Does Turbulence Create Small-Scale Patchiness of Phytoplankton?

本研究项目将重点研究小尺度湍流与浮游植物颗粒空间分布之间的相互作用。不可压缩、各向同性湍流的直接数值模拟（DNS）的初步结果表明，当悬浮在模拟流场中时，密度与藻类相似的颗粒发展出非随机空间分布，包括峰值数量密度为全球平均值40倍的聚集体。将进行实验室测试，以确定实际的藻类颗粒在实际湍流中是否形成斑块，以及它们的行为是否与数值模拟预测的一致。将建造和校准一种特殊的装置，该装置可以产生可重复的网格产生的湍流，并允许直接观察悬浮的藻类颗粒。将评估颗粒大小、形状、浮力密度和固有运动性（“游泳”能力）对颗粒空间分布的影响。将经验数据与从改进模型中得出的DNS预测进行比较。研究结果将为小规模流体动力学在影响浮游植物空间分布中的作用提供开创性的见解：这种见解对于理解海洋和五大湖中藻类获取资源的动力学以及草食-藻类相互作用至关重要。＊＊＊

9409073 SQUIRES This research project will focus on the interaction between small- scale turbulence and the spatial distribution of phytoplanktonic particles. Preliminary results from Direct Numerical Simulations (DNS) of incompressible, isotropic turbulence have shown that particles of a density similar to that of algae develop non-random spatial distributions including aggregates at peak number densities of 40 times the global mean value when suspended in a simulated flow field. Laboratory tests to determine whether actual algal particles in real turbulent flow form patches and whether they behave as predicted from numerical simulations will be undertaken. A special apparatus which creates reproducible grid-generated turbulent flow and which allows for direct observation of suspended algal particles will be constructed and calibrated. The effect of particle size, shape, buoyant density, and inherent motility ("swimming" capacity) on particle spatial distributions will be evaluated. Empirical data will be compared to DNS predictions derived from a refined model. Results will provide pioneering insight into the role of small-scale fluid dynamics in influencing phytoplankton spatial distributions: such insight is essential for understanding the dynamics of resource acquisition by algae and herbivore-algal interactions in oceans and the Great Lakes. ***