Rare Earth Elements In Seawater Research Articles

Formation conditions of Jixian System cherts in the Qishan area, Ordos Basin: Implications for marine redox conditions and paleoecology

Abundant chert bands and nodules are discovered throughout the Mesoproterozoic Jixian System in the Ordos Basin. These cherts faithfully record the Jixian period oceanic conditions and paleoecology. However, the diagenetic mechanism of the cherts remains unclear and controversial. To understand the origin of these cherts, we performed a multitracer study by combining field reconnaissance, petrological analyses, Si isotope analysis, and major and trace element analysis of chert samples from the Qishan section. The results show that Jixian cherts had a high Al/(Al + Fe + Mn) value (~0.48), showed a flat distribution of rare earth elements in seawater, and most of the Fe/Ti values are <20. A weak negative Ce anomaly (~0.97) indicates the contribution of REY to weakly oxygenated seawater. The high isotopic composition of silicon (δ30Si = 0.74 ‰-1.35 ‰) and the average Siex value of 37.52 indicate that there is a source of biological silica, and the relationship between Eu/Eu* and Y/Ho and δ30Si shows that the hydrothermal and volcanic influences were less and correlated with seawater. The chert bands were closely related to biological activities. The chert nodules were influenced by hydrothermal activity. Secondary cherts were related to diagenesis, but the nature of siliceous fluids remains unchanged, still characterized by biogenic activity origins. The sea oxygen concentration in the Jixian period had increased, with periodic variations in the intensity of biological activities affecting the pH of the water body, or biological photosynthesis binding SiO2 colloid in water, affecting chert sediments, leading to frequent interlayering between dolomite and chert bands. Episodic hydrothermal fluids and late-stage diagenetic processes jointly influenced the formation of cherts. This study bears significant significance in enhancing our understanding of the sedimentary environment and the origin of cherts during the Jixian period in the Ordos Basin.

Rare earth element geochemistry of reef carbonates in the South China Sea since the Miocene: Insights into paleoclimatic significance

Seawater chemistry critically affects the functioning of ocean ecosystems. However, the evolution of the seawater chemistry in the South China Sea (SCS) since the Miocene is not fully resolved, and its links to tectonic and climate changes remain unclear. In-situ, shallow marine carbonates can provide insights into long-term changes in seawater chemistry and associated environmental processes. In this study, we conducted the rare earth element (REE) analysis of the NK-1 core in the southern SCS since the Miocene. The results reveal poor relationships between siliciclastic/diagenetic indicators (mineralogical, isotopic, and elemental data) and REE proxies, which demonstrate that the REE compositions are insensitive to non-carbonate contaminations and diagenesis. The results exhibit seawater-like REE patterns with LREE depletion, positive La anomaly, superchondritic Y/Ho ratio, and negative Ce anomaly, which demonstrate that this core has preserved a signal of the primary seawater REE composition. The Y/Ho ratios range from 45 to 80 and La anomalies range from 1.0 to 2.3 during ∼23–13 Ma, and they then decrease after ∼13 Ma, with the Y/Ho ratios ranging from 30 to 52 and La anomalies ranging from 0.6 to 1.5. Considering that seawater REE components are mainly sourced from terrigenous sources which exhibit lower La anomalies and Y/Ho ratios, our results indicate an enhanced terrigenous input since ∼13 Ma. We consider that the climate cooling and aridity since ∼13 Ma might be responsible for the phenomenon.

Evolution of rare earth element and εNd compositions of Gulf of Mexico seawater during interaction with Mississippi River sediment

