| 1. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 2. |
- Pattaro, Cristian, et al.
(författare)
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Genetic associations at 53 loci highlight cell types and biological pathways relevant for kidney function
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, 19 associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biological pathways.
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| 3. |
- German, C, et al.
(författare)
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Hydrothermal impacts on trace element and isotope ocean biogeochemistry
- 2016
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Ingår i: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-503X .- 1471-2962. ; 374:2081
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal activity occurs in all ocean basins, releasing high concentrations of key trace elements and isotopes (TEIs) into the oceans. Importantly, the calculated rate of entrainment of the entire ocean volume through turbulently mixing buoyant hydrothermal plumes is so vigorous as to be comparable to that of deep-ocean thermohaline circulation. Consequently, biogeochemical processes active within deep-ocean hydrothermal plumes have long been known to have the potential to impact global-scale biogeochemical cycles. More recently, new results from GEOTRACES have revealed that plumes rich in dissolved Fe, an important micronutrient that is limiting to productivity in some areas, are widespread above mid-ocean ridges and extend out into the deep-ocean interior. While Fe is only one element among the full suite of TEIs of interest to GEOTRACES, these preliminary results are important because they illustrate how inputs from seafloor venting might impact the global biogeochemical budgets of many other TEIs. To determine the global impact of seafloor venting, however, requires two key questions to be addressed: (i) What processes are active close to vent sites that regulate the initial high-temperature hydrothermal fluxes for the full suite of TEIs that are dispersed through non-buoyant hydrothermal plumes? (ii) How do those processes vary, globally, in response to changing geologic settings at the seafloor and/or the geochemistry of the overlying ocean water? In this paper, we review key findings from recent work in this realm, highlight a series of key hypotheses arising from that research and propose a series of new GEOTRACES modelling, section and process studies that could be implemented, nationally and internationally, to address these issues. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
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| 4. |
- Havenhand, Jonathan N., 1959, et al.
(författare)
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Ecological and functional consequences of coastal ocean acidification : Perspectives from the Baltic-Skagerrak System
- 2019
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 48:8, s. 831-854
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Forskningsöversikt (refereegranskat)abstract
- Ocean temperatures are rising; species are shifting poleward, and pH is falling (ocean acidification, OA). We summarise current understanding of OA in the brackish Baltic-Skagerrak System, focussing on the direct, indirect and interactive effects of OA with other anthropogenic drivers on marine biogeochemistry, organisms and ecosystems. Substantial recent advances reveal a pattern of stronger responses (positive or negative) of species than ecosystems, more positive responses at lower trophic levels and strong indirect interactions in food-webs. Common emergent themes were as follows: OA drives planktonic systems toward the microbial loop, reducing energy transfer to zooplankton and fish; and nutrient/food availability ameliorates negative impacts of OA. We identify several key areas for further research, notably the need for OA-relevant biogeochemical and ecosystem models, and understanding the ecological and evolutionary capacity of Baltic-Skagerrak ecosystems to respond to OA and other anthropogenic drivers.
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| 5. |
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| 6. |
- Urban, Edward R., et al.
(författare)
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The importance of bottom-up approaches to international cooperation in ocean science: The iron story
- 2020
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Ingår i: Oceanography. - : The Oceanography Society. - 1042-8275. ; 33, s. 11-15
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- © 2020, Oceanography Society. All rights reserved. In the past decade, several international efforts developed to address urgent societal issues have been identified through, for example, the United Nations 2030 Agenda for Sustainable Development and its associated 17 Sustainable Development Goals and the United Nations Decade of Ocean Science for Sustainable Development (2021–2030). These worthy efforts will bring ocean science research to bear on problems that need attention in the short term. Yet, there is also a continuing need at the international level to support fundamental ocean science and solve methodological issues over the long term. While knowledge needs to be created before it can be applied, national and international science strategy documents often do not mention the need to maintain the health of the basic science enterprise. We argue that international organizations designed to create knowledge must be maintained and strengthened to inform decisions on how to allocate funding for generating knowledge about the ocean versus solving ocean problems. We use the ocean iron cycle as an example of the benefits of using such a “bottom-up” approach to knowledge generation.
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| 7. |
- Andersson, K, et al.
