| 11. |
- Nerentorp, Michelle, 1986, et al.
(författare)
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Seasonal and spatial evasion of mercury from the western Mediterranean Sea
- 2017
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 193, s. 34-43
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Tidskriftsartikel (refereegranskat)abstract
- Continuous measurements of gaseous elemental mercury (GEM) in air and dissolved gaseous mercury (DGM) in surface seawater were performed during two oceanographic campaigns (Fenice 2011 (25/10-11/11) and Fenice 2012 (11-29/8)), carried out in the Tyrrhenian Sea (Fenice 211), western Mediterranean Sea and the Atlantic Ocean (Fenice 2012) as part of the GMOS project (Global Mercury Observation System). Measured GEM and DGM were used to estimate the air-sea exchange of elemental mercury by using a two-thin film gas exchange model. Measured GEM concentrations showed significantly higher values in fall (1.7 +/- 0.4 ng m(-3)) compared to summer (1.5 +/- 03 ng m(-3), p
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| 12. |
- Nerentorp, Michelle, 1986, et al.
(författare)
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Speciation of mercury in the waters of the Weddell, Amundsen and Ross Seas (Southern Ocean)
- 2017
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 193, s. 20-33
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Tidskriftsartikel (refereegranskat)abstract
- Despite the distance from large anthropogenic emission sources, toxic mercury is transported via the atmosphere and oceans to the Southern Ocean. Seawater samples were collected at selected stations and were analysed for total mercury (HgT) (8 stations), dissolved gaseous mercury (DGM) (62 stations) and methylmercury (12 stations) during winter (Weddell Sea), spring (Weddell Sea) and summer (Amundsen and Ross Seas) in the Southern Ocean. The HgT distribution in water columns was found to not vary significantly with depth. In the Weddell Sea the average column concentration was higher in spring (2.6 +/- 1.3 pM, 2 stations) than in winter (2.0 +/- 1.0 pM, 6 stations). We hypothesize that the seasonal HgT increase is due to atmospheric deposition of particulate Hg(II) formed during atmospheric mercury depletion events (AMDEs), as well as the addition of inorganic mercury species from melting sea ice and snow. Furthermore, HgT concentrations found in this study were significantly higher than previously measured in the Southern Ocean (Cossa et al., 2011), which was hypothesized to be due to seasonal variations in atmospheric deposition. The average water column DGM concentration in the Weddell Sea was 454 +/- 254 fM in winter and 384 +/- 239 fM in spring. The lowest average DGM concentration was found in summer in the Amundsen and Ross Seas (299 +/- 137 fM). The highest observed concentration in winter was hypothesized to be caused by the larger sea ice coverage, which is known to reduce the evasion of Hg(0) from the sea surface. The average monomethylmercury (MMHg) concentration in the Weddell Sea was 60 +/- 30 fM in winter (6 stations) and 95 +/- 85 fM in spring (2 stations), showing no significant seasonal difference. In the Amundsen and Ross Seas the summer average concentration of MeHg (MMHg and dimethylmercury; DMHg) was 135 +/- 189 fM (4 stations). The highest MeHg concentration was found in modified circumpolar deep water, which is known to have high primary production. 2017 Elsevier B.V. All rights reserved.
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| 13. |
- Nilsson, Madeleine, et al.
(författare)
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Organic carbon recycling in Baltic Sea sediments – An integrated estimate on the system scale based on in situ measurements
- 2019
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 209, s. 81-93
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Tidskriftsartikel (refereegranskat)abstract
- In situ measured benthic fluxes of dissolved inorganic carbon (DIC), a proxy for organic carbon (OC) oxidation or recycling rates, are used together with burial rates based on measured sediment accumulation rates (SAR) and vertical distribution of OC in the sediment solid phase to construct a benthic OC budget for the Baltic Sea system. The large variability in recycling rates (4.3 ± 0.87–33 ± 17 mmol C m−2 d−1) and burial rates (1.2 ± 0.8–5.9 ± 1.8 mmol C m−2 d−1) between different sub-basins and between different depositional areas within the basins is accounted for in the budget. Our results indicate that sediments in the Baltic Sea have much higher recycling rates and lower burial rates of OC than previously found. The sediment budget calculations show that 22 ± 7.8 Tg C yr−1 of OC is recycled to the water column due to organic matter oxidation, while long term burial amounts to 1.0 ± 0.3 Tg C yr−1. For the Baltic Sea as a whole, 96% of the particulate OC (POC) deposited on the sea floor (23 ± 7.8 Tg C yr−1; the sum of recycling and burial) is recycled back to the water column. However, the burial efficiency (i.e. the fraction buried of the total deposition) shows large variability between the different basins (2.5–16%). The total benthic POC deposition is approximately 20% higher than the estimated POC source originating from primary production in the water column and riverine input. This difference is likely within the uncertainty range of our budget calculations, however it indicates that the POC sources might be underestimated. The results from this study enhance the understanding of OC delivery, deposition and cycling in the Baltic Sea, and help improving existing Baltic OC budgets.
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| 14. |
- Ploug, Helle, et al.
