31 results on '"Stephen D. Archer"'
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2. Benefits and Challenges of a Stakeholder-Driven Shellfish Toxicity Forecast in Coastal Maine
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Nicholas R. Record, Johnathan Evanilla, Kohl Kanwit, Craig Burnell, Carmen Cartisano, Bryant J. Lewis, Jill MacLeod, Benjamin Tupper, David W. Miller, Adrienne T. Tracy, Carol White, Matt Moretti, Ben Hamilton, Cameron Barner, and Stephen D. Archer more...
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Global and Planetary Change ,Ocean Engineering ,Aquatic Science ,Oceanography ,Water Science and Technology - Abstract
Paralytic shellfish poison (PSP) is a human health concern for shellfish aquaculture and wild harvest. This paper discusses lessons learned from a forecasting program for PSP in coastal Maine, USA, designed based on stakeholder input, and run in an operational mode for the 2021 season. The forecast uses a deep learning algorithm to make site-specific, probabilistic forecasts at a weekly forecast range for toxin levels measured in shellfish tissue. Forecasts had high accuracy in the 2021 season, correctly predicting closure events and locations despite a highly unusual season. Stakeholders reported a positive view of the forecast system, and stakeholder input continues to be of key importance as further modifications are made to the system. There are benefits and challenges to the stakeholder-based design of the system. more...
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- 2022
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3. Saturation Approach to Determine Grazing Mortality in Picoeukaryote and Synechococcus Populations
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Stephen D. Archer, Laura C. Lubelczyk, Moriah Kunes, Kathryn McPhee, Walter Dawydiak, Michael Staiger, Kevin M. Posman, and Nicole J. Poulton
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Global and Planetary Change ,fungi ,Ocean Engineering ,Aquatic Science ,Oceanography ,Water Science and Technology - Abstract
A substantial component of phytoplankton production in the oceans is channeled through protistan grazers but understanding what dictates the magnitude of this process on a regional and temporal basis is limited, in part, by a shortage of experimental options. A novel saturation approach based on the functional response of planktonic grazers to increasing prey abundance was developed using laboratory cultures of the predator-prey combination of Ochromonas danica and Micromonas pusilla and tested in the coastal waters of the Gulf of Maine. In incubation series, 2 μm polystyrene microspheres were used as surrogate prey to generate increasing levels of saturation of predator ingestion rates of natural prey, resulting in increased rates of apparent growth of the picophytoplankton populations. The relationship between level of addition of surrogate prey to apparent growth, consistently provided significant estimates of maximal growth in the absence of grazing and grazing mortality for populations of picoeukaryotes and Synechococcus. Estimates of gross growth and grazing mortality were comparable to results from dilution experiments carried out in the same waters. The saturation approach represents an additional tool to investigate predator-prey interactions in planktonic communities. Further investigations may show that it can be used to quantify group-specific grazing mortality and growth rates beyond coastal waters and in multiple size classes of prey. more...
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- 2022
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4. Limitation of dimethylsulfoniopropionate synthesis at high irradiance in natural phytoplankton communities of the Tropical Atlantic
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Stephen D. Archer, Richard J. Geider, Timothy J Smyth, Jacqueline Stefels, Tracy Lawson, Andrew P. Rees, Ruth L. Airs, and Stefels lab
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0106 biological sciences ,Photoinhibition ,010504 meteorology & atmospheric sciences ,Irradiance ,Aquatic Science ,Biology ,Oceanography ,Dimethylsulfoniopropionate ,01 natural sciences ,chemistry.chemical_compound ,Total inorganic carbon ,SULFURIC-ACID ,Phytoplankton ,MARINE-ALGAE ,DIMETHYL SULFIDE DMS ,Diel vertical migration ,0105 earth and related environmental sciences ,OCEANIC PHYTOPLANKTON ,HIGH-LIGHT ,SEA ,010604 marine biology & hydrobiology ,Carbon fixation ,fungi ,PHOTOINHIBITION ,chemistry ,EMILIANIA-HUXLEYI ,Environmental chemistry ,SUMMER PARADOX ,Dimethyl sulfide ,ULTRAVIOLET-RADIATION - Abstract
Predictions of the ocean-atmosphere flux of dimethyl sulfide will be improved by understanding what controls seasonal and regional variations in dimethylsulfoniopropionate (DMSP) production. To investigate the influence of high levels of irradiance including ultraviolet radiation (UVR), on DMSP synthesis rates (mu DMSP) and inorganic carbon fixation (mu POC) by natural phytoplankton communities, nine experiments were carried out at different locations in the low nutrient, high light environment of the northeastern Tropical Atlantic. Rates of mu DMSP and mu POC were determined by measuring the incorporation of inorganic C-13 into DMSP and particulate organic carbon. Based on measurements over discrete time intervals during the day, a unique mu DMSP vs. irradiance (P vs. E) relationship was established. Comparison is made with the P vs. E relationship for mu POC, indicating that light saturation of DMSP occurs at similar irradiance to mu POC and is closely coupled to carbon fixation on a diel basis. Photoinhibition during the middle of the day was exacerbated by exposure to UVR, causing an additional 55-60% inhibition of both mu DMSP and mu POC at the highest light levels. In addition, decreased production of DMSP in response to UVR-induced photoxidative stress, contrasted with the increased net synthesis of photoprotective xanthophyll pigments. Together these results indicate that DMSP production by phytoplankton in the tropical ocean is not regulated in the short term by the necessity to control increasing photooxidative stress as irradiance increases during the day. The study provides new insight into the regulation of resource allocation into this biogeochemically important, multi-functional compatible solute. more...
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- 2018
5. Virus infection ofEmiliania huxleyideters grazing by the copepodAcartia tonsa
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AI Vermont, Ilana C. Gilg, Stephen D. Archer, AH Leavitt, J. Martínez Martínez, David M. Fields, Sheri A. Floge, JD Waller, and William H. Wilson
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0301 basic medicine ,Ecology ,biology ,ved/biology ,ved/biology.organism_classification_rank.species ,Zoology ,Aquatic Science ,biology.organism_classification ,Virus ,Fishery ,03 medical and health sciences ,030104 developmental biology ,Grazing ,Ecology, Evolution, Behavior and Systematics ,Copepod ,Acartia tonsa ,Emiliania huxleyi - Published
- 2016
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6. Differential gene expression is tied to photochemical efficiency reduction in virally infected Emiliania huxleyi
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William H. Wilson, David M. Fields, Sheri A. Floge, Stephen D. Archer, J. Martínez Martínez, Ilana C. Gilg, AH Leavitt, and AI Vermont
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0301 basic medicine ,Coccolithovirus ,Ecology ,biology ,Chemistry ,Aquatic Science ,biology.organism_classification ,Bioinformatics ,Molecular biology ,Reduction (complexity) ,03 medical and health sciences ,030104 developmental biology ,Gene expression ,Digital polymerase chain reaction ,Ecology, Evolution, Behavior and Systematics ,Emiliania huxleyi - Published
- 2016
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7. Fluorescent Detection of Bromoperoxidase Activity in Microalgae and Planktonic Microbial Communities Using Aminophenyl Fluorescein
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Stephen D. Archer, Janice DeStefano, Daniel P. Witt, Elizabeth A. Cheff, Kevin M. Posman, Albertha Ladina, and Amelia O. Harrison
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0106 biological sciences ,Hypohalite ,010504 meteorology & atmospheric sciences ,lcsh:QH1-199.5 ,Corallina officinalis ,Ocean Engineering ,Aquatic Science ,lcsh:General. Including nature conservation, geographical distribution ,Oceanography ,bromoperoxidase ,01 natural sciences ,chemistry.chemical_compound ,haloperoxidase ,Haloperoxidase ,Fluorescein ,Hydrogen peroxide ,lcsh:Science ,0105 earth and related environmental sciences ,Bromoperoxidase ,Water Science and Technology ,chemistry.chemical_classification ,Global and Planetary Change ,biology ,010604 marine biology & hydrobiology ,microalgae ,fungi ,biology.organism_classification ,diatom ,enzyme activity ,Enzyme ,Diatom ,chemistry ,Biochemistry ,biology.protein ,lcsh:Q ,fluorescent assay - Abstract
Among planktonic communities haloperoxidase enzymes may play a role in the control of intracellular and extracellular reactive oxygen species, in the generation of halogenated organic compounds and in chemical interactions between microbes. We introduce a sensitive fluorometric assay with a large dynamic range that is based on the dearylation of aminophenyl fluorescein (APF) to fluorescein by highly reactive oxygen species. Bromoperoxidase and chloroperoxidase enzymes catalyze the reaction between hydrogen peroxide and halides to generate highly reactive hypohalite intermediates able to dearylate APF. The fundamentals and standardization of the approach are illustrated using a partially purified, vanadium-dependent bromoperoxidase from the red seaweed Corallina officinalis. Laboratory cultures of two polar diatoms, Porosira glacialis and Fragilariopsis cylindrus, are used to illustrate the sensitivity and potential applications of the approach for in vitro, in vivo and in situ measurements of bromoperoxidase activity. These two diatoms differ in biovolume-specific bromoperoxidase activity by 2-orders of magnitude, from 5.4 to 0.044 fmol fluorescein μm-3 h-1, respectively. The approach is also used to investigate the partition of haloperoxidase activity between different size fractions of summer coastal planktonic communities, illustrating that generally more than 50% of the haloperoxidase activity occurred in a >10 μm size fraction that was dominated by diatoms. The assay has the potential to be of value in many aspects of haloperoxidase research, including developing an improved understanding of the roles of haloperoxidase enzymes in microbial planktonic communities. more...
