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Martin Frank - One of the best experts on this subject based on the ideXlab platform.
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tracing water mass mixing and continental inputs in the southeastern atlantic ocean with dissolved Neodymium Isotopes
Earth and Planetary Science Letters, 2020Co-Authors: Peer Rahlf, Ed C Hathorne, Marcus Gutjahr, Georgi Laukert, Syee Weldeab, Martin FrankAbstract:Abstract In contrast to the vigorous deep ocean circulation system of the north- and southwestern Atlantic Ocean, no systematically sampled datasets of dissolved radiogenic Neodymium (Nd) isotope signatures exist to trace water mass mixing and provenance for the more restricted and less well ventilated Angola Basin and the Cape Basin in the southeastern Atlantic Ocean, where important parts of the return flow of the Atlantic Meridional Overturning Circulation are generated. Here, to improve our understanding of water mass mixing and provenance, we present the first full water column Nd isotope (expressed as eNd values) and concentration data for a section across the western Angola Basin from 3° to 30° S along the Zero Meridian and along an E-W section across the northern Cape Basin at 30° S sampled during GEOTRACES cruise GA08. Compared with the southwestern Atlantic basin we find overall less radiogenic eNd signatures reaching −17.6 in the uppermost 200 m of the Angola and Cape basins. In the western Angola Basin these signatures are the consequence of the admixture of a coastal plume originating near 13° S and carrying an unradiogenic Nd signal that likely resulted from the dissolution of Fe-Mn coatings of particles formed in river estuaries or near the West African coast. The highly unradiogenic Nd isotope signatures in the upper water column of the northern Cape Basin, in contrast, originate from old Archean terrains of southern Africa and are introduced into the Mozambique Channel via rivers like the Limpopo and Zambezi. These signatures allow tracing the advection of shallow waters via the Agulhas and Benguela currents into the southeastern Atlantic Ocean. The Nd isotope compositions of the deep water masses in both basins primarily reflect conservative water mass mixing with the only exception being the central Angola Basin, where the signatures are significantly overprinted by terrestrial inputs. Bottom waters of the Cape Basin show excess Nd concentrations of up to 6 pmol/kg (20%), originating from resuspended bottom sediments and/or dissolution of dust, but without significantly changing the isotopic composition of the waters due to similar eNd values of particles and bottom waters ranging between −9.6 and −10.5. Given that bottom waters within the Cape Basin today are enriched in Nd, non-conservative Nd isotopic effects may have been resolvable under past glacial boundary conditions when bottom waters were more radiogenic.
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the distribution of Neodymium Isotopes and concentrations in the eastern tropical north atlantic
Chemical Geology, 2019Co-Authors: Moritz Zieringer, Martin Frank, Roland Stumpf, Ed C HathorneAbstract:Abstract Dissolved Neodymium (Nd) and its radiogenic isotope composition (143Nd/144Nd, expressed as eNd) belong to the key parameters of the international GEOTRACES program, which aims to investigate the processes controlling the distribution of trace elements and their Isotopes in the global ocean. We present Nd isotope and concentration ([Nd]) data from eleven full depth water column profiles from the eastern (sub)tropical Atlantic Ocean between 2°N and 29°N and from the Romanche Fracture Zone sampled during Meteor cruise M81/1 (GEOTRACES cruise GA11) in February/March 2010. The eNd signatures range from −12.9 in upper North Atlantic Deep Water (UNADW) at the equator to −8.1 in the mixed layer near the Canary Islands. Nd concentrations range from 11.9 pmol/kg observed within the Equatorial Undercurrent to 40.2 pmol/kg in Antarctic Bottom Water (AABW) in the Romanche Fracture Zone. Large variations in surface water Nd isotope compositions (−12.7 ≤ eNd ≤ −8.1) and concentrations (15.7 pmol/kg ≤ [Nd] ≤ 27.7 pmol/kg) are caused by partial dissolution of Saharan dust particles between 2°N and 13°N and volcanic island weathering (Canaries) between 25°N and 29°N. In contrast to dust inputs, which predominantly affect the Nd concentrations and isotope compositions of surface waters and underlying South Atlantic Central Water (SACW), contributions originating from the Canary Islands affect the Nd isotope composition of the entire surrounding water column without significantly altering Nd concentrations, thus confirming the concept of boundary exchange in its strictest sense. The results confirm that the composition of lower North Atlantic Deep Water (LNADW, eNd = −12.1) in the abyssal plains of the eastern North Atlantic is exclusively set by the mixing ratio of LNADW and Antarctic Bottom Water (AABW). Upper North Atlantic Deep Water (UNADW), in contrast, is characterized by eNd signatures between −12.7 and − 12.0 between 2°N and 10°N, whereas further north it is clearly affected by admixture of Mediterranean Water (MW) and radiogenic inputs from the Canary Islands and likely also the Cape Verde Islands. This article is part of a special issue entitled: “Cycles of trace elements and Isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. Gonzalez.
