SEASONAL-VARIATION OF CDOM AND DOC IN THE MIDDLE ATLANTIC BIGHT - TERRESTRIAL INPUTS AND PHOTOOXIDATION

Extensive surveys of the fluorescence and absorption of chromophore-co ntaining dissolved organic matter (CDOM), dissolved organic C (DOC) co ncentration, chlorophyll fluorescence, and salinity were performed dur ing August and November 1993 and March and April 1994 along a cruise l ine extending from the mouth of Delaware Bay southeast to the Sargasso Sea. With shallow stratification in August, photobleaching dramatical ly altered the optical properties of the surface waters, with similar to 70% of the CDOM absorption and fluorescence lost through photooxida tion in the waters at the outer shelf. S, the slope of the log-lineari zed absorption spectrum of CDOM, increased offshore and seemed to incr ease with photodegradation. The increase in S combined with the season al variation in the relationship between Chl and CDOM underscores the difficulty in developing algorithms to predict Chl concentrations in t urbid coastal waters with ocean color data. Despite the photooxidation of CDOM, the seasonal variation in the CDOM fluorescence-absorption r elationship and fluorescence quantum yields was <15%. When using appro priate methods, the airborne lidar approach for remote determination o f CDOM absorption coefficients seems to be a very robust technique. Th e photooxidation of CDOM in August also affected the relationship betw een CDOM and DOC concentration in the surface waters, although for the rest of the year the relationship was reasonably linear. The results of a simple model suggest similar to 10% of the DOC in the mixed layer was directly convened photochemically to dissolved inorganic C (DIC).