Johan Ingri

Temporal variations in the fractionation of the rare earth elements in a boreal river; the role of colloidal particles.

Rare earth element (REE) data from weekly sampling of the filtered (<0.45 μm) and suspended particulate phase during 18 months in the Kalix River, Northern Sweden, are presented together with data on colloidal particles and the solution fraction (<3 kDa). The filtered REE concentration show large seasonal and temporal variations in the river. Lanthanum varied between approximately 300 and 2100 pM. High REE concentration in the filter-passing fraction is related to increased water discharge and there is a strong correlation between the REE concentration, organic carbon, Al and Fe. Physical erosion of detrital particles plays a minor role for the yearly transport of particulate REE in this boreal river system. The suspended particulate fraction, which is dominated by non-detrital fractions, accounted for only 35% of the yearly total transport of La in the river. Approximately 10% of the REE were transported in detrital particles during winter. At spring-flood in May, about 30% of the LREE and up to 60% of the HREE where hosted in detrital particles. Ultrafiltration of river water during spring-flood shows that colloidal particles dominate the transport of filter-passing REE. Less than 5% of the filtered REE are found in the fraction smaller than 3 kDa. The colloidal fraction shows a flat to slightly LREE enriched pattern whereas the solution fraction (<3 kDa) show an HREE enriched pattern, compared with till in the catchment. Suspended particles show a LREE enriched pattern. Data indicate that the REE are associated with two phases in the colloidal (and particulate) fraction, an organic-rich phase (with associated Al–Fe) and an Fe-rich (Fe–oxyhydroxide) inorganic phase. The Ce-anomaly in the suspended particulate fraction in the river shows systematic variations, and can be used to interpret fractionation processes of the REE during weathering and transport. There was no anomaly at maximum spring-flood but during the ice-covered period the anomaly became more and more negative. The temporal and seasonal variations of the Ce-anomaly in the suspended particulate phase reflect transport of REE–C–Al–Fe-enriched colloids from the upper section of the till (and/or from mires) to the river at storm events.

Characterization of Siberian Arctic coastal sediments: Implications for terrestrial organic carbon export

Surface sediments were collected during the 2000 TransArctic Expedition along the Siberian Arctic coastline, including the Ob, Yenisey, Khatanga, Lena, and Indigirka estuaries. Sediments were chara ...

Thallium isotope variations in seawater and hydrogenetic, diagenetic, and hydrothermal ferromanganese deposits

Results are presented for the first in-depth investigation of Tl isotope variations in marine materials. The Tl isotopic measurements were conducted by multiple collector-inductively coupled plasma mass spectrometry for a comprehensive suite of hydrogenetic ferromanganese crusts, diagenetic Fe–Mn nodules, hydrothermal manganese deposits and seawater samples. The natural variability of Tl isotope compositions in these samples exceeds the analytical reproducibility (±0.05‰) by more than a factor of 40. Hydrogenetic Fe–Mn crusts have ϵ205Tl of +10 to +14, whereas seawater is characterized by values as low as −8 (ϵ205Tl represents the deviation of the 205Tl/203Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 104). This ∼2‰ difference in isotope composition is thought to result from the isotope fractionation that accompanies the adsorption of Tl onto ferromanganese particles. An equilibrium fractionation factor of α∼1.0021 is calculated for this process. Ferromanganese nodules and hydrothermal manganese deposits have variable Tl isotope compositions that range between the values obtained for seawater and hydrogenetic Fe–Mn crusts. The variability in ϵ205Tl in diagenetic nodules appears to be caused by the adsorption of Tl from pore fluids, which act as a closed-system reservoir with a Tl isotope composition that is inferred to be similar to seawater. Nodules with ϵ205Tl values similar to seawater are found if the scavenging of Tl is nearly quantitative. Hydrothermal manganese deposits display a positive correlation between ϵ205Tl and Mn/Fe. This trend is thought to be due to the derivation of Tl from distinct hydrothermal sources. Deposits with low Mn/Fe ratios and low ϵ205Tl are produced by the adsorption of Tl from fluids that are sampled close to hydrothermal sources. Such fluids have low Mn/Fe ratios and relatively high temperatures, such that only minor isotope fractionation occurs during adsorption. Hydrothermal manganese deposits with high Mn/Fe and high ϵ205Tl are generated by scavenging of Tl from colder, more distal hydrothermal fluids. Under such conditions, adsorption is associated with significant isotope fractionation, and this produces deposits with higher ϵ205Tl values coupled with high Mn/Fe.

