Gd Anomalies Research Articles

Mobilization and re-distribution of major and trace elements during extreme weathering of basalt in Hainan Island, South China

Major, trace and organic elements of a laterite profile developed on Neogene basalts in northern Hainan Island, South China were reported in this paper, the aim of which was to investigate element mobilization and re-distribution during extreme weathering. The results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution. Organic matter (OM) can significantly improve the transport of insoluble elements. Among all the elements, Th is the least mobile. As for the general conservative elements during incipient chemical weathering, such as Fe, Ti, Zr, Hf, Nb and Ta, the removals are up to 20–40% in the upper profile. However, these elements behave as conservatively as Th in the lower profile. In the middle profile, oxic environment occurs, accompanied with significant OM decomposition. The Mn and Ce transferred downward are readily oxidized into insoluble Mn(IV) and Ce(IV) and precipitate in the oxic front. Important OM decomposition decreases the capacity of transfer of insoluble elements in aqueous solution. Consequently, Al significantly precipitates in the oxic front, and REEs, with the exception of Ce, precipitate largely in the OM-depleted layers. Co and U are also concentrated in the oxic front in association with Mn and Ce, respectively. However, Cr shows a negative correlation with Mn because its response to redox condition changes is reversed from that of Mn. Mn oxides/hydroxides, Fe oxides/hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for REEs except for Ce in the profile; REEs with high concentrations in the profile seem closely associated with Mn oxides/hydroxides. Remarkable, highly correlated, Ce and Gd anomalies are observed in the profile. Ce anomalies are caused by Ce precipitation in the oxic environment and successive decomposition of organic matter. Gd anomalies are likely to have resulted from lower stability constants of Gd–OM complexes compared to those of neighboring REEs. The overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re-distribution of the elements during extreme weathering.

Hydrochemical processes in the lower Jordan valley and in the Dead Sea area

Changes in the concentrations of major, some minor and trace elements occurring in both surface and groundwater of the lower Jordan River–Dead Sea drainage basin have been investigated in order to identify the characteristics of the regional aquifers and their recharge areas. Spider patterns of elements and rare earth distribution patterns pinpoint the characteristic chemical features of groundwater. As compared to seawater, the high Br/Cl ratios in groundwater are caused either by high Br/Cl ratios in precipitation, by leaching of Br from bituminous matter or by mixing with brines beyond the epsomite stage. The locations of groundwater samples with enhanced B contents coincide with the distribution of gypsum in the beds of the Lisan Formation, which produces water with nearly constant B/SO 4 2− molar ratios. Aeolian distribution of the unconsolidated Lisan sediments influences the B/SO 4 ratio in the area of Lake Tiberias and in the Jordan Highlands. The high Gd anomaly in the Dead Sea water is of geologic origin whereas that in the Jordan River and in Nahal (stream) Qidron is largely anthropogenic. The anthropogenic Gd input to the Dead Sea is insignificant compared to the actual amount in the water of the Dead Sea. Hot saline water encountered along the western shores of the Dead Sea with high Gd anomalies indicate that they contain large amounts of ancient Dead Sea water that mix (as hot ascending brines) with fresh water. The recharge area of groundwater in the lower Jordan Valley extends largely over limestone and dolomite outcrops of the Upper Cretaceous Judea Group. Weathering of locally underlying Lower Cretaceous volcanics in the area of Pezael–Beqaot, and Argaman yield groundwater with δ 34S(SO 4 2−) values ranging from − 2 to + 4‰. The presence of sulphide-bearing bodies in this area is attested to magnetic anomalies detected at depths of several kilometres. δ 34S(SO 4 2−) indicates very deep groundwater circulation. High δ 34S(SO 4 2−) > 15‰ is typical for marine sulphates from the Judea and Avedat Group limestone. The springs located along the northwestern shore of the Dead Sea discharge water replenished on the eastern Judea Mountains. The increase in the salinity of this water is due to brines flushed from sediments and from adjacent sedimentary rocks, which host entrapped brines from the precursors of the Dead Sea formed during the late stages of Lake Lisan. Fresher water flushes out these residual brines as a result of falling sea level. Salinity increase in groundwater is also affected by the ascent of deep-seated hot brines from pre-Sedom periods along the Rift faults. Calculations of mixing between fresh and highly saline end-members show that leaching of anhydrite from sediments, precipitation of calcite, formation of dolomite, albitization of plagioclase and ion exchange with abundant clay minerals control the major-element composition of the saline groundwater.