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- 2019
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8. Processes That Contribute to Decreased Dimethyl Sulfide Production in Response to Ocean Acidification in Subtropical Waters
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Patricia A. Matrai, Kerstin Suffrian, Lennart T. Bach, Kevin M. Posman, Peter D. Countway, Stephen D. Archer, Andrea Ludwig, and Ulf Riebesell
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010504 meteorology & atmospheric sciences ,lcsh:QH1-199.5 ,Population ,Ocean Engineering ,ocean acidification ,010501 environmental sciences ,Aquatic Science ,lcsh:General. Including nature conservation, geographical distribution ,Oceanography ,Dimethylsulfoniopropionate ,01 natural sciences ,Mesocosm ,chemistry.chemical_compound ,Nanophytoplankton ,14. Life underwater ,education ,lcsh:Science ,DMSP ,0105 earth and related environmental sciences ,Water Science and Technology ,Global and Planetary Change ,education.field_of_study ,DMS ,fungi ,bacterial metabolism ,subtropical North Atlantic ,Ocean acidification ,phytoplankton composition ,Plankton ,chemistry ,13. Climate action ,Environmental chemistry ,Atmospheric chemistry ,Dimethyl sulfide ,lcsh:Q - Abstract
Long-term time series data show that ocean acidification is occurring in the subtropical oceans. As a component of an in situ mesocosm experiment carried out off Gran Canaria in the subtropical North Atlantic, we examined the influence of ocean acidification on the net production of dimethylsulfide (DMS). Over 23 days under oligotrophic conditions, time-integrated DMS concentrations showed an inverse relationship of −0.21 ± 0.02 nmol DMS nmol−1 H+ across the gradient of H+ concentration of 8.8–23.3 nmol l−1, equivalent to a range of pCO2 of 400–1,252 atm. Proportionally similar decreases in the concentrations of both dissolved and particulate dimethylsulfoniopropionate (DMSP) were observed in relation to increasing H+ concentration between the mesocosms. The reduced net production of DMSP with increased acidity appeared to result from a decrease in abundance of a DMSP-rich nanophytoplankton population. A 35S-DMSP tracer approach was used to determine rates of dissolved DMSP catabolism, including DMS production, across the mesocosm treatments. Over a phase of increasing DMS concentrations during the experiment, the specific rates of DMS production were significantly reduced at elevated H+ concentration. These rates were closely correlated to the rates of net DMS production indicating that transformation of dissolved DMSP to DMS by bacteria was a major component of DMS production. It was not possible to resolve whether catabolism of DMSP was directly influenced by H+ concentrations or was an indirect response in the bacterial community composition associated with reduced DMSP availability. There is a pressing need to understand how subtropical planktonic communities respond to the predicted gradual prolonged ocean acidification, as alterations in the emission of DMS from the vast subtropical oceans could influence atmospheric chemistry and potentially climate, over a large proportion of the Earth's surface. more...
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- 2018
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9. Combining cell sorting with gas chromatography to determine phytoplankton group-specific intracellular dimethylsulphoniopropionate
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Stephen D. Archer, John Stephens, Lindsay J. Butcher, Glen A. Tarran, and Susan A. Kimmance
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biology ,fungi ,Prokaryote ,Aquatic Science ,Cell sorting ,Plankton ,Photosynthesis ,biology.organism_classification ,Synechococcus ,Nanophytoplankton ,Phytoplankton ,Botany ,Seawater ,Ecology, Evolution, Behavior and Systematics - Abstract
An approach combining flow-cytometric fluorescence-activated cell sorting (FACS) of specific phytoplankton groups and subsequent quantification of dimethylsulphoniopropionate (DMSP) content by gas chromatography (GC) is introduced and applied to cultivated microalgae and natural seawater samples. The FACS-GC based method produces statistically robust estimates of the intracellular DMSP content of a variety of phytoplankton groups ranging from prokaryotic Synechococcus spp. to eukaryotic nanophytoplankton. Comparison between FACS and traditional filtration approaches to determine intracellular DMSP content of cultivated microalgae illustrates variable responses between species to the 2 methods. Natural photosynthetic nanoeukaryote populations contained high intracellular DMSP content; comparable to many cultivated prymnesiophyte taxa. A surprisingly high DMSP content was found in natural populations of Synechococcus spp., in contrast to previous values measured in cultivated strains, but possibly confirming the uptake and retention of DMSP by this photosynthetic prokaryote. When combined, the DMSP contributions of each phytoplankton group amounted to between 40 and 57 % of total DMSP in each water sample, with the bulk of the total comprising nanoeukaryote-DMSP. The approach has high potential to provide information that enables better parameterisation of phytoplankton functional types in mechanistic dimethyl sulphide models and to help elucidate the environmental controls that govern the extent and diversity of DMSP production in the oceans. more...