(författare)
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Colloidal rare earth elements in a boreal river: Changing sources and distributions during the spring flood
- 2006
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 70:13, s. 3261-3274
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Tidskriftsartikel (refereegranskat)abstract
- Variations in the physico-chemical speciation of the rare earth elements (REE) have been investigated in a subarctic boreal river during an intense spring flood event using prefiltered (< 100 mu m) samples, cross-flow (ultra)filtration (CFF), flow field-flow fractionation (FIFFF), and diffusive gradients in thin films (DGT). This combination of techniques has provided new information regarding the release and transport of the REE in river water. The colloidal material can be described in terms of two fractions dominated by carbon and iron, respectively. These two fractions, termed colloidal carrier phases, showed significant temporal changes in concentration and size distribution. Before the spring flood, colloidal carbon concentrations were low, the colloids being dominated by relatively large iron colloids. Colloidal concentrations increased sharply during the spring flood, with smaller carbon colloids dominating. Following the spring flood, colloidal concentrations decreased again, smaller carbon colloids still dominating. The REE are transported mainly in the particulate and colloidal phases. Before the spring flood, the REE composition of all measured fractions was similar to local till. During the spring flood, the REE concentrations in the colloidal and particulate fractions increased. The increase was most marked for the lighter REE, which therefore showed a strong enrichment when normalized to local till. Following the spring flood, the REE concentrations decreased again and reverted to a distribution similar to local till. These changes in the concentration and distributions of carbon iron and REE are interpreted in terms of changing hydrological flow paths in soil and bedrock which occur during the spring flood. (c) 2006 Elsevier Inc. All rights reserved.
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| 8. |
- Baker, Alex R., et al.
(författare)
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Changing atmospheric acidity as a modulator of nutrient deposition and ocean biogeochemistry
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:28
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic emissions to the atmosphere have increased the flux of nutrients, especially nitrogen, to the ocean, but they have also altered the acidity of aerosol, cloud water, and precipitation over much of the marine atmosphere. For nitrogen, acidity-driven changes in chemical speciation result in altered partitioning between the gas and particulate phases that subsequently affect long-range transport. Other important nutrients, notably iron and phosphorus, are affected, because their soluble fractions increase upon exposure to acidic environments during atmospheric transport. These changes affect the magnitude, distribution, and deposition mode of individual nutrients supplied to the ocean, the extent to which nutrient deposition interacts with the sea surface microlayer during its passage into bulk seawater, and the relative abundances of soluble nutrients in atmospheric deposition. Atmospheric acidity change therefore affects ecosystem composition, in addition to overall marine productivity, and these effects will continue to evolve with changing anthropogenic emissions in the future.
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| 9. |
- Breitbarth, Eike, et al.
(författare)
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Iron biogeochemistry across marine systems – progress from the past decade
- 2010
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Ingår i: Biogeosciences. - 1726-4170. ; 7, s. 1075-1097
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Forskningsöversikt (refereegranskat)abstract
- Based on an international workshop (Gothenburg, 14–16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas.
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| 10. |
- Turner, David R., 1951, et al.
(författare)
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The SWEDARP 1997/98 Expedition.
- 2004
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Ingår i: Deep Sea Research Part II. ; 51, s. 2543-2879
-
Tidskriftsartikel (refereegranskat)
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| 11. |
- Ulfsbo, Adam, 1985, et al.
(författare)
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Modelling organic alkalinity in the Baltic Sea using a Humic-Pitzer approach
- 2015
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 168, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- Significant excess alkalinity, of the order of 30 μmol kg− 1 and attributed to dissolved organic matter, has recently been measured in the Baltic Sea. Chemical speciation modelling shows that the measured excess alkalinity is consistent with an organic alkalinity derived from dissolved organic carbon, assuming that this dissolved organic carbon consists entirely of terrestrial humic substances. The contribution of polydisperse material such as humic substances to titration alkalinity invalidates the assumptions on which the current definition of titration alkalinity is based. It is therefore concluded that alkalinity should currently not be one of the parameters used to characterise the CO2 system in organic-rich waters. The use of a simple relationship to estimate organic alkalinity from the dissolved organic carbon concentration is assessed for the limited Baltic Sea data set currently available.
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| 12. |
- Abbas, Zareen, 1962, et al.