The sources and transport of Sr and Nd isotopes in the Baltic Sea

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 e^(Sr)(SW) = 0 in seawater to e_(Sr)^(BW)(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 e_(Sr)^*(SW) for each sample show that the riverine input into the Gulf of Bothnia has e_(Sr)^*(SW) = 120–200 and 10–50 e 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 e_(Nd)(O) in Baltic water yields a good correlation with the calculated freshwater end member e_(Sr)^*(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.

238U234U and232Th230Th in the Baltic Sea and in river water

The concentration (C) of dissolved238U,234U,232Th and230Th in fresh and brackish waters from the Baltic Sea were determined using TIMS. The brackish waters range in salinity from that of sea water (SW) to 2.5‰. C238U in oxygen-saturated, surface waters is well correlated with salinity and shows quasi-conservative behavior, as does Sr. Samples from the redox water interface show depletion in C238U, demonstrating that dissolved U is being removed by FeMn oxyhydroxides. From a simple mixing relationship for the brackish water,δ234U* = 1000‰ was calculated for the fresh water source in the northern Baltic. A study of the Kalixalven River over an annual cycle yields highδ234U during spring and summer discharge and lower values during fall and winter, showing that different sources contribute to the U load in the river during different seasons. C232Th and C230Th in river water are governed by the discharge, reflecting the importance of the increased abundance of small particles ( < 0.45 μm) for the232Th230Th load at high discharge.232Th/238U in river water is about 40 times less than in detrital material. In the brackish water, C232Th drops 2 orders of magnitude in the low salinity region ( < 5‰), reaching a value close to that of sea water at a salinity of 7.5‰. Almost all of the riverine232Th must be deposited in the low-salinity regions of the estuary. The230Th/232Th in river waters is about twice the equilibrium value for232Th/238U (3.8). In the brackish waters,230Th/232Th is greater by a factor of 10–100 than both river water and SW. The big increase in230Th/232Th in the Baltic Sea waters over the riverine input indicates that the Th isotopes enter the estuary as a mixture of two carrier phases. We infer that about 96% of232Th in river water is carried by detrital particles, whereas the other phase (solution, colloidal) has a much higher232Th/232Th. Entering the estuary, the detrital particles sediment out rapidly, whereas the non-detrital phase is removed more slowly, causing a marked increase in230Th/232Th in the brackish water. In SW,230Th/232Th is closer to river input and detrital material than in brackish water. We conclude that in the deep sea,232Th is almost exclusively dominated by windblown dust and can be used to monitor dust flux. The230Th excess in Baltic rivers is produced in U-rich,232Th-poor peatlands and trapped in authigenic particles and transported with the particles. Time scales for producing the230Th excess are ∼ 2000–8000 yr. This is younger than, but comparable to, the time of the latest deglaciation, which ended some 9000 yr ago when the mires were forming. These results have implications for the possible mobility of actinides stored in repositories.

Solid speciation and fractionation of rare earth elements in a spodosol profile from northern Sweden as revealed by sequential extraction

A sequential extraction has been carried out on seven soil samples from a spodosol profile in till with granitic composition. The soil profile was sampled in northern Sweden. Five fractions were selected for extraction: (A) CH_3COONa-extractable (exchangeable/adsorbed/carbonate); (B) Na_4P_2O_7-extractable (labile organics); (C) 0.25 M NH_2OH⋅HCl-extractable (amorphous Fe-oxyhydroxides/Mn-oxides); (D) 1 M NH_2OH⋅HCl-extractable (crystalline Fe-oxides); and (E) KClO_3/HCl-extractable (organics and sulphides). Extracted rare earth elements (REE) were determined with High Resolution ICP-MS. In addition to the soil, stream water suspended particulate matter was also analysed for REE. Total concentrations in the soil samples show that the REE have been fractionated during weathering. In the acidic (pH 4.28) E-horizon all REE are depleted relative to the unweathered till. The depletion decreases with increasing atomic number. Also in the B-horizon (pH 5.86) the REE are depleted, although to a lesser extent compared to the E-horizon. Secondary phases in the B-horizon fractionate the REE in different ways. Rare earth elements extracted in extractions A and C were enriched in the intermediate REE relative to heavy and light REE if normalized to local till. In extractions B and D, the heavy REE were enriched relative to the light REE, and in extraction E a large enrichment of light REE relative to heavy REE was found. Stream water suspended particulate matter is enriched in all REE relative to local till. The light REE are more enriched than the heavy REE. Normalized La/Lu ratios in the suspended matter ranged from 1.5 to 2.4, and were negatively correlated with stream water discharge as well as with content of detrital inorganic matter in the suspended load. The only extracted phase that potentially can explain the high normalized La/Lu ratio in the suspended matter is the phase extracted in extraction E, which has a ratio of 2.0–4.2. The normalized La/Lu ratio for the rest of the extractions ranged from 0.5 to 1.2. It is concluded that organic matter seems to be important for the particulate transport of REE in northern coniferous areas.

