Collaborative Research: Lateral mixing and dispersion on the inner shelf

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该奖项旨在表彰一套全面的实地观察，以阐明和量化内部大陆架的混合过程，并直接检查这些过程对内部大陆架生物分布的影响。沿海流动的预测建模需要对亚网格尺度过程进行参数化，这些过程在水平维度上具有10到1000米的特征长度尺度。这项研究将提供在这些尺度上的内大陆架水平色散的全面图景及其对标量分布的影响。假设垂直边界和分层所施加的物理限制限制了垂直运动和交换过程，导致流场的强各向异性和内部陆架的分散。先前的工作表明，尽管底边界层有限制作用，但在水平方向上，底边界层的混合是尺度相关的。在水柱中，由于分层可能产生更大的各向异性和对垂直传输速率的限制，在表层混合层中，由于波浪、风以及地表加热和冷却的影响，尺度依赖性可能会有所不同。本项目将直接测量不同强迫条件下内陆架底部混合层、分层内部和表面混合层的横向分散速率，以量化任何依赖尺度的混合，突出不同深度横向混合的异同。一旦确定了分散率和尺度依赖性，它们将用于检查混合的横向速率如何与生物薄层的发育、维持和降解相对应。两个为期两周的实地实验将在蒙特利湾北部的内大陆架进行，以检查这些问题。在部署了一系列系泊仪器来测量物理、光学和声学特性之后，研究团队将在北加州上升流季节的早期和后期分别在底部边界层、分层内部和表面混合层中释放示踪染料。染料?S的空间和时间分布将使用配备快速响应荧光计的自主水下航行器以及配备荧光计和辅助仪器的拖体进行测量，这些仪器可同时测量感兴趣的生物和地球化学特性。染料测量将用于量化横向混合，方法是将数据拟合到尺度相关定律，并比较和对比在这两个测量期间不同气候和流体动力学强迫条件（风、表面波、内波、分层和湍流）下相应的分散率。将横向混合过程和强迫条件与测量的生物分布（薄层）联系起来，将有助于确定水平混合在均匀化和/或重新分配生物标量中的作用。这项工作将为沿海地区尺度的运输和混合提供有价值的新见解，特别是在10到1000米的“中间”尺度上。它将产生广泛的科学影响，特别是对内部冰架的跨学科建模工作，其中对横向混合的估计和/或参数化造成了重大的不确定性。随着沿海人口的持续增长和海洋生态系统的压力持续增加，了解决定近岸环境中运输和/或保留的潜在机制将变得越来越重要。了解沿海环境中的横向扩散不仅对海洋幼虫和有害藻华的运输/滞留有重要意义，而且对污染物的运输/滞留也有重要意义。更好地了解这些混合过程最终将有利于环境规划者、政策制定者和沿海社区的其他利益相关者。拟资助博士后1人，博士生2人。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Intellectual Merit This award is for a suite of comprehensive field observations to elucidate and quantify the mixing processes in the inner shelf and to directly examine the impact of these processes on inner shelf biological distributions. Predictive modeling of coastal flows requires parameterizations of sub-gridscale processes, which, in the horizontal dimension have characteristic length-scales of 10s to 1000s of meters. This study will provide a comprehensive picture of horizontal dispersion on the inner shelf at these scales and its implications for scalar distributions. It is hypothesized that the physical limitations imposed by vertical boundaries and stratification restrict vertical motions and exchange processes leading to strong anisotropies in the flow field and dispersion in the inner shelf. Previous work has shown that mixing in the bottom boundary layer is scale-dependent in the horizontal direction in spite of the limiting effects of the bottom boundary. It is likely that scale-dependency may be different higher in the water column where stratification may create even greater anisotropies and restrictions on vertical transfer rates, and in the surface mixed layer due to the influence of waves, winds, as well as surface heating and cooling. This project will directly measure lateral dispersion rates in the bottom mixed layer, stratified interior, and surface mixed layer on the inner shelf under different forcing conditions in order to quantify any scale-dependent mixing and highlight the similarities and differences in lateral mixing at different depths. Once the dispersion rates and scale dependencies are determined, they will be used to examine how the lateral rates of mixing may correspond with biological thin layer development, maintenance and degradation. Two, two-week long field experiments will be conducted on the inner shelf of northern Monterey Bay to examine these issues. After deploying an array of moored instruments to measure physical, optical and acoustical properties, the research team will release a tracer dye, in separate releases, within the bottom boundary layer, stratified interior, and surface mixed layer during both the early and late portions of the upwelling season in northern California. The dye?s spatial and temporal distribution will be measured using an autonomous underwater vehicle equipped with a fast response fluorometer, as well as a tow body equipped with a fluorometer and ancilliary instrumentation that measure concurrently biological and geochemical properties of interest. The dye measurements will be used to quantify the lateral mixing by fitting the data to scale dependent laws, and comparing and contrasting the corresponding rates of dispersion with different climatological and hydrodynamics forcing conditions (winds, surface waves, internal wave, stratification, and turbulence) during these two measurement periods. Connecting the lateral mixing processes and forcing conditions with measured biological distributions (thin layers) will help determine the role of horizontal mixing in homogenizing and/or redistributing biological scalars. Broader Impacts This work will provide valuable new insights into the transport and mixing of scalars in the coastal region, particularly at the 'intermediate' scales of 10s to 1000s of meters. It will have a broad scientific impact, especially on interdisciplinary modeling efforts of the inner shelf where estimates and/or parameterizations of lateral mixing cause significant uncertainty. As coastal populations continue to grow, and pressure on marine ecosystems continues to increase, it will be increasingly important to understand the underlying mechanisms determining transport and/or retention in the nearshore environment. Understanding lateral dispersion in the coastal environment has significant implications not only for the transport/retention of marine larvae, and harmful algal blooms but also for the transport/retention of pollutants. Better understanding of these mixing processes will ultimately be of interest to environmental planners, policy makers and other stakeholders in coastal communities. The proposed research will also support one postdoctoral scholar and two PhD students.