The Experts below are selected from a list of 7704 Experts worldwide ranked by ideXlab platform
J. Ingri - One of the best experts on this subject based on the ideXlab platform.
-
Fractionation of Iron species and Iron Isotopes in the Baltic Sea euphotic zone
Biogeosciences, 2010Co-Authors: J. Gelting, E. Breitbarth, B. Stolpe, M. Hassellöv, J. IngriAbstract:Abstract. To indentify sources and transport mechanisms of Iron in a coastal marine envIronment, we conducted measurements of the physiochemical speciation of Fe in the euphotic zone at three different locations in the Baltic Sea. In addition to sampling across a salinity gradient, we conducted this study over the spring and summer season. Moving from the riverine input characterized low salinity Bothnian Sea, via the Landsort Deep near Stockholm, towards the Gotland Deep in the Baltic Proper, total Fe concentrations averaged 114, 44, and 15 nM, respectively. At all three locations, a decrease in total Fe of 80–90% from early spring to summer was observed. Particulate Fe (PFe) was the dominating phase at all stations and accounted for 75–85% of the total Fe pool on average. The Fe isotope composition (δ 56Fe) of the PFe showed constant positive values in the Bothnian Sea surface waters (+0.08 to +0.20‰). Enrichment of heavy Fe in the Bothnian Sea PFe is possibly associated to input of aggregated land derived Fe-oxyhydroxides and oxidation of dissolved Fe(II). At the Landsort Deep the isotopic fractionation of PFe changed between −0.08‰ to +0.28‰ over the sampling period. The negative values in early spring indicate transport of PFe from the oxic-anoxic boundary at ∼80 m depth. The average colloidal Iron fraction (CFe) showed decreasing concentrations along the salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM, and Gotland Deep 0.5 nM. Field Flow Fractionation data indicate that the main colloidal carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid associated compound, likely of riverine origin. A strong positive correlation between PFe and chl-a indicates that cycling of suspended Fe is at least partially controlled by primary production. However, this relationship may not be dominated by active uptake of Fe into phytoplankton, but instead may reflect scavenging and removal of PFe during phytoplankton sedimentation.
-
Fractionation of Iron species and Iron Isotopes in the Baltic Sea euphotic zone
2009Co-Authors: J. Gelting, E. Breitbarth, B. Stolpe, M. Hassellöv, J. IngriAbstract:Abstract. Measurements of the physiochemical speciation of Fe in the euphotic zone were performed at three different locations, over a well defined salinity gradient, during spring and summer in the Baltic Sea. The average of total Fe changed from 114 nM in the Bothnian Sea, 44 nM at Landsort Deep and 15 nM at Gotland Deep. Particulate Fe (PFe) was the dominating phase at all stations and on average accounted for 75–85% of the total Fe pool. At all three locations, a decrease in total Fe of 80–90% from initial measurements compared to the summer was found. A strong positive correlation between PFe and chl-a was observed. Hence, primary production strongly regulates cycling of suspended Fe. However, this relation is not dominated by active uptake of Fe in phytoplankton; instead this reflects cycling of phosphorus, growth of diatoms, and removal of PFe during phytoplankton sedimentation. The average colloidal Iron fraction, CFe, showed decreasing concentrations along the salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM and Gotland Deep 0.5 nM. Field Flow Fractionation data indicate that the main colloidal carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid associated compound, likely of riverine origin. The Fe isotope composition (δ56Fe) of the PFe showed constant positive values in the Bothnian Sea surface waters (+0.08 to +0.20‰). Enrichment of heavy Fe in the Bothnian Sea PFe is most likely associated to input of aggregated land derived Fe-oxyhydroxides and a rapid overturn of Fe(II). At the Landsort deep, the fractionation of PFe changed between −0.08‰ to +0.28‰. The negative values, in early spring, probably indicate exchange over the oxic-anoxic boundary at ~80 m depth.
