Phytoplankton accessory pigments are commonly used to estimate phytoplankton size classes, particularly during development and validation of biogeochemical models and satellite ocean color‐based algorithms. The diagnostic pigment analysis (DPA) is based on bulk measurements of pigment concentrations and relies on assumptions regarding the presence of specific pigments in different phytoplankton taxonomic groups. Three size classes are defined by the DPA: picoplankton, nanoplankton, and microplankton. Until now, the DPA has not been evaluated against an independent approach that provides phytoplankton size calculated on a per‐cell basis. Automated quantitative cell imagery of microplankton and some nanoplankton, used in combination with conventional flow cytometry for enumeration of picoplankton and nanoplankton, provide a novel opportunity to perform an independent evaluation of the DPA. Here, we use a data set from the North Atlantic Ocean that encompasses all seasons and a wide range of chlorophyll concentrations (0.18–5.14 mg m⁻³). Results show that the DPA overestimates microplankton and picoplankton when compared to cytometry data, and subsequently underestimates the contribution of nanoplankton to total biomass. In contrast to the assumption made by the DPA that the microplankton size class is largely made up of diatoms and dinoflagellates, imaging‐in‐flow cytometry shows significant presence of diatoms and dinoflagellates in the nanoplankton size class. Additionally, chlorophyll b is commonly attributed solely to picoplankton by the DPA, but Chl b‐containing phytoplankton are observed with imaging in both nanoplankton and microplankton size classes. We suggest revisions to the DPA equations and application of uncertainties when calculating size classes from diagnostic pigments.

中文翻译：

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评估诊断性色素以估计浮游植物大小等级

浮游植物辅助色素通常用于估计浮游植物的大小等级，特别是在生物地球化学模型和基于卫星海洋颜色的算法的开发和验证过程中。诊断性色素分析（DPA）基于色素浓度的整体测量，并基于关于不同浮游植物分类组中特定色素的存在的假设。DPA定义了三种大小类别：微型浮游生物，纳米浮游生物和微型浮游生物。到目前为止，尚未针对提供基于每个细胞计算的浮游植物大小的独立方法对DPA进行评估。微型浮游生物和一些纳米浮游生物的自动定量细胞成像，与常规流式细胞仪结合使用，可对微微浮游生物和纳米浮游生物进行枚举，提供了进行DPA独立评估的新机会。在这里，我们使用来自北大西洋的数据集，涵盖了所有季节和广泛的叶绿素浓度（0.18–5.14 mg / m^-3）。结果显示，与细胞计数数据相比，DPA高估了微浮游生物和微微浮游生物，随后低估了纳米浮游生物对总生物量的贡献。与DPA的假设相反，微浮游生物的大小类别主要由硅藻和鞭毛藻组成，而流式细胞成像显示纳米浮游生物的大小类别中存在大量的硅藻和鞭毛藻。此外，叶绿素 b通常由DPA归因于微浮游生物，但是在纳米浮游生物和微浮游生物大小类别中，通过成像都可以观察到含有Chl  b的浮游植物。从诊断颜料计算尺寸类别时，我们建议对DPA方程进行修订并应用不确定性。