Anthropogenic gadolinium as a micropollutant in river waters in Pennsylvania and in Lake Erie, northeastern United States

“Anthropogenic” gadolinium, Gd, used in contrast agents in magnetic resonance imaging, is a micropollutant that enters river and lake waters with the discharge from wastewater treatment plants, WWTPs. Such discharge is also the source of other micropollutants, for example pharmaceuticals, such as steroids, antihistamins, and antibiotics. Together with the “natural” Gd, the anthropogenic Gd produces positive Gd anomalies in rare-earth element distribution patterns and is, therefore, easily detectable. This pilot study reports on the occurrence of anthropogenic Gd in rivers in Pennsylvania (Ohio, Beaver, Allegheny, Monongahela, Juniata, and Susquehanna) and in near-shore surface water from Lake Erie close to the city of Buffalo. Additional data are reported for the Delaware River and the headwaters of Spring Creek in Central Pennsylvania, and for Lake Ontario and Niagara River, all of which do not show significant anthropogenic Gd. Most pronounced impact of anthropogenic Gd discharged from WWTPs is observed in the Pittsburgh Metropolitan area. Such contamination is similar to that observed in densely populated areas with highly developed medical and healthcare systems in Europe and Japan. Its worldwide applicability adds to the promising potential of anthropogenic Gd as a cost-effective tracer for the presence of WWTP effluent in river, lake, ground, and drinking waters.

Rare earth and trace elements of microbialites in Upper Jurassic coral- and sponge-microbialite reefs

Major, trace (Y, Zr, Pb, Th and U), rare earth element (REE) and Sm–Nd isotope analyses were carried out on microbialites and detrital carbonate sediments collected in Upper Jurassic coral- and sponge-microbialite reef settings. Selected bioconstructions developed in various palaeogeographic settings and depositional environments on northwestern Tethys and eastern Atlantic margins: pure carbonate lagoon, carbonate-dominated deep shelf to epicontinental basin and mixed carbonate-siliciclastic shallow ramp and lagoon. The proximity to terrigenous sources directly controlled REE patterns of carbonate samples. Lateral and intra-reef sediments, and to a lesser degree stromatolitic microbial crusts, are more susceptible to contamination by terrigenous material than are microbialites of thrombolitic fabric. In mixed carbonate-siliciclastic settings, microbialites display a flat shale-normalized REE pattern. In pure carbonate lagoonal settings, microbialites have shale-normalized REE patterns similar to those of modern seawaters with a negative Ce anomaly [(Ce/Ce ⁎) up to 0.14], positive La and Gd anomalies, and light REE depletion relative to heavy REE. These data imply that similar REE chemistry than modern seawater already occurred on the northwestern Tethys margin at the Upper Jurassic. Strong negative Ce anomalies (< 0.4) imply microbialite formation in well-oxygenated seawaters both in coral reefs of pure carbonate lagoonal environments (Pagny-sur-Meuse) and sponge bioherms of deep-shelf settings (Plettenberg). Absence of positive Ce anomalies rules out an influence of alkaline and high-pH seawaters. Thus, REE patterns and Nd isotopic signatures, which are in perfect agreement with existing results for Tethysian seawater, confirm that microbialites can be used as proxies of palaeoenvironmental seawater chemical characteristics.

Rare earth element abundances in some seawaters and related river waters from the Osaka Bay area, Japan: Significance of anthropogenic Gd

Some major and trace elements in seawaters and related river waters from the Osaka Bay area, Japan were analyzed in order to examine rare earth element (REE) behaviors, especially the relationship between anthropogenic gadolinium (Gd) and nutrient concentrations. The local silicic rock normalized REE patterns for the seawaters show features of light REE depletion, negative Ce anomaly, and very small Eu anomaly. Moreover, some samples have obvious positive Gd anomalies due to contamination of Magnetic Resonance Imaging (MRI) contrast agents in medical use. We calculated the anthropogenic Gd concentrations by subtracting the assumed natural Gd concentration from the measured one. The anthropogenic or excess Gd concentrations of the seawater samples are well correlated with nutrient concentrations (NH4-N, NO2-N, NO3-N, PO4-P). Because both anthropogenic Gd and nutrients are abundant in sewage treatment plant (STP) effluents and much less abundant in non-contaminated river and seawaters, the observed trends can be explained by dilution of STP effluents with non-contaminated river and seawaters. It was found that the nutrient concentrations for a hypothetical STP effluent calculated by using these correlation lines are consistent with the average nutrient contents for the STP effluents in the study area. Moreover, we made a rough estimation of Gd budget in Osaka Bay. The estimated amount of the Gd MRI contrast agents consumed in the area seems to be consistent with the excess Gd concentrations of river and STP waters. The Gd observations in this study suggest that the Gd anomaly data can be used as a geochemical tracer of wastewater component in urban areas.