A closed-system batch reaction experiment was conducted for 270 days to evaluate the effects of interaction between Gulf of Mexico (GOM) seawater and Mississippi River sediments on the system’s dissolved rare earth elements (REE) concentrations and neodymium isotopic compositions (εNd). This study specifically focuses on geochemical reactions involving silicic sediments derived from weathering of the North American continent as they affect the REEs and εNd of seawater along continental margins, in contrast to previous studies that investigated the influence of basaltic rocks and sediments on REEs and εNd in the ocean. Our results show that the dissolution of labile phases of lithogenic Mississippi River sediments leads to an approximately 100-fold increase in dissolved REE concentrations within the first 33 days of the experiment. Secondary mineral precipitation appears to lower the REE concentrations between days 33 and 270 of the experiment, although seawater REE concentrations remain elevated compared to initial values. The two-way elemental transfer involving dissolution and precipitation results in a net increase by a factor of 24 ± 12 (mean ± 1σ) in the dissolved REE concentrations by the end of the experiment (i.e., day 270). The dissolved REE concentration maxima observed after 33 days of the experiment represent the mobilization of approximately 0.37 % of the REE content of the operationally defined “exchangeable” fraction of the riverine sediments. The εNd values of the reactive lithogenic components were −9.77 and −9.95, which are similar to the GOM value of −9.81 ± 0.36. Because of the similarity between εNd values, changes in the seawater Nd isotope value throughout the experiment were subtle (mean ± std, reacted seawater εNd of −9.87 ± 0.17). The highest REE concentrations coincided with the most radiogenic εNd (-9.65 ± 0.23; day 33), which suggests that REE concentrations and εNd compositions of the GOM may be buffered by fluxes from sediments in the system. Our results are comparable to previous studies involving basaltic rocks and/or sediments of basaltic composition in that they demonstrate that silicic, river sediments are highly reactive in marine environments with regard to REE mobilization. The experimental results further suggest that “boundary exchange” plays an important role in influencing the εNd of seawater along continental margins dominated by large river systems, although the impacts of boundary exchange will be most profound where ambient seawater and river sediments have distinct Nd isotopic compositions (e.g., basaltic, or Precambrian shield material). Finally, our results indicate that the εNd value of GOM seawater is largely controlled by the lithogenic sediment delivered to the basin by the Mississippi River.

Capabilities of size exclusion chromatography (in off- and on-line modes) to reduce matrix effects in ICP-MS analysis of complex solutions

The analytical capabilities of frontal size exclusion chromatography are studied using neutral polystyrene sorbents. When studying the separation of mineral acids and their salts, it is shown that clear separation of the zone of thorium ions and rare-earth elements from the following acid zone is observed on the microporous hypercrosslinked polystyrene sorbents Purolite NN-381 and MN-270. However, separation of the ions of highly charged elements (Zr, Hf, Nb, Ta) from the acid on the studied Purolite sorbents failed. Peaks of significant self-concentration appear in the zone of thorium and rare-earth element release at a concentration of 0.1 – 50 μg/liter. The factors affecting concentration of the analytes were studied. The nature and concentration of the acid, as well as concentration of the analytes, affect the concentration coefficients which attain maximum values in the solutions of nitric acid compared to hydrochloric and phosphoric acids. The degree of analyte concentration depends on the structure of internal pores and dispersion of the sorbent, as well as on the rate of solution passage through the column. Macro-components of seawater are not retained or concentrated on hypercrosslinked polystyrene. Sodium and magnesium at a concentration of 0.1 wt.% do not affect the value of the concentration factor of the target analytes. After chromatographic separation, weakly acidic fractions of the solution with concentrated ions of REE and thorium can be obtained by simple passing of a portion of the test solution through the sorbent layer for 15 – 30 min. The resulting concentrate can be directly introduced into a mass spectrometer. The possibility of combining chromatographic separation and concentration of elements and on-line ICP-MS detection is studied. Optimal conditions for on-line detection have been selected; the accuracy of the developed approach is demonstrated in the determination of rare earth elements in seawater using the spiked test.

Development of a fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater.

Rare earth elements (REEs) are useful geological indicators of marine geochemistry. However, extremely low concentrations (sub-ng L−1) and high-salt matrices result in inefficient measurements. A fully automatic separation system (ELSPE-2 Precon) is used in the online determination of ultra-trace REEs in seawater using inductively coupled plasma mass spectrometry. This system mainly comprises three sections: (i) an auto-sampler (eas-2A) with 120 positions; (ii) a poly(styrene-divinylbenzene) resin column (Prin-Cen Col007) with iminodiacetic and ethylenediaminetriacetic acid functional groups to eliminate the high-salt matrix (e.g., Na, Ca, K, Mg, Al, Ba, Fe, Sr, P, and S) and preserve the target REEs; and (iii) a Trp002 cleanup column for the reduction of the reagent and procedural blank values. The detection limits (3σ) were in the range 0.002 (Dy)–0.097 ng L−1 (La), and the long-term reproducibility (8 h) was between 80% and 120% for all REEs in a 3.5% NaCl matrix solution. The accuracy of this method was verified using a seawater reference material (NASS-6), and the measured REE concentrations were consistent with those previously reported. The proposed online system was used to investigate coastal water samples with varying salinities from the Pearl River Estuary (Guangdong, China). Variations in the REE distribution patterns of different layers of seawater were observed, which could be due to the mixing of potentially light rare earth element-enriched bottom seawater. Moreover, a positive Gd anomaly in river water and seawater might be attributed to anthropogenic pollution from hospitals and the pharmaceutical industry.