-
Fractionation of Iron Isotopes during estuarine mixing in Ob, Yenisey and Lena freshwater plumes
Geochimica et Cosmochimica Acta, 2009Co-Authors: J. Ingri, J. Gelting, Fredrik Nordblad, Emma Engström, Ilya Rodushkin, P.s. Andersson, Don Porcelli, Ö. Gustafsson, Igor Semiletov, Björn ÖhlanderAbstract:Iron Isotopes were measured in suspended matter (>0.2 µm) in the Ob, Yenisey and Lena River freshwater plumes during the International Siberian Shelf Study 2008 (ISSS-08). The δ56Fe value was ar ...
Olivier Rouxel - One of the best experts on this subject based on the ideXlab platform.
-
total dissolvable and dissolved Iron Isotopes in the water column of the peru upwelling regime
Geochimica et Cosmochimica Acta, 2015Co-Authors: Olivier Rouxel, Fanny Chever, Peter Croot, Emmanuel Ponzevera, Kathrin Wuttig, Maureen E AuroAbstract:Vertical distributions of Iron (Fe) concentrations and Isotopes were determined in the total dissolvable and dissolved pools in the water column at three coastal stations located along the Peruvian margin, in the core of the Oxygen Minimum Zone (OMZ). The shallowest station 121 (161 m total water depth) was characterized by lithogenic input from the continental plateau, yielding concentrations as high as 456 nM in the total dissolvable pool. At the 2 other stations (stations 122 and 123), Fe concentrations of dissolved and total dissolvable pools exhibited maxima in both surface and deep layers. Fe isotopic composition (δ56Fe) showed a fractionation toward lighter values for both physical pools throughout the water column for all stations with minimum values observed for the surface layer (between −0.64 and −0.97‰ at 10–20 m depth) and deep layer (between −0.03 and −1.25‰ at 160–300 m depth). An Fe isotope budget was established to determine the isotopic composition of the particulate pool. We observed a range of δ56Fe values for particulate Fe from +0.02 to −0.87‰, with lightest values obtained at water depth above 50 m. Such light values in the both particulate and dissolved pools suggest sources other than atmospheric dust deposition in the surface ocean, including lateral transport of isotopically light Fe. Samples collected at station 122 closest to the sediment show the lightest isotope composition in the dissolved and the particulate pools (−1.25 and −0.53‰ respectively) and high Fe(II) concentrations (14.2 ± 2.1 nM) consistent with a major reductive benthic Fe sources that is transferred to the ocean water column. A simple isotopic model is proposed to link the extent of Fe(II) oxidation and the Fe isotope composition of both particulate and dissolved Fe pools. This study demonstrates that Fe isotopic composition in OMZ regions is not only affected by the relative contribution of reductive and non-reductive shelf sediment input but also by seawater-column processes during the transport and oxidation of Fe from the source region to open seawater.
-
The role of paragneiss assimilation in the origin of the Voisey's Bay Ni-Cu sulfide deposit, Labrador: Multiple S and Fe isotope evidence
Economic Geology, 2013Co-Authors: R.s. Hiebert, A. Bekker, B.a. Wing, Olivier RouxelAbstract:Isotopic and geochemical studies conducted on the Voisey's Bay deposit, Labrador, Canada, suggest crustal contamination of the primary magma as a trigger for sulfur saturation and formation of the deposit. The use of multiple S Isotopes has allowed for the identification of a bacterial sulfate reduction biosignature in the Tasiuyak gneiss in the footwall to the Voisey's Bay deposit. This putative biosignature is preserved in the deposit even at high silicate magma/sulfide melt ratios (R-factor) and links the S present in the Voisey's Bay deposit to the Tasiuyak gneiss. Iron Isotopes in the Voisey's Bay deposit have been reset to magmatic values at R-factors > ≈100, but S isotope data can be used to model higher R-factors. A contamination model results in calculated R-factors of 433 ± 177. The multiple S isotope data are a new proxy to directly link S from the deposit to crustal S sources even in deposits with high R-factors where the equilibration with large amounts of silicate magma can make interpreting a link between the deposit and the sulfur source difficult
-
Mass spectrometry and natural variations of Iron Isotopes.