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- 2011
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10. The role of dissolved infochemicals in mediating predator-prey interactions in the heterotrophic dinoflagellate Oxyrrhis marina
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Mark N. Breckels, Stephen D. Archer, Emily C. Roberts, Gill Malin, and Michael Steinke
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Ecology ,Aquatic ecosystem ,Foraging ,Heterotroph ,Dinoflagellate ,Aquatic Science ,Biology ,biology.organism_classification ,Oxyrrhis marina ,Predation ,Phytoplankton ,Selective advantage ,Ecology, Evolution, Behavior and Systematics - Abstract
Microzooplankton are ecologically important grazers of phytoplankton and bacteria in aquatic systems. Inhabiting a three-dimensional realm, the ability of a microzooplankter to detect and respond to infochemical cues from its prey will confer a strong selective advantage. The heterotrophic dinoflagellate Oxyrrhis marina has been repeatedly used to study the effect of infochemicals on foraging success and the results from such investigations have stimulated further research on other microzooplankton. Here, we present a case study that highlights the utility of O. marina for infochemistry research and review current knowledge on its behavioural response to dissolved infochemicals. Through a series of microcapillary assays, we show that 0.1–100 µM source concentrations of the algal secondary metabolite dimethylsulphoniopropionate elicit a motile chemosensory response in O. marina. We outline some of the technical limitations in infochemistry research and provide examples where studies on O. marina resulted in recent progress, before emphasizing the role of the diffusion limited boundary layer or “phycosphere” in chemodetection. The ability of O. marina to detect prey exudates in the phycosphere effectively increases the predator–prey encounter radius and has significant implications to the outcome of encounter rate models. Finally, we introduce a new direction of research that utilizes O. marina as a model microzooplankter to elucidate the function of infochemicals in multi-trophic interactions. more...
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- 2010
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11. Dimethyl sulfoniopropionate and dimethyl sulfide production in response to photoinhibition in Emiliania huxleyi
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Richard J. Geider, Stephen D. Archer, Richard Webster, Ruth L. Airs, and Maria Ragni
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chemistry.chemical_classification ,Photoinhibition ,biology ,fungi ,Aquatic Science ,Oceanography ,biology.organism_classification ,Photosynthesis ,chemistry.chemical_compound ,Light intensity ,chemistry ,Photosynthetically active radiation ,Environmental chemistry ,Xanthophyll ,Botany ,Cloud condensation nuclei ,Dimethyl sulfide ,Emiliania huxleyi - Abstract
The response in intracellular dimethyl sulfoniopropionate (DMSP) and dissolved DMSP and dimethyl sulfide (DMS) concentrations when Emiliania huxleyi was exposed to acute (1-h) increases in photon flux densities of photosynthetically active radiation (PAR) and ultraviolet (UV) radiation was examined in cells acclimated to low light (LL, 30 mmol photons m22 s21) and high light (HL, 300 mmol photons m22 s21). LL-acclimated cells displayed greater photoinhibition, assessed as a decrease in maximum photochemical efficiency (Fv:Fm). Photoinhibition was increased by exposure to UV wavelengths. LL-acclimated cells also exhibited more light dissipation through the xanthophyll cycle, evident as changes in de-epoxidation state. Greater photoinhibition in LL-acclimated cells corresponded with increased accumulation of DMSP of 21% 6 4% relative to initial concentrations, contrasting with a slight decrease of 5% 6 6% in HL-acclimated cells. Exposure to UV appeared to decrease the rates of intracellular accumulation of DMSP. Conversely, PAR + UV exposure stimulated the net production of dissolved DMSP and DMS in both HL-acclimated and LL-acclimated cultures, compared with high PAR alone. The results indicate a direct link between acute photo-oxidative stress and DMSP synthesis by E. huxleyi. The physiological basis for increased release of DMSP and DMS from cells due to high PAR + UV exposure is unclear. However, the timescales of changes in intracellular DMSP, dissolved DMSP, and DMS are consistent with variations in light intensity experienced by phytoplankton in a turbulent mixed layer and are similar to rates of change in photosynthetic parameters associated with photoacclimation. Emission of dimethyl sulfide (DMS) from the oceans may contribute to the nucleation and growth of aerosol particles, enhancing formation of cloud condensation nuclei in the marine boundary layer; and thereby increasing the Earth’s albedo (Shaw 1983; Charlson et al. 1987). DMS is generally supersaturated in oceanic waters and its sea-toair flux is dictated to a large extent by surface seawater concentration and the gas transfer velocity. Understanding more...
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- 2010
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12. Modelling the concentration of exuded dimethylsulphoniopropionate (DMSP) in the boundary layer surrounding phytoplankton cells
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Stephen D. Archer, Michael Steinke, Mark N. Breckels, Gill Malin, Daniel E. Boakes, and Edward A. Codling
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Boundary layer ,chemistry.chemical_compound ,Ecology ,chemistry ,Environmental chemistry ,Metabolite ,Phytoplankton ,Botany ,Aquatic Science ,Plankton ,Ecology, Evolution, Behavior and Systematics - Abstract
Using a steady-state diffusion model, we calculated the concentration of the ecologically relevant algal metabolite dimethylsulphoniopropionate (DMSP) in the phycosphere. Incorporating diffusive losses, the concentration was predicted to be 106-fold lower than previously suggested. more...
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- 2009
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13. Phytoplankton taxa, irradiance and nutrient availability determine the seasonal cycle of DMSP in temperate shelf seas
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Carole A. Llewellyn, James R Fishwick, D.G. Cummings, and Stephen D. Archer
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Chlorophyll a ,Ecology ,biology ,fungi ,Diadinoxanthin ,Dinoflagellate ,Diatoxanthin ,Aquatic Science ,Annual cycle ,biology.organism_classification ,chemistry.chemical_compound ,Water column ,chemistry ,Nitrate ,Phytoplankton ,Botany ,Ecology, Evolution, Behavior and Systematics - Abstract
The influences of physico-chemical and biological variables on the concentrations of di- methyl sulphide (DMS) and its precursor β-dimethylsulphoniopropionate (DMSP) were investigated through an annual cycle in the temperate shelf seas of the western English Channel. Total DMSP to chlorophyll a ratios (DMSPt/chl a) varied seasonally by 40-fold, and DMS and DMSP concentrations became temporally uncoupled, with elevated relative DMS concentrations during spring and mid- summer. Taxonomic succession of high DMSP-producing phytoplankton, including Phaeocystis pouchetii, Scrippsiella trochoidea and Prorocentrum minimum, is apparent in the seasonal pattern of DMSPt concentrations. Peridinin and DMSPt concentrations showed similar seasonal trends (p < 0.0001), illustrating the substantial contribution by dinoflagellate taxa to DMSP production. Summer- time stratification of the water column coincided with increased mixed layer doses of photosyntheti- cally active radiation (PAR), increased surface ultraviolet-B (UVB) irradiance relative to PAR and a de- crease in nitrate and phosphate availability. PAR dose explained 68% of the variability in DMSP/chl a during the seasonal study; whilst nitrate concentrations were inversely related to DMSP/chl a and explained 64% of the variability in log-transformed DMSP/chl a. PAR dose explained only 25% of the variation in DMS concentration, whilst nitrate concentration was inversely related to DMS and explained 49% of the variation in log-transformed DMS concentration. The highly significant relation- ship between DMSP/chl a and PAR dose was similar to those observed for the chlorophyll-specific accumulation of the photoprotective xanthophyll compounds diadinoxanthin and diatoxanthin and the chlorophyll-specific concentrations of UV-absorbing mycosporine-like amino acids. These results lend further, indirect evidence for a photoprotective role of DMSP, possibly associated with physiological stress caused by high PAR and UV radiation and intensified by nutrient limitation. more...
- Published
- 2009
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14. Modified dilution technique to estimate viral versus grazing mortality of phytoplankton: limitations associated with method sensitivity in natural waters
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Stephen D. Archer, William H. Wilson, and Susan A. Kimmance
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Picoeukaryote ,biology ,Serial dilution ,Ecology ,fungi ,Aquatic Science ,Plankton ,Synechococcus ,biology.organism_classification ,Zooplankton ,Dilution ,Animal science ,Grazing ,Phytoplankton ,Ecology, Evolution, Behavior and Systematics - Abstract
This study tested the validity of the modified dilution method approach to partition nat- ural phytoplankton mortality into grazer versus virus-induced fractions. A series of experiments was conducted weekly between August and October 2005 from an offshore site in the western English Channel. The phytoplankton community during this period was dominated numerically by Syne- chococcus spp. and picoeukaryotes. Despite highly significant regression results, no discernible viral lysis of Synechococcus spp. or picoeukaryote populations was apparent during the 3 mo period. Microzooplankton grazing was the major source of mortality for Synechococcus spp. and picoeukary- otes during this time. Statistical analysis indicates that, using our experimental design, the modified dilution approach was not sensitive enough to be able to measure significant viral lysis during the experimental period. Sensitivity analysis indicated that viral mortality occurred at rates of more...
