A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment

[摘要] The ratio of two in situ optical measurements – chlorophyll fluorescence(Chl F) and optical particulate backscattering (b_bp) – variedwith changes in phytoplankton community composition during the North AtlanticBloom Experiment in the Iceland Basin in 2008. Using ship-based measurementsof Chl F, b_bp, chlorophyll a (Chl), high-performance liquid chromatography (HPLC) pigments,phytoplankton composition and carbon biomass, we found that oscillations inthe ratio varied with changes in plankton community composition; hence werefer to Chl F/b_bp as an "optical community index". The indexvaried by more than a factor of 2, with low values associated with pico-and nanophytoplankton and high values associated with diatom-dominatedphytoplankton communities. Observed changes in the optical index were driven bytaxa-specific chlorophyll-to-autotrophic carbon ratios and by physiologicalchanges in Chl F associated with the silica limitation. A Lagrangian mixed-layerfloat and four Seagliders, operating continuously for 2 months, madesimilar measurements of the optical community index and followed theevolution and later demise of the diatom spring bloom. Temporal changes inoptical community index and, by implication, the transition in communitycomposition from diatom to post-diatom bloom communities were notsimultaneous over the spatial domain surveyed by the ship, float and gliders.The ratio of simple optical properties measured from autonomous platforms,when carefully validated, provides a unique tool for studying phytoplanktonpatchiness on extended temporal scales and ecologically relevant spatialscales and should offer new insights into the processes regulatingpatchiness.

[学科分类] 地球化学与岩石