Dark Community Respiration Research Articles

Controlling mechanisms and cross linkages of ecosystem metabolism and atmospheric CO2 flux in the northern South China Sea

This study aims to understand the controlling mechanisms of ecosystem metabolic states and air-sea CO2 fluxes and their cross linkages in the northern South China Sea (NSCS). The integrated gross production (IGP), integrated dark community respiration (IDCR), and integrated bacterial respiration (IBR) were all higher in summer than in winter ranging from 851, 435, and 243 to 5032, 10707, and 7547 mg C m−2 d−1, respectively. The discrete estimates of gross production (GP) and dark community respiration (DCR) were modulated by temperature, salinity and nutrient availability through different mechanisms in summer and winter and in shallow (Zhujiang River plumes and shelves) and deep (slope and basin) sampling stations. GP was correlated with DCR (r = 0.74, p < 0.0001), which in turn was largely attributed (65%) to bacterial respiration in the NSCS. Most spatial and summer-winter variability in the IGP/IDCR ratios was less than 1 (heterotrophic), except for in two ratios in winter in the Zhujiang River plume. However, these ratios were higher in winter than in summer because of the vertical pumping of nutrient in winter. Given the higher level of seawater pCO2 in summer than in winter, the NSCS appears to act as a balance to minor source of atmospheric CO2 in summer but a sink in winter. The air−sea fluxes of CO2 and ecosystem metabolic states share a close link in summer but separate in winter. Internal and external sources of dissolved organic carbon may play a key role in causing the heterotrophic conditions and atmospheric CO2 sink in winter.

Regulation and linkages of metabolic states and atmospheric CO2 fluxes in a tropical coastal sea off southwestern Taiwan

The present study aims to understand the mechanisms controlling ecosystem metabolic states and atmospheric CO2 fluxes and explore their linkages through monthly investigations along the tropical Kaoping Submarine Canyon (KPSC) in southwestern Taiwan. The magnitudes of integrated gross production (IGP) and integrated dark community respiration (IDCR) were higher in summer than in winter, likely supported by greater inputs of freshwater in summer with high loads of nutrients and organic carbon. Strong positive correlations were observed between gross production (GP) (or dark community respiration (DCR)) and temperature, photosynthetically active radiation and nutrients, but negative correlations were observed between GP (or DCR) and salinity in discrete water samples; these results reveal the significant impacts of freshwater inputs on GP and DCR. GP was determined largely by DCR, and DCR was attributed largely (78%) to bacterial respiration in the KPSC. Approximately 60% of measurements were autotrophic conditions (IGP/IDCR >1) in most wet seasons except for certain offshore stations, which were apparently driven by higher temperature and nutrient availability, whereas 40% of measurements revealed heterotrophic conditions (IGP/IDCR <1) in most offshore stations. The air-sea fluxes of CO2 revealed that about 64% of all measurements were sinks of atmospheric CO2, but those sinks did not completely coincide temporally with autotrophic conditions. Biological controls [GP correlated significantly with nutrients and chlorophyll a and was primarily determined by DCR] and temperature effects may overwhelmingly dictate metabolic states and air-sea fluxes of atmospheric CO2, respectively, though the combined effects were evident in this coastal ecosystem. The study may shed light on implications of recent increases in nutrient inputs for shifting the coastal ecosystem from heterotrophic to autotrophic conditions, and the global warming per se may increase the chance for tropical coastal ecosystems acting as a source of atmospheric CO2.

