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Characterization of the microbial plankton metabolism in oligotrophic oceans is of relevance for the quantification of the global carbon balance; however whether the plankton community metabolism in oligotrophic gyres is net autotrophic or heterotrophic is still under debate. Discrepancies have been in part attributed to the difficulties of the standard snapshot estimations, based on in vitro measurements, to adequately represent the temporal scale of trophic processes. This work presents concurrent measurements of gross primary production and community respiration carried out in the North Atlantic Oligotrophic Gyre throughout two 7-day Lagrangian experiments that allowed us to investigate the effect of short term (daily) variability on the microbial metabolism quantification. Physicochemical and biological variables showed a low variability in each Lagrangian experiment and a balanced net plankton metabolism was found in 83% of the sampling days.

Size-fractionated chlorophyll-a and carbon incorporation rates were determined on a series of 13 cruises carried out from 1992 to 2001with the aim of investigating the patterns and causes of variability in phytoplankton chlorophyll and production in the Eastern North Atlantic Subtropical Gyral Province (NASE). Averaged (±SE) integrated chlorophyll-a concentration and primary production rate were 17±1 mg m−2 and 253±22 mg C m−2 d−1. Small-sized cells (

13 pages, 7 figures, 2 tables.-- Available online Nov 17, 2008.-- Issue title: "The Atlantic Meridional Transect Progamme"., We present, test and implement two contrasting models to predict euphotic zone net community production (NCP), which are based on 14C primary production (PO14CP) to NCP relationships over two latitudinal (ca. 30°S–45°N) transects traversing highly productive and oligotrophic provinces of the Atlantic Ocean (NADR, CNRY, BENG, NAST-E, ETRA and SATL, Longhurst et al., 1995 [An estimation of global primary production in the ocean from satellite radiometer data. Journal of Plankton Research 17, 1245–1271]). The two models include similar ranges of PO14CP and community structure, but differ in the relative influence of allochthonous organic matter in the oligotrophic provinces. Both models were used to predict NCP from PO14CP measurements obtained during 11 local and three seasonal studies in the Atlantic, Pacific and Indian Oceans, and from satellite-derived estimates of PO14CP. Comparison of these NCP predictions with concurrent in situ measurements and geochemical estimates of NCP showed that geographic and annual patterns of NCP can only be predicted when the relative trophic importance of local vs. distant processes is similar in both modeled and predicted ecosystems. The system-dependent ability of our models to predict NCP seasonality suggests that trophic-level dynamics are stronger than differences in hydrodynamic regime, taxonomic composition and phytoplankton growth. The regional differences in the predictive power of both models confirm the existence of biogeographic differences in the scale of trophic dynamics, which impede the use of a single generalized equation to estimate global marine plankton NCP., This paper shows the potential of a systematic empirical approach to predict plankton NCP from local and satellite-derived P estimates., This work was supported by the NERC AMT programme (NER/O/S/2001/00680; this is contribution number 168. http://www.amt-uk.org) and the CYCIT project CIRCANA (MAR1999-1072-C03-01). P.S. was funded by EU Marie Curie Research Training and Return Grants and a MECD Contrato de Reincorporación, C.R. by a NERC Advanced Research Fellowship, E.T. and E.F. by MECD grants and the EU contract CANIGO (MAS3CT960060), and G.H.T. by an EU MAST fellowship.

Heterotrophic bacteria have long been considered as the major respirers of the open ocean. During a survey in the eastern N Atlantic Subtropical Gyre we measured H-leucine heterotrophic bacterial production (BP), C particulate primary production (PPP) and the O2 community metabolism rates: gross primary production (GPP), net community production (NCP) and community respiration (CR). We estimated heterotrophic bacterial respiration (BR) from BP and literature models of bacterial growth efficiency [BGE BP/(BP BR)]. BP was an order of magnitude lower than PPP (integrated means of 17 2 and 207 29 mg C m d, respectively). Although volumetric PPP and GPP were significantly correlated (r 0.51; p 0.009; n 25), CR (1120 122 mg C m d) bore no significant relationship with either primary or heterotrophic bacterial production and exceeded GPP (578 117 mg C m d) at 5 out of 6 sampling stations. Integrated values of CR were only significantly correlated, but negatively, with chlorophyll a values (r 0.95; p 0.001; n 6). Integrated BR tended to decrease with increasing CR and, with a mean estimated BGE of 6%, it accounted on average for a much lower fraction of CR (33 7%) than currently assumed. By estimating the contributions of other trophic groups a large amount (48 10%) of the measured CR remained unaccounted for. This gap in respiration estimates casts some doubt on the magnitude of the net heterotrophic balance frequently observed in oligotrophic waters from changes of O2 over 24 h dark in vitro incubations.

