Precision Assessment of the HPLC Phytoplankton Pigment Dataset Analyzed by NASA to Quantify Global Variability in Support of Ocean Color Remote Sensing

The ability to generate measurements from ocean color orbital sensors, such as VIIRS and MODIS, that satisfy climate data record (CDR) requirements is contingent on the quality of the in situ ground or sea truth observations for vicarious calibration and algorithm validation. NASA has the charge to collect, analyze, and distribute in situ data of the highest possible quality with documented uncertainties and in keeping with established performance metrics. Using a dataset of over 18,000 HPLC phytoplankton pigment samples representing waters collected in all major ocean basins analyzed at a central laboratory (Field Support Group, Ocean Ecology Laboratory, NASA Goddard Space Flight Center), we performed an assessment of the global precision among sample replicates of chlorophyll a (Chl a), as well as major accessory pigments (primary pigments, PPig). We investigated the impact of filtration volume, water basin, collection technique, pigment concentration, and different filtration volumes on replicate filter precision, as well as investigating any pigment-specific differences. Our results quantify sample variability with the goal of understanding any systemic biases or biogeographic influences. Filtration volume did not have a large effect on sample precision, and no significant differences in precision were found among Pacific, Atlantic, and Arctic Oceans for both Chl a and PPig. Mean precision, as well as confidence intervals, increased dramatically for some pigments at the extreme of their concentration ranges. Precision degraded as the difference in filtration volume between duplicates increased for most of the pigments assessed, including Chl a. Recommendations for sample collection and processing are presented to reduce pigment measurement uncertainty.