Effects of river inputs on nutrient and organic-carbon conditions and net ecosystem metabolism in the Kaoping (Taiwan) coastal sea

This study aims to understand the variability of net ecosystem metabolism in a tropical sea. The contrasting pattern of metabolic state between wet and dry seasons was caused by the pronounced difference of river exports in the Kaoping coastal sea. The depth-integrated gross primary production (IGPP) through the euphotic zone ranged from 2451 to 16 230 mg C m–2 day–1 in summer, and from 844 to 5549 mg C m–2 day–1 in winter, and was apparently regulated by oceanic temperature, nutrients and organic carbon. The depth-integrated dark community respiration (IDCR), attributed largely to bacterial respiration (BR, ~69%), ranged from 861 to 12 418 mg C m–2 day–1 in summer, and from 997 to 5781 mg C m–2 day–1 in winter. GPP and DCR correlated inversely with salinity but positively with nutrients, Chlorophyll a, dissolved organic carbon (DOC) and particulate organic carbon (POC). The autotrophic state (IGPP : IDCR &gt; 1) prevailed in most stations in summer, whereas the heterotrophic state (IGPP : IDCR &lt; 1) occurred in all but Station B1 in winter. Bacterial production (BP) and bacterial respiration (BR) also correlated inversely with salinity but positively with nutrients and DOC. Bacterial carbon demand (BCD) was 0.15 GPP in summer and 0.64 GPP in winter, supporting the autotrophic and heterotrophic conditions in summer and winter, respectively. The metabolic state is apparently determined by seasonal variation of temperature and river exports.

The effects of nutrient additions on particulate and dissolved primary production and metabolic state in surface waters of three Mediterranean eddies

Abstract. We examined the effects of nutrient additions on rates of 14C-based particulate and dissolved primary production as well as O2-based metabolic rates in surface waters (8 m) of three anticyclonic eddies, located in the Western, Central and Eastern Mediterranean. Ship-board microcosm experiments employing additions of inorganic nitrogen (+N) and phosphorus (+P), alone and in combination (+NP), were conducted in June/July 2008 during the BOUM (Biogeochemistry from the Oligotrophic to the Ultra-oligotrophic Mediterranean) cruise. In all three experiments, particulate primary production was significantly stimulated by the additions of nitrogen (+N, +NP) while no effect was observed with the addition of phosphorus alone (+P). Percent extracellular release of photosynthate (PER) displayed the lowest values (4–8 %) in the +NP treatment. Among the three treatments (+N, +P, +NP), the +NP had the strongest effect on oxygen metabolic rates, leading to positive values of net community production (NCP &gt; 0). These changes of NCP were mainly due to enhanced gross primary production (GPP) rather than reduced dark community respiration rates (DCR). In all three sites, in +NP treatment autotrophic production (whether expressed as GPP or PPtotal) was sufficient to fulfil the estimated carbon requirements of heterotrophic prokaryotes, while addition of nitrogen alone (+N) had a weaker effect on GPP, resulting in metabolically balanced systems. At the three sites, in treatments with N (+N, +NP), phytoplankton and heterotrophic prokaryote production were positively correlated. Heterotrophic conditions were observed in the Control and +P treatment at the central and eastern sites, and autotrophic production was not sufficient to supply estimated bacterial carbon demand, evidence of a decoupling of phytoplankton production and consumption by heterotrophic prokaryotes.

Microbial food webs and metabolic state across oligotrophic waters of the Mediterranean Sea during summer

Abstract. The abundance and activity of the major members of the heterotrophic microbial community – from viruses to ciliates – were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to-east gradient of deepening of DCM (deep chlorophyll maximum) and increasing oligotrophy reflected in gradients of biomass and production. However, within this well documented longitudinal trend, hydrological mesoscale features exist and likely influence microbial dynamics. Here we present data from a W-E transect of 17 stations during the period of summer stratification. Along the transect the production and fate of organic matter was investigated at three selected sites each one located in the centre of an anticyclonic eddy: in the Algero-Provencal Basin (St. A), the Ionian Basin (St. B), and the Levantine Basin (St. C). The 3 geographically distant eddies showed low values of the different heterotrophic compartments of the microbial food web, and except for viruses in site C, all integrated (0–150 m) stocks were higher in reference stations located in the same basin outside the eddies. During our study the 3 eddies showed equilibrium between GPP (Gross Primary Production) and DCR (Dark Community Respiration). Integrated PPp (Particulate Primary Production) values at A, B and C varied from ~140 to ~190 mg C m−2.

Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)

Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores ( Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO 2 fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers.

