Size Distribution and Fluorescent Characteristics of Colloidal CDOM: Indicators of the Provenance and Reactivity of CDOM in Coastal Waters?

摘要

LONG-TERM GOAL. Our long-term research goal is to ascertain the nature and magnitude of optical effects (absorbance / fluorescence / scattering) in surface seawaters associated with the production and cycling of marine colloidal organic matter. We are particularly interested in determining how these effects are driven or modulated by the productivity dynamics of phytoplankton and marine heterotrophic bacteria in addition to terrestrially derived materials. OBJECTIVES. Marine chromophoric dissolved organic matter (CDOM) imparts highly variable optical signatures in surface waters over short spatial and temporal scales for reasons not yet understood. While considerable research efforts are currently underway on the specific absorption and fluorescence characteristics of the bulk CDOM and FDOM, our primary objective is to follow the chromophoric signatures of different molecular weight fractions to determine if the production (or allochthonous input) and removal of colloidal organic matter contributes to the high variability in bulk CDOM. We know that a signficant fraction (10-40%) of non-living dissolved organic matter resides in the colloidal size fraction (1-1000 nm) (Benner et al., 1992; Buesseler et al., 1996; Chen and Schnitzer, 1989), and that this fraction is very reactive to both bio-degradation (to soluble substances) (Benner et al., 1992) and aggregation (to large sinking particles)(Baskaran et al., 1992; Chin et al., 1998; Moran and Buesseler, 1992) The challenge is to determine to what extent these dynamic, opposing processes influence the behavior of CDOM and FDOM in surface seawaters, and how these biogeochemical effects interweave with photochemical degradation pathways.