PLANT PIGMENTS AS BIOMARKERS OF HIGH-MOLECULAR-WEIGHT DISSOLVED ORGANIC-CARBON

We used plant pigments as tracers of high-molecular-weight dissolved organic C (HMW DOG) (<0.2 mu m and >1,000 Da). Water samples were collected from four stations along a transect on cruises in June 1992 and January 1993 in the Gulf of Mexico. Samples were also collected from three stations on the continental shelf of Cape Hatteras for comparison. Chlorophylls a and b were at detectable levels in HMW DOG; concentrations of the carotenoids zeaxanthin and fucoxanthin in HMW DOC indicated that cyanobacteria, prochlorophytes, and diatoms contributed to the total HMW DOC pool across the continental margin in the gulf. The extremely low concentrations of pheopigments (except for chlorophyllide) in particulate organic C and HMW DOC suggested that direct exudation from phytoplankton and sloppy feeding by zooplankton were the major mechanisms of release. However, significant and selective pigment loss, due to light and thermal degradation in the reservoir, did occur in the absence of any cooling or light-shielding precautions. This study demonstrated that pigments can be used to acquire qualitative information on the sources of HMW DOC and to gain insight on its relative age-based on pigment turnover.