Mass spectrometry reviews, 2006Co-Authors: Nicolas Dauphas, Olivier RouxelAbstract:Although the processes that govern Iron isotope variations in nature are just beginning to be understood, multiple studies attest of the virtue of this system to solve important problems in geosciences and biology. In this article, we review recent advances in the geochemistry, cosmochemistry, and biochemistry of Iron Isotopes. In Section 2, we briefly address the question of the nucleosynthesis of Fe Isotopes. In Section 3, we describe the different methods for purifying Fe and analyzing its isotopic composition. The methods of SIMS, RIMS, and TIMS are presented but more weight is given to measurements by MC-ICPMS. In Section 4, the isotope anomalies measured in extraterrestrial material are briefly discussed. In Section 5, we show how high temperature processes like evaporation, condensation, diffusion, reduction, and phase partitioning can affect Fe isotopic composition. In Section 6, the various low temperature processes causing Fe isotopic fractionation are presented. These involve aqueous and biologic systems.
-
subsurface processes at the lucky strike hydrothermal field mid atlantic ridge evidence from sulfur selenium and Iron Isotopes
Geochimica et Cosmochimica Acta, 2004Co-Authors: Olivier Rouxel, Yves Fouquet, John LuddenAbstract:At Lucky Strike near the Azores Triple Junction, the seafloor setting of the hydrothermal field in a caldera system with abundant low-permeability layers of cemented breccia, provides a unique opportunity to study the influence of subsurface geological conditions on the hydrothermal fluid evolution. Coupled analyses of S Isotopes performed in conjunction with Se and Fe Isotopes have been applied for the first time to the study of seafloor hydrothermal systems. These data provide a tool for resolving the different abiotic and potential biotic near-surface hydrothermal reactions. The δ34S (between 1.5‰ and 4.6‰) and Se values (between 213 and 1640 ppm) of chalcopyrite suggest a high temperature end-member hydrothermal fluid with a dual source of sulfur: sulfur that was leached from basaltic rocks, and sulfur derived from the reduction of seawater sulfate. In contrast, pyrite and marcasite generally have lower δ34S within the range of magmatic values (0 ± 1‰) and are characterized by low concentrations of Se (<50 ppm). For 82Se/76Se ratios, the δ82Se values range from basaltic values of near −1.5‰ to −7‰. The large range and highly negative values of hydrothermal deposits observed cannot be explained by simple mixing between Se leached from igneous rock and Se derived from seawater. We interpret the Se isotope signature to be a result of leaching and mixing of a fractionated Se source located beneath hydrothermal chimneys in the hydrothermal fluid. At Lucky Strike we consider two sources for S and Se: (1) the “end-member” hydrothermal fluid with basaltic Se isotopic values (−1.5‰) and typical S isotope hydrothermal values of 1.5‰; (2) a fractionated source hosted in subsurface envIronment with negative δ34S values, probably from bacterial reduction of seawater sulfate and negative δ82Se values possibly derived from inorganic reduction of Se oxyanions. Fluid trapped in the subsurface envIronment is conductively cooled and has restricted mixing and provide favorable conditions for subsurface microbial activity which is potentially recorded by S Isotopes. Fe isotope systematic reveals that Se-rich high temperature samples have δ57Fe values close to basaltic values (∼0‰) whereas Se-depleted samples precipitated at medium to low temperature are systematically lighter (δ57Fe values between −1 to −3‰). An important implication of our finding is that light Fe isotope composition down to −3.2‰ may be explained entirely by abiotic fractionation, in which a reservoir effect during sulfide precipitation was able to produce highly fractionated compositions.
Un J Nabi - One of the best experts on this subject based on the ideXlab platform.
