BACTERIAL PRODUCTION IN THE WESTERN EQUATORIAL PACIFIC - IMPLICATIONSOF INORGANIC NUTRIENT EFFECTS ON DISSOLVED ORGANIC-CARBON ACCUMULATION AND CONSUMPTION

Bacterial production and concentrations of dissolved and particulate o rganic carbon (DOC and POC), in the upper 200 m water column were meas ured in the western equatorial Pacific Ocean (0 degrees S-8 degrees N, 137 degrees-159 degrees E). To test the effect of inorganic nutrients (NH4+ and PO4-3) on the turnover rates of glucose, nutrient enrichmen t experiments were performed with 0.8 mu m filtrates of the surface se awater. Depth profiles of bacterial biomass, production and turnover r ates ranged 1.4-9.4 mgC m(-3), 0.34-4.06 mgC m(-3) d(-1) and 0.13-0.36 d(-1), respectively. They were comparable to those reported in the ce ntral equatorial Pacific. POC varied 4-fold ranging from 13 to 54 mgC m(-3). DOC values at the surface waters and the aphotic zone (>100 m) were 112-128 and 48-54 mu M, respectively. In comparison, the differen ces of DOC between the upper (<50 m) and lower (>50 m) parts of the eu photic zone in this area (40-60 mu M) were greater than those observed by other researches in the central equatorial Pacific (10-30 mu M). T he enrichment experiments showed that surface water bacteria could not utilize excess glucose efficiently without inorganic nutrients, indic ating that availability of inorganic nutrients might play an important role in regulating accumulation and consumption of the bio-reactive D OC in the water column. We propose that the high DOC accumulated at th e surface waters probably could be ascribed to either the very slow co nsumption of DOC or higher DOC production due to the shortage of (or v ery low) inorganic nutrients supply or both. The ecological implicatio ns of our findings for oceanic DOC distribution and bacterial producti on may be far reaching, if other so-called ''labile'' DOC molecules sh ow similar dependency on inorganic nutrients.