Decoupling of primary production and community respiration in the ocean : implications for regional carbon studies

Abstract

Primary production (P) and community respiration (R) were measured in vitro along 2 transects of a trans-oceanic section crossing the oligotrophic North Atlantic waters, and during a drifter experiment in the eutrophic waters of the Northwest Africa upwelling system. Our results indicate that the scales of variability of P and R are different, R being less variable than Pin the 2 studies. In the first transect of the oceanic study, the mean P:R ratio was < 1 (0.8), while in the second transect it was > 1 (1.1), the difference being statistically significant. The cause was a significant increase in P in the second transect, which was decoupled from changes in chlorophyll a (chl a) or R. In upwelling waters, however, R was always significantly lower than P (P:R > 1), and enhancements in P were paralleled by increases in chl a but not in R. The close correlation between the P:R ratio and P (and the lack of correlation between P:R and R) supports the view that changes in P but not in R control the transition of the system from net heterotrophy to net autotrophy (in our study at P > 56 mmol C m(-2) d(-1)). The observed decoupling between P and R. at temporal scales of days to weeks, has strong implications for addressing metabolic balances from in vitro experiments carried out during limited field samplings. We conclude that unless the scales of variability are established for the 2 metabolic rates, and particularly for P, it will not be feasible to accurately establish regional metabolic balances at seasonal to annual scales.