Elemental and isotopic evidence for the presence of a microbial thriving environment during the deposition of Early Cambrian Xiaoerbulake Formation in the Tarim Basin, NW China

Microbial communities regained prominence in the Cambrian after a prolonged downturn in the Neoproterozoic, but the reasons for their revival are unclear. The earliest microbialites formed during this period within the Tarim Basin are well displayed in the Xiaoerbulake Formation in the Keping area. Major, trace, rare earth element (REE) analyses were carried out using samples collected from two sections of the Xiaoerbulake Formation which present two different palaeogeographical settings, namely, the intraplatform and platform margin. The samples were divided into seven groups based on their REE + Y (yttrium) distributions. Among these, the YG3, YG4, and PG3 groups correspond to microbial boom phases. The high contents of Al and other nutrient elements (e.g., P, Ni, U, Cu, Fe, Mn) in these three groups indicate that the microbial booms are controlled by nutrient concentration of different sources. In relatively deep‐water settings, aeolian dust and suspension particles modified the seawater geochemical characteristics to form shale‐like (REE + Y)N patterns. The nutrient‐rich fine‐grained deposits were blown up by storms and released nutrients. This eutrophication ultimately promoted microbial development and is demonstrated by light rare earth element enrichment patterns. In shallow‐water environments, microbes seemed to prefer quiet conditions, with sufficient nutrients provided by fluvial influx. In contrast, excess clastic materials inputs, be they carbonate or terrigenous debris, are unfavourable to the development of microbialites. Hence, it is expected that seawater REE preserved in ancient carbonates are capable of providing information on the impacts of seawater geochemical conditions on the evolution of microbialites.

Multielemental Determination of Rare Earth Elements in Seawater by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) After Matrix Separation and Pre-concentration With Crab Shell Particles

Considering the unique characteristics of rare earth elements (REEs), the presence of REEs beyond specific limits will adversely affect the environment and it can be employed as a powerful probe for investigating hydrogeochemical processes. This requires sensitive determination of REEs in natural seawater. A matrix separation and pre-concentration technique using the mini-column packed with crab shell particles (CSPs) by inductively coupled plasma mass spectrometry (ICP-MS) as a means of determination has been developed. The aim of the proposed method was to simultaneously determine 16 REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) at trace or ultra-trace concentrations in seawater. The biosorption capacity of CSPs was found to achieve 1.246–1.250 mg g−1 for all elements. In order to optimize performance of the method, the effects of analytical parameters concerning oscillation time, solution pH, salt concentration and eluent concentration were explored. Under the optimal conditions, the detection limits of REEs ranged 0.0006–0.0088 μg L−1, and relative standard deviations (n = 7) varied between 0.55 and 1.39%. The accuracy of developed method was evidenced by applying it to the analysis of REEs in seawater samples, with the overall recoveries at a level of 95.3 and 104.4%. Together, this work provides a promising and cost-effective CSPs-based pretreatment approach for REEs detection in sea environment.