-
weak interaction mediated rates on Iron Isotopes for presupernova evolution of massive stars
European Physical Journal A, 2009Co-Authors: Un J NabiAbstract:During the presupernova evolution of massive stars, the Isotopes of Iron, 54, 55, 56Fe , are advocated to play a key role inside the cores primarily decreasing the electron-to-baryon ratio (Ye) mainly via electron capture processes thereby reducing the pressure support. Electron decay and positron capture on 55Fe , on the other hand, also have a consequential role in increasing the lepton ratio during the silicon burning phases of massive stars. The neutrinos and antineutrinos produced, as a result of these weak-interaction reactions, are transparent to the stellar matter and assist in cooling the core thereby reducing the entropy. The structure of the presupernova star is altered both by the changes in Ye and the entropy of the core material. The aim of this paper is to report the improved microscopic calculation of Gamow-Teller (GT±) strength distributions of these key Isotopes of Iron using the pn-QRPA theory. The main improvement comes from the incorporation of experimental deformation values for these nuclei. Additionally six different weak-interaction rates, namely electron and positron capture, electron and positron decay, and, neutrino and antineutrino cooling rates, were also calculated in presupernova matter. The calculated electron capture and neutrino cooling rates due to Isotopes of Iron are in good agreement with the large-scale shell model (LSSM) results. The calculated beta decay rates, however, are suppressed by three to five orders of magnitude.
Seth G John - One of the best experts on this subject based on the ideXlab platform.
-
tracing and constraining anthropogenic aerosol Iron fluxes to the north atlantic ocean using Iron Isotopes
Nature Communications, 2019Co-Authors: Tim M Conway, D S Hamilton, Rachel U Shelley, Ana M Aguilarislas, William M Landing, Natalie M Mahowald, Seth G JohnAbstract:Atmospheric dust is an important source of the micronutrient Fe to the oceans. Although relatively insoluble mineral Fe is assumed to be the most important component of dust, a relatively small yet highly soluble anthropogenic component may also be significant. However, quantifying the importance of anthropogenic Fe to the global oceans requires a tracer which can be used to identify and constrain anthropogenic aerosols in situ. Here, we present Fe isotope (δ56Fe) data from North Atlantic aerosol samples from the GEOTRACES GA03 section. While soluble aerosol samples collected near the Sahara have near-crustal δ56Fe, soluble aerosols from near North America and Europe instead have remarkably fractionated δ56Fe values (as light as −1.6‰). Here, we use these observations to fingerprint anthropogenic combustion sources, and to refine aerosol deposition modeling. We show that soluble anthropogenic aerosol Fe flux to the global surface oceans is highly likely to be underestimated, even in the dusty North Atlantic. The relative importance of crustal vs. anthropogenic dust deposition for Iron cycling in the surface ocean is unclear. Based on analysis of Iron isotope data from North Atlantic aerosol samples, the authors can reveal the relative importance of anthropogenic Iron emissions and its impact on marine biogeochemistry.
-
dissolved Iron and Iron Isotopes in the southeastern pacific ocean
Global Biogeochemical Cycles, 2016Co-Authors: Jessica N Fitzsimmons, Tim M Conway, Jongmi Lee, Richard A Kayser, Kristen M Thyng, Seth G JohnAbstract:The Southeast Pacific Ocean is a severely understudied yet dynamic region for trace metals such as Iron, since it experiences steep redox and productivity gradients in upper waters and strong hydrothermal Iron inputs to deep waters. In this study, we report the dissolved Iron (dFe) distribution from seven stations and Fe isotope ratios (δ56Fe) from three of these stations across a near-zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen-deficient zone (ODZ), with light δ56Fe implicating porewater fluxes of reduced Fe. However, temporal dFe variability and rapid δ56Fe shifts with depth suggest gradients in ODZ Fe source and/or redox processes vary over short-depth/spatial scales. The dFe concentrations decreased rapidly offshore, and in the upper ocean dFe was controlled by biological processes, resulting in an Fe:C ratio of 4.2 µmol/mol. Calculated vertical diffusive Fe fluxes were greater than published dust inputs to surface waters, but both were orders of magnitude lower than horizontal diffusive fluxes, which dominate dFe delivery to the gyre. The δ56Fe data in the deep sea showed evidence for a −0.2‰ Antarctic Intermediate Water end-member and a heavy δ56Fe of +0.55‰ for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ56Fe values were contrasted with the near-crustal δ56Fe recorded in the hydrothermal plume reaching Station ALOHA in the North Pacific. The heavy hydrothermal δ56Fe precludes a nanopyrite composition of hydrothermal dFe and instead suggests the presence of oxides or, more likely, binding of hydrothermal dFe by organic ligands in the distal plume.
