Marine dissolved organic matter (DOM) is one of the largest reservoirs of organic carbon on the earth’s surface. Colored, or chromophoric organic matter (CDOM) is a variable component of the total DOM which interferes significantly with light propagation in surface and deep waters and greatly complicates the interpretation of remote sensing data. More importantly, the abundance and spectral characteristics of CDOM varies unpredictably over both temporal and spatial scales independently of traditional parameters (e.g. chl a, cell numbers, DOC, etc.). As a result, it is not possible to definitively correct remote sensing data for optical interferences arising from CDOM. Recent work in an adjacent oceanographic field has demonstrated that a major fraction (30-60%) of bulk marine DOM is colloidal (> 1 kDa) in nature, and preliminary evidence suggests that the optical signature of this organic colloidal matter differs markedly from the bulk CDOM. In addition, the colloidal organic fraction appears to cycle more rapidly than truly soluble organic matter. My working hypothesis is that a major part of the highly variable CDOM signal in surface waters can be explained mechanistically by short term fluctuations in the composition and cycling dynamics of colloidal CDOM. The two primary goals for this project are: 1) measure the optical signature of marine colloidal matter in nearshore waters and determine the extent to which this signature changes in response to biological activity (the source and likely sink of marine colloids), and 2) determine the extent to which photochemical processes differentially affect the optical characteristics and residence time of soluble and colloidal CDOM in seawater. The work proposed here takes the first critical steps towards physically teasing apart marine CDOM components to better explain their nature and cycling in seawater.