Net community production and dark community respiration in a Karenia brevis (Davis) bloom in West Florida coastal waters, USA

Oxygen-based productivity and respiration rates were determined in West Florida coastal waters to evaluate the proportion of community respiration demands met by autotrophic production within a harmful algal bloom dominated by Karenia brevis. The field program was adaptive in that sampling during the 2006 bloom occurred where surveys by the Florida Wildlife Research Institute indicated locations with high cell abundances. Net community production (NCP) rates from light-dark bottle incubations during the bloom ranged from 10 to 42 μmole O 2 L −1 day −1 with highest rates in bloom waters where abundances exceeded 10 5 cells L −1. Community dark respiration ( R) rates in dark bottles ranged from <10 to 70 μmole O 2 L −1 day −1 over 24 h. Gross primary production derived from the sum of NCP and R varied from ca. 20 to 120 μmole O 2 L −1 day −1. The proportion of GPP attributed to NCP varied with the magnitude of R during day and night periods. Most surface communities exhibited net autotrophic production (NCP > R) over 24 h, although heterotrophy (NCP < R) characterized the densest sample where K. brevis cell densities exceed 10 6 cells L −1.

Bacterial production and respiration in subtropical Hong Kong waters: influence of the Pearl River discharge and sewage effluent

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 58:167-179 (2010) - DOI: https://doi.org/10.3354/ame01346 Bacterial production and respiration in subtropical Hong Kong waters: influence of the Pearl River discharge and sewage effluent Xiangcheng Yuan1,2, Kedong Yin2,3,*, Paul J. Harrison1, Wei-Jun Cai4, Lei He2, Jie Xu1 1Atmospheric, Marine and Coastal Environment (AMCE) Program, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 2Key Laboratory of Tropical Marine Environmental Dynamics, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, PR China 3Australian Rivers Institute, Griffith University (Nathan Campus), Brisbane, Queensland 4111, Australia 4Department of Marine Sciences, University of Georgia, Athens, Georgia 30602, USA *Corresponding author. Email: k.yin@griffith.edu.au ABSTRACT: Hong Kong waters are influenced by the Pearl River discharge in the west, coastal/ oceanic waters in the east, and year-round domestic sewage effluent in the Victoria Harbour area. Seven cruises were conducted at 12 stations across the Hong Kong water in the dry and wet seasons to examine how the Pearl River outflow and sewage effluent discharge influenced the distributions of dissolved oxygen (DO), dissolved inorganic carbon (DIC), bacterial production (BP) and bacterial respiration (BR). Surface DO saturation was usually ~80%, and surface partial pressure of carbon dioxide (pCO2) averaged ~570 µatm at all 12 stations. The undersaturated DO and supersaturated pCO2 indicated that Hong Kong waters were heterotrophic and a net source of CO2 to the atmosphere, except during periods of phytoplankton blooms when pCO2 became very low (<200 µatm). The Pearl River discharge in the wet season decreased DO and increased pCO2 and BP in the estuarine-influenced waters in comparison with the coastal/oceanic waters. Sewage effluent exerted a strong influence on carbon dynamics and CO2 efflux as surface pCO2 was significantly correlated with NH4, an indicator of sewage effluent. BR in Hong Kong waters was ~100 to 400 mmol C m–2 d–1 in July and November 2005. The BR fraction accounted for 50 to 80% of total dark community respiration (DCR) in coastal/oceanic waters with less eutrophic inputs, but increased to >90% of DCR in more eutrophic waters near the sewage discharge site, likely due to the decrease in phytoplankton biomass. Contribution of BR to the CO2 efflux was ~3 to 10 mmol C m–2 d–1, which was ~50% (varied from 16 to 130%) of the total CO2 efflux. This study has important implications for severely anthropogenically impacted coastal areas, as they may be an important source of atmospheric CO2 due to active BR. KEY WORDS:Bacterial production · Bacterial respiration · CO2 · Sewage effluent · Pearl River estuary Full text in pdf format PreviousNextCite this article as: Yuan X, Yin K, Harrison PJ, Cai W, He L, Xu J (2010) Bacterial production and respiration in subtropical Hong Kong waters: influence of the Pearl River discharge and sewage effluent. Aquat Microb Ecol 58:167-179. https://doi.org/10.3354/ame01346 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 58, No. 2. Online publication date: January 07, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.