Speciation of yttrium and the rare earth elements in seawater: Review of a 20-year analytical journey

This review describes a program that we have conducted for more than 20 years, first at the University of South Florida and then at the University of Maryland Center for Environmental Science, to systematically measure stability constants for solution complexes of yttrium and all rare earth elements (YREE), except Pm, at the ionic strength of seawater (I ~ 0.7). This effort informs our goal of better characterizing and understanding YREE speciation in the marine environment, in the presence of both inorganic and organic ligands (and sorbents). Since all YREE appear to show similar behavior as a function of ionic strength, patterns of stability constants for individual ligands have been extrapolated to I = 0 whenever sufficient data for at least one member of the series are available. Complexes with hydroxide, fluoride and chloride, carbonate, and sulfate, are treated in detail, being the most prominent inorganic YREE ligands. A natural siderophore (DFOB) and synthetic polyaminopolycarboxylic acids (NTA, EDTA, DTPA) are given as examples of strong organic YREE complexation which, while remaining poorly quantified, is thought to be important. Several YREE ligands that play a negligible role in seawater, or for which data are as yet scarce, are also briefly discussed. Many different and sometimes novel analytical approaches were used in our experiments and these are summarized in the introductory sections, along with a primer on the theory of chemical speciation. This paper is intended as a retrospective of our work, not as a critical review of all available data. Literature values are thus cited primarily for comparison with our results, to support specific arguments, or to highlight prior discrepancies that prompted our own studies.

How Feasible is Direct Determination of Rare Earth Elements in Seawater by ICP-MS?

With the increasingly wide industrial use of rare earth elements (REEs), their release into marine systems makes it important to understand in what quantities they occur and to what geochemical processes they contribute, preferably using direct analytical methodology. In this study, analytical performance of high-resolution ICP-MS was assessed with regard to quantification of REEs in seawater without matrix separation and analyte preconcentration. With optimized sample dilution, precise and interference-free quantifications of most of the REEs in samples taken from Kara Sea were obtained, with an accuracy of 3 to 9% (against the independently asserted values), repeatability of 3 to 5%, and intermediate precision and reproducibility, averaging 4 and 11%, respectively. The method was further validated by using a certified reference material for nearshore seawater. However, the limits of detection obtained (0.04 - 0.38 ng L-1), while not significantly inferior to those obtained after sample enrichment, appear to be not low enough to analyze high salinity sea samples (over 30 parts per thousand) or open-ocean water samples, which require higher dilution factors or contain (much) lower REE concentrations, respectively. Therefore, it was concluded that the direct determination of REEs is only possible from samples with moderate salinity such as estuarine or shallow-sea water. In the latter case, the longitudinal REE profiling assayed by ICP-MS allowed us to assume that the export of the contaminated material from land areas into estuaries and then to the sea by rivers may substantially contribute to the seawater pool of REEs.

Contrasted release of insoluble elements (Fe, Al, rare earth elements, Th, Pa) after dust deposition in seawater: a tank experiment approach

Abstract. Lithogenic elements such as aluminum (Al), iron (Fe), rare earth elements (REEs), thorium (232Th and 230Th, given as Th) and protactinium (Pa) are often assumed to be insoluble. In this study, their dissolution from Saharan dust reaching Mediterranean seawater was studied through tank experiments over 3 to 4 d under controlled conditions including controls without dust addition as well as dust seeding under present and future climate conditions (+3 ∘C and −0.3 pH). Unfiltered surface seawater from three oligotrophic regions (Tyrrhenian Sea, Ionian Sea and Algerian Basin) were used. The maximum dissolution was low for all seeding experiments: less than 0.3 % for Fe, 1 % for 232Th and Al, about 2 %–5 % for REEs and less than 6 % for Pa. Different behaviors were observed: dissolved Al increased until the end of the experiments, Fe did not dissolve significantly, and Th and light REEs were scavenged back on particles after a fast initial release. The constant 230Th/232Th ratio during the scavenging phase suggests that there is little or no further dissolution after the initial Th release. Quite unexpectedly, comparison of present and future conditions indicates that changes in temperature and/or pH influence the release of Th and REEs in seawater, leading to lower Th release and a higher light REE release under increased greenhouse conditions.

Rare earth elements and Nd isotopes as tracers of modern ocean circulation in the central Mediterranean Sea

Seawater rare earth element (REE) concentrations and Nd isotopic composition (εNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and εNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the εNd values here. On the other side, distributions of dissolved heavy REE (HREE) and εNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and εNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW takes on major importance when considering HREE in the model, EMDW fractions are preferentially detected with εNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before.

