Bo Tong, Ralston David K, Geyer W Rockwell, McWilliams James C
Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.
Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA 90095.
Proc Natl Acad Sci U S A. 2024 Aug 27;121(35):e2401498121. doi: 10.1073/pnas.2401498121. Epub 2024 Aug 19.
Estuaries, as connectors between land and ocean, have complex interactions of river and tidal flows that affect the transport of buoyant materials like floating plastics, oil spills, organic matter, and larvae. This study investigates surface-trapped buoyant particle transport in estuaries by using idealized and realistic numerical simulations along with a theoretical model. While river discharge and estuarine exchange flow are usually expected to export buoyant particles to the ocean over subtidal timescales, this study reveals a ubiquitous physical transport mechanism that causes retention of buoyant particles in estuaries. Tidally varying surface convergence fronts affect the aggregation of buoyant particles, and the coupling between particle aggregation and oscillatory tidal currents leads to landward transport at subtidal timescales. Landward transport and retention of buoyant particles is greater in small estuaries, while large estuaries tend to export buoyant particles to the ocean. A dimensionless width parameter incorporating the tidal radian frequency and lateral velocity distinguishes small and large estuaries at a transitional value of around 1. Additionally, higher river flow tends to shift estuaries toward seaward transport and export of buoyant particles. These findings provide insights into understanding the distribution of buoyant materials in estuaries and predicting their fate in the land-sea exchange processes.
河口作为陆地与海洋的连接地带，河流和潮汐流相互作用复杂，影响着诸如漂浮塑料、石油泄漏、有机物和幼体等漂浮物质的输运。本研究通过理想化和实际数值模拟以及理论模型，研究了河口表面捕获的漂浮颗粒输运。虽然通常认为在亚潮汐时间尺度上，河流流量和河口交换流会将漂浮颗粒输送到海洋，但本研究揭示了一种普遍存在的物理输运机制，该机制导致漂浮颗粒在河口滞留。潮汐变化的表面辐合锋影响漂浮颗粒的聚集，颗粒聚集与振荡潮流之间的耦合导致在亚潮汐时间尺度上向陆输运。小型河口的漂浮颗粒向陆输运和滞留情况更为明显，而大型河口则倾向于将漂浮颗粒输送到海洋。一个包含潮汐角频率和横向速度的无量纲宽度参数在约为1的过渡值处区分了小型和大型河口。此外，较高的河流流量往往会使河口向向海输运和漂浮颗粒输出方向转变。这些发现为理解河口漂浮物质的分布以及预测它们在陆海交换过程中的归宿提供了见解。