Comparison of in vitro and in situ plankton production determinations

Plankton production was measured using 8 techniques at 4 stations in the Celtic Sea, North Atlantic Ocean, in April 2002. Primary production (PP) was derived from 14 C incorporation into particulate carbon after 24 h simulated in situ, PP( 14 CSIS), and 2 h photosynthesis-irradiance incuba- tions, PP( 14 CPUR), and from 2 published satellite algorithms, PP(VGPM) and PP(M91). Gross production (GP) was calculated from O2 evolution, GP(O2), and 18 O enrichment of dissolved O2, GP( 18 O), after 24 h simulated in situ incubations, and from in situ active fluorescence measured by fast repetition rate fluorometry (FRRF). Net community production (NCP) was determined from changes in in situ dissolved oxygen, NCP(ΔO2), and from changes in oxygen during 24 h simulated in situ incubations, NCP(O2). Dark community respiration (DCR) was derived from changes in oxygen during a 24 h dark incubation, DCR(O2), and daily oxygen uptake, DOU( 18 O, O2), was calculated from the difference between GP( 18 O) and NCP(O2). Three stations were dominated by picoautotrophs and the fourth station was dominated by diatoms. While most of the comparisons between techniques fell within previously published ranges, 2 anomalies occurred only at the diatom-dominated station. Rates of PP( 14 CPUR) were oxygen uptake in the dark. The low rates of PP( 14 CPUR) in relation to PP( 14 CSIS) may have resulted from the heterogeneous nature of the bloom and differences in sampling time. However, it is also possible that dissolved organic material (DOM) released by the stressed diatom population restricted the diffusion of 14 C into the cells, thereby causing a greater underestimate of PP by techniques using short incuba- tions. The significantly higher rates of oxygen uptake in the light are difficult to reconcile, and we do not know whether the light enhanced oxygen uptake was directly linked to carbon fixation. How- ever, the release of DOM may also have provided substrate for enhanced respiration in the light. These anomalies were only revealed through the concurrent measurement of plankton production by this wide range of techniques. Further investigation of DOM excretion and light-enhanced respira- tion during diatom blooms is warranted.

The metabolic balance at two contrasting sites in the Southern Ocean: The iron-fertilized Kerguelen area and HNLC waters

Abstract We investigated the balance between autotrophic and heterotrophic processes during the third month of an intense phytoplankton bloom induced by natural iron enrichment above the Kerguelen plateau (Southern Ocean). Gross (GCP)- and net community production (NCP) and dark community respiration (DCR) were determined using concurrent measurements of dissolved oxygen (O2) and total carbon dioxide (TCO2) evolution in light- and dark-bottle incubations. Experiments were carried out during four visits to one station located in the core of the phytoplankton bloom and at a high-nutrient low-chlorophyll (HNLC) site. Within the bloom, euphotic zone (around 45 m) integrated fluxes of NCP were high during the first three visits, varying between 64 and 92 mmol O2 m−2 d−1 and between −43 and −105 mmol TCO2 m−2 d−1. On the last visit, however, fluxes of NCP indicated a shift from autotrophic to heterotrophic plankton metabolism, with a net consumption of O2 (−72 mmol O2 m−2 d−1) and a net production of TCO2 (64 mmol TCO2 m−2 d−1). This shift was accompanied by a 5-fold increase in DCR, while integrated fluxes of GCP remained similar throughout the sampling period (110±21 mmol O2 m−2 d−1 and −100±27 mmol TCO2 m−2 d−1). Fluxes of NCP integrated to the euphotic zone (around 100 m) were low at a typical HLNC site, ranging from 0 to 5 mmol O2 m−2 d−1 during three visits. These data suggest that above the Kerguelen plateau organic matter production largely exceeded its immediate respiration, while at the HLNC site autotrophic and heterotrophic processes are close to balance. During the spring phytoplankton bloom above the Kerguelen plateau, a substantial part of primary production is therefore potentially available for mesozooplankton grazing and export, or respiration at a different time period.