(författare)
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Oxygen diffusion limitation and ammonium production within sinking diatom aggregates under hypoxic and anoxic conditions
- 2015
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 176, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- Sinking diatom aggregates are important components of vertical elemental fluxes and represent 'hotspots' of microbial-driven remineralization in the water column. A combined analytical approach of microsensors and fluorometry was used to measure oxygen (02) and ammonium (NH4+) concentrations in sinking diatom aggregates as a function of the ambient 02 concentrations. Diffusive fluxes of 02 and NH4+ within and around sinking aggregates were subsequently analyzed using a diffusion reaction model. Diffusion limitation of 02 within the diatom aggregates occurred when ambient 02 concentrations decreased beneath 100 mu M. At ambient 02 concentrations of 20 mu M, the measured flux of 02 to aggregates was equivalent to 33% of fluxes when 02 concentrations were in equilibrium with the atmosphere and approximately 50% of the aggregate volume was anoxic. When the diatom aggregates were maintained under hypoxic conditions, was produced in a ratio of 8.9 mol O-2 consumed:1 mol NH4+ produced which is within the expected range during ammonification. The average POC-specific respiration rate and the average PON-specific NH4+ production rate under hypoxic conditions were 0.065 d(-1) and 0.052 d(-1), respectively. Under anoxic conditions, the NH4+ release was 18% of that measured under hypoxic conditions. Our empirical and modeled data revealed diatom aggregates to be microenvironments of elevated NI-It concentrations ranging from 1 to 8 mu M and therefore to be potential sources of NH4+ in the oxygen minimum zones in the ocean. (C) 2015 Elsevier B.V. All rights reserved.
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| 15. |
- Rowe, Owen F., et al.
(författare)
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Major differences in dissolved organic matter characteristics and bacterial processing over an extensive brackish water gradient, the Baltic Sea
- 2018
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Ingår i: Marine Chemistry. - : Elsevier. - 0304-4203 .- 1872-7581. ; 202, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic matter (DOM) in marine waters is a complex mixture of compounds and elements that contribute substantially to the global carbon cycle. The large reservoir of dissolved organic carbon (DOC) represents a vital resource for heterotrophic bacteria. Bacteria can utilise, produce, recycle and transform components of the DOM pool, and the physicochemical characteristics of this pool can directly influence bacterial activity; with consequences for nutrient cycling and primary productivity. In the present study we explored bacterial transformation of naturally occurring DOM across an extensive brackish water gradient in the Baltic Sea. Highest DOC utilisation (indicated by decreased DOC concentration) was recorded in the more saline southerly region where waters are characterised by more autochthonous DOM. These sites expressed the lowest bacterial growth efficiency (BGE), whereas in northerly regions, characterised by higher terrestrial and allochthonous DOM, the DOC utilisation was low and BGE was highest. Bacterial processing of the DOM pool in the south resulted in larger molecular weight compounds and compounds associated with secondary terrestrial humic matter being degraded, and a processed DOM pool that was more aromatic in nature and contributed more strongly to water colour; while the opposite was true in the north. Nutrient concentration and stoichiometry and DOM characteristics affected bacterial activity, including metabolic status (BGE), which influenced DOM transformations. Our study highlights dramatic differences in DOM characteristics and microbial carbon cycling in sub-basins of the Baltic Sea. These findings are critical for our understanding of carbon and nutrient biogeochemistry, particularly in light of climate change scenarios.
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| 16. |
- Ulfsbo, Adam, 1985, et al.
(författare)
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Activity coefficients of a simplified seawater electrolyte at varying salinity (5–40) and temperature (0 and 25 °C) using Monte Carlo simulations
- 2015
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 171, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- Mean salt activity coefficients of a simplified seawater electrolyte (Na+, Mg2+, Ca2+, Cl−, SO42−, HCO3−, CO32−) at varying salinity (5–40) and temperature (0–25 °C) were estimated by Monte Carlo (MC) simulations, and compared with Pitzer calculations. The MC simulations used experimentally determined dielectric constants of water at different temperatures, and optimal agreement with the experimental data and the Pitzer calculations was achieved by adjusting the ionic radii. The results, together with a previous study of the carbon dioxide system in sodium chloride solution by the authors, suggest that a complete Monte Carlo description of seawater activity coefficients may be achievable using the charged hard sphere approach with a very limited number of fitted parameters (effective ionic radii), in contrast to the large number of fitted parameters required for a Pitzer model.
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| 17. |
- 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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| 18. |
- Wuensch, Urban, 1986, et al.
(författare)
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Quantifying the impact of solid-phase extraction on chromophoric dissolved organic matter composition
- 2018
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 207, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- Advancing our understanding of the behaviour of dissolved organic matter (DOM) in aquatic environments necessitates efforts to combine complementary analytical data sets. However, some analytical measurements require sample pre-treatment, while others are carried out on bulk water samples, and it remains unclear if the resulting data sets can be compared. Here, we investigated the impact of solid-phase extraction with PPL resins on DOM optical properties. In samples from contrasting Arctic fjords, extraction efficiencies based on optical properties varied spectrally with averages between 31 ± 13% at 411 nm and 40 ± 12% at 363 nm for chromophoric DOM. Similarly, the extraction efficiency for specific fluorescence components varied between 37 ± 16% and 58 ± 18%. Solid-phase extraction also decreased S275–295, fluorescence index, and the freshness index, but increased S350–400, and apparent fluorescence quantum yields, indicating that the extraction process was qualitatively selective. Six fluorescence components identified independently in bulk water samples and extracted DOM using parallel factor analysis exhibited different behaviours. Three had identical spectral properties before and after extraction, although their extraction efficiencies varied with water mass characteristics and DOM composition, whereas three other components appeared to change after extraction. With the exception of one fluorescence component, the dynamics of optical properties in bulk water samples were not accurately reflected by DOM extracts. These results indicate that solid-phase extraction imparts a qualitative selectivity that leads to the homogenization of DOM extracts relative to their original samples. Efforts to integrate chemical information from different analytical methods should prioritize comparisons of measurements obtained on the same samples.
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| 19. |
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