9315821 MOPPER Light-initiated reactions play important roles in chemical and biological processes in the sea, including redox reactions, carbon cycling and photoinhibition. Despite the importance of photochemical processes, almost nothing is known about photochemical pathways and reaction sites within marine DOM that are responsible for production of reactive sites within Marine DOM that are responsible for production of reactive transients at the sea surface. The focus will be shifted from oceanic carbon cycling to the study of precursors and mechanisms involved in the photochemical formation of LMW carbonyl compounds and OH radicals form marine DOM and DOM isolates, e.g., humic substances. Some of the key questions are: Are LMW carbonyl compounds and OH radicals formed mainly by primary or by secondary photoprocesses? What is the role of oxidants, e.g., O2, superoxide peroxides, in the photoproduction of these species in seawater? Is photobleaching of DOM fluorescence (and absorbance) in seawater accompanied by an actual loss of humic substances or only of chromophoric moieties? Can the marine DOM pool be physically fractionated into photoreactive (humic) and photo-unreactive fractions? What is the nature of the chromophoric sites within marine DOM? This study will provide new basic information on the photochemical, chemical, and spectroscopic properties of marine DOM.