(författare)
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Monte Carlo simulation of the dissociation constants of CO2 in 0 to 1 molal sodium chloride between 0 and 25 °C
- 2013
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 150:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric dissociation constants of the carbon dioxide system in NaCl solution between 0 and 1 mol and 0 to 25 °C were estimated by Monte Carlo (MC) simulations, and compared with Pitzer calculations and experimental measurements. The MC simulations used experimentally determined dielectric constants of water at different temperatures, and optimal agreement with the experimental data and Pitzer calculations was achieved by adjusting the ionic radii. This simple procedure resulted in effective ionic radii which were further used to simulate the activity coefficients of salt mixtures. The first and second stoichiometric dissociation constants of carbonic acid in NaCl solution (pK1⁎ and pK2⁎) were estimated from the MC-derived activity coefficients of mixed salts in NaCl. The MC results are in good agreement with the experimental data as well as with the Pitzer calculations. This study shows that Monte Carlo simulations in the temperature and ionic strength range relevant to seawater can provide pK values of the same quality as Pitzer calculations, and constitutes the first step in developing a temperature-dependent MC model for seawater. While MC calculations require greater computing resources, the number of parameters derived by fitting to thermodynamic data is substantially smaller than for Pitzer calculations.
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| 13. |
- Braungardt, C. B., et al.
(författare)
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Analysis of dissolved metal fractions in coastal waters: An inter-comparison of five voltammetric in situ profiling (VIP) systems
- 2009
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 114:1-2, s. 47-55
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of an inter-comparison exercise undertaken to test the reliability and performance of a voltammetric in situ profiling system (VIP system) and carried out by partners based in Italy, Sweden, Switzerland and the UK. The VIP system was designed to allow in situ simultaneous monitoring of the dynamic fractions (i.e. the maximum potentially bioavailable fractions) of Cu(II). Pb(II) and Cd(II) in natural waters at a frequency of 2-3 analyses h(-1). The four participating groups used the VIP systems under laboratory conditions to determine dissolved concenterations of Cu, Pb and Cd in river, estuarine and coastal water reference materials (SLRS-3/4, SLEW-2/3 and CASS3/4, respectively). The accuracy of the VIP method was comparable to that of established methodologies, including inductively coupled plasma mass spectrometry and voltammetric methods using mercury-electrodes. The VIP systems were also applied to determine the dynamic fractions of the target analytes in freshly collected samples ex situ, as well as in situ in contrasting European marine waters. There was good agreement between the concentrations of the dynamic metal fractions determined in laboratory analyses, and observed during the Simultaneous deployment of up to five VIP instruments for periods of several hours in coastal waters. The simultaneous in situ deployment of two VIP instruments in an estuary showed a consistent analytical performance over several days of continuous operation. The results of this inter-comparison exercise show that the VIP system is a reliable submersible probe for accurate, sensitive and high resolution in situ monitoring of dissolved metal fractions in the picomolar (Cd, Pb) and nanomolar (Cu) concentration ranges. (C) 2009 Elsevier B.V. All rights reserved.
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| 14. |
- Breitbarth, Eike, et al.
(författare)
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Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development
- 2009
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Ingår i: Biogeosciences. ; 6, s. 2397-2420
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Tidskriftsartikel (refereegranskat)abstract
- Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA) and reveal several origins of Fe(II) to the water column. Photoreduction of Fe(III)-complexes and deposition by rain are main sources of Fe(II) (up to 0.9 nmol L−1) in light penetrated surface waters. Indication for organic Fe(II) complexation resulting in prolonged residence times in oxygenated water was observed. Surface dwelling heterocystous cyanobacteria where mainly responsible for Fe(II) consumption in comparison to other phytoplankton. The significant Fe(II) concentrations in surface waters apparently play a major role in cyanobacterial bloom development in the Baltic Sea and are a major contributor to the Fe requirements of diazotrophs. Second, Fe(II) concentrations up to 1.44 nmol L−1 were observed at water depths below the euphotic zone, but above the oxic anoxic interface. Finally, all Fe(III) is reduced to Fe(II) in anoxic deep water. However, only a fraction thereof is present as ferrous ions (up to 28 nmol L−1) and was detected by the CL-FIA method applied. Despite their high concentrations, it is unlikely that ferrous ions originating from sub-oxic waters could be a temporary source of bioavailable iron to the euphotic zone since mixed layer depths after strong wind events are not deep enough in summer time.
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| 15. |
- Chierici, Melissa, 1968, et al.
