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The project OLCAPP was aimed at exploring the response of a natural, eutrophic system to ocean liming by slaked lime (calcium hydroxide) dispersal in the wake of ships. The main objectives were:- to monitor and model the slaked lime dissolution kinetics and the carbonate equilibrium (alkalinity, pH spikes/alteration, Dissolved Inorganic Carbon);- to assess Dissolved Organic Matter changes in quantity and composition;- to assess possible changes in primary production, photosynthetic efficiency and phytoplankton abundance and associations;- to assess the short and medium-term response of planktonic and benthic calcareous primary producers (calcareous red algae = maerl) to alkalinization and potential precipitation of carbonate crystals induced by the treatments.In the framework of the Transnational Access provided by AQUACOSM-plus, at the ECIMAT-UVIGO facility (Vigo, Spain) we had the opportunity to test ocean liming in nine mesocosm tanks. A sediment trap and a basket of calcareous algae (maerl) were positioned at the bottom of each tank. Mearl was previously collected in the Ria de Vigo at 7m depth and prepared for the experiment. Successively, each tank was filled with natural coastal seawater (~1m3).Out of the nine mesocosms, three tanks were treated with calcium hydroxide 0.02g/L (High) and three tanks with 0.006g/L (Low) per treatment, repeated on days 1, 3 and 5 (multiple exposure). The remaining three tanks were kept as control. A record of pH, O2, salinity, temperature and PAR was performed in the mesocosms during the experiment with a ten-minutes frequency.Nutrient concentration is monitored on a long-term basis in the Ria de Vigo, and was also tested on days 1, 3 and 5 for all treatments and controls. Seawater samples were collected from the mesocosms before (pre-treatment), and after 1h, 4h, and 24h from each treatment, with a 5L Niskin bottle. Dissolved Organic Matter as Dissolved Organic Carbon (DOC) and Chromophoric Dissolved Organic Matter (CDOM) were analysed, along with the Dissolved Inorganic Carbon (DIC). Moreover, samples collected after 1h from treatments were used for assessing also the bacterial association, the size-fractionated Chl-a concentration and the plankton primary production and photosynthetic efficiency. Gross primary production, community respiration and net community production were measured by changes in oxygen concentrations after 24 h light-dark bottle incubations. Dissolved oxygen was measured by Winkler titration. A total of 165 samples were obtained from filtering 2L of mesocosm water from pre-treatments, 4h and 24h samples, for the collection of the phytoplankton community, to be analysed under optical and scanning electron microscope.Preliminary observations during the experiment and the first data on the plankton community suggest that the High treatment leads to important flocculation and sedimentation affecting both the transparency of the water and the bottom environment, with significant and stable pH increase and decrease in phytoplankton production and efficiency. The mineralogical nature of the flocculation, the response of benthic calcareous algae and phytoplankton community, in term of composition and abundance of the major components, is here discussed.

The Ría de Vigo is a dynamic and productive upwelling ecosystem. We measured 14C incorporation (TO14CP) and gross primary production (GPP), community respiration (DCR), net production (NCP) and size-fractioned chlorophyll a (chl a) fortnightly from May 2012 to May 2013 in the euphotic layer of the Ría. Our aim was to improve the depiction of plankton metabolism in the Ría and to test the general hypothesis that community structure determines the degree of heterotrophy in planktonic ecosystems. Higher primary production was measured after upwelling episodes and during the spring bloom, when the community was dominated by microphytoplankton (>70% chl a>20μm). Lower primary production was observed during summer stratification periods (~65% chl a>20μm), and during the pico- and nanophytoplankton-dominated winter (~25% chl a>20μm). Coupling between phytoplankton photosynthesis and biomass varied seasonally, mainly driven by environmental conditions. DCR was 3 times lower and 8 times less variable than GPP, and its variability was mainly driven by the changes in chl a. The integrated metabolic balance was autotrophic most of the year, despite the negative NCP rates at depth. There was an inverse relationship between the DCR:GPP ratio and the percentage of microphytoplankton (% chl a>20μm) only in the summer. However, DCR:GPP and DCR:chl a ratios were similar in winter and spring, despite the seasonal differences in primary production and size structure. The similar TO14CP:NCP and chl a:DCR relations in spring (>70% chl a>20μm) and winter (~25% chl a>20μm), and the differences in summer (>70% chl a>20μm) confirm cell size independence in trophic functioning. We conclude that respiration variability is relevant for the metabolic balance in the Ría, and that the degree of heterotrophy is not systematically related to phytoplankton size over the scales of our study.

Here we assess the temperature dependence of the metabolic rates (gross primary production - GPP, community respiration - CR and the ratio GPP/CR) of oceanic plankton communities. We compile data from 133 stations of the Malaspina 2010 Expedition, distributed among the subtropical and tropical Atlantic, Pacific and Indian oceans. We used the in vitro technique to measured metabolic rates during 24 h incubations at three different sampled depths: surface, 20% and 1% of the photosynthetically active radiation measured at surface. We also measured the % of ultraviolet B radiation (UVB) penetrating at surface waters. GPP and CR rates increased with warming, albeit different responses were observed for each sampled depth. The overall GPP/CR ratio declined with warming. Higher activation energies (Ea´s) were derived for both processes (GPPChla = 0.97; CRChla = 1.26; CRHPA= 0.95 eV) compared to those previously reported. The Indian Ocean showed the highest Ea (GPPChla = 1.70; CRChla = 1.48; CRHPA= 0.57 eV), while the Atlantic Ocean showed the lowest (GPPChla = 0.86; CRChla = 0.77; CRHPA= -0.13 eV). We believe that the difference between previous assessments and the ones presented here can be explained by the overrepresentation of Atlantic communities in the previous data sets. We found that UVB radiation also affects the temperature dependence of surface GPP, which decreased rather than increased under high levels of UVB. Ocean warming, which causes stratification and oligotrophication of the subtropical and tropical oceans, may lead to reduced surface GPP as a result of increased penetration of UVB radiation.

