Dynamic sinking behavior in diatoms: New insights from individual-based high resolution video observations

硅藻从光线充足的海洋上层下沉，负责将物质运输到深海，是控制这种海洋草总体丰度的重要因素。它们的下沉特征对于详细了解它们非常重要，这样它们就可以在海洋动力学模型中准确地表示出来。 人们假设这些无鞭毛的微观细胞的所有成员都以近似相同的速率下沉，以恒定的速率下沉，并且运动方向是向下的。然而，在单个单元水平上重新检查下沉率表明，所有三个假设都是不正确的。 利用复杂的光学和计算技术，这些研究人员正在研究单个硅藻细胞如何下沉，它们开始和停止的能力，并评估哪些部分可以实际上升。 这项研究将对硅藻如何通过改变它们在外部环境中的运动与外部环境相互作用产生新的见解。它还将解决这些种群中有哪些部分实际上是向上移动的，从而增强营养物质向上移动到海洋中光线充足的部分。 这些都是关于小型单细胞物种如何与周围海洋相互作用的新见解，将大大丰富我们对一个被认为已经很好理解的问题的理解。 本项目将培养一名研究生和两名本科生从事这项研究。推广也提供了K-12活动将全息仪器带入课堂，并在我们的研究所公开讲座系列。 硅藻的下沉速率是重要的生活史特征，控制着细胞表面的损失速率和营养通量。正浮力（米每小时率）是最大的硅藻细胞的属性，并在垂直迁移生活史策略中发挥作用。然而，在较小的硅藻速率通常从修改的斯托克斯方程描述，并通常假设为均匀和向下。研究人员先前观察到，一个物种的下沉速率在样本中不是单调的，而是围绕一个平均值分布的，可能是向上和向下的，并且在第二个时间尺度上从接近零到最大速度受到细胞的控制。因此，上升行为可以被限制在一小部分人口与一个相当大的下降率。该项目的目标是确定这些特征有多普遍，确定这种独特的启停下沉行为的作用，并使用一系列精心控制的实验室研究和一系列广泛的硅藻物种来研究正浮力的普遍性。 这些特点将被认为是在一个框架内的复杂的形式/功能模式，发生在硅藻。细胞周围的边界层在停止/开始序列期间差异很大，并且可以通过我们的技术直接可视化。在快速下沉过程中，营养物质向细胞的扩散加速;研究人员假设，通过使用恒定的体积下沉速率，向细胞表面的扩散被低估了。这项工作只有在高分辨率相机和先进处理技术的出现下才有可能实现，这些技术允许在动态水柱中量化颗粒和流体流动。

The sinking of diatoms out of the well-lit upper layers of the ocean is responsible for transport of material to the deep-sea and is an important factor in controlling the overall abundance of this grass of the sea. Their sinking characteristics are important to understand in detail so they can be accurately represented in models of ocean dynamics. It has been assumed that all members of these non-flagellated, microscopic cells sink at approximately the same rate, at a constant rate, and that the direction of motion is downward. However, a re-examination of sinking rates at an individual cell level indicates that all three assumptions are incorrect. Using sophisticated optical and computing techniques, these researchers are examining how individual diatom cells sink, their ability to start and stop, and assessing what fraction can actually ascend. This study will yield new insights into how diatoms interact with their external environment by altering their movement through it. It will also address what fraction of these populations are actually moving upwards, thereby enhancing the movement of nutrients upward into the well-lit portions of the ocean. These are novel insights into how small unicellular species interact with the ocean around them and will significantly enrich our understanding of a problem that had been thought to be well understood. The project will train one graduate student and two undergraduate students in this research. Outreach is also provided by K-12 activities bringing holographic instruments into the classroom, and a public lecture series at our institute. Diatom sinking rates are important life history characteristics that control both loss rates and nutrient flux to the cell surface. Positive buoyancy (m per hour rates) is an attribute of the largest diatom cells and plays a role in a vertical migration life history strategy. However, rates in smaller diatoms are typically described from a modified Stokes equation and are generally assumed to uniform and downward. The investigators previously observed that a species sinking rate is not monotonic within a sample but is distributed around a mean value, may be both upward and downward, and is under cellular control from near-zero to maximum velocity over second time scales. Thus, ascending behavior can be limited to a small portion of a population with a substantial downward rate. The goal of this project is to determine how widespread these characteristics are, determine the role of this unique start-stop sinking behavior, and examine how pervasive positive buoyancy is using a series of carefully controlled laboratory studies and a broad suite of diatom species. These characteristics will be considered within a framework of the complex form/function patterns that occur in diatoms. Boundary layers around cells differ vastly during the stop/start sequence and can be directly visualized by our techniques. Nutrient diffusion to the cell is accelerated during fast sinking; the investigators hypothesize that diffusion to cellular surfaces has been underestimated by using a constant bulk sinking rate. This work is only possible with the advent of high resolution cameras and advanced processing that allows particle and fluid flow to be quantified in a dynamic water column.