(författare)
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Variability in pH, fCO(2), oxygen and flux of CO2 in the surface water along a transect in the Atlantic sector of the Southern Ocean
- 2004
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Ingår i: Deep-Sea Research Part Ii-Topical Studies in Oceanography. - : Elsevier BV. - 0967-0645. ; 51:22-24, s. 2773-2787
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Tidskriftsartikel (refereegranskat)abstract
- Underway sampling and measurements of pH, fCO(2), oxygen and Chlorophyll a (Chl a) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated fCO(2) the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. fCO(2) was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 muatm with a mean value of 346 +/- 13 muatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO2 with a mean sea-air flux for the entire transect of -3+/-5 mmol m(-2) d(-1) with a large variability between -20 mmol m(-2) d(-1) (oceanic uptake) to 1.3 mmol m(-2) d(-1) (oceanic source). The lowest fCO(2) values (largest oceanic uptake Of COD were found at the southern boundary of the APF at 53degreesS, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50degreesS to 63degreesS and varied between 324 and 359 mumol kg(-1) with a mean value of 347 +/- 9 mumol kg(-1). In general only small deviations from equilibrium oxygen saturation were observed (mean value = 99+/-2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO2 in the SIE during the mesoscale survey. (C) 2004 Elsevier Ltd. All rights reserved.
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| 16. |
- Clegg, Simon L., et al.
(författare)
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Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties. II. Tris buffers in artificial seawater at 25 °C, and an assessment of the seawater ‘Total’ pH scale
- 2022
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- The substance Tris (or THAM, 2-amino-2-hydroxymethyl-1,3-propanediol, CAS 77–86-1), and its protonated form TrisH+, is used in the preparation of pH buffer solutions for applications in seawater chemistry. The development of an acid-base chemical speciation model of buffer solutions containing Tris, TrisH+, and the major ions of seawater is desirable so that: (i) the effects of changes in the composition of the medium on pH can be calculated; (ii) pH on the free (a measure of [H+]) and total (a measure of ([H+] + [HSO4−])) scales can be interconverted; (iii) approximations inherent in the definition of the total pH scale can be quantified; (iv) electrode pairs such as H+/Cl− and H+/Na+ can more easily be calibrated for the measurement of pH. As a first step towards these goals we have extended the Pitzer-based speciation model of Waters and Millero (Mar. Chem. 149, 8–22, 2013) for artificial seawater to include Tris and TrisH+, at 25 °C. Estimates of the variances and covariances of the additional interaction parameters were obtained by Monte Carlo simulation. This enables the total uncertainty of any model-calculated quantity (e.g., pH, speciation) to be estimated, as well as the individual contributions of all interaction parameters and equilibrium constants. This is important for model development, because it allows the key interactions to be identified. The model was tested against measured EMFs of cells containing Tris buffer in artificial seawater at 25 °C, and the mean deviation was found to be 0.13 ± 0.070 mV for salinities 20 to 40. Total variances for calculated electromotive forces of the buffer solutions are dominated by contributions from just a few interaction parameters, making it likely that the model can readily be improved. The model was used to quantify the difference between various definitions of total pH and –log10([H+] + [HSO4−]) in Tris buffer solutions at 25 °C, for the first time (item (iii) above). The results suggest that the total pH scale can readily be extended to low salinities using the established approach for substituting TrisH+ for Na+ in the buffer solutions, especially if the speciation model is used to quantify the effect on pH of the substitution. The relationships between electromotive force (EMF), and pH on the total scale, with buffer molality in artificial seawater at constant salinity are shown to be linear above about 0.01 to 0.02 mol kg−1 buffer molality. The pH of Tris buffers containing ratios of TrisH+ to Tris that vary from unity can be calculated very simply. Technical aspects of the total pH scale, such as the extrapolation of pH to zero buffer (at constant salinity), are clarified. Recommendations are made for further work to extend the model to the temperature range 0–45 °C, and improve accuracy, so that requirements (i) to (iv) above can be fully met.
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| 17. |
- Clegg, S. L., et al.