Heterotrophic bacterial production in the eastern South Pacific: longitudinal trends and coupling with primary production

Abstract. Spatial variation of heterotrophic bacterial production and phytoplankton primary production were investigated across the eastern South Pacific Ocean (−141° W, −8° S to −72° W, −35° S) in November–December 2004. Bacterial production (3H leucine incorporation) integrated over the euphotic zone encompassed a wide range of values, from 43 mg C m−2 d−1 in the hyper-oligotrophic South Pacific Gyre to 392 mg C m−2 d−1 in the upwelling off Chile. In the gyre (120° W, 22° S) records of low phytoplankton biomass (7 mg Total Chla m−2) were obtained and fluxes of in situ 14C-based particulate primary production were as low as 153 mg C m−2 d−1, thus equal to the value considered as a limit for primary production under strong oligotrophic conditions. Average rates of 3H leucine incorporation rates, and leucine incorporation rates per cell (5–21 pmol l−1 h−1 and 15–56×10−21 mol cell−1 h−1, respectively) determined in the South Pacific gyre, were in the same range as those reported for other oligotrophic subtropical and temperate waters. Fluxes of dark community respiration, determined at selected stations across the transect varied in a narrow range (42–97 mmol O2 m−2 d−1), except for one station in the upwelling off Chile (245 mmol O2 m−2 d−1). Bacterial growth efficiencies varied between 5 and 38%. Bacterial carbon demand largely exceeded 14C particulate primary production across the South Pacific Ocean, but was lower or equal to gross community production.

Phytoplankton size structure and water column metabolic balance in a coastal upwelling system: the Ría de Vigo, NW Iberia

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 50:169-179 (2008) - DOI: https://doi.org/10.3354/ame01160 Phytoplankton size structure and water column metabolic balance in a coastal upwelling system: the Ría de Vigo, NW Iberia B. Arbones*, C. G. Castro, F. Alonso-Pérez, F. G. Figueiras CSIC, Instituto de Investigacións Mariñas, Eduardo Cabello 6, 36208 Vigo, Spain *Email: belen@iim.csic.es ABSTRACT: The metabolic balance between gross primary production (GPP) and community respiration and its relationship with the plankton community structure was investigated in the Ría de Vigo, in the coastal upwelling system of the NW Iberian Peninsula. Measurements of in situ GPP, dark community respiration (DCR), size-fractionated biomass, size-fractionated primary production (14C PP) and GPP from photosynthetic-irradiance incubations (14C PPP-I) were carried out in the Ría de Vigo between April 2004 and January 2005. Seasonal patterns of phytoplankton biomass and primary production were in phase with one another. The highest 14C PP and biomass values, accounting mainly for the large-size phytoplankton (>20 µm), were observed under upwelling-favourable conditions (spring and summer). Minimum values of 14C PP and phytoplankton biomass were registered in winter with a shift to small phytoplankton dominance (>80%). Integrated water column DCR varied between a summer maximum of 132 mmol O2 m–2 d–1 and a winter minimum of 31 mmol O2 m–2 d–1. Community respiration was significantly related to primary production for the 2 upwelling cruises, pointing to a close coupling between these processes. However, no direct relationship was found for the other periods. Our results suggest that the water column metabolic balance inside the Ría de Vigo is dependent on phytoplankton size structure. The autotrophy degree of the system is high when the contribution of large-size phytoplankton is dominant, whereas it is almost in balance when the small phytoplankton fraction prevails. KEY WORDS: Primary production · P/R balance · Microplankton size structure · Upwelling ·Ría de Vigo Full text in pdf format PreviousNextCite this article as: Arbones B, Castro CG, Alonso-Pérez F, Figueiras FG (2008) Phytoplankton size structure and water column metabolic balance in a coastal upwelling system: the Ría de Vigo, NW Iberia. Aquat Microb Ecol 50:169-179. https://doi.org/10.3354/ame01160 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 50, No. 2. Online publication date: January 31, 2008 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2008 Inter-Research.