Aquatic geochemistry of the rare earth elements and yttrium in the Pioneer River catchment, Australia

The rare earth elements are strong provenance indicators in geological materials, yet the potential for tracing provinciality in surface freshwater samples has not been adequately tested. Rare earth element and yttrium concentrations were measured at 33 locations in the Pioneer River catchment, Mackay, central Queensland, Australia. The rare earth element patterns were compared on the basis of geological, topographical and land-use features in order to investigate the provenancing potential of these elements in a small freshwater system. The rare earth element patterns of streams draining single lithological units with minor land modification show strongly coherent normalised behaviour, with a loss of coherence in agricultural locations. Evidence is reported for an anthropogenic Gd anomaly that may provide a useful hydrological tracer in this region since the introduction of magnetic resonance imaging in 2003. Several samples display a superchondritic Y/Ho mass ratio (up to 44), which is not explainable within the constraints imposed by local geology. Instead, it is suggested that the additional Y is derived from a marine source, specifically marine phosphorites, which are a typical source of fertiliser phosphorus. The data indicate that, under some circumstances, scaled and normalised freshwater rare earth patterns behave conservatively.

Aqueous Stability of Gadolinium in Surface Waters Receiving Sewage Treatment Plant Effluent, Boulder Creek, Colorado

In many surface waters, sewage treatment plant (STP) effluent is a substantial source of both regulated and unregulated contaminants, including a suite of complex organic compounds derived from household chemicals, pharmaceuticals, and industrial and medical byproducts. In addition, STP effluents in some urban areas have also been shown to have a positive gadolinium (Gd) anomaly in the rare earth element (REE) pattern, with the Gd derived from its use in medical facilities. REE concentrations are relatively easy to measure compared to many organic wastewater compounds and may provide a more widely utilized tracer of STP effluents. To evaluate whether sewage treatment plant-associated Gd is a useful tracer of treatment plant effluent, an investigation of the occurrence, fate, and transport of rare earth elements was undertaken. The rare earth element patterns of four of five STP effluents sampled display positive Gd anomalies. The one site that did not have a Gd anomaly serves a small community, population 1200, with no medical facilities. Biosolids from a large metropolitan STP are not enriched in Gd even though the effluent is, suggesting that a substantial fraction of Gd remains in the aqueous phase through routine treatment plant operation. To evaluate whether STP-derived Gd persists in the fluvial environment, a 14-km study reach downstream of an STP was sampled. Gadolinium anomalies were present at all five downstream sites, but the magnitude of the anomaly decreased. Effluent from STPs is a complex mixture of organic and inorganic constituents, and to better understand the chemical interactions and their effect on REEs, the aqueous speciation was modeled using comprehensive chemical analyses of water samples collected downstream of STP input. These calculations suggest that the REEs will likely remain dissolved because phosphate and carbonate complexes dominate over free REE ions. This study supports the application of Gd anomalies as a useful tracer of urban wastewater.

A trace element study of siderite–jasper banded iron formation in the 3.45 Ga Warrawoona Group, Pilbara Craton—Formation from hydrothermal fluids and shallow seawater

Shale-normalised rare earth element and yttrium (REE + Y) patterns for siderite–jasper couples in a banded iron formation of the 3.45 Ga Panorama Formation, Warrawoona Group, eastern Pilbara Craton, display distinct positive Y and Eu anomalies and weak positive La and Gd anomalies, combined with depleted light REE relative to middle and heavy REE. Ambient seawater and hydrothermal fluids are identified as major sources of REE + Y for the BIF. In the case of siderites, strong correlations between incompatible trace elements and trace element ratios diagnostic of seawater indicate variable input from a terrigenous source (e.g. volcanic ash). We propose a volcanic caldera setting as a likely depositional environment where jasper and siderite precipitated as alternating bands in response to episodic changes in ambient water chemistry. The episodicity was either driven by fluctuations in the intensity of hydrothermal activity or changes in magma chamber activity, which in turn controlled relative sea level. In this context, precipitation of jasper probably reflects background conditions during which seawater was saturated in silica due to evaporative conditions, while siderites were deposited most likely during intermittent periods of enhanced volcanic activity when seawater was more acidic due to the release of exhalative phases (e.g. CO 2).

