Validated radiative transfer modeling reveals exceptional subsurface light enhancement in coccolithophore blooms

We assess radiative transfer model results for a coupled atmosphere-ocean system using measured optical properties at two contrasting fjord sites: one visibly discolored by a coccolithophore bloom and one without visible discoloration. With minimal free parameters, the modeled top-of-atmosphere (TOA) radiances agree with Sentinel-3A Ocean and Land Colour Instrument (OLCI) data to within 4 %, excluding the 1020 nm channel. At the bloom site, water constituents contributed 86 % of the green radiance, associated with a threefold higher backscattering ratio and a 45-fold increase in the backscattering coefficient. The validated model revealed that scalar irradiance was 100 % higher down to 1 m depth during the coccolithophore bloom compared to conditions without marine particles, highlighting potential ecological implications of enhanced scattering in dense coccolithophore blooms.