- Published
- 2007
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15. Modelling of the seasonal patterns of dimethylsulphide production and fate during 1989 at a site in the North Sea
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Jerry Blackford, Philip D. Nightingale, Francis J. Gilbert, J. Icarus Allen, and Stephen D. Archer
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Geography ,Forestry ,Aquatic Science ,North sea ,Ecology, Evolution, Behavior and Systematics - Abstract
Notre etude de modelisation vise a placer dans un cycle annuel nos connaissances de la biogeochimie du sulfure de dimethyle (DMS), un gaz qui affecte le climat, dans les eaux marines superficielles. Nous avons incorpore les processus impliques dans la production et le sort du DMS et de son precurseur le β-dimethylsulfoniopropionate (DMSP), un produit de synthese du phytoplancton, dans le modele ERSEM (« European Regional Seas Ecosystem Model »), un modele physique, complexe, unidimensionel et couple de l'ecosysteme et dans le modele GOTM (« General Ocean Turbulence Model »). Nous avons ainsi mis au point un modele de la biogeochimie du DMS applique a des donnees de 1989 provenant d'un site a stratification saisonniere de la mer du Nord. Nous l'avons valide avec des donnees de concentrations de nutriments, de biomasses biologiques, de production biologique, de concentrations de DMS et de DMSP et de flux de DMS de la mer a l'atmosphere obtenues en 1989 dans le cadre du Projet de la mer du Nord (« North Sea Project »). Les resultats de cette validation demontrent que des modeles complexes de l'ecosysteme, combines a un reseau complet des processus qui controlent la production et le sort du DMSP et du DMS, peuvent representer de facon exacte la biogeochimie du DMS. Le modele fournit des perspectives interessantes sur l'impact du forcage physique, qui varie d'une saison a l'autre, sur les contributions relatives des divers processus particuliers a la production du DMS et a son passage de la mer a l'atmosphere. more...
- Published
- 2004
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16. Microzooplankton grazing in Phaeocystis and diatom-dominated waters in the southern North Sea in spring
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Peter H. Burkill, Stephen D. Archer, Jacqueline Stefels, Claire E. Stelfox-Widdicombe, and Elzenga lab
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ATLANTIC ,IMPACT ,DUTCH COASTAL WATERS ,PRYMNESIOPHYCEAE ,Aquatic Science ,Oceanography ,PLANKTONIC FOOD-WEB ,Zooplankton ,Algal bloom ,Grazing pressure ,seawater dilution ,microzooplankton ,Grazing ,Phytoplankton ,grazing ,chlorophyll ,Ecology, Evolution, Behavior and Systematics ,FEEDING RATES ,Biomass (ecology) ,biology ,Ecology ,PHYTOPLANKTON BLOOM ,biology.organism_classification ,Diatom ,Productivity (ecology) ,POUCHETII HAPTOPHYCEAE ,ZOOPLANKTON ,GROWTH ,Phaeocystis globosa ,North Sea - Abstract
The impact of microzooplankton grazing upon phytoplankton production was quantified in surface waters of the Southern Bight of the North Sea, during April 1998. Two sites were studied in order to examine the impact of microzooplankton grazing on phytoplankton communities dominated by either Phaeocystis globosa and large phytoplankton or small phytoplankton taxa. The nearshore site was characterised by a phytoplankton community comprised mainly of P. globosa and chains of diatoms with high productivity (av. 346 F 185 AgC l � 1 d � 1 ) and biomass (280 F 171 AgC l � 1 d � 1 ). In contrast, in the offshore waters relatively small diatoms dominated the phytoplankton where productivity and biomass were more than ca. five times lower than in nearshore waters. Contrary to expectations, the nearshore site supported a high biomass of microzooplankton (av. 22.4 F 10.6 AgC l � 1 d � 1 ) which was dominated by large heterotrophic dinoflagellates, mostly Gyrodinium cf. spirale. Offshore the microzooplankton community contained one-third the biomass of the nearshore community and was dominated by smaller individuals, in particular oligotrich ciliates, Strombidium spp. Dilution experiments were conducted in order to quantify phytoplankton growth and losses due to microzooplankton grazing in the more...
- Published
- 2004
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17. Is dimethyl sulphide production related to microzooplankton herbivory in the southern North Sea?
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Stephen D. Archer, Claire E. Stelfox-Widdicombe, Peter H. Burkill, and Gill Malin
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Biogeochemical cycle ,Herbivore ,Ecology ,biology ,Sulfur cycle ,Aquatic Science ,Particulates ,biology.organism_classification ,Zooplankton ,Oceanography ,Algae ,Grazing ,Phytoplankton ,Ecology, Evolution, Behavior and Systematics - Abstract
Microzooplankton herbivory is considered to be a key process by which dimethylsulphoniopropionate (DMSP) in phytoplankton is transformed to climatically active dimethyl sulphide (DMS). However, there is little firm evidence to show that this occurs in natural waters. We used direct measurements of microzooplankton grazing rates and net DMS production in the southern North Sea to examine the impact of herbivory on DMS production. Estimates of the particulate DMSP ingested by microzooplankton in the form of Phaeocystis sp. were found to account for the DMS production rates observed. more...
- Published
- 2003
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18. Direct estimates of the contribution of viral lysis and microzooplankton grazing to the decline of a Micromonas spp. population
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Claire Evans, Stéphan Jacquet, William H. Wilson, and Stephen D. Archer
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0106 biological sciences ,0303 health sciences ,Chlorophyll a ,education.field_of_study ,010604 marine biology & hydrobiology ,Population ,Aquatic Science ,Biology ,biology.organism_classification ,01 natural sciences ,Grazing pressure ,Mesocosm ,Dilution ,03 medical and health sciences ,chemistry.chemical_compound ,Animal science ,chemistry ,Grazing ,Botany ,Phytoplankton ,education ,Ecology, Evolution, Behavior and Systematics ,030304 developmental biology ,Micromonas - Abstract
During a mesocosm study in Raunefjorden, Norway, a Micromonas spp. population, ini- tially showing exponential net growth, dramatically declined after Day 4 of the experiment. Using a modification of the dilution approach originally developed to quantify grazing by microzooplankton on phytoplankton, it was possible to partition the mortality of Micromonas spp. between grazing and viral lysis on Days 5, 6 and 7 during the population decline. Parallel dilution experiments were car- ried out in which 0.2 µm- and 10 kDa-filtered water was used as the diluents. In this way, gradients of grazing pressure (0.2 µm series) and grazing pressure + viral concentration (10 kDa series) were produced. Model 1 linear regression of the fraction of whole water versus the apparent growth rate of chlorophyll a and Micromonas spp. provided an estimate of mortality in the 0.2 µm and 10 kDa dilution series. On Days 5, 6 and 7, the slopes of the linear regressions of 0.2 µm and 10 kDa dilution series were significantly different at p = 0.083, 0.001 and 0.093 respectively. From the differences in slope between the series, estimates of viral mortality amounted to a turnover rate of the Micromonas spp. standing stocks of 10, 25 and 9% d -1 . This compares to a turnover rate by the microzooplankton of 48, 26 and 23% d -1 . On all 3 d the combined viral lysis and grazing mortality exceeded estimates of the potential production of Micromonas spp., in part accounting for the population decline. This study demonstrates that the dilution approach can be adapted to directly determine virus-induced mortality rates of specific phytoplankton. However, further work is required to determine how the specificity of viral infection and variety of viral infection cycles affect the results of this modified dilution approach when applied to other phytoplankton taxa and communities. more...
