Dissimilation of sinking organic aggregates is a central issue in the regulation of carbon fluxes from the ocean's surface into its depths. The role of attached bacteria in particle decomposition has been unclear. High concentrations (108-109 ml-1) of slowly growing bacteria commonly found on aggregates create intense ectohydrolase activities which rapidly solubilize (0.2-2.1 d turnover time) particulate combined amino acids but allow most hydrolysate to be released into seawater. This "uncoupled solubilization", particularly if it applies generally to aggregate's carbon pool, could have profound implications for downward flux of carbon. Using SCUBA collected marine snow and laboratory-made 14C labeled phytodetritus aggregates studies will 1) quantify DOC release (measured by high temperature catalytic oxidation) and POC turnover rates and how they vary with variation in colonization and enzyme activities on aggregates. 2) characterize the released DOC in terms of molecular size distribution (with molecular sieves), whether it contains colloids and sub-micron particles (by transmission electron microscopy), and whether some of it is refractory to bacterial utilization (or has long turnover time); 3) test whether enzyme action on aggregates causes differential solubilization of C, N and P. This work will be done on aggregates collected in waters off La Jolla, Santa Barbara, and at several offshore stations in Southern California Bight during 4 cruises. The proposed study will contribute to an understanding of the role of attached bacteria in POC DOC transition and hence in carbon cycling in the ocean.