Rare earth elements in oyster shells: provenance discrimination and potential vital effects

Abstract. Rare earth elements (REEs) and yttrium in seawater originate from atmospheric fallout, continental weathering, and transport from rivers, as well as hydrothermal activity. Previous studies have reported the use of REE and Y measurements in biogenic carbonates as a means to reconstruct these surface processes in ancient times. As coastal seawater REE and Y concentrations partially reflect those of nearby rivers, it may be possible to obtain a regional fingerprint of these concentrations from bivalve shells for seafood traceability and environmental monitoring studies. Here, we present a dataset of 297 measurements of REE and Y abundances by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) from two species (Crassostrea gigas and Ostrea edulis). We measured a total of 49 oyster specimens from six locations in France (Atlantic Ocean and Mediterranean Sea). Our study reports that there is no significant difference in concentrations from shell parts corresponding to winter and summer periods for both species. Moreover, interspecific vital effects are reported from specimens from both species and from the same locality. REE and Y profiles as well as t-distributed stochastic neighbour embedding processing (t-SNE; a discriminant statistical method) indicate that REE and Y measurements from C. gigas shells can be discriminated from one locality to another, but this is not the case for O. edulis, which presents very similar concentrations in all studied localities. Therefore, provenance studies using bivalve shells based on REEs and Y have to first be tested for the species. Other methods have to be investigated to be able to find the provenance of some species, such as O. edulis.

Rare Earth Elements in Andaman Island Surface Seawater: Geochemical Tracers for the Monsoon?

The Asian summer monsoon affects the lives of billions of people. With the aim of identifying geochemical tracers for the monsoon related freshwater input from the major rivers draining into the Bay of Bengal and Andaman Sea we have taken surface seawater samples from various locations up and down the Andaman Islands during 2011. Importantly, in some locations samples have been taken in March, July and November, covering most of a seasonal cycle and different monsoon phases. Samples were collected from the side of small wooden boats or while swimming and were filtered within a few hours at 0.45 or 0.22 microns using the vacuum produced by a water jet or a hand operated peristaltic pump. Filtered and unfiltered samples were acidified to < pH 2 and analysed for Y and the REEs with an automated online preconcentration ICP-MS technique [1]. The local input of REEs from streams and sediment rich areas such as mangrove environments is clearly identified by middle REE enrichments in the shale normalised patterns of some samples. These middle REE bulges accompany large increases in dissolved REE concentrations at some locations, especially for the July samples obtained during the peak monsoon season with frequent storms. Y/Ho fractionation aslo occurs during the local input of dissolved REEs with affected samples having lower Y/Ho ratios. Conversly, some samples, in particular those taken after heavy rainfall in March, show strong REE scavenging accompanied by the prefferential removal of dissolved light REEs and higher Y/Ho ratios. The time series at a location away from local input sources shows remarkably similar REE patterns and concentraions in March and July. Then in October-November, following the peak in monsoon river discharge, the dissolved REE concentration increases by almost a factor of 2. The notable exception to this seasonal pattern is the Ce anomally which is around 0.3 in March and November but 0.6 in July, implying less oxidative removal of Ce(IV) during the peak summer monsoon rains. With the exception of elevated dissolved Ce concentrations, the North Pacific Deep Water normalised REE patterns are similar to those reported for offshore samples from the Bay of Bengal and Andaman Sea [2]. These seawater normalised patterns are distinctive having a middle REE enriched arc with similar light and heavy REE values suggesting the input from large rivers in the region is traceable using seawater REE chemistry. [1] Hathorne et al. (2012), Online preconcentration ICP-MS analysis of rare earth elements in seawater, Geochem. Geophys. Geosyst., 13, Q01020, doi:10.1029/2011GC003907. [2] Amakawa et al. (2000), Geochim. Cosmochim. Acta 64, 1715-1727.

