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  • 1.
    Andersson, P.S.
    et al.
    Oxford University.
    Porcelli, D.
    Oxford University.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nordblad, F.
    Stockholms Universitet.
    Gustafsson, O.
    Stockholms Universitet.
    Semiletov, I.
    University of Alaska.
    The importance of river water inflow and shelf sediment-sea water exchange in the East Siberian Sea for the Nd isotopic composition of Arctic Ocean water2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, no 13, Suppl. 1, p. A41-Article in journal (Other academic)
    Abstract [en]

    With data generated from cruises to the Canada Basin in 2000, to the Eurasian and Central Arctic Ocean basins in 2001, to the Fram Strait in 2002 and to the Chuckchi Sea in 2005 we now have a good general view of the distribution and isotopic composition of Nd (εNd) in the Arctic Ocean [1, 2]. The restricted Arctic Ocean basin is surrounded by large continental shelves, covering more than 50% of its total area.Distinct from other oceans, with surface water Nd depletion, there is throughout the Arctic a pattern of high Nd concentrations, up to 58pM, at the surface that gradually diminish with depth to 15-18pM in the deep waters. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water and Nd is the Atlantic (εNd= -10.7). Radiogenic isotope Nd signatures can be traced in Pacific water flowing into the Canada Basin and further into the Eurasian Basin (up to εNd= -6.5). The variation of εNd and concentration in the Arctic Ocean suggest that Nd input from rivers and shelf sediments is also of great importance.Improving our understanding of the vast Siberian Shelves influence on Nd and trace element behaviour in the Arctic Ocean was one of the main objectives of the International Siberian Shelf Study 2008 (ISSS-08). The ISSS-08 cruise recovered filtered water (<0.2µm), particles and sediments from the Laptev and East Siberian Seas as well as estuarine and river water from Lena, Indigirka and Kolyma. Crucial processes, including loss of river water Nd in the estuarine region and shelf sediment-sea water exchange will be discussed in terms of controlling the Nd concentration and isotopic composition of sea water.[1] Andersson et al. (2008) GCA 72, 2854-2867. [2] Porcelli et al. (2009, in press) GCA. (2009, in press)

  • 2.
    Breitbarth, Eike
    et al.
    Department of Chemistry, University of Otago, Dunedin.
    Gelting, Johan
    Walve, Jakob
    Department of Systems Ecology, Stockholm University.
    Hoffmann, Linn
    Department of Chemistry, University of Otago, Dunedin.
    Turner, David
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Hassellöv, Martin
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no Special issue, p. 2397-2420Article in journal (Refereed)
    Abstract [en]

    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). Up to 0.9 nmol Fe(II) L−1 were detected in light penetrated surface waters, which constitutes up to 20% to the dissolved Fe pool. This bioavailable iron source is a major contributor to the Fe requirements of Baltic Sea phytoplankton and apparently plays a major role for cyanobacterial bloom development during our study. Measured Fe(II) half life times in oxygenated water exceed predicted values and indicate organic Fe(II) complexation. Potential sources for Fe(II) ligands, including rainwater, are discussed. Fe(II) concentrations of up to 1.44 nmol L−1 were detected at water depths below the euphotic zone, but above the oxic anoxic interface. Mixed layer depths after strong wind events are not deep enough in summer time to penetrate the oxic-anoxic boundary layer. However, Fe(II) from anoxic bottom water may enter the sub-oxic zone via diapycnal mixing and diffusion.