Recent experimental data from the subtropical NE Atlantic appear to support the prevalence of net heterotrophy in unproductive pelagic ecosystems. However, the proximity of these studies to the NW African upwelling does not exclude the possibility that remote areas of the oceanic gyres are in metabolic balance. Here we present measurements of plankton gross photosynthesis (GPP) and community respiration (CR) made during a latitudinal transect (Atlantic Meridional Transect (AMT) cruise 11, 49°N–33°S) that traversed five biogeochemical provinces of the Atlantic Ocean, including both the subtropical NE Atlantic and the central part of the South Atlantic subtropical gyre. In these oligotrophic provinces, the euphotic zone average chlorophyll a concentration (0.15±0.01 and 0.16±0.02 mg m−3, respectively), the relative contribution of picoplankton (%Chla

Size-fractionated phytoplankton biomass and primary production, together with net community metabolism, were measured in a coastal ecosystem (Ria de Vigo, NW-Spain) during a full annual cycle (July 2001-July 2002). On a seasonal scale, this ecosystem was characterized by two distinct oceanographic conditions, namely upwelling and downwelling favourable seasons. During the upwelling season, total chlorophyll a (Chl a) and particulate organic carbon production rates (POC-pr) were in the range 36-129 mg Chl a m(-2) and 89-834 mg C m(-2) h(-1), respectively, and were mainly accounted for (> 80%) by the microphytoplankton size fraction (> 20 pm). During the downwelling season, total Chl a and POC-pr were much lower (< 27 mg Chl a m(-2) and < 97 mg C m(-2) h(-1), respectively), and the pico- (< 2 mu m) and nano-(2-20 mu m) phytoplankton size fractions significantly increased their contribution to total Chl a (46-87%) and POC-pr (30-86%). The seasonal and short-time scale variability in the hydrographic conditions, in particular upwelling intermittency, provides a feasible explanation for the continuous dominance of large-sized phytoplankton during the upwelling period. Shelf water intrusions, continuous vertical mixing and the size-dependent limitation in light acquisition (package effect), suffered in a higher degree by larger phytoplankton, were likely to account for the shift in phytoplankton size structure during the downwelling period. During the upwelling season, community respiration represented a minor fraction of gross primary production (15-30%), which highlights the large export potential of organic matter by this ecosystem. On the contrary, community respiration accounted for a major fraction of primary production (85%) during the downwelling period, which suggests that most of the photosynthesised organic matter was remineralised within the ecosystem. Although the microbial plankton community of the Rfa de Vigo exhibits a net autotrophic functioning throughout the year, the magnitude of the carbon flows and budgets seems to be dependent on phytoplankton size structure. (c) 2005 Elsevier Ltd. All rights reserved.

Ninety-four stations were sampled in the Atlantic subtropical gyres during 10 cruises carried out between 1995 and 2001, mainly in boreal spring and autumn. Chlorophyll a (Chl-a) and primary production were measured during all cruises, and phytoplankton biomass was estimated in part of them. Picoplankton (o2mm) represented 460% of total Chl-a concentration measured at the surface, and their contribution to this variable increased with depth. Phytoplankton carbon concentrations were higher in the upper metres of the water column, whereas Chl-a showed a deep maximum (DCM). At each station, the water column was divided into the upper mixed layer (ML) and the DCM layer (DCML). The boundary between the two layers was calculated as the depth where Chl-a concentration was 50% of the maximum Chl-a concentration. On average DCML extends from 67 to 126 m depth. Carbon to Chl-a (C:Chl-a) ratios were used to estimate phytoplankton carbon content from Chl-a in order to obtain a large phytoplankton carbon dataset. Total C:Chl-a ratios averaged (7s.e.) 1037 7( n ¼ 22) in the ML and 247 4( n ¼ 12) in the DCML and were higher in larger cells than in picoplankton. Using these ratios and primary production measurements, we derived mean specific growth rates of 0.1770.01 d � 1 (n ¼ 173) in the ML and 0.2070.01 d � 1 (n ¼ 165) in the DCML although the differences were not significant (t-test, p40.05). Our results suggest a moderate contribution of the DCML (43%) to both phytoplankton biomass and primary production in the Atlantic subtropical gyres. r 2006 Elsevier Ltd. All rights reserved.