Coral-inferred monsoon and biologically driven fractionation of offshore seawater rare earth elements in Beibu Gulf, northern South China Sea

We present a monthly dataset (AD 2002–2005) of rare earth elements (REEs) recorded in Porites coral, which were obtained from the Weizhou Island (WZI), Beibu Gulf, northwest of South China Sea (SCS). This offshore coral shows a strong seasonal cycle in REE/Ca ratios, with enriched REEs (total REEs, 100~140 ppb) in winter and depleted REEs (40~60 ppb) in summer. Since the influence of the river discharge is limited to the river mouth, its contribution to the dissolved REEs is negligible for the offshore area of WZI. Given the similar seasonal pattern of Ba/Ca, we suggest that the remobilization of REEs from river-transported sediments on the shelf of SCS through winter monsoon-driven mixing is the major source of REEs to WZI. Moreover, the peak time of the Nd/Yb ratio (occurred in spring) is not coupled with the occurrence of the maximum REEs, which could mainly be attributed to the degradation of biogenic particles that causes more light REE released in comparison to heavy REE. The Ce anomaly also displays a distinct seasonality (i.e., enhanced anomaly in winter and summer and diminished anomaly in spring), likely reflecting the microbial oxidation activities driven by seasonal temperature and nutrient cycles. Large Gd anomaly (Gd/Gd* up to 1.7) recorded in coral skeletons is unlikely originated from the natural sources, but reflects anthropogenic activities through the recent excessive use of Gd complexes by magnetic resonance imaging of medical examination in this region.

Mineralogy and geochemistry of silicate, sulfide, and oxide iron formations in Norway: evidence for fluctuating redox states of early Paleozoic marine basins

Laterally extensive silicate and sulfide iron formation associated with jasper (hematitic chert) beds and volcanogenic massive sulfide (VMS) deposits in Norway provide evidence of early mineral assemblages and redox conditions within coeval early Paleozoic seawater. Calculated detrital-free compositions record mixed hydrothermal (e.g., Fe, Cu) and seawater ± biogenic (e.g., Si, Ni, S, REE, P) components. Rare earth element (REE) patterns are characterized by small to large negative Ce anomalies and insignificant to locally large positive Eu anomalies, reflecting seawater REE carried to the seafloor by Fe–P-rich particles later modified by diagenetic processes. Protoliths of silicate iron formation precipitated in anoxic and intermittently euxinic deep waters by the diagenetic modification of amorphous Si–Fe oxyhydroxides and/or Si–Fe–OOH gels, based on possible modern analogues in the Red Sea. Diagenetic minerals include nontronite, greenalite, stilpnomelane, magnetite, manganosiderite, apatite, and iron sulfides. In sulfide iron formation, a local predominance of pyrrhotite over pyrite records highly reducing conditions caused by organic material. The geochemical data provide evidence for Mn–Fe–P shuttle and redox processes in a stratified basin with oxic or suboxic shallow waters and silica concentrations much higher than those of modern seawater. Hydrothermal plume-derived Fe present within the anoxic layer and near the chemocline formed mixed-valence oxyhydroxides and silicates and, intermittently, sulfides by reaction with aqueous Si and H2S, respectively, the latter derived from bacterial reduction of seawater sulfate at the chemocline. Major sustained fluxes of hydrothermally derived reductants (Fe2+, Mn2+, H2S, H2) produced from large seafloor systems such as Lokken may have changed the redox state of seawater in local, and possibly regional, basins from weakly or moderately oxic to intermittently anoxic or euxinic conditions.

Fraction-specific rare earth elements enable the reconstruction of primary seawater signatures from iron formations

Rare earth element (REE) abundances in iron formations (IFs) provide key evidence to track the redox evolution of the Precambrian oceans. Deriving information about processes and sources from IFs is complicated by the variable roles of diagenetic dissolution and precipitation that modify primary depositional signals in the rocks. Iron formations are typically mineralogically heterogeneous with varying amounts of carbonate (ankerite + siderite), oxide (predominantly magnetite) and silicate (chert and Fe-silicates). To date, little is known about the respective contributions of these fractions to the bulk-rock REE signal, and which fraction most accurately records primary seawater signals. Here we evaluate an optimized sequential extraction scheme for REE analysis in the ca. 2.46 Ga Asbestos Hills IFs from the Griqualand-West Basin in South Africa. These rocks were deposited immediately before the Great Oxidation Event and are potentially an important archive for large-scale redox changes in the (near) surface environment.To fully evaluate our method, we measured lanthanide elements plus ytrrium (REY) in individual minerals, in bulk rock samples and in three separate fractions using acetate, oxalate and total digestion sequential extractions. The extraction techniques were then verified using a mass balance approach, the first time that this has been comprehensively applied to IFs. Similarities between the carbonate fraction data and modern seawater, coupled with strong measurement reproducibility and systematic stratigraphic variability suggests that carbonate most closely tracks the primary seawater composition. The Asbestos Hills IFs show distinctive REY signatures with strongly variable (Yb/Pr)SN ratios, positive La anomalies, positive and constant Y/Ho, weakly positive Eu anomalies and a lack of Ce anomalies in their carbonate fraction. Stratigraphic variations in these parameters suggest deposition in a stratified fully anoxic ocean, which became shallower over time. The silicate fraction was influenced by various amounts of allochthonous material (detrital and volcanic ash), although some minerals including greenalite, minnesotaite and stilpnomelane may have tracked seawater REE variability. The oxide fraction was found to be the most REY-depleted and therefore susceptible to allochthonous influences as well as diagenetic controls. It shows a systematic MREE enrichment that has not been described in IFs before, but has been seen in sub-oxic, ferrous environments. An increase in the ratio of carbonate to oxide minerals ongoing upwards through the Asbestos Hills IF, from deep to shallow water conditions, most likely reflected an increase in dissimilatory iron reduction close to the margin of the anoxic basin.

