The Experts below are selected from a list of 33 Experts worldwide ranked by ideXlab platform
Seth G John - One of the best experts on this subject based on the ideXlab platform.
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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.
Artigue Lise - One of the best experts on this subject based on the ideXlab platform.
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Cycles biogéochimiques océaniques : apports des traceurs élémentaires et isotopiques, l'aluminium et le fer couplés à une approche hydrodynamique
HAL CCSD, 2020Co-Authors: Artigue LiseAbstract:The overall objective of this thesis is to further our understanding of ocean biogeochemical cycles (sources, internal cycles, sinks) using tracers present in seawater (the concentration of Dissolved aluminium and the isotopic composition of Dissolved iron) combined with hydrodynamic tools. Aluminum is used as a tracer from lithogenic sources to the ocean, while iron isotopes tell us about the iron cycle in the ocean. This thesis focuses first on the analysis of water masses of the 22ºN longitudinal section in the North Atlantic carried out in the framework of the GEOTRACES GApr08 campaign. This study combines for the first time an extended optimum multiparameter analysis (eOMPA) of water masses with an estimation of their Lagrangian trajectories from a hydrodynamic model. In addition, the Dissolved aluminium (dAl) measurements carried out have made it possible to produce a first section of dAl at 22ºN and these same tools have enabled an advanced analysis. The joint use of the 1D model of surface dust advection-deposition and the eOMPA results highlighted the predominant processes associated with the measured dAl concentrations. (i) At the surface, both advection and deposition of atmospheric dust are essential to explain the observed dAl concentrations, although in the west, an additional external source is required. This source could come either from the Amazon River or from erosion in the Petites Antilles. (ii) Between 200 and 800m, in an area of strong atmospheric deposition (below the Saharan plume), high dAl concentrations result from oceanic transport. The net balance of Dissolved-Particle interactions, however, is a subtraction of dAl, probably by adsorption onto Particles. (iii) Below 800 m, the effect of Dissolved-Particle interactions is reversed and reversible scavenging results in a net source of dAl. (iv) Below 3340 m, the Snakepit hydrothermal source is found to be a significant local source of dAl. Unlike aluminium, iron (Fe) is an essential micronutrient for primary production. This micronutrient limits the primary production in 30-40% of the ocean. In the framework of the GEOTRACES KEOPS 1 and 2 campaigns, the Fe isotope measurements presented in this thesis allow the study of micronutrient sources in a naturally fertilized area of the Southern Ocean, the Kerguelen Islands. Our Fe isotope measurements reveal several elements on its cycle. (i) In the absence of external input, the Fe isotope signatures of water masses are preserved over 4500 kilometers, which allows us to use this tracer to follow the origin of Fe in the ocean. (ii) A reducing sedimentary source of Dissolved Fe from the Kerguelen Island margin feeds primary production downstream. (iii) A local non-reducing sedimentary source of Dissolved Fe impacts the bottom waters of the Kerguelen Plateau stations, but does not appear to contribute significantly to the shallower waters. This result is identified for the first time directly in an HNLC region. This PhD work highlights the key importance of 1) taking into account horizontal transport, if possible quantitatively, in the interpretation of trace element and isotope distributions, and 2) the interactions of Dissolved Particles, in particular the so-called reversible scavenging process (adsorption-desorption), on the cycles of trace elements and isotopes.L'objectif global de cette thèse est de progresser sur la compréhension des cycles biogéochimiques océaniques (sources, cycles internes, puits) à l'aide de traceurs présents dans l'eau de mer (la concentration d'aluminium dissous et la composition isotopique du fer dissous) combinés à des outils hydrodynamiques. L'aluminium est utilisé comme traceur des sources lithogéniques à l'océan alors que les isotopes du fer nous renseignent sur le cycle du fer dans l'océan. Cette thèse se concentre en premier lieu sur l'analyse de masses d'eau d'une section longitudinale à 22ºN dans l'Atlantique Nord réalisée dans le cadre de la campagne GEOTRACES GApr08. Cette étude combine pour la première fois une analyse multiparamétrique optimale des masses d'eau (extended optimum multiparameter analysis eOMPA) à une estimation de leurs trajectoires Lagrangiennes issues d'un modèle hydrodynamique. Par ailleurs, les mesures d'aluminium dissous (dAl) effectuées ont permis de produire une première section de dAl à 22ºN et ces mêmes outils, une analyse poussée. En effet, l'utilisation conjointe du modèle 1D d'advection-dépôt de poussière en surface et des résultats de l'eOMPA a mis en valeur