DISSOLVED ORGANIC-CARBON IN CORAL-REEF LAGOONS BY HIGH-TEMPERATURE CATALYTIC-OXIDATION AND UV SPECTROMETRY

Two surveys were carried out on ten atolls in the Tuamotu archipelago (French Polynesia, Pacific Ocean). In vitro UV (250-400 nm) spectra of water samples gave absorption at 254 nm, A(254), and spectrum slope, 5 (computed from In A(lambda) versus lambda). These two descriptors a re negatively correlated, and data points are arrayed along a hyperbol a spanned between an oceanic pole (high S, low A(254)) and a confined pole (low S, high A(254)). Dissolved organic carbon (DOG) concentrat ions, [C], as assessed by HTCO, exhibit a narrow range (0.7-2.0 mg C.L -1 for most lagoons) contrasting with the wide diversity of optical ch aracteristics. [C] and A(254) are positively correlated, with a signif icant intercept (0.5 mg C.L-1) representing non-chromophoric DOG. Carb on-specific absorption, epsilon(254), increases (from 0.4 to 1.3 m(2). g(-1)) with increasing [C], mainly according to the literature) owing to increased average molecular weight (MW) of the chromophoric DOC fra ction, which also lowers 5. Our optical data thus illustrate a gradie nt of confinement (or residence time) that corresponds to a continuum in DOC nature, especially in MW and hence in bioavailability. Optical methods are confirmed as quick and effective means of assessing DOM di stribution.