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  • 3.
    Conrad, Sarah
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nordblad, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Engström, Emma
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. ALS Laboratory Group, ALS Scandinavia AB, Luleå, Sweden .
    Rodushkin, Ilia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. ALS Laboratory Group, ALS Scandinavia AB, Luleå, Sweden .
    Andersson, Per S.
    Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    Porcelli, Don
    Department of Earth Sciences, Oxford University, Oxford, UK.
    Gustafsson, Örjan
    Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden.
    Semiletov, Igor
    International Arctic Research Center (IARC), University of Alaska, Fairbanks, AK, USA. Pacific Oceanological Institute (POI), Far Eastern Branch of the Russian Academy of Sciences (FEBRAS), Vladivostok, Russia. Tomsk National Research Politechnical University, Arctic Seas Carbon International Research Laboratory, Tomsk, Russia.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea2019In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, no 6, p. 1305-1319Article in journal (Refereed)
    Abstract [en]

     Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate ( >  0.22 μm), colloidal (0.22 μm–1 kDa), and truly dissolved (<  1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57μM with Fe dominantly as particulate Fe. The loss of >  99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about -0.20 ‰) and positive δ56Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. The positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.

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  • 4. Forsberg, Jerry
    et al.
    Dahlqvist, Ralf
    Department of Geology and Geochemistry, Stockholm University.
    Gelting, Johan
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trace metal speciation in brackish water using diffusive gradients in thin films and ultrafiltration: comparison of techniques2006In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 40, no 12, p. 3901-3905Article in journal (Refereed)
    Abstract [en]

    Diffusive gradients in thin films (DGT) and ultrafiltration were used to measure trace metal concentrations in the Baltic Sea. The results provide the first comparison of these two fundamentally different speciation methods for trace metals. Cd, Cu, Mn, Ni, and Zn were measured at two sites with different total trace metal concentrations. DGT units prepared with APA-gel as diffusive layer and Chelex 100 resin as binding agent were used throughout the study. The ultrafiltration was performed with Millipore Prep/Scale modules with cutoffs of 1 and 10 kDa. Concentration levels of Mn, Zn, and Cd measured by DGT agreed with the concentrations measured in 1 kDa ultrafiltered samples. For Cu and Ni the ultrafiltered concentrations exceeded the DGT-labile concentrations. The ability of DGT to preconcentrate metals was found to be an analytical advantage compared with ultrafiltration. DGT appears to be a good alternative to 1 kDa ultrafiltration for measurement of truly dissolved Mn, Cd, and Zn in the Baltic Sea.

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  • 5.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Speciation of trace metals in the Baltic Sea with focus on the Euphotic zone2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Physicochemical speciation of iron (Fe) and the trace metals Cd, Cu, Co, Mn, Ni, and Zn were performed at four different locations in surface waters of the Baltic Sea. Measurements were performed during several months of the growth season at each station to obtain a detailed picture of the temporal variation in relation to phytoplankton growth. The main target was to understand the speciation of iron, and to evaluate if Fe was limiting in primary production. A methodological aim of the thesis work was focused on comparison between trace metal speciation methods; where the DGT method was calibrated to other methods and also to use the DGT method find out which mechanisms that control the labile fraction. Other methods, such as CSV, CL-FIA and Fe isotope measurements (MC-ICP-MS) were used to further evaluate the changes in the Fe fractions.Concentrations of Mn, Zn and Cd measured by DGT during 2003 and 2004 were similar to concentrations measured in