Gadolinium Anomaly in the Distributions of Rare Earth Elements Observed for Coastal Seawater and River Waters around Nagoya City

Abstract Coastal seawater and river water samples were collected near Nagoya port, located in the coastal area of the Ise Bay, and in six rivers around Nagoya City. The rare earth elements (REEs) in these samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) with chelating resin preconcentration. The concentrations of all REEs except for Pm in coastal seawater and river water samples could be determined at the concentration level from sub-ng L−1 to 10 ng L−1. In order to examine the relative concentration variations, the REE patterns were estimated by normalizing the concentrations of REEs in the water samples to those in Post Archean Average Australian Shale (PAAS). Significantly positive Gd anomalies in the REE patterns were observed for river waters down from the urban areas as well as for coastal seawater. Such Gd anomalies were especially remarkable for river water collected near sewage treatment facilities in the Tenpaku river. It was, thus, concluded that the Gd anomalies in the REE patterns were artificially caused by anthropogenic sources mainly due to recent use of a gadolinium compound as a contrast reagent for magnetic resonance imaging (MRI) in medical diagnosis.

Geochemistry of late Archaean stromatolites from Zimbabwe: evidence for microbial life in restricted epicontinental seas

We report comprehensive trace element and Sr-isotope data for microbial carbonates from the Archaean Mushandike limestone, Masvingo Greenstone Belt, Zimbabwe. The stromatolites have very coherent REE+Y patterns and share the essential shale-normalised characteristics of other Archaean marine precipitates (positive La and Gd anomalies, absence of a negative Ce anomaly and a strongly superchondritic Y/Ho ratio). Mixing models constrain the maximum amount of shale contamination to 0.25–1% and calculated detritus-free carbonate REE+Y systematics require precipitation from seawater. In terms of light-REE over heavy-REE depletion, however, the studied samples are very different from all other known Archaean marine precipitates. In shale-normalised plots, the Mushandike samples yield a negative slope. A very restricted, regional input source of the dissolved load is indicated because normalisation with locally occurring tonalite gneiss REE+Y data yields a pattern closely resembling typical shale-normalised Archaean marine chemical sediments. The disappearance of a negative Eu anomaly when patterns are normalised with local tonalite gneiss strengthens this interpretation. Sr-isotope ratios are strongly correlated with trace element contents and ratios, which explains the modest scatter in Sr-isotope ratios as representing (minor) clastic contamination. Importantly, even the least contaminated samples have very radiogenic initial 87 Sr/ 86 Sr ratios (0.7184) implying Sr input from an ancient high Rb/Sr source, such as the early Archaean gneisses of south-central Zimbabwe. A local ancient (3.5–3.8 Ga) source is also indicated by previously published Pb-isotope datasets for the Mushandike stromatolites. This is entirely compatible with the occurrence of 3.7–3.8 Ga zircons in quartzites and metapelites from comparably old greenstone belts within less than 150 km of the studied locality. Comparison of the Pb-isotope ratios of the Mushandike stromatolites with 2.7 and 2.6 Ga old stromatolites from the neighbouring Belingwe Greenstone Belt demonstrates differences in initial isotope composition that relate to the extent of exchange with the open ocean. The development of numerous basins on old continental crust, with water masses variably restricted from the open ocean, suggests a lack of strong vertical topography on this late Archaean craton.

Tracing element sources of hydrothermal mineral deposits: REE and Y distribution and Sr-Nd-Pb isotopes in fluorite from MVT deposits in the Pennine Orefield, England

