TEMPORAL VARIABILITY IN DISSOLVED ORGANIC-CARBON AND RADIOCARBON IN THE EASTERN NORTH PACIFIC-OCEAN

The factors regulating the steady state inventories and residence time s of dissolved organic carbon (DOG) in the deep ocean are not well est ablished. Previous studies of DOC have been limited to single time-poi nt profiles that provide general information on the potential role of vertical advective-diffusive processes in controlling DOC distribution s and mean apparent ages. We present results from a 2-year time series station in the eastern North Pacific (station M) where short-term (mo nths) changes in inventories and Delta(14)C signatures of DOC as measu red in deep profiles were examined in conjunction with changes in part iculate organic carbon (POC) pools. Significant long-term (i.e., month s to years) changes in both DOC concentrations and Delta(14)C values w ere observed. These changes were especially evident at mesopelagic (si milar to 450 and 700 m) depths, close to the oxygen minimum. Both with in the mixed layer and at mesopelagic depths, positive relationships w ere found between DOC Delta(14)C values and concentrations of station M, primarily reflecting diminishing vertical inputs of ''recent'' DOC throughout the main thermocline. At abyssal depths (greater than or eq ual to 1600 m), however, Delta(14)C was inversely correlated with DOC concentration. The Delta(14)C signature of the less abundant suspended and sinking POC pools has been observed to fluctuate over seasonal ti mescales at station M, presumably due:in part to sorption of DOC to PO C [Druffel et al., 1996]. However, the Delta(14)C values and concentra tions of the correspondingly much larger DOC pool do not appear to be related to seasonal changes in either sinking POC fluxes or suspended POC abundances. Significantly elevated concentrations of DOC were obse rved at station M when compared with a previously occupied site in the north central Pacific (NCP) in all regions of the water column except mesopelagic depths, where concentrations were lower. The correspondin g Delta(14)C values of DOC at all depths at station M were lower than in the NCP. We speculate that dissimilarities in the size and Delta(14 )C signature of the DOC pools at seasonally productive station M and t he oligotrophic NCP result from differences in DOC sources and sinks b etween the two regions, as well as from the magnitude of interaction b etween DOC and POC at these sites.