On the decomposition processes of particulate organic matter using 14C-labeled diatom, Skeletonema c0statum

Decomposition processes of 14C-labeled diatom, Skeletonema costatum (14C-POM) were examined during the summer-fall of 1979 in Funka Bay using R/V Ushio Maru. Decomposition of 14C-POM can be approximately described by a first-order reaction equation. It was possible to express the reaction in two steps having differing slopes on a semi-logarithmic plot with time. In the initial incubation periods, the decomposition of 14C-POM proceeded rapidly (expressed as first step), after which the decomposition was remarkably lower (second step). The apparent rate constants for decomposition were calculated as 0.08 to 0.3 day-1 for the first step and 0.06 day-1 for the second step. In situ experiment during June to September, the mineralization rates, which were estimated from evolved 14CO2, were lower than those compared with the decomposition of 14C-POM. This fact suggests that 14C-DOM was released in water as an intermediate step during decomposition. The mineralization rates per day were in the range of 2 to 13 % (mean 7 %) at 20 m, and 0.2 to 0.6 % (mean 0.4 %) at 60 m. Major organic composition of 14C-POM was changed during decomposition process in seawater. Each constituents of 14C-POM tended to be decomposed preferentially in the order of protein, carbohydrate and then lipid. (author)