Measurements of phytoplankton color index (PCI), an indicator of phytoplankton biomass, represent one of the largest datasets acquired through the continuous plankton recorder (CPR) survey. PCI has been used to describe changes in the spatial and temporal distribution of phytoplankton, especially in the North Atlantic, where the methodology was developed and primarily applied. The method functions by grouping samples, based on their color shade, into four categories. Each category is assigned a numerical value to aid spatial and temporal averaging. Recently a CPR has been operated in the Eastern Mediterranean, one of the most oligotrophic areas of the global oceans. To capture the specific characteristics of the area, an additional greenness grading is introduced. In this study, we use satellite‐derived chlorophyll a (Chl a) data to examine whether PCI categories can be distinguished within the low and narrow range of Chl a values found in the study area and to calculate the range of Chl a concentrations expressed by each category. Furthermore, a newly calculated numerical system for the general use of PCI in oligotrophic areas and previously calculated PCI numerical value systems utilizing a variety of in situ, laboratory and remote sensing experiments, were tested for their applicability in the area. Present results indicate the feasibility of employing PCI measurements to provide an estimate of Chl a concentration in the Eastern Mediterranean. This provides confidence in the implementation of a new category system for PCI, as well as the use of the new PCI numerical system for the assessment of phytoplankton in oligotrophic waters.

中文翻译：

---

绿色的第五种阴影：贫营养系统中浮游植物颜色指数评估的新方法

浮游植物颜色指数（PCI）的测量是浮游生物生物量的指标，它是通过连续浮游生物记录器（CPR）调查获得的最大数据集之一。PCI已被用来描述浮游植物的时空分布变化，特别是在北大西洋地区，该方法的开发和主要应用。该方法通过根据样本的色泽将样本分为四类来发挥作用。为每个类别分配一个数值，以帮助进行空间和时间平均。最近，在全球海洋中营养最贫瘠的地区之一的地中海东部开展了心肺复苏术。为了捕获该区域的特定特征，引入了附加的绿色等级。在这项研究中，我们使用了卫星衍生的叶绿素a（叶绿素一个）数据来检查是否PCI类别可以在低和叶绿素的窄的范围内被区分一在研究区域中找到的值，并计算叶绿素的范围一个由每个类别表示浓度。此外，对在贫营养地区普遍使用PCI的新计算的数值系统和利用各种原位，实验室和遥感实验的先前计算的PCI数值系统进行了测试，以确定它们在该地区的适用性。目前的结果表明采用PCI测量的可行性提供叶绿素的估计一集中在东地中海。这为实施PCI的新类别系统提供了信心，并为新的PCI数值系统用于贫营养水域浮游植物的评估提供了信心。