Fluorite from Mississippi Valley Type (MVT) deposits in the South Pennine Orefield, England, displays significantly different distributions of rare earths and yttrium (REY) compared to fluorite from similar MVT deposits in the North Pennine Orefield. Samples from the South Pennine Orefield display negative Ce and positive Gd and Y anomalies but lack any Eu anomaly, indicating that the REY were mobilized from relatively pure marine sedimentary carbonates. In marked contrast, fluorite from the North Pennine Orefield lacks any Ce and Gd anomalies but shows a pronounced positive Eu anomaly, suggesting that the REY were provided by different source rock(s), that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation, and that it was derived from deeper crustal levels in the north compared to the south. The isotopic composition of Sr in Blue John fluorite from the South Pennine Orefield suggests that Sr was mobilized from Lower Carboniferous (Tournaisian) limestones, whereas Pb isotopes suggest that in contrast to REY and Sr, Pb was derived from aluminosilicate rocks. Neither Nd nor Sr or Pb isotopes can be used to radiometrically date the formation of Blue John fluorite. All isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid. Our results show that different solutes in a natural water (hydrothermal fluid, groundwater, etc.) may be derived from different sources, and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid. Our data provide evidence for the uncoupling of Sr, Nd and Pb during fluid-rock interaction and fluid migration, and show that the use of plots such as 87Sr/86Sr vs. eNd. to learn about mixing relationships (as is commonly done in igneous geochemistry) is unreliable when applied to natural waters and their precipitates.

Dissolved rare earth elements in the Southern Ocean, southwest of Australia: Unique patterns compared to the South Atlantic data.

Dissolved yttrium and rare earth elements (YREEs) have been measured in the Antarctic Circumpolar Current Region, southwest of Australia. Their vertical features are fairly smooth, irrespective of the different water masses in the water column, suggesting that the biogeochemical processes including reversible scavenging reactions and sinking particulate matter are important control on their distribution. Comparison to the previous data at nearly the same latitude of ∼40°S in the Southern Ocean of the Atlantic sector (German et al., 1995) indicates that our concentrations are significantly depleted in the lighter REEs. The difference in their mean concentrations systematically decreases with increasing atomic number, i.e., 67% for La, 40% for Nd, 15% for Sm and less than 5% for the REEs heavier than Tb and Y. Gadolinium is an exception to this trend with a deficit that is anomalously high at ∼36% compared to those of its neighbors, Eu and Tb. Negative Gd-anomalies exceeding 30% are recorded for the subsurface waters, which contrast with positive Gd anomalies of up to ∼20% in the North Pacific Deep Water (Alibo and Nozaki, 1999). The relative deficit of 62% for Ce(IV), perhaps fortuitously, fits well between those of La and Nd, despite its vertical profile being different from those of strictly tri-valent YREE(III)s. These observations cannot be explained simply by the REE fractionation during scavenging of particulate matter and/or regional variation of scavenging intensity alone, and suggest that there must be a REE compositional difference in the external sources, e.g., from shallow water sediments and lithogenic materials sinking through the water column. The unique REE(III) patterns of the Circumpolar Deep Water (CDW) and the Antarctic Bottom Water (AABW) with a LREE depletion in the southeastern Indian Ocean appear to be originated from igneous rocks around the Indonesian Archipelago. This is in contrast to the REE(III) patterns of a LREE enrichment with a maximum at Nd-Sm, reflecting continental sedimentary rocks, in the CDW and AABW in the South Atlantic and the western Indian Ocean. The markedly different REE patterns in the eastern and western components of CDW and AABW indicate that they can serve as novel tracers in elucidating the deep water circulation of the Indian Ocean.

Dissolved indium and rare earth elements in three Japanese rivers and Tokyo Bay: Evidence for anthropogenic Gd and In

New data on the dissolved (<0.04 μm) rare earth elements (REEs) and In in the Japanese Ara, Tama, and Tone river-estuaries and Tokyo Bay are presented. Unique shale-normalized REE patterns with a distinct positive Gd anomalies and a strong heavy-REE enrichment were seen throughout the data. The dissolved Gd anomaly is caused by local anthropogenic input mainly due to recent use of Gado-pentetic acid as a medical agent for magnetic resonance imaging (MRI) in hospitals. The heavy-REE enrichment may be attributed to fractionation during weathering and transport in the upstream of the rivers, and only partially to removal of light- and middle-REE enriched river colloids by the use of a new ultrafiltration technique. Dissolved In concentrations in the Japanese rivers are extraordinarily high as compared to those in the pristine Chao Phraya river of Thailand reported elsewhere (Nozaki et al., in press). Like Gd, the high dissolved In in the study area can also be ascribed to recent use of In-containing organic compound, In(DTPA) 2− in medical diagnosis. Thus, in the highly populated and industrialized area, dissolved heavy metal concentrations in rivers and estuaries may be significantly perturbed by human activities and the fate of those anthropogenic soluble substances in the marine environment needs to be investigated further.