Microplankton composition, production and upwelling dynamics in Sagres (SW Portugal) during summer of 2001

Microplankton community, production, and respiration were studied alongside physical and chemical conditions at Sagres (SW Portugal) during the upwelling season, from May to September 2001. The sampling station was 5 km east of the upwelling centre off Cabo S. Vicente, and 2 km west of an offshore installation for bivalve aquaculture. Three major periods were distinguished according to sea surface temperature (SST): period 1 (P1; May and June), characterised by high temperature values (17.0±1.8°C); period 2 (P2; July), characterised by lower temperatures (14.6±0.3°C), identified as an upwelling-blooming stage; and period 3 (P3; August), characterised by a high temperature pattern (16.25±1.14°C). Chaetoceros spp., Thalassiosira spp., Lauderia spp., Detonula spp. and Pseudo-nitzschia spp. were the major taxa contributing to the dissimilarities between P2 (July) and the other periods. In July (P2), the average gross production (GP; 52.5±12.3 µM O 2 d -1 ) and net community production (NCP; 46.9±15.3 µM O 2 d -1 )) peaked with the maximal concentrations of diatom-chl a. Dark community respiration (DCR) remained low and more constant throughout (4.6±3.6 µM O 2 d -1 ). The plankton assemblage was dominated by diatoms throughout the survey. Physical events were the primary factors determining the microplankton structure and distribution at this location.

Microbial community production, respiration, and structure of the microbial food web of an ecosystem in the northeastern Atlantic Ocean

Gross community production (GCP), dark community respiration (DCR), and the biomass of the different size classes of organisms in the microbial community were measured in the northeastern Atlantic basin as part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) project. The field experiment was conducted during three seasons (winter, spring, and late summer–fall) in 2001. Samples were collected from four different mesoscale structures within the upper 100 m. GCP rates increased from winter (101 ± 24 mmol O2 m−2 d−1) to spring (153 ± 27 mmol O2 m−2 d−1) and then decreased from spring to late summer (44 ± 18 mmol O2 m−2 d−1). DCR rates increased from winter (−47 ± 18 mmol O2 m−2 d−1) to spring (−97 ± 7 mmol O2 m−2 d−1) and then decreased from spring to late summer (50 ± 7 mmol O2 m−2 d−1). The onset of stratification depended on latitude as well as on the presence of mesoscale structures (eddies), and this largely contributed to the variability of GCP. The trophic status of the POMME area was defined as net autotrophic, with a mean annual net community production rate of +38 ± 18 mmol O2 m−2 d−1, exhibiting a seasonal variation from +2 ± 20 mmol O2 m−2 d−1 to +57 ± 20 mmol O2 m−2 d−1. This study highlights that small organisms (picoautotrophs, nanoautotrophs, and bacteria) are the main organisms contributing to biological fluxes throughout the year and that episodic blooms of microphytoplankton are related to mesoscale structures.

Mesoscale and seasonal variability of community production and respiration in the surface waters of the N.E. Atlantic Ocean

Gross community production (GCP) and dark community respiration (DCR) rates were measured in the N.E. Atlantic Basin (38–45°N and 15°20′–21°20′W) during the Programme Océanographique Multidisciplinaire Méso-Echelle (POMME). Three cruises were conducted over a one-year period (2001), and GCP and DCR were measured at 20 stations using seawater taken from 5 m. In winter, GCP is light limited whereas DCR, which is mainly due to bacteria, is limited by substrate availability. GCP and DCR were under the influence of mesoscale features, with the cyclonic structure enhancing the autotrophy. In spring, light and resource availability remain the major controlling parameters, which are constrained by north–south zonation, rather than mesoscale features. The most productive area is south of 41°N at the start of the bloom and is associated with greater DCR as autotrophs contribute to community respiration. The late-summer period is oligotrophic, which contrasts with the previous winter and spring period, characterised by a large quantity of TOC accumulated (+13.2 μM C from spring to late-summer) and with greater DCR in the southern area. The GCP/DCR ratio greatly varied seasonally, ranging from 0.6 in late summer to 1.3 in winter and 2.4 in spring. These results, even restricted to surface ecosystem metabolism (5 m), strongly suggest that the trophic status of a regional system in the open ocean should be determined over a seasonal cycle.

