NSFGEO-NERC: Novel imaging, physiology and numerical approaches for understanding biologically mediated, unsteady sinking in marine diatoms

硅藻占海洋初级生产力的40%以上，下沉行为是一种重要的物种特有属性，它可以决定群落组成、聚集体的形成和向海底流失的物质数量。虽然它们不会游泳，但硅藻远不是被动的，它们在很长一段时间内控制它们的下沉速度，以应对环境因素，如营养浓度、光照和温度，以及生物因素，如繁殖状态。早期对硅藻下沉的研究表明，硅藻有能力在几小时到几天内调节它们的浮力，以应对不断变化的环境条件。然而，一些物种也可以在更短的时间尺度上控制它们的下沉速度，执行最近发现的不稳定的下沉行为。到目前为止，硅藻悬浮液研究主要使用沉淀柱(SETCOLS)等散装测量，因为测量容易，而且假设散装速率充分反映了这一组的基本特征。我们提供了证据证明这一假设是不合理的，并提出了一系列实验室实验，使用先进的光学技术、测量单细胞周围过程的生理学工具和数值方法来研究一系列环境条件下非稳定下沉的分类学和形态变异性，并检查观察到的差异的影响。该项目将利用跨学科合作，包括创新的光学技术、先进的细胞生理学工具和数值模拟方法，以表征单个细胞水平的硅藻悬浮液特性。从时间平均下沉测量到小时间尺度的转变表明，下沉速度可能在几秒钟内变化几个数量级。我们将讨论瞬时速度控制行为的几个方面，以确定非稳定下沉的适应性意义。这一新的观察结果表明，扩散限制运输的模型需要修订，以适应特定物种的差异。我们将使用来自各种物种和环境条件的单个细胞水平的实验数据来提供3D数值模型，这些模型将被用于表征硅藻不稳定下沉的适应性意义，以及为什么它可能被限制在某些分类群中。

Diatoms account for up to 40% of oceanic primary production sinking behavior is an important species-specific property that can determine the community composition, aggregate formation and the amount of material lost to depth. Although they are unable to swim, diatoms are far from passive, controlling their sinking speeds over long time scales in response to environmental factors, such as nutrient concentration, irradiance, and temperature and biological factors, such as reproductive state. Early work on diatom sinking demonstrated the capacity of diatoms to regulate their buoyancies over hours to days in response to changing environmental conditions. However, some species can also control their sinking speeds over much shorter time scales of seconds, performing a recently discovered unsteady sinking behavior. To date, diatom suspension studies have largely used bulk measurements such as settling columns (SETCOLSs) due to the ease of measurement and assumption that bulk rates adequately capture the essential characteristics of this group. We offer evidence that this assumption is not justified and propose a series of laboratory experiments using advanced optical techniques, physiological tools that measure processes around single cells and numerical approaches to investigate taxonomic and morphological variability in unsteady sinking over a range of environmental conditions and examine the implications the observed differences. This project will leverage an interdisciplinary collaboration involving innovative optical techniques, advanced cell physiology tools and numerical modeling approaches to characterize diatom suspension properties at the individual cell level. The shift from time-averaged sinking measurements to small time scales has indicated that sinking speeds can vary orders of magnitude over seconds. We will address several aspects of instantaneous velocity control behavior in order to determine the adaptive significance of unsteady sinking. This novel observation suggests that models of diffusion limited transport need to be revised in order to accommodate species-specific differences. We will use individual cell level experimental data from a variety of species and environmental conditions to inform 3D numerical models which will be used to characterize what, if any, adaptive significance unsteady sinking in diatoms has and why it may be constrained to certain taxonomic groups.