Relationships between phytoplankton specific properties and multi-spectral particulate backscattering

Robust relationships between optical proxies and phytoplankton specific parameters (e.g. phytoplankton carbon, size, abundance) are critical for carbon cycle science applications using in-situ and remote sensing data. Refining optical retrievals of these critical properties requires in-depth knowledge of the phytoplankton present when making optical measurements. Particulate backscattering (b_bp) at a single wavelength has shown great promise for retrieving phytoplankton specific properties based on both field applications and modeling studies. Multi- or hyper-spectral backscattering measurements, such as those planned to be inverted from the NASA PACE-OCI instrument, provide novel opportunities for exploring and improving these relationships. Here, we describe connections between phytoplankton specific properties and optical parameters with a focus on multi-spectral b_bp data collected during the NASA NAAMES and EXPORTS field campaigns. Combining traditional flow cytometry with imaging flow cytometry provides a full resolution of the phytoplankton communities encountered, which spanned from populations dominated by prokaryotes to populations dominated by larger eukaryotic cells. Our breadth of sampling over multiple seasons and ocean basins provides the dynamic range in cell types and optics required for a robust exploration of important phytoplankton-optics relationships.