A comprehensive in situ dataset of chlorophyll a (Chl a; N = 18,001), net primary production (NPP; N = 165) and net community production (NCP; N = 95), were used to evaluate the performance of Moderate Resolution Imaging Spectroradiometer on Aqua (MODIS-A) algorithms for these parameters, in the South Atlantic Ocean, to facilitate the accurate generation of satellite NCP time series. For Chl a, five algorithms were tested using MODIS-A data, and OC3-CI performed best, which was subsequently used to compute NPP. Of three NPP algorithms tested, a Wavelength Resolved Model (WRM) was the most accurate, and was therefore used to estimate NCP with an empirical relationship between NCP with NPP and sea surface temperature (SST). A perturbation analysis was deployed to quantify the range of uncertainties introduced in satellite NCP from input parameters. The largest reductions in the uncertainty of satellite NCP came from MODIS-A derived NPP using the WRM (40%) and MODIS-A Chl a using OC3-CI (22%). The most accurate NCP algorithm, was used to generate a 16 year time series (2002 to 2018) from MODIS-A to assess climate and environmental drivers of NCP across the South Atlantic basin. Positive correlations between wind speed anomalies and NCP anomalies were observed in the central South Atlantic Gyre (SATL), and the Benguela Upwelling (BENG), indicating that autotrophic conditions may be fuelled by local wind-induced nutrient inputs to the mixed layer. Sea Level Height Anomalies (SLHA), used as an indicator of mesoscale eddies, were negatively correlated with NCP anomalies offshore of the BENG upwelling fronts into the SATL, suggesting autotrophic conditions are driven by mesoscale features. The Agulhas bank and Brazil-Malvinas confluence regions also had a strong negative correlation between SLHA and NCP anomalies, similarly indicating that NCP is forced by mesoscale eddy generation in this region. Positive correlations between SST anomalies and the Multivariate ENSO Index (MEI) in the SATL, indicated the influence of El Niño events on the South Atlantic Ocean, however the plankton community response was less clear. UK Natural Environment Research Council | Ref. NERC; NE / L002434 / 1 European Space Agency | Ref. AMT4SentinelFRM (ESRIN / RFQ / 3-14457 / 16 / I-BG) European Space Agency | Ref. AMT4OceanSatFlux (4000125730/18 / NL / FF / gp) NERC International Opportunity Fund Grant Satellite estimates of marine net community production in the South Atlantic from Sentinel-3 | Ref. SemSAS; NE / P00878X / 1 P&D ANP / BRASOIL | Ref. 48610.011013 / 2014-66 Oceanographic Institute of the University of São Paulo | Ref. FAPESP 2015 / 01373-0 Oceanographic Institute of the University of São Paulo | Ref. CNPq 442926 / 2015-4 Oceanographic Institute of the University of São Paulo | Ref. FAPESP 2014 / 50820-7 Oceanographic Institute of the University of São Paulo | Ref. CNPq 565060 / 2010-4 NERC | Ref. NE / R015953 / 1

This is a contribution to the Malaspina Expedition 2010, funded by the INGENIO 2010 CONSOLIDER programme (ref. CDS2008-00077) of the Spanish Ministry of Economy and Competitiveness. We thank the captain and the crew of R/V Hesperides and the UTM for their help onboard and technical support. We also want to thank A. M. Cabello, P. Rial, M. Estrada, M. Latasa, F. Rodriguez and P. Mozetic for providing chlorophyll-a data, J. M. Gasol and X. A. G. Moran for provid- ing HPA data, E. Fraile-Nuez and V. Benitez-Barrios for their work analysing the CTD data and all the Malaspina Expedition participants for their support. L.S.G.-C. was supported by a JAE Pre-doc fellowship from the Spanish National Research Council (CSIC) and the BBVA Foundation, Spain.

The temperature dependence of planktonic metabolism in the subtropical North Atlantic Ocean was assessed on the basis of measurements of gross primary production (GPP), community respiration (CR) and net community production (NCP), as well as experimental assessments of the response of CR to temperature manipulations. Metabolic rates were measured at 68 stations along three consecutive longitudinal transects completed during the Malaspina 2010 Expedition, in three different seasons. Temperature gradients were observed in depth and at basin and seasonal scale. The results showed seasonal variability in the metabolic rates, the highest rates being observed during the spring transect. The overall mean integrated GPP / CR ratio was 1.39 ± 0.27 decreasing from winter to summer, and the NCP for the subtropical North Atlantic Ocean during the cruises exhibits net autotrophy (NCP > 0) in about two-thirds (66%) of the total sampled communities. Also, we reported the activation energies describing the temperature dependence of planktonic community metabolism, which was generally higher for CR than for GPP in the subtropical North Atlantic Ocean, as the metabolic theory of ecology predicts. Furthermore, we made a comparison of activation energies describing the responses to in situ temperature in the field (EaCR Combining double low line 1.64 ± 0.36 eV) and those derived experimentally by temperature manipulations (EaCR Combining double low line 1.45 ± 0.6 eV), which showed great consistency. © 2014 Author(s)., This is a contribution to the Malaspina Expedition 2010, funded by the INGENIO 2010 CONSOLIDER program (ref. CDS2008-00077) of the Spanish Ministry of Economy and Competitiveness. L. S. García-Corral was supported by a JAE Pre-doc fellowship from the Spanish National Research Council (CSIC) and the BBVA Foundation, Spain

