Effects of microbial particles on oceanic optics: A database of single-particle optical properties

Abstract

We describe a database of the single-particle optical properties of marine microbial particles. This database includes representatives from five classes of particles: viruses (VIR), heterotrophic bacteria (BAC), cyanobacteria (CYA), small nanoplanktonic diatoms (DIA), and nanoplanktonic chlorophytes (CHLO). The optical properties of VIR, whose mean size is 0.07 µm, were determined from Mie scattering calculations using reasonable approximations about the size distribution and refractive index of viral particles. The database for BAC, CYA, DIA, and CHLO was created from laboratory measurements of microbial cultures and modeling of particle optics. BAC are represented by a mixed natural population of bacterial species (∼0.55 µm in size), CYA by Synechococcus (clone WH 8103, ∼1 µm), DIA by Thalassiosira pseudonana (∼4 pm), and CHLO by Dunaliella tertiolecta (∼7.5m). The database includes the single-particle optical properties that are useful in radiative transfer modeling: the absorption and scattering cross sections and scattering phase functions. Additionally, the database includes the attenuation cross sections, optical efficiency factors, single-scattering albedos, and backscattering properties. For phytoplankton species, chlorophyll- and carbon-specific optical coefficients are also available. The optical quantities are generally determined at 1-nm intervals in the spectral region from 350 to 750 nm. The scattering phase function is determined at 5-nm intervals in wavelength and 1° intervals in scattering angle. The size distribution and refractive index of the particles are also included. This database, when combined with radiative transfer modeling, provides a powerful approach to advancing our understanding of oceanic optics.