- Published
- 2003
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19. DMS production in a coccolithophorid bloom: evidence for the importance of dinoflagellate DMSP lyases
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Gill Malin, Stephen D. Archer, Peter S. Liss, Peter H. Burkill, and Michael Steinke
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Biogeochemical cycle ,biology ,Phototroph ,Dinoflagellate ,Aquatic Science ,biology.organism_classification ,chemistry.chemical_compound ,Peridinin ,chemistry ,Phytoplankton ,Botany ,Bloom ,Lyase activity ,Ecology, Evolution, Behavior and Systematics ,Emiliania huxleyi - Abstract
During an experiment in the North Atlantic in June 1998, water samples were collected approximately 400 km south of Iceland inside and outside of a bloom of the coccolithophorid Emilia- nia huxleyi. In vitro dimethylsulphoniopropionate (DMSP) lyase activity (DLA) was quantified using gas chromatography and found to vary from 0.1 to 142.3 nM dimethyl sulphide (DMS) h -1 . Inside the bloom area the majority of DLA (> 74%) occurred in particles >10 µm, indicating that E. huxleyi (5 to 7 µm diameter) made only a minor contribution to total DLA. In surface waters, phototrophic dino- flagellates (>10 µm) made up a high proportion of the total phytoplankton biomass (~27%) towards the end of the coccolithophorid bloom and may have been the source of most of the DLA. This was also indicated by a significant correlation (p < 0.02) between DLA and the concentration of peridinin, a pigment used as a chemotaxonomic marker for dinophytes. The data presented here are the first field measurements of DLA in a coccolithophorid bloom and suggest that even a relatively low con- centration of photosynthetic dinoflagellates larger than 10 µm (during our study 18 to 105 cells ml -1 ) may contribute significantly to DMS production. Although dinoflagellates are recognised as an important source of particulate DMSP, recognition of their significance for DMS production in the field has previously been limited to a few observations in highly concentrated coastal and shelf blooms. Very little information exists on DLA in dinophytes and further investigations are warranted in order to improve our understanding of the biogeochemical and ecophysiological significance of DMSP lyases in this group of phytoplankton. more...
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- 2002
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20. Production and turnover of particulate dimethylsulphoniopropionate during a coccolithophore bloom in the northern North Sea
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Glen A. Tarran, Peter H. Burkill, Claire E. Widdicombe, Andrew P. Rees, and Stephen D. Archer
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Chlorophyll a ,biology ,Coccolithophore ,Heterotroph ,Aquatic Science ,Particulates ,biology.organism_classification ,chemistry.chemical_compound ,Oceanography ,chemistry ,Environmental chemistry ,Phytoplankton ,Oligotrich ,Bloom ,Ecology, Evolution, Behavior and Systematics ,Emiliania huxleyi - Abstract
Dimethylsulphoniopropionate (DMSP) synthesised by phytoplankton is the principal precursor of the climatically active gas dimethyl sulphide (DMS). The rates of production of particulate DMSP (DMSPp) and turnover by microzooplankton were determined in surface waters of the northern North Sea, using a dilution approach. The phytoplankton communities were characterised by DMSP-rich taxa including Emiliania huxleyi and Prorocentrum minimum and DMSPp:chlorophyll a (chl a) ratios of 64 to 162 nM ?g-1. Microzooplankton biomass varied from 25.5 to 56.7 ?g C l-1 and was dominated by oligotrich ciliates and heterotrophic dinoflagellates. DMSPp production rates ranged from 14.8 to 45.6 nM d-1 and represent a doubling time of the ambient DMSPp pool of between 1.2 and 3.1 d. Consumption rates of DMSPp by microzooplankton varied between 11.4 and 59.9 nM d-1 and were equivalent to turnover rates of the ambient DMSPp pool of between 16 and 43% d-1. In general, production rates of DMSPp were lower than those of chl a and E. huxleyi, with respective mean doubling times of 1.9, 1.5 and 1.3 d. Loss rates due to grazing were similar for DMSPp and E. huxleyi but generally significantly lower than those of the bulk phytoplankton, with mean turnover rates of 31, 30 and 40% d-1 of the standing stock of DMSPp, E. huxleyi and chl a, respectively. E. huxleyi contributed an estimated 2 to 25% of the total DMSPp production and 6 to 23% of the DMSPp ingested by microzooplankton, indicating the importance of other phytoplankton to DMSPp dynamics in ŒE. huxleyi blooms¹. At the depths sampled, DMSPp production was closely coupled to primary production and was equivalent to approximately 11% of the carbon fixation. DMSPp may be an important component of the diets of microzooplankton. Ingested DMSPp could have provided 2 to 3% of the microzooplankton carbon demand and 26 to 44% of their sulphur demand. DMSPp production and turnover rates were closely matched and suggest that in these waters microzooplankton grazing may be the principal determinant of the fate of DMSPp. The quantity of ŒDMSP¹ excreted by microzooplankton, calculated from ingestion rates, biomass and assumed growth rates and growth efficiencies, ranged from 8.0 to 41.9 nM d-1. This is equivalent to 13 to 35% d-1 of the DMSPp standing stocks and sufficient to support a daily turnover of the DMS plus dissolved DMSP (DMS+DMSPd) pool. more...
- Published
- 2001
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21. A dilution approach to quantify the production of dissolved dimethylsulphoniopropionate and dimethyl sulphide due to microzooplankton herbivory
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Stephen D. Archer, Claire E. Stelfox-Widdicombe, Gillian Malin, and Peter H. Burkill
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biology ,Dinoflagellate ,Aquatic Science ,Plankton ,biology.organism_classification ,Oxyrrhis marina ,Grazing pressure ,Dilution ,Isochrysis galbana ,Oceanography ,Nanophytoplankton ,Environmental chemistry ,Grazing ,Environmental science ,Ecology, Evolution, Behavior and Systematics - Abstract
A dilution approach for quantifying the grazing-mediated production of dissolved di- methylsulphoniopropionate (DMSPd) and dimethyl sulphide (DMS) was tested using laboratory cul- tures and in natural marine waters. We attempted to make simultaneous estimates of microzoo- plankton grazing rate and grazing-mediated production of DMS and DMSPd. In the laboratory, the dinoflagellate Oxyrrhis marina grazed on the prymnesiophyte Isochrysis galbana at a rate equivalent to a turnover of 57% d -1 of the standing stock. Three experiments using natural waters are presented; 1 in the southern North Sea on 13 April 1998 and 2 in the Iceland Basin on 27 June and 4 July 1998. In all cases there was significant microzooplankton grazing with a turnover of 20% d -1 of the chloro- phyll a in the southern North Sea on 13 April and 19 and 15% d -1 of the nanophytoplankton on 27 June and 4 July in the Iceland Basin, respectively. Production rates of DMS, DMSPd and DMS+DMSPd due to grazing were calculated from the slope of the regression between algal-specific production and the level of dilution, a proxy of the grazing pressure. DMS+DMSPd production rates due to microzooplankton grazing of 31 ± 6, 28 ± 2, 14 ± 3 and 10 ± 1 nM d -1 (± SE), were measured in the laboratory and on 13 April, 27 June and 4 July. These values represent a conversion of 19, 14, 15 and 9% d -1 of the standing stock of DMSPp to DMS+DMSPd. The potential impact of bacterial metabolism of DMS and DMSPd on estimates of grazing mediated production together with other competing production/loss processes are discussed. We suggest that in marine surface waters micro- zooplankton grazing plays an important role in the generation of the dissolved pool of DMS+DMSPd. more...
