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

Abstract

A knowledge of the balance between plankton gross primary production (GPP) and community respiration (CR) in the open ocean is vital to the accurate determination of the global carbon cycle, yet the paucity of open ocean measurements severely limits our understanding. This study measured GPP, net community production, dark CR, and size-fractionated primary production in the upper 200 m of a 12,100 km latitudinal (32ЊS-48ЊN) transect in the Eastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrasting plankton regimes, including two open ocean oligotrophic provinces, is used to derive a GPP : CR relationship, which suggests that net heterotrophy (GPP Ͻ CR) prevails in the eastern Atlantic when primary production falls below ϳ100 mmol O 2 m Ϫ2 d Ϫ1 . The predictive capability of this relationship is compared with that of the only other published relationship based on similar methodologies and is found to give a more representative description of the autotrophic (GPP Ͼ CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved predictive power is attributed to the increased representativeness of the current 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 wide range in the magnitude of primary production.

Photosynthetic electron turnover in the tropical and subtropical Atlantic Ocean

“…Furthermore, the northern subtropical gyre is on average 50-100% more productive, when expressed per unit chla, than the southern subtropical gyre. These trends of P max ðP max chla Þ are consistently observed in other independent investigations based on O 2 evolution (Serret et al, 2001;Robinson et al, 2002, Gonza´lez et al, 2002 and C assimilation (Serret et al, 2001;Teira et al, 2005;Pe´rez et al, 2005) measurements.…”

“…Fluxes of these elements between phytoplankton and their surrounding environment indicate the net community metabolism and thus the trophic structure of the food web and significance of carbon sequestration (Karl et al, 1998;Serret et al, 2001;Gonza´lez et al, 2002). Furthermore, the light-response of these productivity measurements describe the physiological status of photoautrophic communities that then can be applied to models investigating environmental change Maran˜o´n and Holligan, 1999).…”

“…Furthermore, the light-response of these productivity measurements describe the physiological status of photoautrophic communities that then can be applied to models investigating environmental change Maran˜o´n and Holligan, 1999). Consequently, considerable effort has been made in recent years to characterise O 2 evolution and C i assimilation in the large and vastly under-sampled oceanic tropical and subtropical regions (Karl et al, 1998;Maran˜o´n et al, 2000;Serret et al, 2001;Gonza´lez et al, 2002;Maran˜o´n, 2005).…”

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“…Our net community production rates integrated over the euphotic layer (NCP int : 132 6 48 to 1328 6 95 mmol O 2 m 22 d 21 ) are among the highest reported rates for the North Atlantic. Previous studies near the western end of our study area reported net autotrophy with NCP int in the region of 50-100 mmol O 2 m 22 d 21 (Serret et al 2001;Gist et al 2009). The Lagrangian nature of our study allowed us to track changes in the biogeochemistry of the upwelled filaments P-1 and P-3.…”

“…Gross production and R incubations-Additional incubations were carried out on deck for the determination of GPP, net primary production, and R (Serret et al 2001;Gist et al 2009). Samples were collected predawn from six depths in 10 liter acid-cleaned carboys (wrapped in black plastic bags to minimize light exposure).…”