| 11. |
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| 12. |
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| 13. |
- Andersson, P. S., et al.
(författare)
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Particle transport of 234U-238U in the Kalix River and in the Baltic Sea
- 1998
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Ingår i: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 62:3, s. 385-392
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Tidskriftsartikel (refereegranskat)abstract
- The role of particles for U isotope transport was investigated in the Kalix River watershed, a particle-poor, Fe/Mn-rich river in northern Sweden, and in the Baltic Sea estuary. Particles >0.45 μm are strongly enriched in U and contain 20-50% of the total riverine uranium budget and <1% of the total U in brackish waters (3-7 PSU). The particles have high δ234U which is close to that of dissolved U in the associated water, indicating that U on particles is dominantly nondetrital and isotopically exchanges rapidly with the ambient dissolved U. Particles at the river mouth are dominated by nondetrital Fe-Mn oxyhydroxides. Uranium and Fe are strongly correlated, clearly demonstrating that secondary Fe-oxyhydroxide is the major carrier of U in river water. There is no evidence for significant association of U with Mn-oxyhydroxide. Apparent U distribution coefficients ... were calculated for U between the authigenic Fe on particles and the solution. These values appear to be relatively constant throughout the year. This suggests an equilibrium between Fe in solution and authigenic Fe-oxyhydroxides on detrital particles. High values of .... calculated for one summer as well as high U concentrations in brackish waters can be explained by U scavenging by biogenic phases with low authigenic Fe content.
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| 14. |
- Andersson, Per S., et al.
(författare)
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Strontium, dissolved and particulate loads in fresh and brackish waters : the Baltic Sea and Mississippi delta
- 1994
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Ingår i: Earth and Planetary Science Letters. - 0012-821X .- 1385-013X. ; 124:1-4, s. 195-210
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Tidskriftsartikel (refereegranskat)abstract
- A study was conducted of the isotopic composition and concentration of Sr and of major elements in dissolved and suspended loads of fresh and brackish waters. The purpose was to establish the contributions of different parent rocks and minerals to Sr during weathering and transport and to identify the role of Fe_Mn oxyhydroxides in the redistribution of Sr in the water column during the sedimentary cycle. Studies were conducted on a profile across an oxic-anoxic boundary in the Baltic and on rivers covering behavior over an annual cycle. In general, the 87Sr/86Sr ratios differ between particulate and dissolved loads, with more radiogenic Sr in the particulate loads. These differences are attributed to differential weathering of minerals, where high Rb/Sr minerals dominate the particulate load and low Rb/Sr the dissolved load. There is broad correlation of 87Sr/86Sr with K/Al in the suspended load. The differences in 87Sr/86Sr between suspended and dissolved load are highly variable and are related to the Fe or Mn concentration on the particulates. In samples with high Fe/Al, the difference becomes small. A good correlation was found between Sr/Al and Fe/Al or Mn/Al in the particulates both in brackish and fresh waters. Sr is removed from solution both in rivers and in the Baltic Sea whenever there is formation of Fe_Mn oxyhydroxide particulates. This precipitation greatly diminishes the difference in isotopic composition of the dissolved and suspended loads. As the particles containing Fe_Mn oxyhydroxides settle, they dissolve in anoxic zones and release Sr. This provides a mechanism for Sr redistribution in the water column. Sr is thus only quasi-conservative in environments where Fe_Mn oxyhydroxides form or dissolve. From consideration of the isotopic differences in Sr between dissolved and suspended loads, it follows that the net Sr input depends upon weathering characteristics of the contributing mineral phases. Changes in weathering mechanisms due to climate change may cause Sr isotopic shifts in the marine environment.
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| 15. |
- Andersson, Per S., et al.
(författare)
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The importance of colloids for the behavior of uranium isotopes in the low-salinity zone of a stable estuary
- 2001
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Ingår i: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 65:1, s. 13-25
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Tidskriftsartikel (refereegranskat)abstract
- Particle-mediated removal processes of U isotopes were investigated during spring flood discharge in the low-salinity zone (LSZ, up to 3 practical salinity units [psu]) of a stable estuary. A shipboard ultrafiltration cross-flow filtration (CFF) technique was used to separate particles (>0.2 μm) and colloids (between 3000 daltons (3 kD) and 0.2 μm) from ultrafiltered water (<3 kD) containing "dissolved" species. Sediment traps were used to collect sinking material. Concentration of Fe and organic C, which are indicators of the major U carrier phases, were used to interpret the behavior of 234U-238U during estuarine mixing. Colloids dominated the river water transport of U, carrying ≈90% of the U. On entering the estuary, colloids accounted for the dominant fraction of U to about a salinity of 1 psu, but only a minor fraction (<5%) at 3 psu. A substantial fraction of the total U is removed at <1 psu by Fe-organic rich colloids that aggregate and sink during initial estuarine mixing in the Kalix River estuary. In contrast, at salinities >1 psu, there is a general correlation between U and salinity in all filtered fractions. The 234U/238U ratios in different filtered fractions and sinking particles were generally indistinguishable at each station and showed enrichment in 234U, compared with secular equilibrium (δ234U = 266-567). This clearly shows that all size fractions are dominated by nondetrital U. Consideration of U isotope systematics across the estuary reveals that substantial U exchange must occur involving larger particles at least to 1 psu and involving colloids at least to ≈1.5 psu. Further exchange at higher salinities may also occur, as the proportion of U on colloids decreases with increasing salinity. This may be due to decreasing colloid concentration and increasing stabilization of uranyl carbonate complexes during mixing in the estuary. The results show that although U is a soluble element that shows generally conservative mixing in estuaries, removal occurs in the very low salinity zone, and this zone represents a significant sink of U. Variation in composition and concentration of colloidal particles between different estuaries might thus be an important factor for determining the varying behavior of U between estuaries.
