AUTHOR=Martínez-Vicente Víctor , Evers-King Hayley , Roy Shovonlal , Kostadinov Tihomir S. , Tarran Glen A. , Graff Jason R. , Brewin Robert J. W. , Dall'Olmo Giorgio , Jackson Tom , Hickman Anna E. , Röttgers Rüdiger , Krasemann Hajo , Marañón Emilio , Platt Trevor , Sathyendranath Shubha 

TITLE=Intercomparison of Ocean Color Algorithms for Picophytoplankton Carbon in the Ocean

JOURNAL=Frontiers in Marine Science

VOLUME=4

YEAR=2017

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2017.00378

DOI=10.3389/fmars.2017.00378

ISSN=2296-7745

ABSTRACT=<p>The differences among phytoplankton carbon (<italic>C</italic><sub><italic>phy</italic></sub>) predictions from six ocean color algorithms are investigated by comparison with <italic>in situ</italic> estimates of phytoplankton carbon. The common satellite data used as input for the algorithms is the Ocean Color Climate Change Initiative merged product. The matching <italic>in situ</italic> data are derived from flow cytometric cell counts and per-cell carbon estimates for different types of pico-phytoplankton. This combination of satellite and <italic>in situ</italic> data provides a relatively large matching dataset (<italic>N</italic> &gt; 500), which is independent from most of the algorithms tested and spans almost two orders of magnitude in <italic>C</italic><sub><italic>phy</italic></sub>. Results show that not a single algorithm outperforms any of the other when using all matching data. Concentrating on the oligotrophic regions (Chlorophyll-a concentration, B, less than 0.15 mg Chl m<sup>−3</sup>), where flow cytometric analysis captures most of the phytoplankton biomass, reveals significant differences in algorithm performance. The bias ranges from −35 to +150% and unbiased root mean squared difference from 5 to 10 mg C m<sup>−3</sup> among algorithms, with chlorophyll-based algorithms performing better than the rest. The backscattering-based algorithms produce different results at the clearest waters and these differences are discussed in terms of the different algorithms used for optical particle backscattering coefficient (<italic>b</italic><sub><italic>bp</italic></sub>) retrieval.</p>