The seasonal variability of phytoplankton in the Equatorial Atlantic was analysed using Sea-viewing Wide Field-of-view Sensor (Sea WiFS)-derived chlorophyll a (Chl a) concentration data from 1998 to 2001, together with in situ Chl a and primary production data obtained during seven cruises carried out between 1995 and 2000. Monthly averaged SeaWiFS Chl a distributions were in agreement with previous observations in the Equatorial Atlantic, showing marked differences between 10° W in the Eastern Tropical Atlantic (ETRA) and 25° W in the Western Tropical Atlantic (WTRA) provinces (Longhurst et al. 1995. J. Plankton Res., 17, 1245-1271). The seasonal cycle of SeaWiFS-derived Chl a concentration calculated for 0-10° S, 0-20° W (ETRA) is consistent with in situ Chl a measurements, with values ranging from 0.16 mg m -3 , from February to April, to 0.52 mg m -3 in August. Lower variability was observed in 10° N-10° S, 20 30° W (WTRA) where minimum and maximum concentrations occurred in April (0.15 mg m -3 ) and in August (0.24 mg m -3 ), respectively. A significant empirical relationship between depth-integrated primary production and in situ measured sea surface Chl a was found for ETRA, allowing us to estimate the seasonal cycle of depth-integrated primary production from SeaWiFS-derived Chl a. As for Chl a, this model was verified in a small area of the Eastern Equatorial Atlantic (0-10° S, 0-20° W), although in this instance it was not completely able to describe the magnitude and temporal variability of in situ primary production measurements. The annual euphotic depth-integrated primary production rate estimated for ETRA by our empirical model was 1.4 Gt C year -1 , which represents 16% of the open ocean primary production estimated for the whole Atlantic Ocean.

International audience; We studied the photosynthetic production of dissolved organic carbon (DOCp) during summer oligotrophic conditions in the Celtic Sea. The production rate of size-fractionated, particulate organic carbon (POCp) was also determined, as well as the relationship between irradiance and DOCp and the kinetics of DOCp during a 24 h light-dark cycle. Mean (1 SE), euphotic layer-integrated POCp was 510 +/- 61 mg C m(-2) d(-1), and cells in the < 5 mu m size fraction accounted for 58 +/- 3 % and 63 +/- 4 % of total integrated chlorophyll a concentration and POCp, respectively. The mean, integrated percentage of extracellular release [PER, calculated as DOCp / (DOCp + POCp)] was 22 +/- 2 %. (DOC)-C-14 accumulation stopped during the dark. In photosynthesis-irradiance experiments, DOCp remained constant across a wide irradiance range, despite the strong light dependence of POCp. These observations suggest that direct release from intact cells is the main pathway for DOCp. Significant DOCp took place throughout the euphotic layer and across a wide irradiance range, suggesting an important role for passive diffusion in the release of recent photosynthate. When comparing our measurements of DOCp in the Celtic Sea with previous observations in a coastal, eutrophic ecosystem, a remarkable continuity is observed, both in the relative significance and likely mechanisms of DOCp. Across a productivity range from < 100 to > 15 000 mg C m(-2) d(-1), PER was relatively constant at similar to 20%, and integrated DOCp could be predicted from integrated POCp with the equation: log (DOCp) = 0.96 x log (POCp) - 0.51 (r(2) = 0.90, n = 35, p < 0.001).