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tracing the origin of arctic sea ice and freshwater by Neodymium Isotopes and rare earth elements
EPIC3Goldschmidt Conference 2017 Paris France 2017-08-13-2017-08-18https: goldschmidt.info 2017 abstracts abstractView?id=2017004266, 2017Co-Authors: Georgi Laukert, Martin Frank, Ed C Hathorne, Thomas Krumpen, Kirstin Werner, Ilka PeekenAbstract:Neodymium (Nd) Isotopes (expressed as eNd) and rare earth elements (REEs) in seawater have been successfully used to trace water mass mixing in the Arctic region [1,2,3]. However, the potential to trace the origin of drifting Arctic sea ice with eNd and REEs has not yet been directly explored. Freshwater originating from various Siberian rivers is mixed and diluted prior to its advection to the central Arctic Ocean and the Fram Strait, thereby inhibiting an assessment of the individual contribution of the different rivers [1,2]. In contrast, sea ice may preserve the marine or riverine eNd and REE signatures from Siberian shelf waters while transported across the Arctic Ocean. This mechanism is demonstrated here for the first time by comparing eNd and REE signatures determined from unfiltered but essentially sediment-free sea ice with corresponding signatures expected for surface seawater in the formation region of the ice. Sea-ice cores were recovered in the Eurasian Basin of the central Arctic Ocean in 2012. Based on satellite-derived ice drift and concentration data, some of the sea-ice floes sampled formed east of Vilkitsky Strait and are characterized by eNd values near -8 in agreement with the incorporation of radiogenic freshwater (eNd- 6) from the Yenisei and Ob rivers [4]. A second sea-ice source was located north of the Laptev Sea as reflected by eNd values near -11, which is consistent with mixed contributions of radiogenic waters from the Kara Sea and northward flowing highly unradiogenic freshwater (eNd< -15) of the Lena River [4]. These first data suggest that Nd Isotopes can trace both the origin of drifting sea ice and of freshwater. The REE concentrations in the ice are depleted compared to those in Siberian shelf waters, indicating salt-associated REE rejection during sea-ice formation. [1] Laukert et al.(2017) Geochim. Cosmochim. Acta 202, 285-309. [2] Porcelli et al. (2009)Geochim. Cosmochim. Acta 73, 2645-2659. [3] Andersson et al. (2008) Geochim. Cosmochim. Acta 72, 2854-2867. [4] Laukert et al.(2016) Goldschmidt Abstracts 2016,1688.