-
Fractionation of Iron Isotopes during leaching of natural particles by acidic and circumneutral leaches and development of an optimal leach for marine particulate Iron Isotopes
Geochimica et Cosmochimica Acta, 2015Co-Authors: Brandi N. Revels, Jess F Adkins, Ruifeng Zhang, Seth G JohnAbstract:Iron (Fe) is an essential nutrient for life on land and in the oceans. Iron stable isotope ratios (δ^(56)Fe) can be used to study the biogeochemical cycling of Fe between particulate and dissolved phases in terrestrial and marine envIronments. We have investigated the dissolution of Fe from natural particles both to understand the mechanisms of Fe dissolution, and to choose a leach appropriate for extracting labile Fe phases of marine particles. With a goal of finding leaches which would be appropriate for studying dissolved-particle interactions in an oxic water column, three particle types were chosen including oxic seafloor sediments (MESS-3), terrestrial dust (Arizona Test Dust – A2 Fine), and ocean sediment trap material from the Cariaco basin. Four leaches were tested, including three acidic leaches similar to leaches previously applied to marine particles and sediments (25% acetic acid, 0.01 N HCl, and 0.5 N HCl) and a pH 8 oxalate-EDTA leach meant to mimic the dissolution of particles by organic complexation, as occurs in natural seawater. Each leach was applied for three different times (10 min, 2 h, 24 h) at three different temperatures (25 °C, 60 °C, 90 °C). MESS-3 was also leached under various redox conditions (0.02 M hydroxylamine hydrochloride or 0.02 M hydrogen peroxide). For all three sample types tested, we find a consistent relationship between the amount of Fe leached and leachate δ56Fe for all of the acidic leaches, and a different relationship between the amount of Fe leached and leachate δ^(56)Fe for the oxalate-EDTA leach, suggesting that Fe was released through proton-promoted dissolution for all acidic leaches and by ligand-promoted dissolution for the oxalate-EDTA leach. Fe isotope fractionations of up to 2‰ were observed during acidic leaching of MESS-3 and Cariaco sediment trap material, but not for Arizona Test Dust, suggesting that sample composition influences fractionation, perhaps because Fe Isotopes are greatly fractionated during leaching of silicates and clays but only minimally fractionated during dissolution of Fe oxyhydroxides. Two different analytical models were developed to explain the relationship between amount of Fe leached and δ^(56)Fe, one of which assumes mixing between two Fe phases with different δ^(56)Fe and different dissolution rates, and the other of which assumes dissolution of a single phase with a kinetic isotope effect. We apply both models to fit results from the acidic leaches of MESS-3 and find that the fit for both models is very similar, suggesting that isotope data will never be sufficient to distinguish between these two processes for natural materials. Next, we utilize our data to choose an optimal leach for application to marine particles. The oxalate-EDTA leach is well-suited to this purpose because it does not greatly fractionate Fe Isotopes for a diversity of particle types over a wide variety of leaching conditions, and because it approximates the conditions by which particulate Fe dissolves in the oceans. We recommend a 2 h leach at 90 °C with 0.1 M oxalate and 0.05 M EDTA at pH 8 to measure labile “ligand-leachable” particulate δ56Fe on natural marine materials with a range of compositions.