Anthropogenic gadolinium as a conservative tracer in hydrology

Surface water and in some cases also groundwaters of industrialised and highly populated areas show REE patterns with outstanding positive Gd anomalies. These are formed by using gadopentetic acid (Gd-DTPA) as a contrast medium in magnetic resonance imaging. This Gd complex is very stable under natural conditions. It is an anion and so not adsorbed onto clay mineral surfaces or particulate organic matter, in contrast to free rare earth element (REE) ions ions. Thus, this complex is a pseudo-natural marker, and allows the study of the origin of certain waters and their fate during mixing processes.

Rare earth elements in Holocene reefal microbialites: a new shallow seawater proxy

The concentration of rare earth elements and yttrium (REE + Y) was determined in Holocene Mg-calcite microbialites from shallow reef framework cavities at Heron Reef, Great Barrier Reef. Shale-normalized REE + Y patterns of 52 microbialite samples show: (1) uniform heavy REE enrichment (Nd SN/Yb SN = 0.236, SD = 0.026); (2) consistent negative Ce and positive La anomalies; (3) marine Y/Ho ratios (56.17, SD = 2.66); and (4) slightly positive Gd anomalies. All of these features are consistent with the geochemistry of well-oxygenated, shallow ambient seawater. REE partition coefficients were calculated relative to shallow Coral Sea seawater. They are uniform (relative SD = 10.2%) across the entire mass range and almost two orders of magnitude higher than those between coral and seawater. Hence, terrigenous detritus-free, modern microbialites are a more reliable proxy for seawater REE chemistry than are skeletal carbonates. Ancient limestones have been considered largely problematic as sources for REE proxies owing to perceived problems with diagenesis, partly on the basis of relatively high REE concentrations in some limestones compared to modern skeletal carbonates. However, high REE concentrations in modern microbialites suggest that ancient limestones with relatively high REE concentrations, if not contaminated by terrigenous detritus, may reflect original seawater chemistry. Terrigenous contamination, if present, is readily detectable on the basis of co-occurring trace element concentrations (Sc, Hf, Th) and Y/Ho ratio. Hence, ancient, particularly reefal, limestones may provide reliable seawater REE proxies. The occurrence of microbialites in clean limestones as old as 3.5 Ga suggests the possibility of reconstructing shallow marine REE chemistry over most of Earth history with important implications for paleogeography and paleoredox studies.

Rare earth elements in seawater: particle association, shale-normalization, and Ce oxidation

Dissolved (<0.04 μm, not <0.4 μm) and total acid-soluble concentrations of rare earth elements (REEs) and yttrium were measured by using ICP mass spectrometry in the seawaters obtained from various depths in the western North Pacific near Japan. The difference, i.e., acid-soluble particulate fraction, was found to be small, 2–5% for all tri-valent light and middle REEs and less than 1% for heavy REEs and yttrium. The high particulate fraction of 31% for Ce is consistent with its predicted oxidation state of tetra-valence. Elevated particulate fraction of all REEs was found within ∼80 m above the bottom due to contribution of flocculated resuspended particles. The vertical profiles of REE(III)s show smoothly increasing convex curves with depth similar to those reported previously. Dissolved Ce concentration decreases from ∼6 pmol/kg near the surface to a minimum at 2.5 pmol/kg around 400 m where the North Pacific Intermediate Water penetrates, and then approaches to nearly constant value of ∼4 pmol/kg below 800 m. Particulate Ce concentration significantly increases from the surface to 200 m depth suggesting oxidation of Ce(III) to Ce(IV) and subsequent scavenging in the upper water column. However, there is no evidence in our data showing that Ce oxidation is continuously taking place even in the deep sea. Shale-normalized patterns of dissolved REEs were examined in detail, based on three datasets of composite shales available in the literature. Distinctively positive La and only slightly positive Gd anomalies were identified together with well-documented negative Ce-anomaly as common features of seawater. These anomalies systematically change with depth. Rapid changes occur in the upper several hundred meters suggesting that their distributions are largely governed by ocean circulation and biogeochemical cycling.