- Published
- 2001
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22. Impact of microzooplankton on the progression and fate of the spring bloom in fjords of northern Norway
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Jacqueline Stefels, P. G. Verity, Stephen D. Archer, and Elzenga lab
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PLANKTON COMMUNITY ,PELAGIC ECOSYSTEMS ,Population ,Fjord ,GONAD MATURATION ,Aquatic Science ,Biology ,Zooplankton ,Norwegian fjords ,Grazing pressure ,Animal science ,METRIDIA-LONGA LUBBOCK ,OVERWINTERING TACTICS ,SEASONAL PATTERNS ,Nanophytoplankton ,Phytoplankton ,grazing ,education ,Ecology, Evolution, Behavior and Systematics ,geography ,education.field_of_study ,geography.geographical_feature_category ,Ecology ,plankton ,LABELED ALGAE FLA ,Spring bloom ,spring bloom ,ECOLOGICAL INVESTIGATIONS ,ZOOPLANKTON COMMUNITY ,Clearance rate - Abstract
The objective of the study was to determine the role of microzooplankton in the fate of primary production and progression of the spring phytoplankton bloom in high latitude fjords. The 3 fjords, Balsfjord, Malangen and Ullsfjord (Norway), varied in oceanic influence and in the rate of development of the spring bloom. The abundance of Phaeocystis pouchetii was relatively low in the spring of 1997 compared to previous years, and diatoms dominated the biomass of the phytoplankton assemblage in all 3 fjords. The mean biomass of microzooplankton in the top 20 m averaged 72, 66 and 80 mg C m -3 and values integrated to 170 m averaged 4560, 4450 and 6820 mg C m -2 in Balsfjord, Malangen and Ullsfjord, respectively. The composition of the microzooplankton was consistent among the fjords and over time, with the proportion of biomass split evenly between nanoflagellates, dinoflagellates and ciliates. Grazing rates of the microzooplankton community were measured with the dilution technique. The impact of microzooplankton grazing was similar among the fjords, accounting for on average 68, 63 and 55% of the production of the < 200 µm phytoplankton in Bals- fjord, Malangen and Ullsfjord, respectively. When integrated to 20 m, based on a microzooplankton biomass-specific ingestion rate, microzooplankton grazing accounted for an estimated 12 to 26% of the gross primary production. However, this does not account for the carbon requirements of a sub- stantial proportion of the microzooplankton that occurred below 20 m. Clearance rates by ciliates of nanophytoplankton cells of a similar size to the single cells of P. pouchetii were determined from the uptake rates of fluorescently labelled algae (FLA). Generally, the taxa of ciliates that were found to ingest FLA accounted for ♢ 50% of the abundance of the ciliate population in each fjord. Taxon-spe- cific ciliate clearance rates of FLA in surface waters varied with ciliate size from 5.6 to 1.3 µl cell -1 h -1 . The FLA-consuming ciliate population cleared a total of 27 〈 10 3 to 141 〈 10 3 µl l -1 d -1 in surface waters. The ingestion rates of the FLA-consuming ciliates were equivalent to between 11 and 29% of the total microzooplankton consumption. It is possible that the grazing pressure exerted by the micro- zooplankton on single cells and small colonies was high enough to decrease the overall competitive- ness of the P. pouchetii populations and contribute to their low abundance. more...
- Published
- 2000
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23. Microbial dynamics in coastal waters of East Antarctica:plankton production and respiration
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Carol V. Robinson, Stephen D. Archer, and Peter J. le B. Williams
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Chlorophyll a ,Ecology ,biology ,fungi ,Bacterioplankton ,Aquatic Science ,Plankton ,biology.organism_classification ,Respiratory quotient ,chemistry.chemical_compound ,Cryptomonas ,Oceanography ,chemistry ,Environmental chemistry ,Dissolved organic carbon ,Respiration ,Phytoplankton ,Ecology, Evolution, Behavior and Systematics - Abstract
The rates of plankton community production and respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen and the incorporation of (NaHCO3)-C-14 at a coastal site in East Antarctica between 16 December 1993 and 12 February 1994. The breakout of seasonal fast ice was associated with a succession of dominant phytoplankton from Cryptomonas to Phaeocystis to a diatom assemblage. Gross production reached 33 mmol C m(-3) d(-1) and C-14 incorporation peaked at 24 mmol C m(-3) d(-1) on 23 January 1994, at the time of the chlorophyll a maximum (22 mg chi a m(-3)). Dark community respiration reached its maximum (13 mmol C m(-3) d(-1)) 4 d later. Photosynthetic rates calculated from C-14 incorporation were significantly lower (17 to 59%) than rates of gross production. The derivation of plankton processes from changes in both dissolved oxygen and dissolved inorganic carbon allowed the direct measurement of photosynthetic and respiratory quotients. A linear regression of all data gave a photosynthetic quotient of 1.33 +/- 0.23 and a respiratory quotient of 0.88 +/- 0.14. Concurrent determinations of bacterial, heterotrophic dinoflagellate, nanoflagellate and ciliate respiration could account for 15 to 58% of measured dark-community respiration. This study has improved the sparse data set of plankton respiration measurements, confirmed that heterotrophic respiration is a significant process in the carbon flux of coastal Antarctic waters and achieved a first apportionment of community respiration to the major microbial groups in this region more...
- Published
- 1999
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24. Microbial dynamics in coastal waters of East Antarctica:herbivory by heterotrophic dinoflagellates
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Stephen D. Archer, Michael A. Sleigh, Peter H. Burkill, and Rjg Leakey
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Ecology ,biology ,Dinoflagellate ,Aquatic Science ,biology.organism_classification ,Algal bloom ,Food web ,Water column ,Grazing ,Phytoplankton ,Botany ,Autotroph ,Clearance rate ,Ecology, Evolution, Behavior and Systematics - Abstract
Heterotrophic dinoflagellates and their herbivory were quantified at a coastal site in East Antarctica in the vicinity of the Australian Antarctic station of Davis (68° 35' S, 77° 58' E). The study period, 14 January to 11 February 1994, coincided with the growth and decline of a diatom-dominated phytoplankton bloom. Nine taxa of heterotrophic dinoflagellates, including 2 naked and 7 armoured forms, were identified and selected for the determination of standing stock and grazing rates. All 9 taxa selected for grazing rate measurements showed an increase in abundance and biomass during the phytoplankton bloom. Total abundance and biomass increased exponentially from 14 January to reach a maximum abundance, when the 9 taxa were combined, of 46400 cells l-1 on the 31 January, equivalent to a standing stock of 114.5 µg C l-1. Taxon-specific grazing rates were determined at in situ predator and prey concentrations by tracing 14C through a 3 compartment (water, phytoplankton, heterotrophic dinoflagellate) model. Mean taxon-specific clearance rates varied more than 10-fold from 0.028 µl cell-1 h-1 in Diplopeltopsis spp. to 0.318 µl cell-1 h-1 in a Protoperidinium sp. In contrast, mean taxon-specific rates of ingestion varied only 3-fold from 0.72 pg chl a cell-1 h-1 in Diplopeltopsis spp. to 2.38 pg chl a cell-1 h-1 in the same Protoperidinium sp. The total ingestion rate of the 9 taxa was 29.7 ng chl a l-1 h-1 on 31 January, of which 92% was consumed by the 3 most abundant taxa, Gyrodinium sp.1, Gyrodinium sp.2 and Diplopeltopsis spp. This activity represented 6.7% of the water column cleared, 4.8% of autotrophic biomass and 25% of daily primary production ingested per day. The estimated rates of specific ingestion and growth of heterotrophic dinoflagellates were lower in the coastal waters of East Antarctica than in laboratory studies carried out at higher temperatures. However, when the environmental parameters, predator size and prey type and concentration are taken into account, values measured in the present study are tenable, comparing well with other in situ measurements. Furthermore, the estimates of grazing impact on phytoplankton biomass and production illustrate that heterotrophic dinoflagellates play an important part in the biotic control of phytoplankton production and therefore of carbon flux through the food web of coastal waters of East Antarctica. more...