Corrigendum to ‘‘Production and respiration control the marine microbial metabolic balance in the eastern North Atlantic subtropical gyre’’ [Deep-Sea Research Part I: Oceanographic Research Papers 58 (7) (2011) 768–775] Maria Aranguren-Gassis , Pablo Serret , Emilio Fernandez , Juan L. Herrera , Jose F. Dominguez , Valesca Perez , Jose Escanez c a Universidad de Vigo, Departamento de Ecologia y Biologia Animal, Carretera Colegio Universitario s/n, 36310 Vigo, Pontevedra, Spain b Universidad de Vigo, Departamento de Fisica Aplicada, Carretera Colegio Universitario s/n, 36310 Vigo, Pontevedra, Spain c Centro Oceanografico de Canarias, Calle General Gutierrez, 4, 38003 Santa Cruz de Tenerife, Canarias, Spain d Centro de Investigacion e Informacion Ambiental—CINA Mde Lourizan, de la Conselleria de Medio Ambientee Desenvolvemento Sostible, Xuntade Galicia, Carretera de Marin km. 4, Apdo. 127, 36080 Pontevedra, Spain

We used data collected at > 60 stations over a 10 yr period to build the carbon budget of the plankton community in the euphotic layer of the Eastern North Atlantic Subtropical Gyre (NASE). Autotrophic biomass exceeded microbial heterotrophic biomass by a factor of 1.7. Mean ( SE), integrated chlorophyll a concentration and net particulate primary production (PP) were 17 +/- 1 Mg m(2) and 271 +/- 29 mg C m(-2) d(-1), respectively. Protist grazing on phytoplankton represented > 90% of PP. Bacterial production (BP) was 17 +/- 3 mg C m(-2) d(-1). In vitro O-2-evolution experiments indicated that net community production was -65 +/- 16 mmolO(2) m(-2) d(-1), while community respiration (CR) averaged 124 +/- 13 mmolO(2) m(-2) d-1, equivalent to 1324 +/- 142 mg C m(-2) d(-1). However, the sum of the respiration rates by each microbial group, estimated from their biomass and metabolic rates, ranged from 402 to 848 Mg C m(-2) d-1. Therefore, CR could not be reconciled with the respiratory fluxes sustained by each microbial group. Comparison between estimated gross photosynthesis by phytoplankton (481 to 616 mg C m(-2) d-1) and the sum of respiration by each group suggests that the microbial community in the NASE province is close to metabolic balance, which would agree with the observed O-2 supersaturation in the euphotic layer. Taking into account the mean open-ocean values for PP, BP, CR and bacterial growth efficiency, we show that bacteria account for approximately 20% of CR. Our results suggest that the view that bacteria dominate carbon cycling in the unproductive ocean must be reconsidered, or else that in vitro incubations misrepresent the real metabolic rates of one or several microbial groups.

The biomass and metabolism of the planktonic microbial community was assessed at 7 stations in the eastern subtropical and tropical domains of the North Atlantic subtropical gyre in autumn 2001. Picoplankton formed the bulk of phytoplankton (70 ± 3% SE of total chlorophyll a), with Prochlorococcus spp. as the dominant group and an increasing importance of picoeukaryotes and Synechococcus spp. in tropical waters. Autotrophic plankton biomass clearly exceeded that of heterotrophic bacteria in the upper 150 m, contradicting previous claims of marked inverted biomass pyramids in the oligotrophic ocean. Despite the dominance of picoplankton in biomass, primary production (range 153 to 337 mgC m -2 d -1 ) was mostly due to cells >2 μm (59 ± 3 %). Primary production by microphytoplankton was significantly greater in the tropical domain. Bacterial heterotrophic production (range 6 to 22 mgC m -2 d -1 ) was always below 10% of primary production. This low value was probably related to the high proportion (56 ± 2 %) of inactive bacteria (identified by their DNA content). Although bacterial activity covaried with primary productivity, bacterial carbon demand estimated by 2 models from the literature generally required organic matter input other than dissolved primary production. Given that community respiration (116 ± 32 mmol O 2 m -2 d -1 ) also exceeded gross primary production (58 ± 32 mmolO 2 m -2 d -1 ) at all but 1 station, our results confirm previous observations of the net heterotrophic balance in the oligotrophic NE Atlantic.