接性减弱的机制包括减弱正压梯度通过羽流以及科里奥利效应的羽流成为地转。 这项工作将继续使用21世纪世纪的电流，水文学和微结构测量的羽流前端和核心，以评估混合使用各种技术，以及流体静力学和非流体静力学的现实和理想化的数值模型。 实地工作的重点是中型的梅里马克和康涅狄格州的河流，这是很好的研究，并提供了一个理想的设置，以观察锋面演变的地区和没有强大的潮流。 现场研究的结果将允许模型的校准和验证，然后可以用来了解类似的锋面过程在一个广泛的参数space.This奖反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

项目成果

Freshwater Composition and Connectivity of the Connecticut River Plume During Ambient Flood Tides

• DOI: 10.3389/fmars.2021.747191
• 发表时间: 2021-10
• 作者: M. Whitney;Yan Jia;K. Cole;D. MacDonald;Kimberly D. Huguenard

Evolving Interior Mixing Regimes in a Tidal River Plume

潮汐河羽流中不断变化的内部混合机制

• DOI: 10.1029/2022gl099633
• 发表时间: 2022
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Spicer, Preston;Huguenard, Kimberly;Cole, Kelly L.;MacDonald, Daniel G.;Whitney, Michael M.
• 通讯作者: Whitney, Michael M.

Mixing of the Connecticut River Plume During Ambient Flood Tides: Spatial Heterogeneity and Contributions of Bottom‐Generated and Interfacial Mixing

• DOI: 10.1029/2023jc020423
• 发表时间: 2024-03
• 期刊: Journal of Geophysical Research: Oceans
• 作者: M. Whitney;P. Spicer;D. MacDonald;Kimberly D. Huguenard;K. Cole;Yan Jia;Nikiforos Delatolas

Calculating lateral plume spreading with surface Lagrangian drifters

使用表面拉格朗日漂移器计算横向羽流扩散

• DOI: 10.1002/lom3.10356
• 发表时间: 2020
• 期刊: Limnology and Oceanography: Methods
• 作者: Kakoulaki, Georgia;MacDonald, Daniel G.;Cole, Kelly
• 通讯作者: Cole, Kelly

Comparison of structure and turbulent mixing between lateral and leading-edge river plume fronts: Microstructure observations from a T-REMUS AUV

横向和前缘河流羽流锋之间的结构和湍流混合比较：T-REMUS AUV 的微观结构观察

• DOI: 10.1016/j.ecss.2023.108234
• 发表时间: 2023
• 期刊: Coastal and Shelf Science
• 作者: Delatolas, Nikiforos;MacDonald, Daniel G.;Goodman, Louis;Whitney, Michael;Huguenard, Kimberly;Cole, Kelly
• 通讯作者: Cole, Kelly