Colloid dynamics and transport of major elements through a boreal river — brackish bay mixing zone

Abstract A range of biogeochemical methodologies were applied to investigate how aggregation processes affected the phase distribution and mixing of Fe, Si, and organic carbon between the Kalix River and the Bothnic Bay, northernmost Baltic Sea (salinity≤3; the low-salinity zone (LSZ) was stretching over 60 km in the spring). During the dynamic springflood conditions studied, small 238 U– 234 Th disequilibria, low sediment trap fluxes, laboratory mixing experiments, as well as results from an independent two-box, two-dimensional mixing model combine to suggest that no significant removal of Fe, Si, or organic C was occurring in the highly-resolved LSZ. While no conclusions may be drawn based solely on property–salinity plots over narrow salinity ranges, apparently linear graphs for Fe and Si over 3 separate years also suggest minimal removal in this regime. At the same time, size distributions both of elements —from cross-flow ultrafiltration — and of bulk suspended solids — from light scattering (photon correlation spectroscopy [PCS]) — indicated that significant aggregation was taking place. The aggregation-without-significant-settling scenario in this low-salinity mixing regime, with a geochemistry similar to that of neighboring Russian Arctic rivers, is hypothesized to result from a comparatively high organic-to-detrital matter characteristic of the aggregates. While first principles would indeed suggest that decreasing electrostatic repulsion during mixing lead to aggregation, a low specific density of mineral-poor amorphous organic aggregates may lead to transport of these authigenic particles further away from the river mouth. The role of detrital “sinkers” on vertical removal of suspended organic matter is discussed in the wider context of scavenging mechanisms in the ocean.

Geochemistry of manganese in the Kalix River, northern Sweden

Dissolved and suspended Mn in the Kalix River, northern Sweden, were measured weekly over a period of eighteen months. During the same period four lakes in the Kalix catchment were sampled at their outlets and in vertical profiles within the lakes, together with a stream draining a series of mires with shallow lakes. Snow melting in mid-May increased the dissolved Mn concentration in the river tenfold, compared with a concentration of 5 μg L−1 during the winter discharge (January to April). We suggest that the increase was caused by Mn-rich mire water mixing with melting snow and being transported to the river. Large concentrations of dissolved Mn built up in the hypolimnion of the lakes studied during the icecovered period. Break-up of the ice and spring-overturn in June increased the dissolved Mn concentration tenfold in lake discharge and a concomitant peak in the dissolved Mn concentration was observed in the river. Lake-derived Mn was the dominant source for Mn in the river during this time. Suspended Mn in the river was hosted mainly in detrital particles during flood in May. In mid-June, non-detrital suspended Mn started to accumulate and reached a maximum in late July and early August. The MnAl ratio was 25 times higher during this period than during flood in May, suggesting the precipitation of an Mn-oxyhydroxide phase. The precipitation of the non-detrital Mn-rich phase was correlated in time with increased temperature, increased pH and increased concentration of suspended biogenic particles. The precipitation of dissolved Mn was biologically mediated. Sedimentation and mineralisation of the non-detrital Mn phase in river and lake sediments resulted in a steady increase of the dissolved Mn concentration in the river water during autumn.

Mobility of rare earth elements during weathering of till in northern Sweden

Abstract Continuous, volume-controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till (typic haplocryods). All the samples were analysed for major and trace elements including the rare earth elements (REE). Eight thousand seven hundred years of weathering since the glacial ice left the area, has resulted in a strong depletion of REE in the E-horizon. This loss decreases as atomic number increases, so that 80–85% of the La and 54–60% of the Yb have been lost. Europium has been lost to a greater degree than have the neighbouring elements. Possible explanations for the release of REE are: weathering of common silicates such as hornblende and epidote (and plagioclase in the case of Eu); weathering of apatite; weathering of rare but REE-rich minerals such as allanite and monazite; and release of REE adsorbed on clay minerals. Further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of REE release. The release of REE continues within and below the Bs1-horizon, but the results from one station show that light REE can be enriched in the Bs1-horizon. This secondary enrichment could be caused by adsorption on secondary oxy-hydroxides, on clay minerals or on organic material. However, the net result of the weathering is that all REE have been released to the groundwater.

PARTICLE TRANSPORT OF 234U-238U IN THE KALIX RIVER AND IN THE BALTIC SEA

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 >0.45μm 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 δ^(234)U 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 (K_d^(Fe)) 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 K_d^(Fe) 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.