There is ongoing debate as to whether the oligotrophic ocean is predominantly net autotrophic and acts as a CO2 sink, or net heterotrophic and therefore acts as a CO2 source to the atmosphere. This quantification is challenging, both spatially and temporally, due to the sparseness of measurements. There has been a concerted effort to derive accurate estimates of phytoplankton photosynthesis and primary production from satellite data to fill these gaps; however there have been few satellite estimates of net community production (NCP). In this paper, we compare a number of empirical approaches to estimate NCP from satellite data with in vitro measurements of changes in dissolved O2 concentration at 295 stations in the N and S Atlantic Ocean (including the Antarctic), Greenland and Mediterranean Seas. Algorithms based on power laws between NCP and particulate organic carbon production (POC) derived from 14C uptake tend to overestimate NCP at negative values and underestimate at positive values. An algorithm that includes sea surface temperature (SST) in the power function of NCP and 14C POC has the lowest bias and root-mean square error compared with in vitro measured NCP and is the most accurate algorithm for the Atlantic Ocean. Nearly a 13 year time series of NCP was generated using this algorithm with SeaWiFS data to assess changes over time in different regions and in relation to climate variability. The North Atlantic subtropical and tropical Gyres (NATL) were predominantly net autotrophic from 1998 to 2010 except for boreal autumn/winter, suggesting that the northern hemisphere has remained a net sink for CO2 during this period. The South Atlantic sub-tropical Gyre (SATL) fluctuated from being net autotrophic in austral spring-summer, to net heterotrophic in austral autumn–winter. Recent decadal trends suggest that the SATL is becoming more of a CO2 source. Over the Atlantic basin, the percentage of satellite pixels with negative NCP was 27%, with the largest contributions from the NATL and SATL during boreal and austral autumn–winter, respectively. Variations in NCP in the northern and southern hemispheres were correlated with climate indices. Negative correlations between NCP and the multivariate ENSO index (MEI) occurred in the SATL, which explained up to 60% of the variability in NCP. Similarly there was a negative correlation between NCP and the North Atlantic Oscillation (NAO) in the Southern Sub-Tropical Convergence Zone (SSTC), which explained 90% of the variability. There were also positive correlations with NAO in the Canary Current Coastal Upwelling (CNRY) and Western Tropical Atlantic (WTRA) which explained 80% and 60% of the variability in each province, respectively. MEI and NAO seem to play a role in modifying phases of net autotrophy and heterotrophy in the Atlantic Ocean.

Euphotic zone gross primary production, community respiration and net community production were determined from in vitro changes of dissolved oxygen, and from in vivo INT reduction capacity fractionated into two size classes, in offshore waters along a latitudinal transect crossing the North, Norwegian and Greenland Seas between the UK and Svalbard. Rates of gross primary production were higher and more variable than community respiration, so net autotrophy prevailed in the euphotic zone with an average net community production of 164±64 mmol O2 m−2 d−1. Respiration seemed to be mainly attributed to large eukaryotic cells (>0.8 µm) with smaller cells, mainly bacteria, accounting for a mean of 25% (range 5–48%) of community respiration. Estimates of bacterial growth efficiency were very variable (range 7–69%) due to uncoupling between bacterial respiration and production. Larger cells tended to contribute more towards total respiration in communities with high gross primary production and low community respiration, while bacteria contributed more towards total respiration in communities with lower gross primary production, typical of microbial-dominated systems. This suggests that community respiration is related to the size structure of the plankton community.

Microbial plankton metabolism was examined during summer 2010 in sea ice-influenced waters of the Fram Strait, eastern Arctic Ocean. Rates of gross primary production and community respiration were tightly coupled over a wide range of values (33±3–143±6 and 20±3–126±6 mmol O2 m−2 −1, respectively) leading to a prevalence of positive net community production. The high variability in community respiration, similar to that of gross primary production, suggests that heterotrophic metabolism may exhibit a significant response to environmental change. Bacterial respiration was assessed at similar time scales to bacterial production measurements, by determining the in vivo INT reduction capacity without pre-filtering the community. Bacteria seem to play a major role in total community respiration, contributing between 5% and 61% of total community respiration, indicating that a high fraction of the organic carbon in Arctic planktonic food webs could flow through these microbes.

Despite its importance to ocean-climate interactions, the metabolic state of the oligotrophic ocean has remained controversial for15 years. Positions in the debate are that it is either hetero- or autotrophic, which suggests either substantial unaccounted for organic matter inputs, or that all available photosynthesis (P) estimations (including (14)C) are biased. Here we show the existence of systematic differences in the metabolic state of the North (heterotrophic) and South (autotrophic) Atlantic oligotrophic gyres, resulting from differences in both P and respiration (R). The oligotrophic ocean is neither auto- nor heterotrophic, but functionally diverse. Our results show that the scaling of plankton metabolism by generalized P:R relationships that has sustained the debate is biased, and indicate that the variability of R, and not only of P, needs to be considered in regional estimations of the ocean's metabolic state.