- Published
- 1996
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25. Microbial ecology of sea ice at a coastal Antarctic site:community composition, biomass and temporal change
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Peter H. Burkill, Rjg Leakey, Michael A. Sleigh, CJ Appleby, and Stephen D. Archer
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geography ,education.field_of_study ,Biomass (ecology) ,geography.geographical_feature_category ,Ecology ,biology ,Population ,Aquatic Science ,biology.organism_classification ,Diatom ,Oceanography ,Fast ice ,Microbial population biology ,Epiphytic bacteria ,Sea ice ,Environmental science ,Autotroph ,education ,Ecology, Evolution, Behavior and Systematics - Abstract
The coastal sea ice in the vicinity of Davis Station, Antarctica (68* 35' S, 77* 58' E), supported a diverse microbial community which varied in composition and biomass in response to increasing insolation and temperature during the austral summer. To understand more fully the fate of photosynthetically fixed carbon in sea ice, we examined the dynamics of community composition, biomass and production in autotrophs, heterotrophic protozoa and bacteria. The microbial community inhabiting the bottom few centimeters of land fast ice differed markedly from the interior communities in taxonomic composition and biomass and in the timing and fate of production. Total microbial biomass integrated throughout the ice depth declined during the season from a mean of 1150 mg C m-2 on 17 November to 628 mg C m-2 by 22 December. This largely reflected a decrease in the biomass of the bottom ice community which was dominated by the diatom Entomoneis spp. In contrast, the biomass of the interior ice community increased during summer and was dominated by autotrophic forms more...
- Published
- 1996
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26. Microbial dynamics in coastal waters of East Antarctica:bacterial production and nanoflagellate bacterivory
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Stephen D. Archer, Jonathan Grey, and Raymond J.G. Leakey
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Biomass (ecology) ,Ecology ,Abundance (ecology) ,Grazing ,Heterotroph ,East antarctica ,Aquatic Science ,Biology ,Clearance rate ,Bay ,Ecology, Evolution, Behavior and Systematics ,Thymidine incorporation - Abstract
Bacterial production and heterotrophic nanoflagellate (HNAN) bacterivory were determined concurrently with measurements of abundance and biomass at weekly intervals between 30 December 1993 and 11 February 1994 at a shallow, coastal location in Prydz Bay, eastern Antarctica. Bacterial production was measured by [3H]thymidine incorporation and HNAN bacterivory by the uptake of fluorescently labelled bacteria. Bacterial abundance, biomass and production ranged from 2 to 8 x 108 l-1, 13 to 64 µg C l-1 and 8 to 14 µg C l-1 d-1, respectively, with maximum values recorded in mid January. The HNAN community comprised choanoflagellate, non-collared and colonial taxa, with non-collared forms dominating abundance and biomass in late January and early February. Total HNAN abundance and biomass ranged from 1.6 to 4.2 x 106 l-1 and 8 to 16 µg C l-1, respectively. HNAN cellular ingestion and clearance rates differed between taxa with maximum rates of 8.28 particles cell-1 h-1 and 9.32 nl cell-1 h-1 recorded for large non-collared forms. During the study period the HNAN community grazed 0.9 to 4.7 µg bacterial C l-1 d-1, equivalent to 3 and 12% of bacterial biomass, and 10 and 36% of daily bacterial production; however, these values are likely to be minimal estimates and grazing impact may have been higher on occasion. Choanoflagellates were responsible for much of the grazing impact at the beginning of the study period, while non-collared HNAN were the dominant grazers in late January and early February. The HNAN community therefore appears to graze substantial bacterial production in Antarctic coastal waters during the austral summer, although alternative sources of bacterial mortality are likely to be of importance. more...
- Published
- 1996
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27. Air-sea exchange of dimethylsulfide in the Southern Ocean: Measurements from SO GasEx compared to temperate and tropical regions
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Stephen D. Archer, Christopher W. Fairall, Byron Blomquist, Mingxi Yang, and Barry J. Huebert
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Atmospheric Science ,Ecology ,Eddy covariance ,Paleontology ,Soil Science ,Breaking wave ,Flux ,Tropics ,Forestry ,Aquatic Science ,Oceanography ,Thermal diffusivity ,chemistry.chemical_compound ,Geophysics ,chemistry ,Space and Planetary Science ,Geochemistry and Petrology ,Carbon dioxide ,Earth and Planetary Sciences (miscellaneous) ,Temperate climate ,Seawater ,Geology ,Earth-Surface Processes ,Water Science and Technology - Abstract
[1] In the Southern Ocean Gas Exchange Experiment (SO GasEx), we measured an atmospheric dimethylsulfide (DMS) concentration of 118 ± 54 pptv (1σ), a DMS sea-to-air flux of 2.9 ± 2.1 μmol m−2 d−1 by eddy covariance, and a seawater DMS concentration of 1.6 ± 0.7 nM. Dividing flux by the concurrent air-sea concentration difference yields the transfer velocity of DMS (kDMS). The kDMS in the Southern Ocean was significantly lower than previous measurements in the equatorial east Pacific, Sargasso Sea, northeast Atlantic, and southeast Pacific. Normalizing kDMS for the temperature dependence in waterside diffusivity and solubility results in better agreement among various field studies and suggests that the low kDMS in the Southern Ocean is primarily due to colder temperatures. The higher solubility of DMS at a lower temperature results in greater airside control and less transfer of the gas by bubbles formed from breaking waves. The final normalized DMS transfer velocity is similar to k of less soluble gases such as carbon dioxide in low-to-moderate winds; in high winds, DMS transfer velocity is significantly lower because of the reduced bubble-mediated transfer. more...
- Published
- 2011
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28. Marked seasonality in the concentrations and sea-to-air flux of volatile iodocarbon compounds in the western English Channel
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D.G. Cummings, Philip D. Nightingale, M.I. Liddicoat, Stephen D. Archer, and Laura Goldson
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Atmospheric Science ,Bromoiodomethane ,Soil Science ,Flux ,chemistry.chemical_element ,Aquatic Science ,Oceanography ,Iodine ,Late summer ,chemistry.chemical_compound ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,medicine ,Diiodomethane ,Earth-Surface Processes ,Water Science and Technology ,Hydrology ,Ecology ,Paleontology ,Forestry ,Seasonality ,Chloroiodomethane ,medicine.disease ,Geophysics ,chemistry ,Space and Planetary Science ,Environmental chemistry ,Seawater - Abstract
[1] In the first seasonal study of volatile iodinated organic compounds (VICs) in the open sea, concentrations of five VICs were measured approximately weekly at four depths, over 20 months from July 2002 to April 2004, in the western English Channel. Seawater concentrations varied seasonally by an order of magnitude for all five compounds, with winter minima and, generally, late summer/autumn maxima. The average contribution to the dissolved VIC pool was chloroiodomethane (39%), diiodomethane (33%), iodomethane (22%), iodoethane (6%), and bromoiodomethane (4%). Total sea-to-air flux of iodine atoms carried by the VICs (15.5 mmol I m � 2 yr � 1 ) was approximately fourfold higher than that for iodomethane alone. This contrasts with previous studies that indicated that iodomethane was the main vector of iodine away from macroalgal beds. The estimated sea-to-air flux takes into account the significant airside control of the gas exchange of certain VICs, particularly diiodomethane; for which a 30% reduction in average daily flux was observed when an additional airside transfer velocity was included in the calculations. Because of their high reactivity, chloroiodomethane and diiodomethane are likely to drive the atmospheric organic iodine chemistry over these shelf seas, rather than the monohalogenated VICs. more...
