Data from: Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake

Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.

浮游植物（phytoplankton）沉降是一项关键属性，可决定真光层（photic zone）内的群落组成，以及向深海输送的物质损失量。迄今为止，有关硅藻（diatom）悬浮的研究均采用总体批量测量方法，并假设整体沉降速率足以涵盖硅藻沉降的核心特征。然而，近期研究表明，单一个体硅藻的沉降速率与总体平均速率存在显著差异。本研究采用高分辨率光学技术、硅藻沉降的个体水平观测手段，以及新近开发的自由沉降细胞周围流动可视化方法。研究结果显示，无论是野外样本还是实验室培养体系，部分大型中心硅藻（centric diatoms）均表现出一种全新行为模式：细胞会以秒级时间尺度交替经历快速沉降爆发与近零沉降速率。我们还证实，该行为直接受细胞自身的代谢调控。本研究围绕该结果对细胞表面营养盐通量（nutrient flux）的影响展开讨论。尽管大型硅藻在快速沉降阶段的营养盐通量会升高，但当前的物质输运模型（mass transport models）无法纳入本研究中观测到的非稳态沉降行为。不过，即便在短暂的近零沉降间歇期，大型硅藻仍可借助快速沉降阶段提升的细胞表面营养盐通量获得生存益处。