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  • 6.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trace metal speciation in the Baltic sea2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Physicochemical speciation of metals in natural waters is very important for understanding their distribution, mobility, bioavailability and toxicity. To be able to understand the behaviour of an aqueous element and the transformation between chemical and physical species, there is a need for reliable methods that enable measurements of specific fractions of metals. Many different techniques are used for metal speciation, of which many suffer from problems. Ultrafiltration has frequently been used to study speciation of metals in natural waters. A possible alternative or complement to ultrafiltration is the technique of diffusive gradients in thin films (DGT), a novel technique which provides an in situ measurement of labile metal species. DGT accumulates metals in a time- integrated way and produces a mean concentration over the chosen deployment period. DGT- labile metals may be regarded as a measure of the bioavailable amount, since the DGT simulates the diffusion process that occurs when a metal is diffusing into a cell membrane. This thesis is focused on the DGT technique for sampling and determination of labile species in the Baltic Sea. The aim of this study was to compare the trace metal speciation methods; DGT, 1 kDa ultrafiltration, 0.22µm membrane filtration and unfiltered water, to study the dynamics for the DGT labile fractions to find out which mechanisms that control the labile fraction. In 2003 and 2004, DGT and 1 kDa ultrafiltration were simultaneously applied at two sampling stations in the Baltic Sea with different salinity and trace metal concentrations. Baltic Sea concentrations of Mn, Zn and Cd measured by DGT during 2004 were similar to the concentrations measured in 1 kDa ultrafiltered samples, especially for Mn. Cu and Ni, showed noticeably higher concentrations in ultrafiltered water than DGT-labile concentrations. This indicates the existence of low molecular weight Cu and Ni species, small enough to pass through the 1 kDa, but can also be a sign of high degree of organic complexation which will lead to an underestimation in the DGT labile fraction. The dynamics of DGT-labile trace metals during 2004 show quite large variations during the season at 0.5 to 40 meters depth. From May to August, Cu, Cd and Mn drop about 35, 50% and 60% respectively. Ni decreased about 25% late April to late June but was slightly recovered at late season. The only elements that showed good correlation between DGT-labile species to dissolved phase (0.22µm filtrate) was Mn and Cd. DGT labile Mn is probably controlled by oxidizing bacteria during most of the sampling period, and DGT labile Co, Cd and to some extent Zn seem to follow this process. It should be noted that Mn is closely correlated to P, a relationship which need further investigations. Cu and Ni are controlled by other processes, where influence from primary production may be one. This is the first comparison of DGT and 1 kDa ultrafiltration regarding trace metals in brackish waters. Strong correlations between the methods imply that DGT can be a simple alternative to an ultrafiltration procedure. It is also the first study on trace metals in the Baltic Sea where measurements were performed at high temporal resolution during several months.

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  • 7. Gelting, Johan
    et al.
    Breitbarth, Eike
    Stolpe, B.
    University of Gothenburg.
    Hassellöv, M.
    University of Gothenburg.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fractionation of iron species and iron isotopes in the Baltic Sea euphotic zone2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 8, p. 2489-2508Article in journal (Refereed)
    Abstract [en]

    To indentify sources and transport mechanisms of iron in a coastal marine environment, we conducted measurements of the physiochemical speciation of Fe in the euphotic zone at three different locations in the Baltic Sea. In addition to sampling across a salinity gradient, we conducted this study over the spring and summer season. Moving from the riverine input characterized low salinity Bothnian Sea, via the Landsort Deep near Stockholm, towards the Gotland Deep in the Baltic Proper, total Fe concentrations averaged 114, 44, and 15 nM, respectively. At all three locations, a decrease in total Fe of 80-90% from early spring to summer was observed. Particulate Fe (PFe) was the dominating phase at all stations and accounted for 75-85% of the total Fe pool on average. The Fe isotope composition (δ 56Fe) of the PFe showed constant positive values in the Bothnian Sea surface waters (+0.08 to +0.20‰). Enrichment of heavy Fe in the Bothnian Sea PFe is possibly associated to input of aggregated land derived Fe-oxyhydroxides and oxidation of dissolved Fe(II). At the Landsort Deep the isotopic fractionation of PFe changed between -0.08‰ to +0.28‰ over the sampling period. The negative values in early spring indicate transport of PFe from the oxic-anoxic boundary at ∼80 m depth. The average colloidal iron fraction (CFe) showed decreasing concentrations along the salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM, and Gotland Deep 0.5 nM. Field Flow Fractionation data indicate that the main colloidal carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid associated compound, likely of riverine origin. A strong positive correlation between PFe and chl-a indicates that cycling of suspended Fe is at least partially controlled by primary production. However, this relationship may not be dominated by active uptake of Fe into phytoplankton, but instead may reflect scavenging and removal of PFe during phytoplankton sedimentation.

