Evaluating the importance of phytoplankton community structure to the optical properties of the Santa Barbara Channel, California

Rebecca K. Barrón, David A. Siegel and Nathalie Guillocheau

Limnol. Oceanogr., 59(3), 2014, 927-946 | DOI: 10.4319/lo.2014.59.3.0927

ABSTRACT: Observations from the Santa Barbara Channel, California, were used to evaluate relationships among optical properties and phytoplankton community structure. Phytoplankton community structure was determined by statistically analyzing 10 diagnostic phytoplankton pigment concentrations using empirical orthogonal function (EOF) analysis. The first four EOF modes explained 82% of phytoplankton community structure variability and were interpreted as a mixed community mode composed mostly of nanoplankton, a mode dominated by microplankton (diatoms and dinoflagellates), a mode describing alternating diatom and dinoflagellate dominance, and a mode reflecting picoplankton presence. Variations in colored dissolved organic matter (CDOM) and phytoplankton absorption spectra were related to changes of the mixed microplankton modal amplitudes. Characteristics of the CDOM spectrum were further dependent on whether diatoms or dinoflagellates were dominant. The particle backscattering coefficient was significantly correlated with EOF modes describing the mixed microplankton and the picoplankton communities. The influence of phytoplankton community structure was also seen in the performance of standard ocean color algorithms using the in situ data set. The present results demonstrate that many optical characteristics vary significantly with changes in phytoplankton community structure and suggest that improvements in remote-sensing algorithms will require model coefficients to vary accordingly. Further, changes in phytoplankton community composition affect both dissolved and particle absorption and scattering properties, not simply the phytoplankton-specific properties, creating challenges for the development of algorithms aimed at assessing phytoplankton community structure from satellite observations.

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