Variability in plankton community structure, metabolism, and vertical carbon fluxes along an upwelling filament (Cape Juby, NW Africa)

The variability in dissolved and particulate organic matter, plankton biomass, community structure and metabolism, and vertical carbon fluxes were studied at four stations (D 1–D 4), placed along a coastal-offshore gradient of an upwelling filament developed near Cape Juby (NW Africa). The filament was revealed as a complex and variable system in terms of its hydrological structure and distribution of biological properties. An offshore shift from large to small phytoplankton cells, as well as from higher to lower autotrophic biomass, was not paralleled by a similar gradient in particulate (POC) or dissolved (DOC) organic carbon. Rather, stations in the central part of the filament (D 2 and D 3) presented the highest organic matter concentrations. Autotrophic carbon (POC Chl) accounted for 53% (onshore station, D 1) to 27% (offshore station, D 4) of total POC (assuming a carbon to chlorophyll ratio of 50), from which nano- and pico-phytoplankton biomasses (POC A < 10 μm ) represented 14% (D 1) to 79% (D 4) of POC Chl. The biomass of small hetrotrophs (POC H < 10 μm ) was equivalent to POC A < 10 μm , except at D 1, where small autotrophs were less abundant. Dark community respiration ( R d) in the euphotic zone was in general high, almost equivalent to gross production ( P g), but decreasing offshore (D 1–D 4, from 108 to 41 mmol C m −2 d −1). POC sedimentation rates (POC sed) below the euphotic zone ranged from 17 to 6 mmol C m −2 d −1. Only at D 4 was a positive carbon balance observed: P g−( R d + POC sed) = 42 mmol C m −2 d −1. Compared to other filament studies from the NE Atlantic coast, the Cape Juby filament presented lower sedimentation rates and higher respiration rates with respect to gross production. We suggest that this is caused by the recirculation of the filament water, induced by the presence of an associated cyclonic eddy, acting as a trapping mechanism for organic matter. The export capacity of the Cape Juby filament therefore would be constrained to the frequency of the interactions of the filament with island-induced eddies.

Response of coccolithophorid Emiliania huxleyi to elevated partial pressure of CO2 under nitrogen limitation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 261:111-122 (2003) - doi:10.3354/meps261111 Response of coccolithophorid Emiliania huxleyi to elevated partial pressure of CO2 under nitrogen limitation Antoine Sciandra1,*, Jérome Harlay2, Dominique Lefèvre3, Rodolphe Lemée1, Peguy Rimmelin3, Michel Denis3, Jean-Pierre Gattuso1 1Laboratoire d¹Océanographie, Université Mixte de Recherche (UMR) 7093, Centre National de la Recherche Scientifique- Université Pierre et Marie Curie (CNRS-UPMC), BP 28, 06234 Villefranche-sur-mer Cedex, France 2Service d¹Océanographie Chimique et Géochimie des Eaux, Université Libre de Bruxelles, Campus Plaine, CP 208, Boulevard du Triomphe, 1050 Brussels, Belgium 3Laboratoire d¹Océanographie et de Biogéochimie, Centre d'Océanologie de Marseille, Université Mixte de Recherche (UMR) 6535, Centre National de la Recherche Scientifique (CNRS)-Université de la Méditerranée, Case 901, 13288 Marseille Cedex 9, France *Email: sciandra@obs-vlfr.fr ABSTRACT: Precipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange of CO2 at the ocean-atmosphere interface. Previous experiments have demonstrated that, under nutrient-sufficient conditions, doubling the partial pressure of CO2 (pCO2) in seawater‹a likely scenario for the end of the century‹can significantly decrease both the rate of calcification by coccolithophorids and the ratio of inorganic to organic carbon production. The present work investigates the effects of high pCO2 on calcification by the coccolithophore Emiliania huxleyi (Strain TW1) grown under nitrogen-limiting conditions, a situation that can also prevail in the ocean. Nitrogen limitation was achieved in NO3-limited continuous cultures renewed at the rate of 0.5 d-1 and exposed to a saturating light level. pCO2 was increased from 400 to 700 ppm and controlled by bubbling CO2-rich or CO2-free air into the cultures. The pCO2 shift has a rapid effect on cell physiology that occurs within 2 cell divisions subsequent to the perturbation. Net calcification rate (C) decreased by 25% and, in contrast to previous studies with N-replete cultures, gross community production (GCP) and dark community respiration (DCR) also decreased. These results suggest that increasing pCO2 has no noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited. KEY WORDS: Calcification · Carbon fixation · Coccolith · Emiliania huxleyi · Nitrate · Alkalinity · CO2 Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 261. Online publication date: October 17, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Plankton respiration in the Eastern Atlantic Ocean