-
the flux of Iron and Iron Isotopes from san pedro basin sediments
Geochimica et Cosmochimica Acta, 2012Co-Authors: Seth G John, Jeffery Mendez, James W Moffett, Jess F AdkinsAbstract:Iron is an important nutrient in the ocean, but the different sources and sinks of Iron are not well constrained. Here, we use measurements of Fe concentration and Fe stable isotope ratios to evaluate the importance of reducing continental margins as a source of Fe to the open ocean. Dissolved Iron concentration ([Fe]) and Iron stable isotope ratios (δ^(56)Fe) were measured in the San Pedro and Santa Barbara basins. Dissolved δ^(56)Fe ranges from −1.82‰ to 0.00‰ in the San Pedro Basin and from −3.45‰ to −0.29‰ in the Santa Barbara Basin, and in both basins the lowest δ^(56)Fe values and highest Fe concentrations are found at the bottom of the basin reflecting the input of isotopically light Fe from reducing sediment porewaters. In the San Pedro Basin, we are also able to fingerprint an advective source of Fe from shallow continental shelves next to the basin and the atmospheric deposition of Fe into surface waters. A one-dimensional model of the Fe isotope cycle has been constructed for the deep silled San Pedro Basin. By fitting model output to data, values of several important Iron cycle parameters are predicted including a flux of Fe from sediment porewaters into the water column of 0.32–1.14 μmol m^(−2) d^(−1), a first-order dissolved Fe precipitation rate constant of 0.0018–0.0053 d^(−1), a flux δ56Fe of −2.4‰, and an isotope effect for Fe precipitation of Δδ^(56)Fe_(particulate-dissolved) = −0.8‰. Applying our model-predicted Fe cycle parameters to the global ocean suggests that continental margins contribute 4–12% of world ocean dissolved Fe and make the ocean’s Fe lighter by −0.08‰ to −0.26‰. The dramatically negative δ^(56)Fe signature seen in the water column of the San Pedro and Santa Barbara basins demonstrate the utility of Fe Isotopes as a tracer for continental margin Fe input from reducing sediments to the oceans, while the isotopic fractionation observed during loss of Fe from the dissolved phase suggests that this signature will be modified by subsequent reactions. Our modeling provides an initial framework for testing how these signals are transmitted into the open ocean.
-
analysis of dissolved Iron Isotopes in seawater
Marine Chemistry, 2010Co-Authors: Seth G John, Jess F AdkinsAbstract:Iron is an important nutrient in the ocean. Measuring the stable Isotopes of dissolved Fe in seawater may help to answer important biogeochemical questions such as what are the sources and sinks for Fe to the oceans, and how is Fe biologically cycled. Because Fe concentrations in seawater are very low, typically less than 1 nM, there are significant challenges both to separate and purify Fe from seawater without introducing contamination, and to accurately analyze δ^(56)Fe on the small quantities of Fe extracted. New techniques are presented here for separation and purification of Fe from seawater by bulk extraction onto a resin with NTA functional groups, followed by anion exchange chromatography. This method recovers 89% of the Fe from 1 L samples of seawater without causing any fractionation of Fe Isotopes, with a total blank of 1.1 ± 0.6 ng Fe. To optimize the analytical procedure for small amounts of Fe, the different sources of error in measurement of δ^(56)Fe have been analyzed. For 252 individual analyses of standards and samples, the internal error is well described by the combination of errors from electronic noise on the detectors (Johnson noise), counting statistics, and a third source of error hypothesized to be short-timescale flicker in instrumental mass bias. With the small amounts of Iron found in natural seawater samples, error is dominated by Johnson noise and counting statistics. Our analyses also include 160 pairs of “intermediate” replicates in which the same post-purification sample was measured during different analytical sessions, and 141 pairs of “external” replicate analyses for samples prepared from the same original seawater carboy but which were extracted and purified separately. The portion of overall mass spectrometry error that derives from intermediate error has been evaluated by comparing the variance in δ^(56)Fe for a single sample measured during multiple analytical sessions with the internal variance in δ^(56)Fe for the multiple cycles of data that make up each single analysis. The portion of total external error that derives from internal error was determined from variance in δ^(56)Fe for external replicates, compared with internal error based on the variance in cycles for each single analysis. We find that the error for multiple analyses of a sample during different analytical sessions is 1.06 times the internal error, and the external error for analysis of Fe samples which have been separately purified and extracted from the same original seawater is 1.26 times the internal analytical error. Based on this error analysis, we suggest that dissolved Fe Isotopes in seawater are best measured by separately extracting the Fe from a single liter of seawater and measuring the entire quantity of extracted Fe in a single short analysis. Using this method, the predicted accuracy for measurements of seawater dissolved δ^(56)Fe ranges from 0.2‰ to 0.05‰ (2σ) for seawater Fe concentrations of 0.1 nM and 1.0 nM, respectively.