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Short-term variability of dissolved rare earth elements and Neodymium Isotopes in the entire water column of the Panama Basin
Earth and Planetary Science Letters, 2017Co-Authors: Patricia Grasse, Katharina Pahnke, L. Bosse, Ed C Hathorne, Philipp Böning, Martin FrankAbstract:Abstract The distribution of dissolved rare earth elements (REEs) and Neodymium Isotopes (eNd) in the open ocean traces water mass mixing and provides information on lithogenic inputs to the source regions of the water masses. However, the processes influencing the REE budget at the ocean margins, in particular source and sink mechanisms, are not yet well quantified. In this study the first dissolved REE concentrations and Nd isotope compositions of seawater from the Panama Basin (RV Meteor cruise M90) in the Eastern Equatorial Pacific (EEP) are presented. The EEP is characterized by one of the world's largest oxygen minimum zones (OMZs). It is dominated by high particle fluxes that are expected to enhance the removal of REEs from the water column by scavenging. The measured REE concentrations peak at the surface indicating high lithogenic input, which is supported by shale-normalized REE patterns in surface waters and highly radiogenic eNd signatures ranging between +1.4 and +4.3, the latter value constituting the most radiogenic value measured for seawater to date. In contrast, intermediate and deep water REE concentrations are low compared to other Pacific Basins and suggest enhanced removal via scavenging associated with high particle fluxes. The eNd signatures of intermediate and deep waters are less radiogenic than surface waters ranging between −1.4 and +1.3 but significantly more radiogenic than source water masses in the EEP. The eNd signatures consequently do not reflect mixing of intermediate and deep water masses entering the Panama Basin but can only be explained by lithogenic inputs originating from source rocks with highly radiogenic Nd isotope signatures such as the Central American Volcanic Arc ( e Nd = + 3 to +10). Our data demonstrate significant surface input via continental particles, which are partially dissolved in the water column and thereby release REEs and particularly radiogenic Nd isotope signatures to the subsurface ocean. Data obtained from a re-occupied station in the southern Panama Basin for the first time shows that these processes can partially reset water mass Nd isotope and REE signatures of the entire water column proximal to continental sources on time scales of a few years.
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constraints on ocean circulation at the paleocene eocene thermal maximum from Neodymium Isotopes
Climate of The Past, 2015Co-Authors: April N Abbott, Brian A. Haley, Aradhna Tripati, Martin FrankAbstract:Abstract. Global warming during the Paleocene–Eocene Thermal Maximum (PETM) ∼ 55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use Neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd Isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean–atmosphere system associated with the PETM.
Germain Bayon - One of the best experts on this subject based on the ideXlab platform.
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extensive wet episodes in late glacial australia resulting from high latitude forcings
Scientific Reports, 2017Co-Authors: Germain Bayon, Sylvain Bermell, Y. Germain, Kazuyo Tachikawa, Patrick De Deckker, John W Magee, Marc D NormanAbstract:Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use Neodymium Isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.
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rare earth elements and Neodymium Isotopes in world river sediments revisited
Geochimica et Cosmochimica Acta, 2015Co-Authors: Germain Bayon, Samuel Toucanne, Sylvain Bermell, Sandrine Chéron, Joël Etoubleau, Charlotte Skonieczny, Luc Andre, Bernard Dennielou, Nicolas FreslonAbstract:Over the past decades, rare earth elements (REE) and their radioactive Isotopes have received tremendous attention in sedimentary geochemistry, as tracers for the geological history of the continental crust and provenance studies. In this study, we report on elemental concentrations and Neodymium (Nd) isotopic compositions for a large number of sediments collected near the mouth of rivers worldwide, including some of the world's major rivers. Sediments were leached for removal of non-detrital components, and both clay and silt fractions were retained for separate geochemical analyses. Our aim was to re-examine, at the scale of a large systematic survey, whether or not REE and Nd Isotopes could be fractionated during Earth surface processes. Our results confirmed earlier assumptions that river sediments do not generally exhibit any significant grain-size dependent Nd isotopic variability. Most sediments from rivers draining old cratonic areas, sedimentary systems and volcanic provinces displayed similar Nd isotopic signatures in both clay and silt fractions, with Delta epsilon Nd(clay-silt) < vertical bar 1 vertical bar. A subtle decoupling of Nd Isotopes between clays and silts was identified however in a few major river systems (e.g. Nile, Mississippi, Fraser), with clays being systematically shifted towards more radiogenic values. This observation suggests that preferential weathering of volcanic and/or sedimentary rocks relative to more resistant lithologies may occur in river basins, possibly leading locally to Nd isotopic decoupling between different size fractions. Except for volcanogenic sediments, silt fractions generally displayed homogeneous REE concentrations, exhibiting relatively flat shale-normalized patterns. However, clay fractions were almost systematically characterized by a progressive enrichment from the heavy to the light REE and a positive europium (Eu) anomaly. In agreement with results from previous soil investigations, the observed REE fractionation between clays and silts is probably best explained by preferential alteration of feldspars and/or accessory mineral phases. Importantly, this finding clearly indicates that silicate weathering can lead to decoupling of REE between different grain-size fractions, with implications for sediment provenance studies. Finally, we propose a set of values for a World River Average Clay (WRAC) and Average Silt (WRAS), which provide new estimates for the average composition of the weathered and eroded upper continental crust, respectively, and could be used for future comparison purposes. (C) 2015 Elsevier Ltd. All rights reserved.