(författare)
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Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties. III. Seawater from the freezing point to 45 & DEG;C, including acid-base equilibria
- 2023
-
Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 250
-
Tidskriftsartikel (refereegranskat)abstract
- A quantitative understanding of pH, acid-base equilibria, and chemical speciation in natural waters including seawater is needed in applications ranging from global change to environmental and water quality management. In a previous study (Humphreys et al., 2022) we implemented a model of solutions containing the ions of artificial seawater, based upon the use of the Pitzer equations for the calculation of activity coefficients and including, for the first time, the propagation of uncertainties. This was extended (Clegg et al., 2022) to include the Tris buffer solutions that are used to calibrate the seawater total pH scale. Here we apply the same methods to develop a model of solutions containing the ions of standard reference seawater, based upon studies by Millero and co-workers. We compare the predictions of the model to literature data for: the dissociation of dissolved CO2 and bicarbonate ion; boric acid dissociation; saturation with respect to calcite, the ion product of water, and osmotic coefficients of seawater. Estimates of the uncertainty contributions of all thermodynamic equilibrium constants and Pitzer parameters to the variance of the calculated quantity are used to determine which elements of the model need improvement, with the aim of agreeing with properties noted above to within their experimental uncertainty. Further studies are recommended. Comparisons made with several datasets for carbonate system dissociation in seawater suggest which are the most reliable, and identify low salinity waters (S < 10) as a region for which dissociation constants of bicarbonate are not yet accurately known. At present, the model is likely to be most useful for the direct calculation of equilibria in natural waters of arbitrary composition, or for adjusting dissociation constants known for seawater media to values for natural waters in which the relative compositions of the major ions are different.
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| 18. |
- Croot, P. L., et al.
(författare)
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The distribution and specification of iron along 6 degrees E in the Southern Ocean
- 2004
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Ingår i: Deep-Sea Research Part Ii-Topical Studies in Oceanography. - : Elsevier BV. - 0967-0645. ; 51:22-24, s. 2857-2879
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Tidskriftsartikel (refereegranskat)abstract
- The distribution and speciation of iron was determined along a transect in the eastern Atlantic sector (6degreesE) of the Southern Ocean during a collaborative Scandinavian/South African Antarctic cruise conducted in late austral summer (December 1997/January 1998). Elevated concentrations of dissolved iron (>0.4 nM) were found at 60degreesS in the vicinity of the Spring Ice Edge (SIE) in tandem with a phytoplankton bloom, chiefly dominated by Phaeocystis sp. This bloom had developed rapidly after the loss of the seasonal sea ice cover. The iron that fuelled this bloom was mostly likely derived from sea ice melt. In the Winter Ice Edge (WIE), around 55degreesS, dissolved iron concentrations were low (<0.2 nM) and corresponded to lower biological productivity, biomass. In the Antarctic Polar Front, at approximately 50degreesS, a vertical profile of dissolved iron showed low concentrations (<0.2 nM); however, a surface survey showed higher concentrations (1-3 nM), and considerable patchiness in this dynamic frontal region. The chemical speciation of iron was dominated by organic complexation throughout the study region. Organic iron-complexing ligands ([L]) ranged from 0.9 to 3.0 nM Fe equivalents, with complex stability log K'(FeL) = 21.4-23.5. Estimated concentrations of inorganic iron (Fe') ranged from 0.03 to 0.79 pM, with the highest values found in the Phaeocystis bloom in the SIE. A vertical profile of iron-complexing ligands in the WIE showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition. This work further confirms the role iron that has in the Southern Ocean in limiting primary productivity. (C) 2004 Elsevier Ltd. All rights reserved.
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| 19. |
- Dahlqvist, Ralf, 1973, et al.
(författare)
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Association of calcium with colloidal particles and speciation of calcium in the Kalix and Amazon rivers
- 2004
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 68:20, s. 4059-4075
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Tidskriftsartikel (refereegranskat)abstract
- A considerable amount of colloidally bound Ca has been detected in water samples from Amazonian rivers and the Kalix River, a sub-arctic boreal river. Fractionation experiments using several analytical techniques and processing tools were conducted in order to elucidate the matter. Results show that on average 84% of the total Ca concentration is present as free Ca. Particulate, colloidal and complexed Ca constitute the remaining 16%, of which the colloidal fraction is significant. Ultrafiltration experiments show that the colloidal fraction in the sampled Amazonian rivers and the Kalix River range between 1% and 25%. In both the Amazonian and the Kalix rivers the technique of cross-flow ultrafiltration was used to isolate particles and colloids. The difference in concentration measured with ICP-AES and a Ca ion-selective electrode in identical samples was used to define the free Ca concentration and thus indirectly the magnitude of the particulate, colloidal and complexed fractions. Results from the Kalix and Amazonian rivers are in excellent agreement. Furthermore, the results show that the colloidal concentrations of Ca can be greatly overestimated (up to 227%) when conventional analysis and calculation of ultrafiltration data is used due to retention of free Ca ions during the ultrafiltration process. Calculation methods for colloidal matter are presented in this work, using complementary data from ISE analysis. In the Kalix River temporal changes in the fractionation of Ca were studied before, during and after a spring-flood event. Changes in the size distribution of colloidally associated Ca was studied using FlFFF (Flow Field-Flow Fractionation) coupled on-line to a HR ICP-MS. The FlFFF-HR ICP-MS fractograms clearly show the colloidal component of Ca, supporting the ultrafiltration findings. During winter conditions the size distribution of colloidally associated Ca has a concentration maximum at similar to5 to 10 nm in diameter, shifting to smaller sizes (<5 mm) during and after the spring flood. This shift in size distribution follows a change in the river during this period from ironoxyhydroxy colloids being the most important colloidal carrier phase to humic substances during and after the spring flood. WHAM and NICA-Donnan models were used to calculate the amount of colloidally bound Ca. The results similar for both models, show that on average 16% of the Ca may be associated to a colloidal phase, which is in broad agreement with the measurements. Copyright (C) 2004 Elsevier Ltd.
