Shifts in Phytoplankton Community Structure Across an Anticyclonic Eddy Revealed From High Spectral Resolution Lidar Scattering Measurements

• Published in: Frontiers in Marine Science
• Main Authors: Schulien, Jennifer A., Della Penna, Alice, Gaube, Peter, Chase, Alison P., Haentjens, Nils, Graff, Jason R., Hair, Johnathan W., Hostetler, Chris A., Scarino, Amy Jo, Boss, Emmanuel S., Karp-Boss, Lee, Behrenfeld, Michael J.
• Other Authors: US Geological Survey Santa Cruz, United States Geological Survey Reston (USGS), Applied Physics Laboratory Seattle (APL-UW), University of Washington Seattle, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), University of Maine, Department of Botany and Plant Pathology, Oregon State University (OSU), NASA Langley Research Center Hampton (LaRC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: ACL; carbon; impact; north-atlantic; mesoscale eddies; satellite-observations; backscatter; depolarization; hsrl; light backscattering; mueller matrix; ocean color; phytoplankton community composition; reflectance; toxic dinoflagellate; envir; geo; Mueller; North Atlantic
• Online Access: https://doi.org/10.3389/fmars.2020.00493; https://hal.archives-ouvertes.fr/hal-03015211/file/Schulien_etal_FiMS_2020.pdf; https://hal.archives-ouvertes.fr/hal-03015211

WOS:000548189100001 International audience Changes in airborne high spectral resolution lidar (HSRL) measurements of scattering, depolarization, and attenuation coincided with a shift in phytoplankton community composition across an anticyclonic eddy in the North Atlantic. We normalized the total depolarization ratio (delta) by the particulate backscattering coefficient (b(b)(p)) to account for the covariance in delta and b(b)(p) that has been attributed to multiple scattering. A 15% increase in delta/b(b)(p) inside the eddy coincided with decreased phytoplankton biomass and a shift to smaller and more elongated phytoplankton cells. Taxonomic changes (reduced dinoflagellate relative abundance inside the eddy) were also observed. The delta signal is thus potentially most sensitive to changes in phytoplankton shape because neither the observed change in the particle size distribution (PSD) nor refractive index (assuming average refractive indices) are consistent with previous theoretical modeling results. We additionally calculated chlorophyll-a (Chl) concentrations from measurements of the diffuse light attenuation coefficient (K-d) and divided by b(b)(p) to evaluate another optical metric of phytoplankton community composition (Chl:b(bp)), which decreased by more than a factor of two inside the eddy. This case study demonstrates that the HSRL is able to detect changes in phytoplankton community composition. High spectral resolution lidar measurements reveal complex structures in both the vertical and horizontal distribution of phytoplankton in the mixed layer providing a valuable new tool to support other remote sensing techniques for studying mixed layer dynamics. Our results identify fronts at the periphery of mesoscale eddies as locations of abrupt changes in near-surface optical properties.