Prokaryotic planktonic organisms are small in size but largely relevant in marine biogeochemical cycles. Due to their reduced size range (0.2 to 1 mu m in diameter), the effects of cell size on their metabolism have been hardly considered and are usually not examined in field studies. Here, we show the results of size-fractionated experiments of marine microbial respiration rate along a latitudinal transect in the Atlantic Ocean. The scaling exponents obtained from the power relationship between respiration rate and size were significantly higher than one. This superlinearity was ubiquitous across the latitudinal transect but its value was not universal revealing a strong albeit heterogeneous effect of cell size on microbial metabolism. Our results suggest that the latitudinal differences observed are the combined result of changes in cell size and composition between functional groups within prokaryotes. Communities where the largest size fraction was dominated by prokaryotic cyanobacteria, especially Prochlorococcus, have lower allometric exponents. We hypothesize that these larger, more complex prokaryotes fall close to the evolutionary transition between prokaryotes and protists, in a range where surface area starts to constrain metabolism and, hence, are expected to follow a scaling closer to linearity., SI

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.

Adequate bacterial respiration (BR) estimations are necessary to understand the flow of carbon through marine plankton food webs. A considerably higher bacterial contribution to total microbial plankton community respiration (CR) has been observed in oligotrophic systems compared to more productive systems. Classical BR estimation procedures, typically oxygen consumption mea- surements, comprise pre-incubation filtration to separate bacteria from the rest of the plankton community and long incubation times (24 h). The resulting disruption of the community linkages over long time periods might affect BR measure- ments, especially in oligotrophic systems charac- terized by tightly coupled microbial food webs. In this study, BR data were compiled from 2 con - trasting environments: the highly productive Ria de Vigo (NW Spain) and the North Atlantic oligotrophic gyre. Standard procedures or in vivo electron transport system (ETS) activity (non pre- filtered and short-time incubation) procedures were used to obtain a total of 209 BR estimations. Bacterial contribution to plankton CR was signifi- cantly higher in oligotrophic than in highly pro- ductive conditions (155% and 42%, respectively) when using standard procedures, while similar values were observed (31% and 30%) with in vivo ETS procedures. The relation between plankton CR and BR along the studied productivity gradient suggests that bacterial contribution to total CR varies less than previously assumed with an aver- age value approximating 30% through different trophic situations.

Experimental results related to the effects of ocean acidification on planktonic marine microbes are still rather inconsistent and occasionally contradictory. Moreover, laboratory or field experiments that address the effects of changes in CO2 concentrations on heterotrophic microbes are very scarce, despite the major role of these organisms in the marine carbon cycle. We tested the direct effect of an elevated CO2 concentration (1000 ppmv) on the biomass and meta- bolic rates (leucine incorporation, CO2 fixation and respiration) of 2 isolates belonging to 2 rele- vant marine bacterial families, Rhodobacteraceae (strain MED165) and Flavobacteriaceae (strain MED217). Our results demonstrate that, contrary to some expectations, high pCO2 did not nega- tively affect bacterial growth but increased growth efficiency in the case of MED217. The elevated partial pressure of CO2 (pCO2) caused, in both cases, higher rates of CO2 fixation in the dissolved fraction and, in the case of MED217, lower respiration rates. Both responses would tend to increase the pH of seawater acting as a negative feedback between elevated atmospheric CO2 concentrations and ocean acidification.

The accurate determination of the balance between plankton production and respiration in the ocean is important for C budgets and global change predictions. Disagreements on the measurement of such a balance at different scales (from microbiological to biogeochemical) have produced a controversy over the trophic status of the ocean. This is especially striking in the oligotrophic open ocean, where plankton community O 2 consumption rates in 24 h incubations have frequently produced a net heterotrophic balance, but similar difficulties emerge in coastal systems. These results have been criticised due to the possibility that the standard 24 h in vitro incubations are biased because of the long incubation time needed and the so-called “bottle effect”. To study the influence of the incubation time and bottle volume on the measurement of plankton net metabolism, we carried out several time series experiments in the NW Iberian coastal system. Here we present measurements of plankton community respiration rates concurrently obtained through (1) standard in vitro changes in dissolved oxygen concentration after different incubation times ranging from 2 to 48 h, and with bottle volumes of 50, 125 and 570 mL, and (2) the decrease in the oxygen concentration measured every 20 s with oxygen microsensors, during 48 h. Our results refute the contention that 24 h dark 125 mL bottle incubations are systematically biased, and highlight the validity of oxygen microsensors to study the dynamics of natural marine plankton respiration.

