Measurement and Characterization of DOM Pools Using EEM Spectroscopy and HPLC

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The major pool of dissolved organic carbon (DOC) in the ocean is an order of magnitude larger than the particulate organic carbon (POC) pool, and twice as large as the atmospheric pool of CO2, yet as much as 90% of DOC remains uncharacterized as to specific chemical identity. One component of this uncharacterized pool is known as "humic substance" or "gelbstoff", two non-specific terms for a complex mixture of compounds having a yellow color and a blue fluorescence. The way in which these compounds have been defined and analyzed in the past has resulted in much confusion and a lack of insight regarding their nature, distribution, and cycling in the ocean. Recent developments in fluorescent spectroscopy and high performance liquid chromatography show promising results when applied to the study of gelbstoff in seawater. Three-dimensional excitation-emission matrix (EEM) analysis of unconcentrated samples has shown for the first time the existence of four different fluorophores in seawater, each of which exhibits characteristic properties and distributions. One of these fluorophores may be indicative of a protein-like, bioreactive substance. Ion-pairing HPLC can resolve gelbstoff into up to twenty individual components. Application of these new technologies in tandem to the analysis of dissolved organic matter in seawater can be used to trace different components of the DOC, thereby leading to an improved understanding of the oceanic carbon cycle.