In situ determination of the quantum yield of phytoplankton chlorophyll a fluorescence: A simple algorithm, observations, and a model

Abstract

Vertical profiles of the in situ quantum yield of fluorescence of chlorophyll a, f , were derived with an algorithm from spectral underwater radiometer measurements. Select inherent optical properties were obtained from an initial radiance reflectance inversion that was optimized by comparing retrieved estimates of phytoplankton absorption with independent measurements. The comparison of chlorophyll concentrations produced by the algorithm to measured values allowed validation of the inversion. Fluorescence quantum yield values were calculated from the retrieved phytoplankton absorption and the upwelling radiance corrected for elastic and inelastic scattering. Raman scattered light was found to be a significant component of the upwelling light field at wavelengths of Chl a fluorescence. Values of f determined using the algorithm, and therefore derived solely from the radiometer measurements, were not significantly different from those estimated using independent measurements of absorption by phytoplankton (r 2 ϭ 0.86). The profiles of f were characterized by an initial increase with depth to a subsurface maximum followed by a subsequent decrease. The irradiances of the subsurface maxima and f at high irradiances appeared to be well conserved. An irradiance-based model including photochemical and nonphotochemical quenching was developed to explain variations in the quantum yield.Variations in phytoplankton biomass have been studied using sun stimulated fluorescence, often termed natural or passive fluorescence, which can be detected as red peaks in both in-water (Gordon 1979;Kishino et al.

Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

“…Babin et al (1996) show frequency distributions for a* and Q a * observed in the open ocean waters of different basins, both vary over nearly an order of magnitude. As for j f , it varies in a more complicated manner (Morrison 2003;Schallenberg et al 2008). As a consequence, the fluorescence-Chl a relationship for a given fluorometer varies according to environmental conditions.…”

“…However, the proportionality of [Chl a] and F is known to be modulated by the taxonomic composition and physiological acclimation mechanisms (essentially related to light and/or nutrient history), which both determine the variability in a*, j f , as well as Q a * (e.g., Falkowski and Kolber 1995;Babin et al 1996;Morrison 2003;Schallenberg et al 2008). Babin et al (1996) show frequency distributions for a* and Q a * observed in the open ocean waters of different basins, both vary over nearly an order of magnitude.…”

New algorithms for MODIS sun-induced chlorophyll fluorescence and a comparison with present data products

“…9, bottom) yields measured in situ in surface waters of the world (Ostrowska et al 1997;Maritorena et al 2000;Morrison 2003). A comparison of ϕ est and CFE is shown in the upper left panel of Fig.…”

“…As such, field validation of fluorescence algorithms will require great care. The time of sampling and the incident irradiance will have to match those encountered by the MODIS sensor, otherwise, the time and irradiance dependence of ϕ will affect the results (e.g., Morrison 2003).…”

“…Also, water absorbs strongly in the red fluorescence waveband, so the depth from which water-leaving fluorescence can be detected is limited to the upper 5 m or so (Babin et al 1996b), where irradiance is also close to maximal. Nonphotochemical quenching is thus important under these midday, clear-sky, near-surface conditions (Maritorena et al 2000;Morrison 2003) and should be considered directly in the interpretation of fluorescence measured from satellites (Dandonneau and Neveux 1997;Morrison 2003).…”