Euphotic zone plankton production ( P ) and respiration ( R ) were determined from the in vitro flux of dissolved oxygen during six latitudinal transects of the Atlantic Ocean, as part of the Atlantic Meridional Transect (AMT) programme. The transects traversed the North and South Atlantic Subtropical Gyres (N gyre, 18–38°N; S gyre, 11–35°S) in April–June and September–November 2003–2005. The route and timing of the cruises enabled the assessment of the seasonal variability of P , R and P / R in the N and S gyres, and the comparison of the previously unsampled N gyre centre with the more frequently sampled eastern edge of the gyre. Mean euphotic zone integrated rates (±SE) were P =63±23 ( n =31), R =69±22 ( n =30) mmol O 2 m −2 d −1 in the N gyre; and P =58±26 ( n =30), R =62±24 ( n =30) mmol O 2 m −2 d −1 in the S gyre. Overall, the N gyre was heterotrophic ( R > P ) and it was more heterotrophic than the S gyre, but the metabolic balance of both gyres changed with season. Both gyres were net heterotrophic in autumn, and balanced in spring. This seasonal contrast was most pronounced for the S gyre, because it was more autotrophic than the N gyre during spring. This may have arisen from differences in nitrate availability, because spring sampling in the S gyre coincided with periods of deep mixing to the nitracline, more frequently than spring sampling within the N gyre. Our results indicate that the N gyre is less heterotrophic than previous estimates suggested, and that there is an apparent decrease in R from the eastern edge to the centre of the N gyre, possibly indicative of an allochthonous organic carbon source to the east of the gyre.

The input of allochthonous matter of continental origin to coastal zones globally may cause changes in the activity (function) as well as the taxonomic composition (structure) of the micro- bial plankton community. The goal of the present study was the simultaneous analysis of microbial plankton community structure (size-fractionated phytoplankton biomass, bacterial community com- position) and function (particulate and dissolved primary production, bacterial production, microbial plankton community respiration) in the northwest Iberian coastal transition zone during a dry (Feb- ruary 2005) and a rainy (October 2005) period. An influence of freshwater input was observed in October, even at an offshore site, but not in February. We found an autotrophic community domi- nated by picophytoplankton during both sampling periods. In contrast, the bacterial groups Beta- and Gammaproteobacteria were significantly more abundant during the high precipitation period. Pri- mary production rates were low and similar during both sampling periods; however, bacterial pro- duction was 8-fold and community respiration was 3-fold higher in October than in February. Conse- quently, the microbial community metabolism was net autotrophic in February and net heterotrophic in October. The high precipitation and the significant presence of bacteria belonging to the Betapro- teobacteria, typical for freshwater systems, in October compared to February, strongly suggest an influence of material of continental origin on microbial metabolism in this coastal transition zone.

Despite its importance to ocean–climate interactions, the metabolic state of the oligotrophic ocean has remained controversial for >15 years. Positions in the debate are that it is either hetero- or autotrophic, which suggests either substantial unaccounted for organic matter inputs, or that all available photosynthesis (P) estimations (including 14C) are biased. Here we show the existence of systematic differences in the metabolic state of the North (heterotrophic) and South (autotrophic) Atlantic oligotrophic gyres, resulting from differences in both P and respiration (R). The oligotrophic ocean is neither auto- nor heterotrophic, but functionally diverse. Our results show that the scaling of plankton metabolism by generalized P:R relationships that has sustained the debate is biased, and indicate that the variability of R, and not only of P, needs to be considered in regional estimations of the ocean's metabolic state., Whether the oligotrophic ocean is net heterotrophic or net autotrophic has been a matter of debate for many years. Here Serret et al. show that, rather than being one or the other, the oligotrophic ocean is functionally diverse, with different metabolic states in different gyres.

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 (

11 páginas, 3 tablas, 5 figuras, The impact of rain water collected at marine, urban and rural sites on coastal phytoplankton biomass, primary production and community composition as well as the effect on microbial plankton metabolism was studied in 3 microcosm experiments conducted under contrasting spring, autumn and winter conditions. The measured responses were highly variable. Rainwater additions increased chlorophyll a (Chl a) concentration (5–68% difference between rainwater treatments relative to the control) in all experiments and reduced or stimulated primary production (PP) depending on the treatment and the experiment (from −10 to +169% relative to the control). Autotrophic stimulation was highest in spring, probably related to the low initial natural nutrient concentrations. Under winter nutrient replete conditions, rainwater inputs changed the phytoplankton community although this change did not promote increases in primary production. Enhancement of net autotrophy (increase of net oxygen production up to 227%) after rainwater inputs were only found during the period of low nutrient availability. Inputs of dissolved organic nitrogen (DON) explained a large fraction of the variability in the response of PP, Chl a, community respiration (CR) and net community production (NCP). Our results suggest that differences in the initial environmental conditions (i.e. nutrient availability), rainwater composition and the ability of the present autotrophic communities to utilize the new nutrients result in substantial changes in the microbial responses and associated biologically-mediated carbon fluxes. As atmospheric nutrient inputs into coastal oceans are increasing rapidly, our results help to understand the effects of different inputs on the metabolism of distinct microbial communities, This research was supported by the Galician Government (Xunta de Galicia) through the grants 07MMA002402PR (IMAN) and PGIDIT06PXIB312222PR (AddEx). S.M-G. and E.E.G-M. were funded by F.P.U. fellowships and E.T. by a Ramón y Cajal contract of the Spanish Ministry of Science and Innovation

In vitro measurements, predictions, and geochemical estimates of the balance between gross primary production (GPP) and community respiration (CR) in the open ocean do not agree. This has generated an active debate about the carbon balance in unproductive pelagic marine ecosystems. The analysis of generalized GPP:CR relationships that sustains this debate assumes a continuous trophic gradient or the simple partition of the World Ocean into productive and unproductive regimes. We measured euphotic zone GPP and CR along a latitudinal (40° N–30° S) transect across the Atlantic Ocean, which included two open-ocean oligotrophic provinces: the eastern area of the North Atlantic Subtropical Gyre (NAST-E) and the center of the South Atlantic Gyre (SATL). Net heterotrophy prevailed in the euphotic zone of the NAST-E, while the plankton community in the central SATL was net autotrophic. A review of published studies of net plankton metabolism in the open ocean substantiates this geographic pattern, suggesting the e...

