Concurrent measurements of dark community respiration (DCR), gross production (GP), size fractionated primary production (14C PP), nitrogen uptake, nutrients, chlorophyll a concentration, and heterotrophic and autotrophic bacterial abundance were collected from the upper 200m of a latitudinal (321S–481N) transect in the Eastern Atlantic Ocean during May/June 1998. The mean mixed layer respiration rate was 2.572.1 mmol O2m 3 d 1 (n ¼ 119) for the whole transect, 2.271.1 mmol O2m 3 d 1 (n ¼ 32) in areas where chlorophyll a was o0.5 mgm 3 and 1.570.7 mmol O2m 3 d 1 (n ¼ 10) where chlorophyll a waso0.2 mgm 3. These values lie within the range of published data collected in comparable waters, they co-vary with indicators of heterotrophic and autotrophic biomass (heterotrophic bacterial abundance, chlorophyll a concentration, beam attenuation and particulate organic carbon concentration) and they can be reconciled with accepted estimates of total respiratory activity. The mean and median respiratory quotient (RQ), calculated as the ratio of dissolved inorganic carbon production to dissolved oxygen consumption, was 0.8 (n ¼ 11). At the time of the study, plankton community respiration exceeded GP in the picoautotroph dominated oligotrophic regions (Eastern Tropical Atlantic [15.51S–14.21N] and North Atlantic Subtropical Gyre [21.5–42.51N]), which amounted to 50% of the stations sampled along the 12,100km transect. These regions also exhibited high heterotrophic: autotrophic biomass ratios, higher turnover rates of phytoplankton than of bacteria and low f ratios. However, the carbon supply mechanisms required to sustain the rates of respiration higher than GP could not be fully quantified. Future research should aim to determine the temporal balance of respiration and GP together with substrate supply mechanisms in these ocean regions

CR was funded by a NERC Advanced Research Fellowship (GT5/96/8/MS), PSI was funded by an EU Marie Curie Research Training Grant (ERBFMBICT972700), E.T. and E.F. were funded by MEC grant MAR98-1417E and the EU contract CANIGO (MAS3CT960060). Funding for equipment and training for CR from the Royal Society is gratefully appreciated. This study was supported by the UK Natural Environmental Research Council through the Plymouth Marine Laboratory Core Strategic Research Programmes ‘‘Ocean Carbon Cycle Changes in the Coastal Zone’’ (OC4Z: 1999–2001) and ‘‘Microbially Driven Biogeochemical Cycles’’ (MDB: 2001–2006) and is MDB contribution number 56.

27 páginas, 3 tablas, 5 figuras

Peer reviewed