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  • Royal Society of Chemistry  (5)
  • American Chemistry Society  (4)
  • National Academy of Sciences  (4)
  • 1
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    Isotopic composition of atmospheric nitrate in a tropical marine boundary layer (2013)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 110 (44). pp. 17668-17673.
    Details
    Publication Date: 2014-01-27
    Description: Long-term observations of the reactive chemical composition of the tropical marine boundary layer (MBL) are rare, despite its crucial role for the chemical stability of the atmosphere. Recent observations of reactive bromine species in the tropical MBL showed unexpectedly high levels that could potentially have an impact on the ozone budget. Uncertainties in the ozone budget are amplified by our poor understanding of the fate of NOx (= NO + NO2), particularly the importance of nighttime chemical NOx sinks. Here, we present year-round observations of the multiisotopic composition of atmospheric nitrate in the tropical MBL at the Cape Verde Atmospheric Observatory. We show that the observed oxygen isotope ratios of nitrate are compatible with nitrate formation chemistry, which includes the BrNO3 sink at a level of ca. 20 ± 10% of nitrate formation pathways. The results also suggest that the N2O5 pathway is a negligible NOx sink in this environment. Observations further indicate a possible link between the NO2/NOx ratio and the nitrogen isotopic content of nitrate in this low NOx environment, possibly reflecting the seasonal change in the photochemical equilibrium among NOx species. This study demonstrates the relevance of using the stable isotopes of oxygen and nitrogen of atmospheric nitrate in association with concentration measurements to identify and constrain chemical processes occurring in the MBL.
    Type: Article , PeerReviewed
    DOI: 10.1073/pnas.1216639110
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Attenuation of sinking particulate organic carbon flux through the mesopelagic ocean (2015)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 112 (4). pp. 1089-1094.
    Details
    Publication Date: 2021-04-23
    Description: The biological carbon pump, which transports particulate organic carbon (POC) from the surface to the deep ocean, plays an important role in regulating atmospheric carbon dioxide (CO2) concentrations. We know very little about geographical variability in the remineralization depth of this sinking material and less about what controls such variability. Here we present previously unpublished profiles of mesopelagic POC flux derived from neutrally buoyant sediment traps deployed in the North Atlantic, from which we calculate the remineralization length scale for each site. Combining these results with corresponding data from the North Pacific, we show that the observed variability in attenuation of vertical POC flux can largely be explained by temperature, with shallower remineralization occurring in warmer waters. This is seemingly inconsistent with conclusions drawn from earlier analyses of deep-sea sediment trap and export flux data, which suggest lowest transfer efficiency at high latitudes. However, the two patterns can be reconciled by considering relatively intense remineralization of a labile fraction of material in warm waters, followed by efficient downward transfer of the remaining refractory fraction, while in cold environments, a larger labile fraction undergoes slower remineralization that continues over a longer length scale. Based on the observed relationship, future increases in ocean temperature will likely lead to shallower remineralization of POC and hence reduced storage of CO2 by the ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1073/pnas.1415311112
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Real-time monitoring of picomolar concentrations of iron(II) in marine waters using automated flow injection-chemiluminescence instrumentation (2002)
    American Chemistry Society
    In:  Environmental Science and Technology, 36 (21). pp. 4600-4607.
    Details
    Publication Date: 2016-12-19
    Description: A shipboard-deployable, flow-injection (FI) based instrument for monitoring iron(II) in surface marine waters is described. It incorporates a miniature, low-power photon-counting head for measuring the light emitted from the iron-(II)-catalyzed chemiluminescence (CL) luminol reaction. System control, signal acquisition, and data processing are performed in a graphical programming environment. The limit of detection for iron(II) is in the range 8-12 pmol L-1 (based on 3s of the blank), and the precision over the range 8-1000 pmol L-1 varies between 0.9 and 7.6 (n = 4). Results from a day-night deployment during a north-to-south transect of the Atlantic Ocean and a daytime transect in the Sub-Antarctic Front are presented together with ancillary temperature, salinity, and irradiance data. The generic nature of the components used to assemble the instrument make the technology readily transferable to other laboratories and the modular construction makes it easy to adapt the system for use with other CL chemistries.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1021/es020045v
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  • 4
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    Species kinetics and heterogeneous reactivity of dissolved CU in natural freshwaters (2002)
    American Chemistry Society
    In:  Environmental Science and Technology, 36 (5). pp. 914-920.