  • 8. Gelting, Johan
    et al.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Physicochemical speciation of iron in the Baltic sea2007In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 71, no 15S, p. A315-Article in journal (Other academic)
    Abstract [en]

    Size fractionated classes of Fe in surface water at two stations, one in central Baltic Sea (the Landsort Deep) and one in Bothnian Sea, were measured from spring until autumn to evaluate temporal variations in the physicochemical speciation. Membrane filtration, cross-flow ultrafiltration and DGT (diffusive gradients in thin films) were among the applied techniques. Average concentrations for total,

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  • 9.
    Ingri, Johan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gelting, Johan
    Nordblad, Fredrik
    Engström, Emma
    Rodushkin, Ilya
    Andersson, P.S.
    Oxford University.
    Porcelli, D.
    Oxford University.
    Gustafsson, O.
    Stockholms Universitet.
    Semiletov, I.
    University of Alaska.
    Öhlander, Björn
    Fractionation of iron isotopes during estuarine mixing in Ob, Yenisey and Lena freshwater plumes2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, no 13, Suppl. S, p. A569-Article in journal (Other academic)
    Abstract [en]

    Iron isotopes were measured in suspended matter (>0.2 µm) in the Ob, Yenisey and Lena River freshwater plumes during the International Siberian Shelf Study 2008 (ISSS-08). The δ56Fe value was around zero within the Lena River and close to the river mouth, but changed to more negative values in the outer parts of the plume. In both the Ob and Yenisey plumes suspended matter in the surface water had clearly negative values whereas samples close to the bottom showed values close to zero.It has previously been suggested that total Fe in river suspended matter (>0.2µm) in boreal regions is roughly a mixture of three phases, detrital particles (δ56Fe around zero), oxyhydroxide particles (δ56Fe positive) and C-Fe particles (δ56Fe negative). We suggest that the δ56Fe pattern observed in this study is the result of relatively rapid removal of detrital particles and Fe-oxyhydroxides, leaving a suspended fraction with negative values in the surface water in the outer parts of the freshwater plumes. Hence, during estuarine mixing of suspended particles heavy iron isotopes are deposited close to the river mouth, whereas light isotopes are exported to open ocean water.

  • 10. Malinovskiy, Dmitry
    et al.
    Hammarlund, Dan
    Lunds universitet.
    Ilyashuk, Boris
    Kola Science Centre, Russian Academy of Sciences, Apatity.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gelting, Johan
    Variations in the isotopic composition of molybdenum in freshwater lake systems2007In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 236, no 3-4, p. 181-198Article in journal (Refereed)
    Abstract [en]

    Variations in molybdenum isotopic composition, spanning the range of ≈ 2.3‰ in the terms of 97Mo/95Mo ratio, have been measured in sediment cores from three lakes in northern Sweden and north-western Russia. These variations have been produced by both isotopically variable input of Mo into the lakes due to Mo isotopic heterogeneity of bedrock in the drainage basins and fractionation in the lake systems due to temporal variations in limnological conditions. Mo isotope abundances of bedrock in the lake drainage basins have been documented by analysis of Mo isotope ratios of a suite of molybdenite occurrences collected in the studied area and of detrital fractions of the lake sediment cores. The median δ97Mo value of the investigated molybdenites is 0.26‰ with standard deviation of 0.43‰ (n = 19), whereas the median δ97Mo value of detrital sediment fractions from two lakes is - 0.40‰ with standard deviation of 0.36‰ (n = 15). The isotopic composition of Mo in the sediment cores has been found to be dependent on redox conditions of the water columns and the dominant type of scavenging phases. Hydrous Fe oxides have been shown to be an efficient scavenger of Mo from porewater under oxic conditions. Oxidative precipitation of Fe(II) in the sediments resulted in co-precipitation of Mo and significant authigenic enrichment at the redox boundary. In spite of a pronounced increase in Mo concentration associated with Fe oxides at the redox boundary the isotopic composition of Mo in this zone varies insignificantly, suggesting little or no isotope fractionation during scavenging of Mo by hydrous Fe oxides. In a lake with anoxic bottom water a chironomid-inferred reconstruction of O2 conditions in the bottom water through the Holocene indicates that increased O2 concentrations are generally associated with low δ97Mo/95Mo values of the sediments, whereas lowered O2 contents of the bottom water are accompanied by relatively high δ97Mo/95Mo values, thus confirming the potential of Mo isotope data to be a proxy for redox conditions of overlying waters. However, it is pointed out that other processes including input of isotopically heterogeneous Mo and Mn cycling in the redox-stratified water column can be a primary cause of variations in Mo isotopic compositions of lake sediments.