les processus prédominants associés aux concentrations de dAl mesurées. (i) En surface, l'advection et le dépôt de poussière atmosphérique sont tous deux essentiels pour expliquer les concentrations de dAl observées bien que dans l'ouest, une source externe supplémentaire est nécessaire. Cette source pourrait provenir soit du fleuve Amazone, soit de l'érosion des petites Antilles. (ii) Entre 200 et 800 m, alors qu'on se situe dans une zone de fort dépôt atmosphérique (sous le panache saharien), les fortes concentrations de dAl résultent du transport océanique. Le bilan net des interactions dissous-particules est pourtant une soustraction de dAl, probablement par adsorption sur les particules. (iii) En dessous de 800 m, l'effet des interactions dissous-particules s'inverse et le scavenging réversible est une source nette de dAl. (iv) En dessous de 3340 m, la source hydrothermale Snakepit s'avère être une source locale importante de dAl. Contrairement à l'aluminium, le fer (Fe) est un micronutriment essentiel à la production primaire. Ce micronutriment limite la production primaire dans 30 à 40 % de l'océan. Dans le cadre des campagnes GEOTRACES KEOPS 1 et 2, nos mesures d'isotopes de Fe présentées dans cette thèse permettent l'étude des sources de micronutriments dans une zone naturellement fertilisée de l'océan Austral, les îles Kerguelen. Nos mesures d'isotopes de Fe révèlent plusieurs éléments sur son cycle. (i) En l'absence d'apport externe, les signatures isotopiques de Fe des masses d'eau sont conservées sur plus de 4500 kilomètres, ce qui permet d'utiliser ce traceur pour suivre l'origine du Fe dans l'océan. (ii) Une source sédimentaire réductrice de Fe dissous provenant de la marge des îles Kerguelen alimente la production primaire en aval. (iii) Une source sédimentaire locale non réductrice de Fe dissous impacte les eaux de fond des stations situées au niveau du plateau des Kerguelen, mais ne semble pas contribuer significativement aux eaux moins profondes. Ce résultat est identifié pour la première fois directement dans une région HNLC. L'ensemble de ces travaux souligne le caractère essentiel 1) de la prise en compte des transports horizontaux, si possible de manière quantitative, dans l'interprétation des distributions d'éléments traces et d'isotopes, 2) des interactions dissous particules, notamment le processus dit de scavenging réversible (adsorption-désorption), sur les cycles des éléments traces et isotopes
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Cycles biogéochimiques océaniques : apports des traceurs élémentaires et isotopiques, l’aluminium et le fer couplés à une approche hydrodynamique.
HAL CCSD, 2020Co-Authors: Artigue LiseAbstract:The overall objective of this thesis is to further our understanding of ocean biogeochemical cycles (sources, internal cycles, sinks) using tracers present in seawater (the concentration of Dissolved aluminium and the isotopic composition of Dissolved iron) combined with hydrodynamic tools. Aluminum is used as a tracer from lithogenic sources to the ocean, while iron isotopes tell us about the iron cycle in the ocean. This thesis focuses first on the analysis of water masses of the 22ºN longitudinal section in the North Atlantic carried out in the framework of the GEOTRACES GApr08 campaign. This study combines for the first time an extended optimum multiparameter analysis (eOMPA) of water masses with an estimation of their Lagrangian trajectories from a hydrodynamic model. In addition, the Dissolved aluminium (dAl) measurements carried out have made it possible to produce a first section of dAl at 22ºN and these same tools have enabled an advanced analysis. The joint use of the 1D model of surface dust advection-deposition and the eOMPA results highlighted the predominant processes associated with the measured dAl concentrations. (i) At the surface, both advection and deposition of atmospheric dust are essential to explain the observed dAl concentrations, although in the west, an additional external source is required. This source could come either from the Amazon River or from erosion in the Petites Antilles. (ii) Between 200 and 800m, in an area of strong atmospheric deposition (below the Saharan plume), high dAl concentrations result from oceanic transport. The net balance of Dissolved-Particle interactions, however, is a subtraction of dAl, probably by adsorption onto Particles. (iii) Below 800 m, the effect of Dissolved-Particle interactions is reversed and reversible scavenging results in a net source of dAl. (iv) Below 3340 m, the Snakepit hydrothermal source is found to be a significant local source of dAl.Unlike aluminium, iron (Fe) is an essential micronutrient for primary production. This micronutrient limits the primary production in 30-40% of the ocean. In the framework of the GEOTRACES KEOPS 1 and 2 campaigns, the Fe isotope measurements presented in this thesis allow the study of micronutrient sources in a naturally fertilized area of the Southern Ocean, the Kerguelen Islands. Our Fe isotope measurements reveal several elements on its cycle. (i) In the absence of external