Franck Poitrasson - One of the best experts on this subject based on the ideXlab platform.
-
Iron Isotopes reveal distinct dissolved Iron sources and pathways in the intermediate versus deep southern ocean
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Cyril Abadie, Francois Lacan, Amandine Radic, Catherine Pradoux, Franck PoitrassonAbstract:Abstract As an essential micronutrient, Iron plays a key role in oceanic biogeochemistry. It is therefore linked to the global carbon cycle and climate. Here, we report a dissolved Iron (DFe) isotope section in the South Atlantic and Southern Ocean. Throughout the section, a striking DFe isotope minimum (light Iron) is observed at intermediate depths (200–1,300 m), contrasting with heavier isotopic composition in deep waters. This unambiguously demonstrates distinct DFe sources and processes dominating the Iron cycle in the intermediate and deep layers, a feature impossible to see with only Iron concentration data largely used thus far in chemical oceanography. At intermediate depths, the data suggest that the dominant DFe sources are linked to organic matter remineralization, either in the water column or at continental margins. In deeper layers, however, abiotic non-reductive release of Fe (desorption, dissolution) from particulate Iron—notably lithogenic—likely dominates. These results go against the common but oversimplified view that remineralization of organic matter is the major pathway releasing DFe throughout the water column in the open ocean. They suggest that the oceanic Iron cycle, and therefore oceanic primary production and climate, could be more sensitive than previously thought to continental erosion (providing lithogenic particles to the ocean), particle transport within the ocean, dissolved/particle interactions, and deep water upwelling. These processes could also impact the cycles of other elements, including nutrients.
-
Iron Isotopes as a potential tool for ancient Iron metals tracing
Journal of Archaeological Science, 2016Co-Authors: Jean Milot, Franck Poitrasson, Sandrine Baron, Marie-pierre CousturesAbstract:Abstract Provenance studies of Iron artefacts have become an important topic in archaeology to better understand the socio-economic organization of ancient societies. Elemental and isotopic tracing methods used so far for Iron metal provenance studies showed some limitations, and the development of new additional tracers are needed. Since the last decade, the rise of cutting edge analytical techniques allows for the development of new isotopic tools for this purpose. The present study explores for the first time the use of Iron Isotopes analyses as a potential method for ancient Iron metal tracing. Ore, slag and metal samples from two experimental reconstitutions of Iron ore reduction by bloomery process were collected. Their Fe isotope compositions were measured by Multi Collector – Inductively Coupled Plasma – Mass Spectrometry (MC-ICP-MS) to assess the possible impact of smelting on the Fe isotope composition of the metal produced. Our results show that the Iron isotope compositions of the slag and metal are for 8 out of 9 samples analyzed undistinguishable from that of the starting ores. This suggests that overall, no significant Fe isotope fractionation occurs along the chaine operatoire of Iron bars production, even if slight isotopic differences might be found in blooms before refinement. This fact, combined with the natural isotopic variability of Iron ores, as reported in the literature, may allow the use of Fe Isotopes as a relevant tracer for archaeological Iron metals. This new tracing approach offers many perspectives for provenance studies. The combination of elemental and Fe isotope analyses should thus be useful to validate origin hypotheses of ancient Iron artefacts.