  • 11.
    Walve, Jakob
    et al.
    Department of Ecology, Environment and Plant Sciences, Stockholm University.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trace metals and nutrients in Baltic Sea cyanobacteria: Internal and external fractions and potential use in nitrogen fixation2014In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 158, p. 27-38Article in journal (Refereed)
    Abstract [en]

    Even though the availability of trace metals influences nitrogen fixation and growth of cyanobacteria, field data on their cellular metal composition are scarce. In this study, contents of Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, and the major elements C, N, P and Si were studied in filamentous, nitrogen-fixing cyanobacteria sampled over the growth season March-October at two locations in the Baltic proper (years 2004 and 2007) and one location in the Bothnian Sea (2006). The Al and Ti contents indicated that lithogenic Fe was an important Fe fraction associated with Nodularia spumigena, but not with Aphanizomenon sp. Treatment with an oxalate-EDTA solution indicated that less than 5% of total Fe was adsorbed as oxides, but relatively high adsorbed fractions were found for Mn and Cu. Despite large variation in biomass and dissolved Fe concentrations, the Fe:C ratio of Aphanizomenon was highly consistent within years and across sampling stations (76 ± 13 μmol mol- 1 C, average ± 1SD), indicating growth controls other than Fe. Species-mixed samples corrected for lithogenic metals indicate similar Fe content in Nodularia as in Aphanizomenon. Calculations based on the use efficiency of Mo for N2 fixation indicates that most Mo in Nodularia and at least a third of the Mo in Aphanizomenon is used in nitrogenase, corresponding to 5-24% of the Fe content. The high Ni content suggests excess storage or extensive use in enzymes such as Ni superoxide dismutase or in Fe-dependent Ni-hydrogenases. The trace metal composition of the investigated Baltic cyanobacteria was similar to that reported for the oceanic genus Trichodesmium, suggesting common physiological requirements of these filamentous nitrogen-fixing cyanobacteria.

  • 12.
    Österlund, Helene
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gelting, Johan
    Nordblad, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Baxter, Douglas
    ALS Scandinavia AB.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Copper and nickel in ultrafiltered brackish water: labile or non-labile?2012In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 132-133, no 1, p. 34-43Article in journal (Refereed)
    Abstract [en]

    Copper and nickel were sampled at three stations in the Baltic Sea using diffusive gradients in thin films (DGT) passive samplers and ultrafiltration (< 1 kDa). Two versions of DGT devices were used, the normal open pore (OP) and a restricted pore (RP). The OP DGT and RP DGT concentrations closely followed each other both in depth profiles and time series. The lack of significant difference between OP and RP DGT suggests that the labile complexes were smaller than the pore size of the RP gel (approximately 1 nm). These data, together with OP DGT measurements at the same location in two different years, clearly demonstrate that the DGT method is robust and indicates reproducible results during routine field conditions.Between 50 and 80% of the ultrafiltered fractions for Ni and Cu could not be detected by the DGT method, using standard procedures. This suggests the presence of complexing ligands for Cu and Ni. Assuming 100% complexation of Ni to fulvic acid ligand gave DGT concentrations similar to ultrafiltered Ni concentrations. The equivalent calculation for Cu indicates that up to 75% of the ultrafiltered Cu fraction is non-labile. The non-labile Cu complexes are proposed to be produced at sea since the fraction increases with decreasing terrestrial influence.

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