Behavior of rare earth elements in seawater at the ocean margin: a study along the slopes of the Sagami and Nankai troughs near Japan

Using a flow injection ICP-MS method, yttrium and all the lanthanides in seawater were determined in the coastal/offshore mixing regime near Japan. Marked enrichments in the trivalent rare earth elements (REEs) in the surface waters are ascribed to the influence of coastal waters from Tokyo Bay in March and perhaps somewhere else in September and October to this region. At less than half of the stations where the detailed vertical profiles were obtained throughout the water column, we found marked excess REE(III) concentrations near the bottom. These bottom concentration anomalies are probably caused by resuspension of underlying sediments. Excluding those surface and bottom anomalous concentrations, the distribution of REE(III)s in the midwater column are very similar to those of the open ocean and are highly correlated with each other (R 2 > 0.95). This suggests that the boundary effects on the chemical fractionation of REE(III)s are small. We find no effect of the boundary scavenging known for 210Pb and 231Pa on the REE distribution, whereas there may be preferential release of light and middle REE(III)s over heavy REEs from slope sediments to the seawater much like 227Ac. From the shale-normalized REE patterns, we obtained up to 90% negative Ce and 10% positive Gd anomalies in the water column.

Anthropogenic origin of positive gadolinium anomalies in river waters

Positive Gd anomalies in shale-normalised rare earth element (REE SN) patterns of natural waters may provide information on the types of ligands which control surface complexation of REE on particle surfaces. However, REE SN patterns of rivers which drain densely populated and industrialised areas in Central Europe and North America are characterised by pronounced positive Gd SN anomalies, whereas rivers in thinly populated, non-industrialised areas in Värmland and Dalarna, central Sweden, and Hokkaido, Japan, do not show such anomalies. Acidification experiments suggest that, unlike the other REE, the excess Gd found in German rivers is almost completely related to the ‘dissolved’ REE fraction (< 0.2 μm) in a water sample and not to the acid-soluble particulate fraction, suggesting a negligible particle reactivity of the excess Gd. The positive Gd SN anomalies are of anthropogenic origin and are most likely to result from the application of gadopentetic acid, Gd(DTPA) 2−, in magnetic resonance imaging (MRI). In MRI, gadopentetic acid, which is an organic aqueous Gd(III) complex with very high stability constant, is used as a paramagnetic contrast agent. Since positive Gd SN anomalies in rivers, lakes, semi-closed sea basins, and coastal seas, which receive riverine REE input from industrialised, densely populated areas may (partly) be of anthropogenic origin, the positive Gd SN anomaly can no longer be used as a natural geochemical indicator.

Complexation of trivalent rare earth elements (Ce, Eu, Gd, Tb, Yb) by carbonate ions

Carbonate stability constants for five rare earth elements (Ce3+, Eu3+, Gd3+, Tb3+, and Yb3+) have been determined at t = 25°C and 0.70 ± 0.02 M ionic strength through solvent exchange techniques. Estimated stability constants for Ce, Eu, and Yb are in close agreement with previous work. Analyses using Gd and Tb provide the first carbonate stability constants for these elements based on direct measurements. Our measured stability constants were used to estimate carbonate stability constants for the entire suite of REEs. Our Eu, Gd, and Tb carbonate stability constants demonstrate the existence of a “Gd-break”: Carbonate stability constants for Gd are smaller than those for Eu and Tb. In analogy to Gd concentration anomalies reported in field observations, Gd stability constant anomalies have been defined in terms of the difference log Lβn(Gd) − log {(Lβn(Eu) + Lβn(Tb))2}, where Lβn(M) = [MLn][M3+]−1[L]−n. Examinations of REE-organic stability constants demonstrate that 106 out of 125 organic ligands have negative Gd anomalies in their first stability constants. The magnitudes of negative Gd anomalies generally become greater with increasing magnitude in Gd-ligand stability constants. Field observations of positive anomalies in shale-normalized Gd concentrations can be explained in terms of REE scavenging by organic surface ligands, such as polyaminocarboxylic acids, which possess a more negative Gd anomaly than carbonate ligands. Our modeling efforts indicate that a mixture of strongly complexing organics such as polyaminocarboxylic acids, and weakly complexing organics such as mono- and dicarboxylic acids is consistent with the pattern of REE scavenging by marine particulate matter.

Isotopic composition of gadolinium in meteorites.

An alternative explanation is presented for the neutron effects observed by EUGSTER et al. (1970) in Gd extracted from the Norton County achondrite. It is suggested that an ‘early’ irradiation of the solar system material occurred at a temperature much higher than 200°K assumed by the above investigators. It appears that the Gd anomalies are closely related to the O and Mg anomalies recently observed in various meteorites.