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 200 m of a latitudinal (32°S–48°N) transect in the Eastern Atlantic Ocean during May/June 1998. The mean mixed layer respiration rate was 2.5±2.1 mmol O 2 m −3 d −1 ( n=119) for the whole transect, 2.2±1.1 mmol O 2 m −3 d −1 ( n=32) in areas where chlorophyll a was <0.5 mg m −3 and 1.5±0.7 mmol O 2 m −3 d −1 ( n=10) where chlorophyll a was <0.2 mg m −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=11). At the time of the study, plankton community respiration exceeded GP in the picoautotroph dominated oligotrophic regions (Eastern Tropical Atlantic [15.5°S–14.2°N] and North Atlantic Subtropical Gyre [21.5–42.5°N]), which amounted to 50% of the stations sampled along the 12,100 km 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.

Plankton community respiration during a coccolithophore bloom

Abstract Plankton dark community respiration (DCR), gross production (GP), bacterial production, protozoan herbivory, and phytoplankton, microzooplankton and heterotrophic bacterial abundance were measured during a bloom of the coccolithophore Emiliania huxleyi. The study, which was conducted in the northern North Sea during June 1999, included a spatial survey and a 6-day Lagrangian time series informed by a sulphur hexafluoride (SF6) tracer-release experiment. E. huxleyi abundance in surface waters ranged from 380 to 3000 cells ml−1, while DCR varied between 2 and 4 mmol O2 m−3 d−1 and GP between 2 and 5 mmol O2 m−3 d−1. Euphotic zone integrated DCR and GP were in approximate balance, with a mean (±SD) P:R ratio of 0.9±0.4 (n=9). However, highest GP occurred at the surface alongside maxima of E. huxleyi, whereas highest rates of DCR occurred at depths of 25–30 m associated with maxima in chlorophyll a and bacterial biomass. DCR was positively correlated with bacterial biomass, microzooplankton biomass, attenuance, particulate organic carbon, and chlorophyll a concentration; and negatively correlated with apparent oxygen utilisation. DCR was not correlated with in situ temperature, dissolved organic carbon concentration or E. huxleyi abundance. A∼100 h incubation of 0.8 μm filtered seawater enabled the estimation of a bacterial respiratory quotient (RQ) and growth efficiency (BGE) from the slopes of the linear regressions of the decrease in dissolved oxygen and increase in dissolved inorganic carbon (DIC) and bacterial carbon with time. During this experiment the bacterial RQ was 0.69 and the growth efficiency was 18%. This measured BGE was used in comparison with literature values to apportion DCR to that associated with bacterial (13–71%), microzooplankton (10–50%), and algal (11–28%) activity. This accounting exercise compared well with measured DCR (to within ±50%), the exact calculation being highly dependent on the BGE used.

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 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 (32°S‐48°N) 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 , CR) prevails in the eastern Atlantic when primary production falls below ~100 mmol O2 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 is found to give a more representative description of the autotrophic (GPP &gt; 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.