Collaborative Research: Trajectories and spatial distributions of diatoms at dissipation scales of turbulence

湍流在浮游植物栖息的上混合层中是普遍存在和重要的。在与单个细胞和菌落相关的尺度上，耗散湍流侵蚀细胞周围的分子扩散边界层，并影响对捕食者-猎物相互作用和聚集等过程至关重要的相遇概率。由于翻滚和下沉，叠加在周围流体运动上的是细胞的局部运动。这些运动如何与周围的湍流相互作用还没有很好的理解，特别是对于形态多样，非能动的硅藻，占主导地位的初级生产力。最近的研究表明，静水下沉速度的颗粒和湍流扩散运动的流体不能简单地加在一起，以解决颗粒的运动;为负和接近中性的浮力颗粒，高湍流强度产生几倍更快的下沉和上升速度比静水中看到的。对云中水滴的大气研究集中在加速的惯性机制上，但本提案的审查表明，在由硅藻的颗粒特征定义的参数空间中，形状在确定湍流相互作用方面可能比惯性重要得多。研究人员建议研究湍流对硅藻沉降轨迹和由此产生的空间分布的影响。采用一种新的体积粒子成像仪，他们将获得受控湍流下硅藻的单个细胞和选定菌株链的3D拉格朗日轨迹。通过针对不同形态和机械特性的物种以及处于不同生长阶段的培养物，将获得关于物理、形态和生理特性如何影响非运动浮游植物下沉速度和轨迹的新见解。下沉是浮游植物重要的生存策略，它与环境流的相互作用对浮游植物在混合层中的停留时间，并最终对透光层中浮游植物的生产力和向深层的元素通量具有重要意义海洋这项研究挑战了导致浮游植物在海洋中下沉的机制的共同观点，并提供了一个从斯托克斯沉降湍流下沉偏离的机械解剖。通过针对不同形态和机械特性的物种以及不同生长阶段的文化，将获得新的见解，了解物理，形态和生理特性如何相互作用，以确定非运动浮游植物的下沉速度和轨迹，特别是在主导湍流的漩涡中及其附近。从这项研究的结果也将推进了解底层的空间分布的浮游植物在分辨率差分米毫米域，丰富的影响觅食领域的食草动物和颗粒aggregation.Broader的影响形成：广泛的阵列的问题涉及粒子运动的湍流。这项研究的结果将适用于许多水生环境，并促进对湍流中非球形低惯性颗粒行为的理解，并应用于大气科学和化学工程等其他领域。该建议还将推进湍流的实验室模拟，并在现有方法中进行新的妥协，从而保证有效模拟耗散尺度湍流。与计算机密集型全息术或粒子成像测速术相比，VoPI还提供了对湍流中粒子的更快速、更有效的识别和跟踪。研究人员提出了一个为期一周的研讨会，将生物海洋学和工程研究生和博士后聚集在一起，探索与浮游生物与环境流的微尺度相互作用相关的丰富问题，以及解决这些问题的方法。两名研究生和两名本科生将获得合作赠款的支持。这项研究的结果将在全国会议上发表，发表在同行评议的期刊上，并纳入PI教授的研究生和本科生课程。

Turbulence is ubiquitous and important in the upper mixed layer where phytoplankton reside. On scales relevant to individual cells and colonies, dissipating turbulence erodes molecular diffusive boundary layers around cells and affects probabilities of encounter critical for processes such as predator-prey interactions and aggregation. Superimposed on ambient fluid motion are local motions of cells due to tumbling and sinking. How these motions interact with ambient turbulence is not well understood, particularly for the morphologically diverse, non-motile diatoms that dominate primary productivity. Recent studies show that still-water sinking velocities of particles and turbulent diffusive motions of fluids cannot simply be added together to solve for particle motions; for negatively and nearly neutrally buoyant particles, high turbulence intensity produces several times faster sinking and rising velocities than seen in still water. Atmospheric studies of water droplets in clouds have focused on inertial mechanisms of acceleration, but the review in this proposal suggests that--in the parameter space defined by the particle characteristics of diatoms--shape may be much more important than inertia in determining plankton-turbulence interactions. The investigators propose to study effects of turbulence on settling trajectories and resultant spatial distributions of diatoms. Employing a novel volumetric particle imager, they will obtain 3D Lagrangian trajectories of individual cells and chains of selected strains of diatoms under controlled turbulence. By targeting species of different morphologies and mechanical properties as well as cultures at different growth stages, new insights will be gained on how physical, morphological and physiological properties affect sinking speeds and trajectories of non-motile phytoplankton.Intellectual Merit:Sinking is an important life strategy of phytoplankton, and its interaction with ambient flows holds significant implications for the residence time of phytoplankton in the mixed layer and ultimately for phytoplankton productivity in the photic zone and fluxes of elements to the deeper ocean. This study challenges common views on mechanisms that cause phytoplankton sinking in the ocean and offers a mechanistic dissection of departures in turbulent sinking from Stokes settling. By targeting species of varied morphologies and mechanical properties, as well as cultures at different growth stages, new insights will be gained into how physical, morphological and physiological properties interact to determine sinking speeds and trajectories of non-motile phytoplankton, particularly in and near the vortices that dominate turbulent flows. Results from this study will also advance understanding of underlying spatial distributions of phytoplankton in the poorly resolved decimeter to millimeter domain, with abundant implications for the foraging fields of grazers and formation of particle aggregates.Broader Impacts :Wide arrays of problems involve particle motions in turbulence. Results from this study will apply to many aquatic environments and advance understanding of the behavior of non-spherical, low-inertia particles in turbulent flows, with applications to other fields such as atmospheric sciences and chemical engineering. This proposal will also advance the laboratory simulation of turbulence with a novel compromise among existing approaches that promises efficient simulation of dissipation-scale turbulence. The VoPI also provides more rapid and efficient identification and tracking of particles in turbulent flows than has been feasible with computer-intensive holography or particle-imaging velocimetry. The investigators propose a week-long workshop that will bring together biological oceanography and engineering graduate students and postdocs to explore the rich set of questions associated with microscale interactions of planktonic organisms with ambient flows, and approaches to address them. Two graduate students and two undergraduate students will be supported by the collaborative grant. Results from this study will be presented at national meetings, published in peer-reviewed journals and incorporated into graduate and undergraduate courses taught by the PIs.