Rare Earth Element Distribution in the NE Atlantic: Evidence for Benthic Sources, Longevity of the Seawater Signal, and Biogeochemical Cycling

Seawater rare earth element (REE) concentrations are increasingly applied to reconstruct water mass histories by exploiting relative changes in the distinctive normalised patterns. However, the mechanisms by which water masses gain their patterns are yet to be fully explained. To examine this, we collected water samples along the Extended Ellett Line (EEL), an oceanographic transect between Iceland and Scotland, and measured dissolved REE by offline automated chromatography (SeaFAST) and ICP-MS. The proximity to two continental boundaries, the incipient spring bloom coincident with the timing of the cruise, and the importance of deep water circulation in this climatically sensitive gateway region make it an ideal location to investigate sources of REE to seawater and the effects of vertical cycling and lateral advection on their distribution. The deep waters have REE concentrations closest to typical North Atlantic seawater and are dominated by lateral advection. Comparison to published seawater REE concentrations of the same water masses in other locations provides a first measure of the temporal and spatial stability of the seawater REE signal. We demonstrate the REE pattern is replicated for Iceland-Scotland Overflow Water (ISOW) in the Iceland Basin from adjacent stations sampled 16 years previously. A recently published Labrador Sea Water (LSW) dissolved REE signal is reproduced in the Rockall Trough but shows greater light and mid REE alteration in the Iceland Basin, possibly due to the dominant effect of ISOW and/or continental inputs. An obvious concentration gradient from seafloor sediments to the overlying water column in the Rockall Trough, but not the Iceland Basin, highlights release of light and mid REE from resuspended sediments and pore waters, possibly a seasonal effect associated with the timing of the spring bloom in each basin. The EEL dissolved oxygen minimum at the permanent pycnocline corresponds to positive heavy REE enrichment, indicating maximum rates of organic matter remineralisation and associated REE release. We tentatively suggest a bacterial role to account for the observed heavy REE deviations. This study highlights the need for fully constrained REE sources and sinks, including the temporary nature of some sources, to achieve a balanced budget of seawater REE.

Fast Determination of Yttrium and Rare Earth Elements in Seawater by Inductively Coupled Plasma-Mass Spectrometry after Online Flow Injection Pretreatment.

A method for daily monitoring of yttrium and rare earth elements (YREEs) in seawater using a cheap flow injection system online coupled to inductively coupled plasma-mass spectrometry is reported. Toyopearl AF Chelate 650M® resin permits separation and concentration of YREEs using a simple external calibration. A running cycle consumed 6 mL sample and took 5.3 min, providing a throughput of 11 samples per hour. Linear ranges were up to 200 ng kg−1 except Tm (100 ng kg−1). The precision of the method was <6% (RSDs, n = 5), and recoveries ranged from 93% to 106%. Limits of detection (LODs) were in the range 0.002 ng kg−1 (Tm) to 0.078 ng kg−1 (Ce). Good agreement between YREEs concentrations in CASS-4 and SLEW-3 obtained in this work and results from other studies was observed. The proposed method was applied to the determination of YREEs in seawater from the Jiulong River Estuary and the Taiwan Strait.

