Investigation of the geochemistry of dissolved organic matter in coastal waters using optical properties

Accurate characterization of dissolved organic matter (DOM) optical properties is crucial for accurate measurement of chlorophyll from remotely sensed color data and for modelling spectral light penetration in the ocean. In coastal areas, changes in the humic acid: fulvic acid ratio of gelbstoff from riverine to marine environments cause significant changes in the spectral slope parameter but are difficult to predict a priori and impossible to measure without extracting gelbstoff from seawater. Our recent results from a wide variety of natural waters show that DOM optical properties are a function of physical, chemical, and biological processes. Detailed fluorescence spectroscopy shows changes in the optical properties of gelbstoff related to the onset of marine productivity in coastal transition zones which are indicative of changes in chemical composition of DOM. In this paper, we discuss our efforts to use fluorescence to aid interpretation of variability in gelbstoff spectral slopes for development of next generation chlorophyll algorithms and for development of an optical tracer of geochemical processes involving dissolved organic carbon.