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, A. Kripounoff, Marie-laure RougetAbstract:We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2-0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases.The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with σREE=109±86ppm (mean±s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285±150ppm; mean±s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water).The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition.Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, Alexis Khripounoff, Emmanuel PonzeveraAbstract:Abstract We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n = 25), estuaries (n = 18), open-ocean settings (n = 15), and cold seeps (n = 12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2–0.02 M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25 M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n = 58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n = 12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display eNd values that typically range between the eNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit eNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.
Ed C Hathorne - One of the best experts on this subject based on the ideXlab platform.
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tracing water mass mixing and continental inputs in the southeastern atlantic ocean with dissolved Neodymium Isotopes
Earth and Planetary Science Letters, 2020Co-Authors: Peer Rahlf, Ed C Hathorne, Marcus Gutjahr, Georgi Laukert, Syee Weldeab, Martin FrankAbstract:Abstract In contrast to the vigorous deep ocean circulation system of the north- and southwestern Atlantic Ocean, no systematically sampled datasets of dissolved radiogenic Neodymium (Nd) isotope signatures exist to trace water mass mixing and provenance for the more restricted and less well ventilated Angola Basin and the Cape Basin in the southeastern Atlantic Ocean, where important parts of the return flow of the Atlantic Meridional Overturning Circulation are generated. Here, to improve our understanding of water mass mixing and provenance, we present the first full water column Nd isotope (expressed as eNd values) and concentration data for a section across the western Angola Basin from 3° to 30° S along the Zero Meridian and along an E-W section across the northern Cape Basin at 30° S sampled during GEOTRACES cruise GA08. Compared with the southwestern Atlantic basin we find overall less radiogenic eNd signatures reaching −17.6 in the uppermost 200 m of the Angola and Cape basins. In the western Angola Basin these signatures are the consequence of the admixture of a coastal plume originating near 13° S and carrying an unradiogenic Nd signal that likely resulted from the dissolution of Fe-Mn coatings of particles formed in river estuaries or near the West African coast. The highly unradiogenic Nd isotope signatures in the upper water column of the northern Cape Basin, in contrast, originate from old Archean terrains of southern Africa and are introduced into the Mozambique Channel via rivers like the Limpopo and Zambezi. These signatures allow tracing the advection of shallow waters via the Agulhas and Benguela currents into the southeastern Atlantic Ocean. The Nd isotope compositions of the deep water masses in both basins primarily reflect conservative water mass mixing with the only exception being the central Angola Basin, where the signatures are significantly overprinted by terrestrial inputs. Bottom waters of the Cape Basin show excess Nd concentrations of up to 6 pmol/kg (20%), originating from resuspended bottom sediments and/or dissolution of dust, but without significantly changing the isotopic composition of the waters due to similar eNd values of particles and bottom waters ranging between −9.6 and −10.5. Given that bottom waters within the Cape Basin today are enriched in Nd, non-conservative Nd isotopic effects may have been resolvable under past glacial boundary conditions when bottom waters were more radiogenic.