    Details
    Publication Date: 2016-12-19
    Description: Using high specific activity 64Cu 2+ as radiotracer, the distribution kinetics among Cu species were established in natural organic-rich freshwaters under steady-state conditions, i.e., with minimal disturbance of existing equilibria. Study sites with contrasting suspended particulate matter (SPM) characteristics were investigated. Our analytical protocol allowed the differentiation between the following Cu species: SPM associated Cu, dissolved reactive (free and labile) Cu, and organically complexed Cu. The data obtained were successfully evaluated by compartmental analysis, which showed the importance of organically complexed Cu in freshwaters, and the dominant role of the interactions between organically complexed Cu and SPM in a SPM-rich water. The kinetic 64Cu measurements indicated that the attainment of equilibrium between dissolved reactive and organically complexed Cu took ca. 〈1-2 h, and 4-15 h for the interaction between dissolved organically complexed and SPM associated Cu. The kinetic study was augmented by voltammetric measurements of the dissolved (stable) Cu equilibrium speciation conditions in the natural waters. These measurements showed that the waters contained very low cupric ion concentrations (10 -12-10 -15 M), with more than 99.9 of the dissolved Cu complexed by strong organic ligands (conditional stability constants: 10 13.4- 10 15.4.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1021/es010109m
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  • 5
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    The ion chromatographic separation of high valence metal cationsusing a neutral polystyrene resin dynamically modified with dipicolinic acid (2000)
    Royal Society of Chemistry
    In:  Analyst, 125 (12). pp. 2157-2159.
    Details
    Publication Date: 2014-02-04
    Description: A neutral polystyrene resin column, dynamically loaded with dipicolinic acid at a concentration of 0.1 mM in 1 M potassium nitrate eluent, was investigated for the separation characteristics of a number of high valence metal cations over the pH range 0-3. The metal species studied were Th(IV), U(VI), Zr(IV), Hf(IV), Ti(IV), Sn(IV), V(IV) and V(V), Fe(III) and Bi(III), of which Ti(IV), Sn(IV), V(IV) and Fe(III) did not show any retention. For the remaining metal ions, significant retention was obtained with good peak shapes, except for Th(IV), which moved only slightly from the solvent front with some tailing. The retention order at pH 0.3 was Th(IV) 〈 V(V) 〈 Bi(III) 〈 U(VI) 〈 Hf(IV) 〈 Zr(IV). A notable feature of this separation system was the high selectivity shown for uranium, zirconium and hafnium, the last two being nearly resolved in 15 min on the relatively short 10 cm column.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/b008235j
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  • 6
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    Determination of cobalt and iron in estuarine and coastal waters using flow injection with chemiluminescence detection (2000)
    Royal Society of Chemistry
    In:  Analyst, 125 (1). pp. 51-57.
    Details
    Publication Date: 2014-02-04
    Description: Flow injection with chemiluminescence detection (FI-CL) was used to determine cobalt and iron in estuarine and coastal waters. Cobalt(II) was determined by means of a pyrogallol-hydrogen peroxide-sodium hydroxide reaction in the presence of methanol and the surfactant cetyltrimethylammonium bromide (CTAB). With pyrogallol, the sensitivity was enhanced compared with the traditional reagent, gallic acid. The practical limit of detection in sea-water was 5 pM (3s) and there was good agreement with certified values for the sea-water CRMs NASS-5 (0.16 ± 0.01 nM), CASS-3 (0.60 ± 0.09 nM) and SLEW-2 (0.93 ± 0.13 nM). Results for an Irish Sea sample gave good agreement with data obtained using cathodic stripping voltammetry. Iron(II + III) was determined using a luminol reaction with dissolved oxygen as the oxidant. The practical limit of detection was 40 pM (3s) and results from shipboard analysis of the CRM NASS-4 (1.95 ± 0.14 nM) were in good agreement with the certified value (1.88 ± 0.29 nM). Field evaluation of the instrumentation and analytical methods was achieved through a series of local surveys in the Tamar Estuary (UK), from which environmental data are presented.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/a907651d
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Predominance of heavily calcified coccolithophores at low CaCO3 saturation during winter in the Bay of Biscay (2012)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 109 (23). pp. 8845-8849.
