An alternative method for correcting fluorescence quenching

• Published in: Ocean Science
• Main Authors: Biermann, L., Guinet, C., Bester, M., Brierley, A., Boehme, L.
• Other Authors: Sea Mammal Research Unit University of St Andrews (SMRU), School of Biology University of St Andrews, University of St Andrews Scotland -University of St Andrews Scotland -Natural Environment Research Council (NERC), Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria South Africa, Pelagic Ecology Research Group, Scottish Oceans Institut
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDE]Environmental Sciences; Austral; Southern Ocean
• Online Access: https://hal.archives-ouvertes.fr/hal-01293313; https://doi.org/10.5194/os-11-83-2015

International audience Under high light intensity, phytoplankton protecttheir photosystems from bleaching through nonphotochemicalquenching processes. The consequence ofthis is suppression of fluorescence emission, which mustbe corrected when measuring in situ yield with fluorometers.We present data from the Southern Ocean, collectedover five austral summers by 19 southern elephant sealstagged with fluorometers. Conventionally, fluorescence datacollected during the day (quenched) were corrected using thelimit of the mixed layer, assuming that phytoplankton areuniformly mixed from the surface to this depth. However,distinct deep fluorescence maxima were measured in approximately30% of the night (unquenched) data. To account forthe evidence that chlorophyll is not uniformly mixed in theupper layer, we propose correcting from the limit of the euphoticzone, defined as the depth at which photosyntheticallyavailable radiation is 1%of the surface value. Mixed layerdepth exceeded euphotic depth over 80% of the time. Underthese conditions, quenching was corrected from the depth ofthe remotely derived euphotic zone Zeu, and compared withfluorescence corrected from the depth of the density-derivedmixed layer. Deep fluorescence maxima were evident in only10%of the day data when correcting from mixed layer depth.This was doubled to 21% when correcting from Zeu, moreclosely matching the unquenched (night) data. Furthermore,correcting from Zeu served to conserve non-uniform chlorophyllfeatures found between the 1% light level and mixedlayer depth.