Collaborative Research: Defining the Structural Basis of the Optical Properties of Chromophoric Dissolved Organic Matter

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ABSTRACTOCE-0443263Chromophoric dissolved organic matter (CDOM) is a complex organic material found ubiquitously in aquatic systems where it plays a central role, not only through its impact on the aquatic light field and on the remote sensing of phytoplankton biomass by satellite ocean color sensors, but also through its photochemical reactions. Although the optical absorption and emission properties of CDOM have been known and studied extensively for over fifty years, no satisfactory explanation has yet been provided that can account for the long-wavelength absorption and emission behavior of these materials. Researchers at the University of Maryland and at Woods Hole Oceanographic Institution have teamed up to propose that this behavior results from intramolecular charge transfer interactions between hydroxy-aromatic donors and quinoid acceptors formed by the partial oxidation of soluble lignin precursors. They will test this hypothesis by combining wavelength-selective monochromatic (laser) and polychromatic photobleaching studies with ultrahigh resolution electrospray ionization mass spectrometry to acquire structural information on the species that are specifically destroyed or produced by the wavelength-selective irradiations. Absorption and fluorescence spectroscopy, gel permeation chromatography and lignin phenol analyses will be employed to provide complementary structural information. Both model humic and lignin systems will be examined, followed by CDOM samples collected during a series of field studies in the Delaware Bay/Mid-Atlantic Bight region. These field studies will provide further tests of this hypothesis through an examination of the relationships among the optical properties and the lignin phenol content, molecular size and mass spectra of CDOM collected across a wide range of oceanic environments and seasons. This work will place fundamental constraints on the origins and modes of formation of CDOM, as well as on its photochemical properties.