10:00–10:15 | ABSTRACT 1261
INVERSION OF HYPERSPECTRAL RADIOMETRIC PROFILES FROM BGC-ARGO FLOATS TO RETRIEVE THE VERTICAL STRUCTURE OF PHYTOPLANKTON PHOTOPHYSIOLOGY
Chlorophyll a (Chl) is the primary proxy for phytoplankton biomass and is routinely measured across the global ocean both at the surface through satellite reflectance and at depth through fluorometry installed on autonomous floats. However, in many oceanic regions, these two estimation methods show substantial differences in magnitude, likely due to two sources of variability: (1) regional variations in backscattering and colored detrital matter (CDM), and (2) differences in the quantum yield of Chl fluorescence. To evaluate the sources of this discrepancy, we analyzed hyperspectral radiometric profiles collected by enhanced BGC-Argo floats. To retrieve the inherent optical properties, we apply a modified inversion approach based on McKee et al. 2003. We separated backscattering into particulate and pure water components and absorption into CDM and phytoplankton components. To estimate quantum yield of chlorophyll fluorescence, we isolated the sun induced fluorescence (SIF). We performed internal validation by comparing upward and downwards diffuse attenuation coefficients as well as SIF fluxes, and found that SIF normalized by PAR was strongly correlated with the raw Chl sensor values. Chl estimated derived from diffuse attenuation also showed good correlation and low bias when compared with the standard empirical MODIS Aqua algorithm. We found that regional differences in SIF quantum yield are correlated with discrepancies between satellite-derived and fluorometric Chl estimates. Overall our results demonstrate that autonomously-acquired hyperspectral radiometric profiles can reveal plankton ecological responses to four-dimensional ocean processes and help resolve discrepancies between fluorometric and reflectance-based biomass estimations.
Bruno Cremella, Laboratoire d’Océanographie de Villefranche (LOV), CNRS/SU, Villefranche-sur-Mer, France, [email protected], https://orcid.org/0000-0001-7010-6386
Yannick Huot, Département de Géomatique Appliquée, Université de Sherbrooke, Sherbrooke, Canada, [email protected], https://orcid.org/0000-0003-1793-761X
Lou Andrés, Laboratoire d’Océanographie de Villefranche (LOV), CNRS/SU, Villefranche-sur-Mer, France, [email protected], https://orcid.org/0009-0006-4494-6350
Edouard Leymarie, Laboratoire d’Océanographie de Villefranche (LOV), CNRS/SU, Villefranche-sur-Mer, France, [email protected]
Vincenzo Vellucci, Laboratoire d’Océanographie de Villefranche (LOV), CNRS/SU, Villefranche-sur-Mer, France, [email protected], https://orcid.org/0000-0001-5392-7457
Hervé Claustre, Laboratoire d’Océanographie de Villefranche (LOV), CNRS/SU, Villefranche-sur-Mer, France, [email protected], https://orcid.org/0000-0001-6243-0258