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| 16. |
- Andersson, Per S., et al.
(författare)
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The sources and transport of Sr and Nd isotopes in the Baltic Sea
- 1992
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Ingår i: Earth and Planetary Science Letters. - 0012-821X .- 1385-013X. ; 113:4, s. 459-472
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Tidskriftsartikel (refereegranskat)abstract
- We have determined the concentration and isotopic composition of Sr and Nd in waters from the Baltic Sea. The Baltic Sea is an intracontinental, stratified, brackish water, estuarine-like system, and the rivers emptying into it drain a suite of terranes ranging from Proterozoic-Archean in the north to Phanerozoic in the south. The sampled brackish waters range in salinity from seawater (SW) at 35.289‰ to a minimum of 2.460‰ at the surface in the innermost part of the Gulf of Bothnia. The Sr concentrations show generally conservative behavior, indicating a simple two-component mixing. However, small deviations (3-70 ‰) from a perfect mixing line reveal that the imprints from rivers with different Sr concentrations are preserved in the blending. Strontium concentrations from a depth profile across the redoxcline in the Baltic proper indicate that vertical particle transport alters the Sr concentration in the water. Our estimated concentration of Sr in the average freshwater input to the Baltic is 0.03 ppm, which is only about 0.4% of the SW concentration. The Sr isotopic data range from εSr(SW) = 0 in seawater to εSrBW(SW) = 7.8 in the least saline Baltic water (BW) sample in the Gulf of Bothnia. The isotopic composition of Sr versus 1/Sr in the Baltic Sea follows an almost perfect mixing line, which shows that seawater Sr is mixed with much more radiogenic components. Calculated end-member values of εSr*(SW) for each sample show that the riverine input into the Gulf of Bothnia has εSr*(SW) = 120-200and10-50 ε units in the Baltic proper. These values are in general agreement with direct measurements of river waters in each region. However, the calculated values in the Gulf of Bothnia are lower than the measured river water input in this region, which indicates the presence of less radiogenic Sr, presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with Sr from the Gulf of Bothnia rivers. The Nd concentration in the Baltic Sea is not conservative, varying between 5 and 45 ppt, with the highest concentrations in the bottom waters due to vertical particulate transport. A plot of εNd(O) in Baltic water yields a good correlation with the calculated freshwater end member εSr*(SW). The data show that it is possible to unravel the different freshwater sources into the Baltic and to identify the zones of particulate removal of both non-conservative species such as the REE and of quasi-conservative species such as Sr. The use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport. It should also be possible to trace lateral movements of freshwater inputs
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Boström, Kurt, et al.
(författare)
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Selective removal of trace elements from the Baltic by suspended matter
- 1981
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Ingår i: Marine Chemistry. - 0304-4203 .- 1872-7581. ; 10:4, s. 335-354
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Tidskriftsartikel (refereegranskat)abstract
- Suspended matter was collected at 30 stations in the Baltic and Kattegatt, at the thermocline and at the bottom, and analysed for Na, Ca, Mg, Si, Ti, Al, Fe, Mn, Ba, Sr, Ni and V. The composition of the suspended matter varies considerably, but can be described as a mixture of: (1) 12-25% terrigenous detritus with much Si, Al, Ti and Fe; (2) 75-88% biological matter with much Ni, V and Ba; and (3) some Mn-oxyhydroxide.The annual efflux of water from the Baltic is about 460 km3, with a suspended load in the Baltic straits of 1.2-3.6 mg ash material l-1 These values imply that much Si, Ti, Al, Fe, Sr, Ni and V and particularly much Ba and Mn are lost from the Baltic in the suspended load.The average suspended matter is richer in Mn(5×), Ba(2.5×), Sr(4×) and V(1.8×) than permanently depositing Baltic sediments. These constituents are relatively enriched in pelagic deposits, i.e. it is likely that much Mn, Ba and V in deep-sea sediments derive from the continents via suspended transport. This conclusion is supported by the similarity between suspended matter and average Atlantic pelagic sediment.
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