27 páginas, 3 tablas, 5 figuras, 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.

From the beginning of December 1995 to the beginning of February of 1996, 29 stations were visited in the area of Bransfield and Gerlache Straits, and Bellingshausen Sea. Size-fractionated chlorophyll and primary production rates (0.2–2, 2–10 and >10 μm), as well as phytoplankton species composition were determined. Primary production experiments were carried out following JGOFS protocols and samples incubated from dawn during 24 h. The study area was divided into three main regions: A— Large diatoms region , Gerlache Strait on both cruises, and shelf break of Bellingshausen Sea area during the cruise FRUELA 95, with high values of primary production and predominance of large (>10 μm) phytosynthetic phytoplankters. Primary production and chlorophyll a (Chl a ) concentration averaged, respectively, 2.1 g C m −2 d −1 and 165 mg Chl a m −2 . Eighty percent of Chl a and 70% of primary production corresponded to cells larger than 10 μm, such as big chain-forming diatoms, the large flagellate Pyramimonas , and colonies of Phaeocystis . B— Cryptophycean region , Bransfield Strait and confluence with Gerlache Strait. Characterised by moderate values of primary production of small size organisms. Mean primary production values were ca. 1.0 g C m −2 d −1 and 62 mg Chl a m −2 , and the phytoplankton community was formed essentially by Cryptomonas species. Approximately 80% of Chl a and primary production corresponded to less than 10-μm cells. Within this region, a subarea could be distinguished in the central zone of Bransfield Strait, with low phytoplankton biomass (around 20 mg Chl a m −2 ) and primary production (ca 0.6 gC m −2 d −1 ). In this subarea, the phytoplankton community was dominated by free cells of Phaeocystis and Cryptomonas ; Sixty-five percent of the Chl a and 80% of primary production corresponded to smaller fractions. C— Region of very low phytoplankton biomass , all Bellingshausen Sea during the FRUELA 96 cruise. Primary production was around 0.2 g C m −2 d −1 and Chl a about 10 mg m −2 . Phytoplankton was dominated by microflagellates ( a corresponded to the smaller than 10-μm fraction. No statistical relationship was found between phytoplankton distribution and hydrography and/or concentrations of dissolved inorganic nutrients for the different regions. The upper mixed layer was always within the photic zone, and levels of nutrients were always high enough to be non-limiting for phytoplankton growth. Grazing pressure as well as sedimentation and respiration losses, in combination with shallow mixed layers, specially in some and very high productive stations of Region A, might be the main factors controlling the phytoplankton distribution in this area of the Antarctic Peninsula.

We carried out 16 photochemical experiments of filtered surface water in a custom-built solar simulator and concomitant measurements of in vitro gross primary production (GPP) and respiration (R) in the Mauritanian upwelling during a Lagrangian study following three sulfur hexafluoride–labeled patches of upwelled water (P1 to P3). Oxygen photolysis rates were correlated with the absorbance of chromophoric dissolved organic matter (CDOM) at 300 nm, suggesting first-order kinetics with respect to CDOM. An exponential fit was used to calculate the apparent quantum yield (AQY) for oxygen photolysis, giving an average AQY of 0.00053 mmol O2 (mole photons m22 s21)21 at 280 nm and slope of 0.0012 nm21. Modeled photochemical oxygen demand (POD) at the surface (3–16 mmol m23 d21) occasionally exceeded R and was dominated by ultraviolet radiation (71– 79%). Euphotic-layer integrated GPP decreased with time during both P-1 and P-3, whereas R remained relatively constant and POD increased during P-1 and decreased during P-3. On Day 4 of P-3, GPP and POD maxima coincided with high CDOM absorbance, suggesting ‘‘new’’ CDOM production. Omitting POD may lead to an underestimation of net community production (NCP), both through in vitro and geochemical methods (here by 2–22%). We propose that oxygen-based NCP estimates should be revised upward. For the Mauritanian upwelling, the POD-corrected NCP was strongly correlated with standard NCP with a slope of 1.0066 6 0.0244 and intercept of 46.51 6 13.15 mmol m22 d21.

Size-fractionated chlorophyll a and photosynthetic carbon incorporation, microbial oxygen production and respiration and particulate vertical flux were measured in January 1996 at three regions, characterized by distinct hydrographic fields and planktonic communities, of the Antarctic Peninsula: (1) a diatom-Phaeocystis sp., dominated community associated with the relatively stratified waters of the Gerlache Strait, (2) a nanoplankton-Cryptomonas sp. dominated assemblage at the Gerlache-Bransfield confluence; and (3) a nano- and picoplankton community in mixed waters of the Bransfield Strait. Despite the marked differences in both community structure and total phytoplankton biomass and primary production, and against predictions from models about trophic control of C export, the lowest respiration rates were measured at Bransfield (pico- and nanoplankton), and no difference was observed between the Gerlache (large diatoms) and Bransfield stations in relative vertical particle flux (6.4 vs. 5.1 % of suspended C; 14.9 vs. 10.4 % of net community production, respectively). Growth and loss rates of the phytoplankton population studied for each community indicate that microbial populations can be explained by in situ growth, but spatial (diatom-Phaeocystis sp., bloom) and temporal (diatom-Phaeocystis sp. bloom and nanoplankton communities) scales of study were shown to be insufficient for addressing the coupling between primary production and biogenic carbon export, especially after the appreciation of the accumulation of dissolved organic carbon in the water column. This would explain the unexpected results and highlights the necessity of including the mechanisms controlling accumulation and consumption of dissolved organic matter into conceptual models about the trophic control of C export.