    Details
    Publication Date: 2014-01-27
    Description: Coccolithophores are an important component of the Earth system, and, as calcifiers, their possible susceptibility to ocean acidification is of major concern. Laboratory studies at enhanced pCO2 levels have produced divergent results without overall consensus. However, it has been predicted from these studies that, although calcification may not be depressed in all species, acidification will produce "a transition in dominance from more to less heavily calcified coccolithophores"Ridgwell A, et al., (2009) Biogeosciences 6:2611-2623. A recent observational study Beaufort L, et al., (2011) Nature 476:80-83 also suggested that coccolithophores are less calcified in more acidic conditions.We present the results of a large observational study of coccolithophore morphology in the Bay of Biscay. Samples were collected once a month for over a year, along a 1,000-km-long transect. Our data clearly show that there is a pronounced seasonality in the morphotypes of Emiliania huxleyi, the most abundant coccolithophore species. Whereas pH and CaCO 3saturation are lowest in winter, the E. huxleyi population shifts from 〈10% (summer) to >90% (winter) of the heavily calcified form. However, it is unlikely that the shifts in carbonate chemistry alone caused the morphotype shift. Our finding that the most heavily calcified morphotype dominates when conditions are most acidic is contrary to the earlier predictions and raises further questions about the fate of coccolithophores in a high-CO2 world.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1073/pnas.1117508109
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  • 8
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    Hydroxamate siderophores: Occurrence and importance in the Atlantic Ocean (2008)
    American Chemistry Society
    In:  Environmental Science and Technology, 42 (23). pp. 8675-8680.
    Details
    Publication Date: 2017-10-24
    Description: Siderophores are chelates produced by bacteria as part of a highly specific iron uptake mechanism. They are thought to be important in the bacterial acquisition of iron in seawater and to influence iron biogeochemistry in the ocean. We have identified and quantified two types of siderophores in seawater samples collected from the Atlantic Ocean. These siderophores were identified as hydroxamate siderophores, both ferrioxamine species representative of the more soluble marine siderophores characterized to date. Ferrioxamine G was widely distributed in surface waters throughout the Atlantic Ocean, while ferrioxamine E had a more varied distribution. Total concentrations of the two siderophores were between 3 and 20 pM in the euphotic zone. If these compounds are fully complexed in seawater, they represent approximately 0.2-4.6 of the 〈0.2 μm iron pool. Our data confirm that siderophore-mediated iron acquisition is important for marine heterotrophic bacteria and indicate that siderophores play an important role in the oceanic biogeochemical cycling of iron. © 2008 American Chemical Society.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1021/es801884r
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  • 9
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    The determination of trace metals in estuarine and coastal waters using a voltammetric in situ profiling system (2003)
    Royal Society of Chemistry
    In:  Analyst, 128 (6). pp. 734-741.
    Details
    Publication Date: 2014-02-04
    Description: This work presents the optimisation, validation and field deployment of a voltammetric in situ profiling (VIP) system for the simultaneous determinations of dynamic Cd(II), Cu(II) and Pb(II) in estuarine and coastal waters. Systematic studies in NaNO3 (as a supporting electrolyte) and seawater, indicated that variations in ionic strength, pH and dissolved oxygen did not affect the response of the instrument, whereas an Arrhenius type temperature response was observed. The VIP instrument allows the determination of 2-3 samples h-1, and has a detection limit (defined as 3σ) in seawater for Cd(II): 23 pM, Cu(II): 1.13 nM, and Pb(II): 23 pM. The VIP system accurately measured the total dissolved concentrations of Cd(II), Cu(II) and Pb(II) in two certified reference materials; SLRS-3, a river water, and SLEW-2, an estuarine water. Field evaluation of the instrumentation and analytical methods was achieved through a series of surveys in the Plym Estuary (Devon, UK), from which environmental data are presented.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/b300712j
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  • 10
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    Visualisation of natural aquatic colloids and particles - A comparison of conventional high vacuum and environmental scanning electron microscopy (2005)
    Royal Society of Chemistry
    In:  Journal of Environmental Monitoring, 7 (2). pp. 115-121.
    Details
    Publication Date: 2014-02-04
    Description: The applicability of environmental scanning electron microscopy (ESEM; imaging of hydrated samples) and conventional high vacuum scanning electron microscopy (SEM; imaging of dried samples at high vacuum) for the observation of natural aquatic colloids and particles was explored and compared. Specific attention was given to the advantages and limitations of these two techniques when used to assess the sizes and morphologies of complex and heterogeneous environmental systems. The observation of specimens using SEM involved drying and coating, whereas ESEM permitted their examination in hydrated form without prior sample preparation or conductive coating. The two techniques provided significantly different micrographs of the same sample. SEM provided sharper images, lower resolution limits (10 nm or lower), but more densely packed particles, suggesting aggregation, and different morphological features than ESEM, suggesting artefacts due to drying. ESEM produced less easily visualised materials, more complex interpretation, slightly higher resolution limits (30-50 nm), but these limitations were more than compensated for by the fact that ESEM samples retained, at least to some extent, their morphological integrity. The results in this paper show that SEM and ESEM should be regarded as complementary techniques for the study of aquatic colloids and particles and that ESEM should be more widely applied to aquatic environmental systems than hitherto. © The Royal Society of Chemistry 2005.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/b413832e
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