Phytoplankton optical fingerprint libraries for development of phytoplankton ocean color satellite products

Quantifying changes in phytoplankton communities using ocean color is essential for predicting ocean food resources, occurrences of harmful algal blooms, and carbon and other elemental cycles, among other predictions.  Here we present a dataset of greater than fifty strains of phytoplankton, from a range of taxonomic lineages, geographic locations, and time in culture, alone and in mixtures, grown to exponential and/or stationary phase for determination of hyperspectral UV-VIS absorption coefficients, multi-angle and multi-spectral backscatter coefficients, volume scattering functions, particle size distributions, fluorescence, and hyperspectral remote sensing reflectance.  The measurements obtained from these experiments are valuable to facilitate development of new global and/or regional ocean color models by the broader scientific community. 

Methods
A range of experimental conditions were used to assess changes in cellular carbon, pigments, ratios and optical properties.  For most of the strains, measurements were made at two growth stages: mid-exponential (Exp) and stationary (Stat) growth phase, but for some strains, measurements were made during only one growth phase. A range of mixed cultures were made to assess the ability of algorithms derived from individual cultures to resolve the known algal components in the prepared mixtures. The potential for changes in pigment composition in response to in vitro culture adaption over time was assessed by studying multiple strains of the same species (Amphidinium carterae, Ditylum brightwellii, and Heterosigma akashiwo) isolated on different historical dates, but from similar geographic areas.  Synechococcus sp., Thalassiosira oceanica, and Ostreococcus lucimarinus were examined for their response in pigment composition, cellular carbon, and optical properties to ‘climate change scenarios’ of elevated temperature, irradiance and decreased pH.  More detail on these manipulations can be found in (Neeley et al. 2022).

Methods are summarized here with more detail found in Neeley et al. (2022) and Lomas et al. (2023).  Samples for pigment concentration were analyzed by HPLC (Agilent RR1200 HPLC) and calculated from pigment response factors, extraction volumes determined from a Vitamin E acetate standard and filtration volumes.  Measurements of filter pad particle optical density (ODfp) were performed using a Cary 4000 UV-Visible scanning spectrophotometer equipped with a 15 cm integrating sphere (Labsphere DRA-CA-900), betwee 290-850 nm with a 2nm Slit Band Width (SBW), 0.2 nm data interval, reduced slit height and 120 nm per minute scan speed. Dissolved Organic Carbon measurements were made on Shimadzu TOC-L or TOC- V unit equipped with a total nitrogen analyzer using the high temperature combustion catalytic oxidation method. CDOM absorbance spectra are measured on a double-beam Cary 100 Ultraviolet-Visible scanning spectrophotometer using Suprasil® quartz cylindrical cells of 100 mm pathlength with ultraviolet oxidized Milli-Q water as the blank and reference.  Samples for particulate organic nitrogen and carbon concentrations were filtered onto 25 mm precombusted Ahlstrom glass fiber filters (nominal pore size 0.7 µm) under low pressure (~125 mm Hg), and rinsed with 0.2 µm-filtered dilution seawater.  Blanks were created by rinsing a pre-combusted filter with filtered dilution seawater to account for any DOC adsorption. A benchtop flow-through apparatus was constructed to measure the inherent optical properties (IOPs) of the diluted phytoplankton cultures. All optical data were processed as described in detail in Lomas et al. 202x. 

Usage Notes

This dataset represents a taxonomically and geographically broad dataset of multiple phytoplankton optical parameters.  The dataset can be used to validate regional to global scale phytoplankton community composition models, as well as develop new models focused on resolving different phytoplankton within the same taxonomic lineage.