Triethylamine-assisted Mg(OH)2 coprecipitation/preconcentration for determination of trace metals and rare earth elements in seawater by inductively coupled plasma mass spectrometry (ICP-MS)

In this paper, we report an improved magnesium hydroxide, Mg(OH)2, coprecipitation method for the determination of 16 trace elements (Al, V, Cr, Mn, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Sb, Sn and Pb) and 18 rare earth elements (REEs), including Sc, Y, U and Th in seawater and estuarine water samples. The procedure involves coprecipitation of the trace elements and REEs on Mg(OH)2 upon addition of a small volume of triethylamine (TEA) followed by analysis of the dissolved pellet solutions by inductively coupled plasma mass spectrometry (ICP-MS). Three-step sequential coprecipitation was carried out on 10 mL aliquots of seawater to eliminate the matrix ions and to preconcentrate the analytes of interest into a 1 mL final volume. Spike recoveries varied from 85% (Th) to 105% (Y). Calcium (Ca), sodium (Na) and potassium (K) matrices were virtually eliminated from the analysis solutions. Collision reaction interface (CRI) technology utilizing H2 and He gases was employed to determine its effectiveness in removing the spectral interferences originating from the residual Mg matrix, TEA and plasma gases. H2 was more effective than He in reducing spectral interferences from TEA and plasma gases. Limits of detection (LODs) ranged from 0.01 ng L−1 (Ho) to 72 ng L−1 (Al). The method was validated by using certified seawater (CASS-4) and estuarine water (SLEW-3) reference materials. Precision for five (n = 5) replicate measurements were between 1.2% (Pr) and 18% (Lu). Fe, Pb, Sn, and Zn impurities in TEA were significant in comparison to the levels in CASS-4 and SLEW-3, while relatively high background signals impacted determinations of low levels of Sc and Th. The effects of these hurdles on precision and accuracy were alleviated by measuring these elements in spiked CASS-4 and SLEW-3.

Geochemistry of the Eocene limestones of the Jaisalmer basin, Rajasthan, India: Implications on depositional conditions and sources of rare earth elements

Major, trace and rare earth elements (REE) concentration of the Eocene limestones, Jaisalmer Basin, Rajasthan, India are analysed to reconstruct the depositional conditions and to identify sources of REEs. Among the major oxides, CaO is the dominant oxide followed by SiO2 in the studied limestones. Trace element Ba dominates over the other trace elements and it shows negative correlation with CaO. The Sr, occurring in small concentration, shows positive correlation with CaO. Other trace elements such as V, Zr, Sc, Y, Rb, Ni, Pb Co, Cu, U occur in small concentrations. The studied limestones show a positive correlation of ΣREE with Fe2O3, Ni, Th, Sc, and Y. These limestones possess sea-water like shale-normalized REE + Y pattern with light REE depletion, slight Gd enrichment, slightly positive La anomaly, positive Y anomaly, positive Eu anomaly, negative Ce anomaly and superchondritic Y/Ho ratio from 23.12 to 28.57. The dominance of CaO and low percentage of MgO suggest that mineral phase is calcite and there is absence of dolomitization. The occurrence of SiO2 and Al2O3 in appreciable percentages may be because of the siliciclastic input during the limestone precipiatetion. The low concentration of Uranium (0.4-3.7) and authigenic Uranium (Average Total U-Th/3 value = 0.74) indicate that the studied limestones were precipitated in oxic condition from seawater. The depletion of LREE suggests that the limestones were precipitated from the seawater. The positive correlation of ΣREE with Al2O3 Fe2O3, Ni, Th, Sc, and Y and negative correlation with CaO suggest an input of siliciclastic sediments from the land during limestone precipitation. The negative Ce anomaly, slightly positive La anomaly, slight Gd enrichment, positive Y anomaly, and positive Eu anomaly also suggest that the limestone was precipitated from the seawater with some siliciclastic input from continent. The low values of the Y/Ho ratio (23.12 to 28.57) in the studied limestones suggest some modification of the seawater by the input of freshwater in a coastal environment. The REEs of the studied limestones are correlable with the shallow sea water REEs with exception of a few elements. We envisage a coastal/shallow marine depositional environment where mixing of the continental material in sea water appears feasible.