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| 20. |
- Dahlqvist, Ralf, et al.
(författare)
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Temporal variations of colloidal carrier phases and associated trace elements in a boreal river
- 2007
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 71:22, s. 5339-5354
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Tidskriftsartikel (refereegranskat)abstract
- Elemental size distributions, from truly dissolved through colloidal to particulate, have been studied in a subarctic boreal river. The measurements, carried out during 2002, ranged from winter to summer conditions, including an intense spring flood event. Results are reported for a total of 42 elements. Size distributions were characterised using a combination of cross-flow (ultra)filtration (CFF), flow field-flow fractionation (FIFFF), and diffusive gradients in thin-films (DGT). The three techniques showed similar trends, but quantitative comparisons reveal some important differences that warrant further investigation. Previous work has identified two colloidal carrier phases in fresh waters, dominated by iron and carbon, respectively. The majority of the elements studied are associated with one or both of these colloidal carrier phases. The exceptions are the alkali metals and several anions that are only very weakly associated with colloidal material, and which therefore occur mainly as truly dissolved material (< 1 kDa in molecular weight). We discuss the likely origin for the two colloidal carrier phases and consider how associated trace elements fit into the geochemical framework. The relative affinities of the elements for iron and carbon colloidal carrier phases are related to their chemistries, and are compared with earlier data from the Delsjo Creek in southern Sweden. Elemental colloidal concentrations show strong seasonal variations related to changes in the colloidal carrier phase(s) with which they associate. In particular, many elements show a strong spring maximum in colloidal concentrations associated with the strong maximum in colloidal carbon concentration during the spring flood.
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| 21. |
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| 22. |
- Endres, Sonja, et al.
(författare)
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A New Perspective at the Ship-Air-Sea-Interface : The Environmental Impacts of Exhaust Gas Scrubber Discharge
- 2018
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Ingår i: Frontiers in Marine Science. - : FRONTIERS MEDIA SA. - 2296-7745. ; 5
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Forskningsöversikt (refereegranskat)abstract
- Shipping emissions are likely to increase significantly in the coming decades, alongside increasing emphasis on the sustainability and environmental impacts of the maritime transport sector. Exhaust gas cleaning systems ("scrubbers"), using seawater or fresh water as cleaning media for sulfur dioxide, are progressively used by shipping companies to comply with emissions regulations. Little is known about the chemical composition of the scrubber effluent and its ecological consequences for marine life and biogeochemical processes. If scrubbers become a central tool for atmospheric pollution reduction from shipping, modeling, and experimental studies will be necessary to determine the ecological and biogeochemical effects of scrubber wash water discharge on the marine environment. Furthermore, attention must be paid to the regulation and enforcement of environmental protection standards concerning scrubber use. Close collaboration between natural scientists and social scientists is crucial for progress toward sustainable shipping and protection of the marine environment.
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| 23. |
- Gallego-Urrea, Julian A., 1977, et al.