input, the Fe isotope signatures of water masses are preserved over 4500 kilometers, which allows us to use this tracer to follow the origin of Fe in the ocean. (ii) A reducing sedimentary source of Dissolved Fe from the Kerguelen Island margin feeds primary production downstream. (iii) A local non-reducing sedimentary source of Dissolved Fe impacts the bottom waters of the Kerguelen Plateau stations, but does not appear to contribute significantly to the shallower waters. This result is identified for the first time directly in an HNLC region. This PhD work highlights the key importance of 1) taking into account horizontal transport, if possible quantitatively, in the interpretation of trace element and isotope distributions, and 2) the interactions of Dissolved Particles, in particular the so-called reversible scavenging process (adsorption-desorption), on the cycles of trace elements and isotopes.L’objectif global de cette thèse est de progresser sur la compréhension des cycles biogéochimiques océaniques (sources, cycles internes, puits) à l’aide de traceurs présents dans l'eau de mer (la concentration d'aluminium dissous et la composition isotopique du fer dissous) combinés à des outils hydrodynamiques. L'aluminium est utilisé comme traceur des sources lithogéniques à l'océan alors que les isotopes du fer nous renseignent sur le cycle du fer dans l’océan. Cette thèse se concentre en premier lieu sur l'analyse de masses d'eau d'une section longitudinale à 22ºN dans l'Atlantique Nord réalisée dans le cadre de la campagne GEOTRACES GApr08. Cette étude combine pour la première fois une analyse multiparamétrique optimale des masses d'eau (extended optimum multiparameter analysis eOMPA) à une estimation de leurs trajectoires Lagrangiennes issues d'un modèle hydrodynamique. Par ailleurs, les mesures d’aluminium dissous (dAl) effectuées ont permis de produire une première section de dAl à 22ºN et ces mêmes outils, une analyse poussée. En effet, l'utilisation conjointe du modèle 1D d'advection-dépôt de poussière en surface et des résultats de l'eOMPA a mis en valeur les processus prédominants associés aux concentrations de dAl mesurées. (i) En surface, l'advection et le dépôt de poussière atmosphérique sont tous deux essentiels pour expliquer les concentrations de dAl observées bien que dans l'ouest, une source externe supplémentaire est nécessaire. Cette source pourrait provenir soit du fleuve Amazone, soit de l'érosion des petites Antilles. (ii) Entre 200 et 800m, alors qu'on se situe dans une zone de fort dépôt atmosphérique (sous le panache saharien), les fortes concentrations de dAl résultent du transport océanique. Le bilan net des interactions dissous-particules est pourtant une soustraction de dAl, probablement par adsorption sur les particules. (iii) En dessous de 800 m, l'effet des interactions dissous-particules s'inverse et le scavenging réversible est une source nette de dAl. (iv) En dessous de 3340 m, la source hydrothermale Snakepit s'avère être une source locale importante de dAl.Contrairement à l’aluminium, le fer (Fe) est un micronutriment essentiel à la production primaire. Ce micronutriment limite la production primaire dans 30 à 40 % de l'océan. Dans le cadre des campagnes GEOTRACES KEOPS 1 et 2, nos mesures d’isotopes de Fe présentées dans cette thèse permettent l'étude des sources de micronutriments dans une zone naturellement fertilisée de l’océan Austral, les îles Kerguelen. Nos mesures d’isotopes de Fe révèlent plusieurs éléments sur son cycle. (i) En l'absence d'apport externe, les signatures isotopiques de Fe des masses d'eau sont conservées sur plus de 4500 kilomètres, ce qui permet d'utiliser ce traceur pour suivre l'origine du Fe dans l'océan. (ii) Une source sédimentaire réductrice de Fe dissous provenant de la marge des îles Kerguelen alimente la production primaire en aval. (iii) Une source sédimentaire locale non réductrice de Fe dissous impacte les eaux de fond des stations situées au niveau du plateau des Kerguelen, mais ne semble pas contribuer significativement aux eaux moins profondes. Ce résultat est identifié pour la première fois directement dans une région HNLC. L'ensemble de ces travaux souligne le caractère essentiel 1) de la prise en compte des transports horizontaux, si possible de manière quantitative, dans l'interprétation des distributions d'éléments traces et d'isotopes, 2) des interactions dissous particules, notamment le processus dit de scavenging réversible (adsorption-désorption), sur les cycles des éléments traces et isotopes
Brandi N. Revels - One of the best experts on this subject based on the ideXlab platform.
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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.
Ruifeng Zhang - One of the best experts on this subject based on the ideXlab platform.
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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.
Jess F Adkins - One of the best experts on this subject based on the ideXlab platform.
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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.