Jed Goldstone

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Photochemistry of chromophoric (light absorbing) dissolved organic matter (CDOM) is an important part of the global carbon cycle. About 34 x 10¹² moles of organic carbon (0.4 teragrams of carbon) reaches the ocean from terrigenous sources each year. Identified removal processes in estuarine and coastal environments account for only 50% this carbon. If the remainder were to be transported to the open ocean, the ocean's dissolved organic carbon (DOC) reservoir would be filled in a mere 4000-6000 years. Alternative sinks for DOC in coastal systems must exist. Photochemical reactions most likely serve as an important control on the fate of DOC in the coastal ocean.

Conceptually, CDOM photochemical reactions can be split into two classes: direct and indirect. Direct photochemistry is the result of the absorption of photons (light) and the subsequent formation of products, including radical species (see Figure 1). Indirect photochemistry is the result of photoproduced intermediates such as superoxide (O₂-), hydroxyl radical (OH*), singlet oxygen (1O₂), hydrogen peroxide (HOOH), and carbonate radical (CO₃^o-) reacting with CDOM (Figure 2).

We have been studying the reactions of superoxide and hydroxyl radical with CDOM derived from both estuarine and coastal regions and from freshwater systems with an eye towards understanding the role of indirect photochemistry in the cycling of DOM. Because the absorption of light serves as the initiator for all photochemical reactions (as well as controlling the underwater light field, with consequences for aquatic biology and remote sensing), we have also been interested in the behavior of the optical properties (absorption and fluorescence) of CDOM and their relationship to both direct and indirect photochemistry.