Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 2179-2194, 2015
https://doi.org/10.5194/bg-12-2179-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
14 Apr 2015
A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment
I. Cetinić1, M. J. Perry1, E. D'Asaro2, N. Briggs1, N. Poulton3, M. E. Sieracki3,*, and C. M. Lee2 1Ira C. Darling Marine Center, School of Marine Sciences, University of Maine, Walpole, Maine, USA
2Applied Physics Laboratory and School of Oceanography, University of Washington, Seattle, Washington, USA
3Bigelow Laboratory for Ocean Sciences, East Boothbay, Maine, USA
*now at: National Science Foundation, Arlington, VA, USA
Abstract. The ratio of two in situ optical measurements – chlorophyll fluorescence (Chl F) and optical particulate backscattering (bbp) – varied with changes in phytoplankton community composition during the North Atlantic Bloom Experiment in the Iceland Basin in 2008. Using ship-based measurements of Chl F, bbp, chlorophyll a (Chl), high-performance liquid chromatography (HPLC) pigments, phytoplankton composition and carbon biomass, we found that oscillations in the ratio varied with changes in plankton community composition; hence we refer to Chl F/bbp as an "optical community index". The index varied by more than a factor of 2, with low values associated with pico- and nanophytoplankton and high values associated with diatom-dominated phytoplankton communities. Observed changes in the optical index were driven by taxa-specific chlorophyll-to-autotrophic carbon ratios and by physiological changes in Chl F associated with the silica limitation. A Lagrangian mixed-layer float and four Seagliders, operating continuously for 2 months, made similar measurements of the optical community index and followed the evolution and later demise of the diatom spring bloom. Temporal changes in optical community index and, by implication, the transition in community composition from diatom to post-diatom bloom communities were not simultaneous 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 phytoplankton patchiness on extended temporal scales and ecologically relevant spatial scales and should offer new insights into the processes regulating patchiness.

Citation: Cetinić, I., Perry, M. J., D'Asaro, E., Briggs, N., Poulton, N., Sieracki, M. E., and Lee, C. M.: A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment, Biogeosciences, 12, 2179-2194, https://doi.org/10.5194/bg-12-2179-2015, 2015.
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The ratio of simple optical properties measured from underwater autonomous platforms, such as floats and gliders, is used as a new tool for studying phytoplankton distribution in the North Atlantic Ocean. The resolution that optical instruments carried by autonomous platforms provide allows us to study phytoplankton patchiness and its drivers in the oceanic systems.
The ratio of simple optical properties measured from underwater autonomous platforms, such as...
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