Abstract: A primary goal of ONR's Chemical Oceanography program is "to enable prediction of chemical distributions and speciation in marine environments, especially as they relate to optical properties of seawater". Chromophoric dissolved organic matter (CDOM) strongly influences the optical and chemical properties of marine waters, yet little is known about the specific chemical groups within CDOM that control the dynamics of this important component of natural organic matter. This proposal focuses on metal-binding moieties as key functionalities influencing the optical properties and photochemical reactivity of particular fractions of CDOM. Our approach to study the involvement of metal-binding groups in CDOM cycling will combine new and promising chromatographic and structural analytical methods with mechanistic experimentation. The primary objectives of this work are to isolate and identify discrete metal-binding ligands within low and high molecular weight fractions of representative coastal and oceanic CDOM; characterize ligand structure, and metal binding characteristics; and determine the influence of metal binding on the overall photochemical reactivity of CDOM. This work will advance ONR and Naval objectives by contributing to the development of a chemical and structural framework within which observations of CDOM optical properties can be interpreted, thereby enhancing the predictive value of optical measurements in seawater.