- Published
- 2007
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29. Microearthquakes on the Endeavour segment of the Juan de Fuca Ridge
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William S. D. Wilcock, G. M. Purdy, and Stephen D. Archer
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Atmospheric Science ,geography ,Focal mechanism ,geography.geographical_feature_category ,Ecology ,Hypocenter ,P wave ,Paleontology ,Soil Science ,Forestry ,Mid-ocean ridge ,Aquatic Science ,Induced seismicity ,Oceanography ,Geophysics ,Ridge push ,Space and Planetary Science ,Geochemistry and Petrology ,Abyssal hill ,Earth and Planetary Sciences (miscellaneous) ,Microearthquake ,Geology ,Seismology ,Earth-Surface Processes ,Water Science and Technology - Abstract
[1] We report the results of a 55-day microearthquake experiment on the Endeavour segment of Juan de Fuca Ridge. The network covered a 5-km section of the ridge axis centered on the Main vent field and extended 15-km off axis on the west flank. The ridge axis and flanks were seismically active, and 1750 earthquakes were located with a minimum of five travel time picks including at least one S wave. Over half the earthquakes occurred in swarms, and a waveform cross-correlation technique was used to obtain relative locations. On the western flank, the hypocenters for four swarms at midcrustal depths are compatible with steeply dipping fault planes that strike at 035–050°N and oblique to the abyssal hills. Focal mechanisms determined from P wave first motions and P/S amplitude ratios are predominantly strike-slip with north-south compression and appear to be affected by the reorganization of the Explorer plate. Earthquakes beneath the ridge axis are concentrated in a band of intense seismicity at 1.5–3.5 km depth. To the north of High Rise vent field, the seismicity defines a plane striking parallel to the ridge axis and dipping east at 70° and the earthquakes appear to extend beneath an axial reflector previously imaged at 2.3 km depth. Farther south, the hypocenters are not compatible with a single fault plane. Focal mechanisms are characterized by subhorizontal tension axes oriented in all directions except parallel to the ridge and suggest a stress field that is about equally influenced by ridge spreading and hydrothermal cooling. more...
- Published
- 2002
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30. Coupled dynamics of dimethylsulfoniopropionate and dimethylsulfide cycling and the microbial food web in surface waters of the North Atlantic
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Stephen D. Archer, Carlos Pedrós-Alió, Claire E. Stelfox-Widdicombe, Linda Gilpin, and Rafael Simo
- Subjects
Biogeochemical cycle ,Microbial food web ,Bacterioplankton ,Aquatic Science ,Plankton ,Oceanography ,Dimethylsulfoniopropionate ,chemistry.chemical_compound ,chemistry ,Phytoplankton ,Dissolved organic carbon ,Environmental science ,Dimethyl sulfide - Abstract
Oceanic dimethylsulfide (DMS), the main natural source of sulfur to the global atmosphere, is suggested to play a key role in the interaction between marine biota and climate. Its biochemical precursor is dimethylsulfoniopropionate (DMSP), a globally distributed, intracellular constituent in marine phytoplankton. During a multidisciplinary Lagrangian experiment in the subpolar North Atlantic, we determined the fluxes of DMSP and DMS through phytoplankton, microzooplankton, and bacterioplankton and compared them with concurrent carbon and sulfur fluxes through primary and secondary productions, grazing, and release and use of dissolved organic matter. We found that DMSP and derivatives contributed most (48-100%) of the sulfur fluxes and 5-15% of the carbon fluxes. Our findings highlight DMSP as a prominent player in pelagic biogeochemical pumps, especially as a major carrier in organic sulfur cycling. Also, our results illustrate the key role played by microzooplankton and heterotrophic bacteria (hence the microbial food web) in controlling the amount of phytoplanktonic DMSP that ultimately vents to the atmosphere in the form of DMS. more...
31. A Lagrangian biogeochemical study of an eddy in the Northeast Atlantic
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M Hamren-Larssen, J.F. Read, P Hadziabdic, deGrandpre, Peter S. Liss, L. Spokes, Wendy Broadgate, AJ Kettle, Linda Gilpin, Stephen D. Archer, Tom Preston, Philip D. Nightingale, F. Carse, Andrew G. Allen, Suzanne M. Turner, Laura M. Cardenas, Angus Thompson, Graham Savidge, Andrew J. Watson, Carlos Pedrós-Alió, Gwenaelle Moncoiffe, M.I. Liddicoat, Claire E. Widdicombe, J. Baker, Robert C. Upstill-Goddard, Tim Jickells, Rgj Bellerby, Michael Steinke, Rafel Simó, AW Jackson, Cliff S. Law, Andrew R. Bowie, and Thomas M. Frost more...
- Subjects
Biogeochemical cycle ,Trace gases ,Air-sea exchanges ,Stratification (water) ,Geology ,Storm ,Nutrients ,Aquatic Science ,Plankton ,Wind speed ,Trace gas ,Nutrient ,Oceanography ,Eddy ,Primary productivity ,Environmental science - Abstract
Jickells, T.D. ... et. al.-- 34 pages, 6 tables, 10 figures We report the results of an experiment in the Northeast Atlantic in which sulphur hexafluoride (SF6) was released within an eddy and the behaviour of trace gases, nutrients and productivity followed within a Lagrangian framework over a period of 24 days. Measurements were also made in the air above the eddy in order to estimate air–sea exchange rates for some components. The physical, biological and biogeochemical properties of the eddy resemble those of other eddies studied in this area, suggesting that the results we report may be applicable beyond the specific eddy studied. During a period of low wind speed at the start of the experiment, we are able to quantitatively describe and balance the nutrient and carbon budgets for the eddy. We also report concentrations of various trace gases in the region which are similar to those observed in other studies and we estimate exchange rates for several trace gases. We show that the importance of gas exchange over other loss terms varies with time and also varies for the different gases. We show that the various trace gases considered (CO2, dimethyl sulphide (DMS), N2O, CH4, non-methane-hydrocarbons, methyl bromide, methyl iodide and volatile selenium species) are all influenced by physical and biological processes, but the overall distribution and temporal variability of individual gases are different to one another. A storm disrupted the stratification in the eddy during the experiment, resulting in enhanced nutrient supply to surface waters, enhanced gas exchange rates and a change in plankton community, which we quantify, although overall productivity was little changed. Emphasis is placed on the regularity of storms in the temperate ocean and the importance of these stochastic processes in such systems This is contribution no. ACP175 of the NERC ACSOE Thematic Programme. NERC grants GST/02/1276 supported the work of Jickells and Spokes, GST/02/1278 the work of Liss and Nightingale together with core funding to the Plymouth Marine Laboratory (PML) while the ACSOE core programme supported Broadgate and the shiptime costs, NERC grant GR9/3467 to G.S. supported Moncoiffé and Gilpin. Steinke was supported by NERC grant GR3/10956. The University of Newcastle upon Tyne Research Committee provided funding to support T. Frost. The work of Simó and Pedrós-Alió was supported by the Spanish McyT grant MAR97-1885-E more...
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