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

Abstract

Abstract.The ratio of two in situ optical measurements -chlorophyll fluorescence (Chl F ) and optical particulate backscattering (b bp ) -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 , b bp , chlorophyll a (Chl), highperformance 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 /b bp 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 diatomdominated phytoplankton communities. Observed changes in the optical index were driven by taxa-specific chlorophyllto-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.

Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry

“…Optical measurements, including back-scattering and fluorescence, should be calibrated through in situ measurements and associated with the specific community composition (Cetinìc et al, 2015). Nevertheless uncalibrated optical data collected during ABACUS mission can still be a useful proxy for the real concentration/ abundance of the phytoplankton community.…”

Seasonal dynamics and disturbance of phytoplankton biomass in the wake of Tahiti as observed by Biogeochemical-Argo floats

“…Cetinić et al (2015) showed that bbp * can be used as a proxy for community composition with high values associated with pico-and nano-to low values associated with diatom-dominated communities. Although the SPSG trophic conditions are very different from that investigated by Cetinić et al (2015) in the North Atlantic Subpolar Gyre, and that bbp * can be also affected by a change in the composition (size and nature) of the particle assemblage, the change in bbp_surf * by a factor of 2 10 between the average FTWake and FOpenO (Figure 3d) suggests a phytoplankton community with a significant contribution of microphytoplankton in the Tahitian wake. Such an increase could be attributed to diatoms, that grow relatively fast and have high affinities for nitrates (Edwards et al, 2012;Glibert et al, 2016;Lomas and Glibert, 2000), and could be in agreement with an increased input of nutrients in the Tahitian wake.…”

Optical Backscattering Measured by Airborne Lidar and Underwater Glider

“…Gliders are small, autonomous underwater vehicles that manipulate their buoyancy to continuously profile the water column [22] while "gliding" horizontally, collecting thousands of measurements during deployments typically ranging between a few days and a few months. Because of their unique propulsion mechanism, gliders allow energy and cost-efficient measurements on spatial and temporal scales that are difficult to make by other means [23]. Gliders outfitted with fluorometers are routinely used for monitoring the phytoplankton community structure of the West Florida Shelf [24][25][26][27], where they have been particularly useful in describing the 3-dimensional structure of blooms of Karenia brevis, the Florida red-tide organism.…”