Dissolved organic carbon (DOC) production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production. Experiments were conducted during four cruises carried out between May 1998 and October 1999, covering three upwelling regions: Benguela (SW Africa), Mauritania (NW Africa) and NW Spain, and the oligotrophic North Atlantic subtropical gyre between 308N and 368N. Photic zone integrated particulate organic carbon (POC) production rates ranged from 10 to 1,178 mg C m 22 h 21 , thus covering a wide productivity spectrum. The percentage of DOC production with respect to total integrated primary production ranged from 4 to 42%, being larger in oligotrophic, picoplankton-dominated waters, where a balanced metabolism of the microbial community was observed, than in productive, net autotrophic waters, where large-sized cells formed the bulk of the phytoplankton biomass. A highly significant relationship was calculated between DOC and POC production rates in upwelling conditions. By contrast, the relationship between these variables in oligotrophic environments was weak, which suggests that different processes could be controlling the release of dissolved organic matter in productive and unproductive waters. Dissolved organic matter (DOM) is one of the least understood pools of marine matter and represents a major reservoir of organic carbon in the ocean. A large fraction of the dissolved organic carbon (DOC) present in the ocean ultimately derives from primary producers. However, a great deal of controversy still exists on the ecological significance and the ultimate control of DOC production in the ocean. The magnitude of DOC-related fluxes remains still largely uncertain, especially in oligotrophic regions. The high rates of DOC uptake by heterotrophic bacteria in relation to primary production recently measured in unproductive waters (e.g., Hansell et al. 1995; del Giorgio et al. 1997), largely justifies the growing biogeochemical interest of measuring and modeling DOC production in planktonic ecosystems. Initially, the radioactive carbon method for primary production estimation was modified for the measurement of direct excretion of dissolved organic compounds from algal cells. More recently, it has been recognized that several processes, besides direct excretion from intact algal cells, are 1

Five oceanographic surveys were conducted at the Great Meteor Tablemount (subtropical NE Atlantic; 30.0 degreesN, 28.5 degreesW) throughout the 1992-1999 period tc, investigate temporal variability in the relationship between the physical structure of the water column associated with the seamount and phytoplankton biomass and/or production rates. Local increases in chlorophyll a, enhanced carbon incorporation rates and changes in phytoplankton species composition were associated with the seamount. These effects were subjected to a large degree of temporal and spatial variability both at seasonal and shorter time scales., Entre 1992 et 1999 cinq campagnes de recherche océanographique ont été réalisées (30,0ºN, 28,5ºO), pour étudier la variabilité temporelle du rapport entre la structure physique de la colonne dˈeau associée aux abords du mont sous-marin dˈune part, et la biomasse et les taux de production phytoplanctonique dˈautre part. On observe une élévation locale de la teneur en chlorophylle a près du mont sous-marin ainsi que des taux élevés de production primaire et des changements de la composition spécifique du phytoplancton. Ces effets connaissent une variabilité spatiale et temporelle élevée, aussi bien à courte échelle de temps quˈà lˈéchelle saisonnière.

The Mauritanian upwelling system is one of the most biologically productive regions of the world's oceans. Coastal upwelling transfers nutrients to the sun-lit surface ocean, thereby stimulating phytoplankton growth. Upwelling of deep waters also supplies dissolved inorganic carbon (DIC), high levels of which lead to low calcium carbonate saturation states in surface waters, with potentially adverse effects on marine calcifiers. In this study an upwelled filament off the coast of northwest Africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological, physical and chemical processes. The initial pH tot in the mixed layer of the upwelled plume was 7.94 and the saturation states of calcite and aragonite were 3.4 and 2.2, respectively. As the plume moved offshore over a period of 9days, biological uptake of DIC (37 μmolkg -1) reduced pCO 2 concentrations from 540 to 410 μatm, thereby increasing pH tot to 8.05 and calcite and aragonite saturation states to 4.0 and 2.7 respectively. The increase (25 μmolkg -1) in total alkalinity over the 9day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity (i.e., evaporation and mixing with other water masses). We found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers. The ongoing expansion of oxygen minimum zones through global warming will likely further reduce the CaCO 3 saturation of upwelled waters, amplifying any adverse consequences of ocean acidification on the ecosystem of the Mauritanian upwelling system. © 2012. American Geophysical Union. All Rights Reserved.

The evolution of a Phaeocystis bloom off Plymouth in spring 1990 is described. Data were obtained (1) during weekly visits to station El to measure physical parameters, nutrient concentrations, primary production and grazing pressure and (2) by regular tows of an Undulating Oceanographic Recorder around a circuit of five stations including El to detect stratification, monitor the geographical distribution of chlorophyll and determine vertical profiles at each station.The data show that the Phaeocystis bloom emanated from near-shore, its spread towards the south-east correlating with the wind direction prevailing at the time. Due to bad weather, seasonal stratification had not been established at the time of the bloom so that a major diatom outburst had not occurred and nutrients remained high as the Phaeocystis moved offshore.Zooplankton populations at El, averaged over 50 m, decreased whilst Phaeocystis was present, resulting in very low grazing pressure. Termination of the bloom was not, therefore, due to consumption by herbivores. It was, instead, caused by Phaeocystis colonies becoming nutrient-depleted and releasing single cells which were transported downwards. As a result of this, chlorophyll concentrations near the bottom remained high for some time after the Phaeocystis had disappeared from the surface water.A scenario is proposed to explain the observations in terms of our current understanding of the ecophysiology of Phaeocystis.

