Latitudinal variation of the balance between plankton photosynthesis and respiration in the eastern Atlantic Ocean

A knowledge of the balance between plankton gross primary production (GPP) and community respiration (CR) in the open ocean is vital to the accurate d etermination of the global carbon cycle, yet the paucity of open ocean meas urements severely limits our understanding. This study measured GPP, net co mmunity production, dark CR, and size-fractionated primary production in th e upper 200 m of a 12,100 km latitudinal (32 degreesS-48 degreesN) transect in the Eastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrasting plankton regimes, including two ope n ocean oligotrophic provinces, is used to derive a GPP: CR relationship, w hich suggests that net heterotrophy (GPP < CR) prevails in the eastern Atla ntic when primary production falls below <similar to>100 mmol O-2 m(-2) d(- 1). The predictive capability of this relationship is compared with that of the only other published relationship based on similar methodologies and i s found to give a more representative description of the autotrophic (GPP > CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved pr edictive power is attributed to the increased representativeness of the cur rent data set. Specifically, the interpretation suggests that the influence of community structure on net ecosystem metabolism implies that prediction of GPP:CR balances in pelagic ecosystems can be best achieved by use of a data set that covers a wide range of community structure and not only a wid e range in the magnitude of primary production.