(författare)
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Determination of pH in estuarine and brackish waters: Pitzer parameters for Tris buffers and dissociation constants for m-cresol purple at 298.15K
- 2017
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 195, s. 84-89
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Elsevier B.V. Measurements of pH in seawater are important to determine the natural and anthropogenic trends in the oceans. Spectrophotometry or glass electrode potentiometry measurements of pH require calibration with help of buffers. One common buffer solution is the Tris/Tris·H + couple, which should be well characterised both experimentally and theoretically for optimum accuracy. Chemical speciation modelling in the complex seawater medium is best addressed with an ion interaction approach, with Pitzer equations being the most widely used. The published Pitzer coefficients for Tris and Tris·H + in artificial seawater are based on isopiestic measurements, which necessarily give strong weight to the third virial coefficient C for the key interaction between Tris·H + and chloride. However, in low salinity waters it is the second virial coefficient B that is of greater importance. We have used Harned cell measurements of Tris solutions at ionic strengths up to 1molkg -1 to reassess the relevant Pitzer parameters, and have found improved agreement with experimental measurements in artificial seawater. We suggest that additional measurements should be undertaken to address the remaining differences between model calculations and experimental data in artificial seawater. We have used the revised Pitzer parameters to reassess the acid-base constant of the indicator m-cresol purple in low salinity waters.
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| 24. |
- Hassellöv, Ida-Maja, 1974, et al.
(författare)
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Shipping contributes to ocean acidification
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:11, s. 2731-2736
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Tidskriftsartikel (refereegranskat)abstract
- The potential effect on surface water pH of emissions of SOX and NOX from global ship routes is assessed. The results indicate that regional pH reductions of the same order of magnitude as the CO2-driven acidification can occur in heavily trafficked waters. These findings have important consequences for ocean chemistry, since the sulfuric and nitric acids formed are strong acids in contrast to the weak carbonic acid formed by dissolution of CO2. Our results also provide background for discussion of expanded controls to mitigate acidification due to these shipping emissions.
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| 25. |
- Hopwood, Mark J., et al.
(författare)
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Experiment design and bacterial abundance control extracellular H2O2 concentrations during four series of mesocosm experiments
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17, s. 1309-1326
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Tidskriftsartikel (refereegranskat)abstract
- © Author(s) 2020. The extracellular concentration of H2O2 in surface aquatic environments is controlled by a balance between photochemical production and the microbial synthesis of catalase and peroxidase enzymes to remove H2O2 from solution. In any kind of incubation experiment, the formation rates and equilibrium concentrations of reactive oxygen species (ROSs) such as H2O2 may be sensitive to both the experiment design, particularly to the regulation of incident light, and the abundance of different microbial groups, as both cellular H2O2 production and catalase-peroxidase enzyme production rates differ between species. Whilst there are extensive measurements of photochemical H2O2 formation rates and the distribution of H2O2 in the marine environment, it is poorly constrained how different microbial groups affect extracellular H2O2 concentrations, how comparable extracellular H2O2 concentrations within large-scale incubation experiments are to those observed in the surface-mixed layer, and to what extent a mismatch with environmentally relevant concentrations of ROS in incubations could influence biological processes differently to what would be observed in nature. Here we show that both experiment design and bacterial abundance consistently exert control on extracellular H2O2 concentrations across a range of incubation experiments in diverse marine environments. During four large-scale (> 1000 L) mesocosm experiments (in Gran Canaria, the Mediterranean, Patagonia and Svalbard) most experimental factors appeared to exert only minor, or no, direct effect on H2O2 concentrations. For example, in three of four experiments where pH was manipulated to 0.4-0.5 below ambient pH, no significant change was evident in extracellular H2O2 concentrations relative to controls. An influence was sometimes inferred from zooplankton density, but not consistently between different incubation experiments, and no change in H2O2 was evident in controlled experiments using different densities of the copepod Calanus finmarchicus grazing on the diatom Skeletonema costatum (< 1 % change in [H2O2] comparing copepod densities from 1 to 10 L-1). Instead, the changes in H2O2 concentration contrasting high-and low-zooplankton incubations appeared to arise from the resulting changes in bacterial activity. The correlation between bacterial abundance and extracellular H2O2 was stronger in some incubations than others (R2 range 0.09 to 0.55), yet high bacterial densities were consistently associated with low H2O2. Nonetheless, the main control on H2O2 concentrations during incubation experiments relative to those in ambient, unenclosed waters was the regulation of incident light. In an open (lidless) mesocosm experiment in Gran Canaria, H2O2 was persistently elevated (2-6-fold) above ambient concentrations; whereas using closed high-density polyethylene mesocosms in Crete, Svalbard and Patagonia H2O2 within incubations was always reduced (median 10 %-90 %) relative to ambient waters.
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