Gross primary production (GPP), community respiration (CR) and net community production (NCP) were studied for about 3 yr (September 2001 to June 2004) within the euphotic layer in the center of Sagami Bay, Japan. Oxygen fluxes exhibited seasonal and annual variations linked to the seasonal cycle of water column conditions and solar irradiance. GPP was > 1 mmol O-2 m(-3) d(-1) above ca. 30 m in summer. CR exhibited seasonal patterns coupled to the variation in GPP. NCP at the surface was generally positive and maximum throughout the observation period, whereas at the subsurface layer it was negative, suggesting a balanced relationship between production and consumption of oxygen in the euphotic zone. GPP, CR and NCP integrated within the euphotic zone ranged from 44 to 264 (mean +/- SE: 111 +/- 13), 10 to 311 (100 +/- 15) and -94 to 112 (11 +/- 8) mmol O-2 m(-2) d(-1), respectively. GPP and CR showed distinct seasonal patterns, and both tended to be higher from spring to summer (high productivity, HP) than from fall to winter (low productivity, 1,13). The threshold GPP for metabolic balance of the community (i.e. GPP:CR, P:R = 1) was higher during the HP period (4.1 mmol O-2 m(-3) d(-1)) than during the LP period (0.4 mmol O-2 m(-3) d(-1)), with a mean value of 1.4 mmol O-2 m(-3) d(-1). These results suggest the importance of organic carbon produced in the past or elsewhere in sustaining a relatively high background CR rate during the HP period in Sagami Bay.
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