-
Iron Isotopes For Characterizing Iron Cycling In The Amazon River Basin
2015Co-Authors: Franck Poitrasson, L.c Vieira, Patrick Seyler, Gm. Dos Santos PinheiroAbstract:With the global climate change and increasing anthropic pressure on nature, it is important to find new indicators of the response of complex systems like the Amazon River Basin. In particular, new isotopic tracers like those of Iron may tell us much on processes such as the chemical exchanges between rivers, soils and the biosphere. Accordingly, early studies revealed that for some river waters, large δ57Fe fractionations are observed between thesuspended and dissolved load, and isotopic variations were also recognized on the suspended matter along the hydrological cycle. Besides, soil studies from various locations have shown that δ57Fe signatures depend mostly on the weathering regime. We therefore conducted Fe isotope surveys through multidisciplinary field missions on rivers from the Amazon Basin. It was confirmed that acidic, organic-rich black waters show strong Fe isotope fractionation between particulate and dissolved loads. Furthermore, this isotopic fractionation varies along the hydrological cycle, like previously uncovered in boreal waters suspended matter. In contrast, unfiltered waters show very little variation with time.It was also found that Fe Isotopes remain a conservative tracer even in the case of massive Iron loss during the mixing of chemically contrasted waters such as the Negro and Solimões tributaries of the Amazon River. Given that >95% of the Fe from the Amazon River is carried as detrital materials, our results lead to the conclusion that the Fe isotope signature delivered to the Atlantic Ocean is undistinguishable from the continental crust value, in contrast to previous inferences.The results indicate that Fe Isotopes in rivers represent a promising indicator of the interaction between organic matter and Iron in rivers, and ultimately the nature of their source in soils. As such, they may become a powerful tracer of changes occurring on the continents in response to both weathering context and human activities.
-
Does planetary differentiation really fractionate Iron Isotopes?
Earth and Planetary Science Letters, 2007Co-Authors: Franck PoitrassonAbstract:The difference in the mean Fe isotope composition of samples from the Earth, Moon, Mars and Vesta has been recently interpreted as tracking contrasted planetary accretion mechanisms [F. Poitrasson, A.N. Halliday, D.C. Lee, S. Levasseur, N. Teutsch, Iron isotope differences between Earth, Moon, Mars and Vesta as possible records of contrasted accretion mechanisms, Earth Planet. Sci. Lett. 223 (2004) 253 266]. Using newly produced Fe isotopic data on terrestrial and lunar samples, pallasites, eucrites and Martian meteorites, Weyer et al. [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger, A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth Planet. Sci. Lett. 240 (2005) 251 264] reinterpreted these data as fingerprinting planetary differentiation. In particular, these authors suggested that partial melting in the terrestrial and lunar mantles produced melts isotopically heavy. It is shown here that the inference of Weyer et al. [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger, A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth Planet. Sci. Lett. 240 (2005) 251 264] is strongly biased by the sampling approach taken. Notably, these authors used olivine in place of the host bulk peridotites ?57Fe signatures despite this mineral has been shown to be frequently isotopically lighter than coexisting phases, and they analyzed lunar samples heavily affected chemically by the meteoritic bombardment, a process known to alter Fe isotope signatures. Their pallasite metal silicate fractionation data are also likely biased by the approach adopted to estimate the Iron isotope composition of the different mineral phases. In fact, their conclusion of Fe isotopic fractionation during basalt extraction from planetary mantles is invalidated by the observation that basaltic shergottites and eucrites have ?57Fe indistinguishable from those of chondrites. Therefore, the heavier Fe isotopic composition of the Moon relative to the Earth, itself heavier than most chondrites and achondrites remains best explained by loss of light Iron Isotopes during the high temperature event accompanying the interplanetary impact that led to the formation of the Moon [F. Poitrasson, A.N. Halliday, D.C. Lee, S. Levasseur, N. Teutsch, Iron isotope differences between Earth, Moon, Mars and Vesta as possible records of contrasted accretion mechanisms, Earth Planet. Sci. Lett. 223 (2004) 253 266., F. Poitrasson, S. Levasseur, N. Teutsch, Significance of Iron isotope mineral fractionation in pallasites and Iron meteorites for the core mantle differentiation of terrestrial planets, Earth Planet. Sci. Lett. 234 (2005) 151 164].