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.

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.

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.

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11 pages, 9 figures, 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 oceanmeasurements 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 (328S–488N) transect in theEastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrastingplankton regimes, including two open ocean oligotrophic provinces, is used to derive a GPP : CR relationship, whichsuggests that net heterotrophy (GPP,CR) prevails in the eastern Atlantic when primary production falls below;100 mmol O2m22d21. The predictive capability of this relationship is compared with that of the only otherpublished relationship based on similar methodologies and is found to give a more representative description of theautotrophic (GPP.CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved predictive power isattributed to the increased representativeness of the current data set. Specifically, the interpretation suggests that theinfluence of community structure on net ecosystem metabolism implies that prediction of GPP : CR balances inpelagic ecosystems can be best achieved by use of a data set that covers a wide range of community structure andnot only a wide range in the magnitude of primary production

Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower., 2

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

Gross oxygen production (GP), dark respiration (DR) and net community production (NCP) were studied for 16 mo in the euphotic layer of 3 stations through the coastal transitional zone of the southern Bay of Biscay, and related to hydrographic and nutrient conditions, phytoplankton biomass and C incorporation. Microbial O 2 fluxes exhibited seasonal patterns linked to the seasonal cycle of water column stratification and mixing, with positive NCP during the spring, negative throughout the summer and close to zero in winter. This pattern was altered at coastal regions, where productive periods were linked to coastal upwelling, whereas in winter persistent net heterotrophy was measured, presumably in relation to increases in organic matter discharge of continental origin. The comparison of NCP with O 2 anomaly and NO 3 concentration in the euphotic zone, the spatial and temporal scales studied and the prevalence of steady-state conditions offshore support the conclusion that the maintenance of summer heterotrophy in the region was based upon the consumption of the surplus of organic matter produced in spring. The uncoupling in the microbial auto- and heterotrophic metabolisms, based on the accumulation and delayed consumption of dissolved organic matter as a consequence of the processes controlling phytoplankton growth and microbial heterotrophic activity in temperate seas, would explain such a pattern. The close relationship observed between the seasonal variability in NCP and the magnitude of spring net production and predictions derived from the seasonal cycles of O 2 anomaly in middle latitudes and atmospheric O 2 led us to conclude that the seasonal compensation of production and respiration processes is a characteristic of the dynamics of the pelagic ecosystem, at least in coastal temperate seas. The implications of this conclusion are of great relevance for the interpretation of new production and the estimation of the trophic status of the ocean from direct measurements of plankton net production.

Size-fractionated chlorophyll a and primary production measurements during 7 latitudinal cruises (56 stations) in the Atlantic Ocean indicate that in subtropical and tropical regions the relative contribution of large (L) (>2 µm) phytoplankton to total (T) chlorophyll a biomass (B) is smaller (BL:BT ratio = 0.25 ± 0.01 SE) than their contribution to total primary production (P) (PL:PT ratio = 0.45 ± 0.02). This implies a lower assimilation number for picoplankton than for larger cells: 1.5 ± 0.2 and 3.7 ± 0.3 mg C mg chlorophyll a h -1 , respectively (n = 90). During short-term time-course experiments in subtropical and tropical waters of the North Atlantic, a >50% reduction in the abun- dance of picoplankton, mainly Prochlorococcus spp., took place as early as the first 2 h of incubation. This suggests that long incubation times in bottle experiments can lead to underestimations of primary production rates, at least in oligotrophic waters. The phytoplankton size-structure remained fairly constant throughout the experiments, suggesting that the high PL:PT ratios in these environ- ments cannot be due to enhanced loss rates of small-sized phytoplankton as a result of bottle enclo- sure. Our results indicate that the observed disagreement between BL:BT and PL:PT ratios is not necessarily an experimental artifact, but could be related to a higher light utilization efficiency of larger phytoplankton.

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.

Contrasting hydrographic regimes were studied in the NW Iberian coastal transition zone in order to gain understanding of the relationship between planktonic community structure, production and loss rates, by concurrently measuring size-fractionated phytoplankton biomass and carbon incorporation as well as dissolved organic carbon production and dark respiration by micro- bial communities. Sampling was carried out in August 1998 and October 1999 at a series of stations representing vertical stratification and coastal upwelling conditions in summer, and vertical mixing and shelf-break poleward flow situations during the autumn. A close relationship was found between size-fractionated phytoplankton biomass and production, the relative allocation of total photosynthe- sis to dissolved and particulate organic carbon fractions, and the balance between production and respiration. Picoplankton-dominated communities showed net heterotrophic metabolism and were associated with relatively high rates of DOC production with respect to total carbon incorporation (>15%). In contrast, in coastal upwelling stations, where >2 µm cells dominated, less than 10% of total fixed carbon flowed to DOC, and the net metabolism of the microbial plankton community was autotrophic.