Spectral variability in particulate light backscattering in the sea: resolving fine-scale optical features and their biogeochemical significance

Accurate characterization of light backscattering in natural waters is critical for interpreting remote sensing reflectance and retrieving marine biogeochemical properties. While light absorption has been extensively measured, resolving fine-scale spectral variability in particulate light backscattering has remained challenging due to instrumental limitations. Here, we present hyperspectral backscattering measurements from the newly developed <i>HyFi-bb</i> instrument during field campaigns in the Baltic Sea and German Bight. The high spectral resolution (∼2 nm, 350-850 nm) reveals distinct bio-optical features, including pigment-specific signatures and anomalous dispersion near the pigment absorption bands, which are not resolved in multispectral measurements. Comparisons across regions show that backscattering ratios are higher in the minerogenic particle-dominated German Bight than in phytoplankton-rich Baltic waters, with spectral slopes of the backscattering ratios reflecting underlying particle composition. Contributions from particles <0.2 µm were found to be minor, suggesting their limited role in total backscattering in coastal waters. Our results demonstrate that hyperspectral backscattering provides new insights into the biogeochemical drivers of optical variability.