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the distribution of Neodymium Isotopes and concentrations in the eastern tropical north atlantic
Chemical Geology, 2019Co-Authors: Moritz Zieringer, Martin Frank, Roland Stumpf, Ed C HathorneAbstract:Abstract Dissolved Neodymium (Nd) and its radiogenic isotope composition (143Nd/144Nd, expressed as eNd) belong to the key parameters of the international GEOTRACES program, which aims to investigate the processes controlling the distribution of trace elements and their Isotopes in the global ocean. We present Nd isotope and concentration ([Nd]) data from eleven full depth water column profiles from the eastern (sub)tropical Atlantic Ocean between 2°N and 29°N and from the Romanche Fracture Zone sampled during Meteor cruise M81/1 (GEOTRACES cruise GA11) in February/March 2010. The eNd signatures range from −12.9 in upper North Atlantic Deep Water (UNADW) at the equator to −8.1 in the mixed layer near the Canary Islands. Nd concentrations range from 11.9 pmol/kg observed within the Equatorial Undercurrent to 40.2 pmol/kg in Antarctic Bottom Water (AABW) in the Romanche Fracture Zone. Large variations in surface water Nd isotope compositions (−12.7 ≤ eNd ≤ −8.1) and concentrations (15.7 pmol/kg ≤ [Nd] ≤ 27.7 pmol/kg) are caused by partial dissolution of Saharan dust particles between 2°N and 13°N and volcanic island weathering (Canaries) between 25°N and 29°N. In contrast to dust inputs, which predominantly affect the Nd concentrations and isotope compositions of surface waters and underlying South Atlantic Central Water (SACW), contributions originating from the Canary Islands affect the Nd isotope composition of the entire surrounding water column without significantly altering Nd concentrations, thus confirming the concept of boundary exchange in its strictest sense. The results confirm that the composition of lower North Atlantic Deep Water (LNADW, eNd = −12.1) in the abyssal plains of the eastern North Atlantic is exclusively set by the mixing ratio of LNADW and Antarctic Bottom Water (AABW). Upper North Atlantic Deep Water (UNADW), in contrast, is characterized by eNd signatures between −12.7 and − 12.0 between 2°N and 10°N, whereas further north it is clearly affected by admixture of Mediterranean Water (MW) and radiogenic inputs from the Canary Islands and likely also the Cape Verde Islands. This article is part of a special issue entitled: “Cycles of trace elements and Isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. Gonzalez.
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tracing the origin of arctic sea ice and freshwater by Neodymium Isotopes and rare earth elements
EPIC3Goldschmidt Conference 2017 Paris France 2017-08-13-2017-08-18https: goldschmidt.info 2017 abstracts abstractView?id=2017004266, 2017Co-Authors: Georgi Laukert, Martin Frank, Ed C Hathorne, Thomas Krumpen, Kirstin Werner, Ilka PeekenAbstract:Neodymium (Nd) Isotopes (expressed as eNd) and rare earth elements (REEs) in seawater have been successfully used to trace water mass mixing in the Arctic region [1,2,3]. However, the potential to trace the origin of drifting Arctic sea ice with eNd and REEs has not yet been directly explored. Freshwater originating from various Siberian rivers is mixed and diluted prior to its advection to the central Arctic Ocean and the Fram Strait, thereby inhibiting an assessment of the individual contribution of the different rivers [1,2]. In contrast, sea ice may preserve the marine or riverine eNd and REE signatures from Siberian shelf waters while transported across the Arctic Ocean. This mechanism is demonstrated here for the first time by comparing eNd and REE signatures determined from unfiltered but essentially sediment-free sea ice with corresponding signatures expected for surface seawater in the formation region of the ice. Sea-ice cores were recovered in the Eurasian Basin of the central Arctic Ocean in 2012. Based on satellite-derived ice drift and concentration data, some of the sea-ice floes sampled formed east of Vilkitsky Strait and are characterized by eNd values near -8 in agreement with the incorporation of radiogenic freshwater (eNd- 6) from the Yenisei and Ob rivers [4]. A second sea-ice source was located north of the Laptev Sea as reflected by eNd values near -11, which is consistent with mixed contributions of radiogenic waters from the Kara Sea and northward flowing highly unradiogenic freshwater (eNd< -15) of the Lena River [4]. These first data suggest that Nd Isotopes can trace both the origin of drifting sea ice and of freshwater. The REE concentrations in the ice are depleted compared to those in Siberian shelf waters, indicating salt-associated REE rejection during sea-ice formation. [1] Laukert et al.(2017) Geochim. Cosmochim. Acta 202, 285-309. [2] Porcelli et al. (2009)Geochim. Cosmochim. Acta 73, 2645-2659. [3] Andersson et al. (2008) Geochim. Cosmochim. Acta 72, 2854-2867. [4] Laukert et al.(2016) Goldschmidt Abstracts 2016,1688.
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Short-term variability of dissolved rare earth elements and Neodymium Isotopes in the entire water column of the Panama Basin
Earth and Planetary Science Letters, 2017Co-Authors: Patricia Grasse, Katharina Pahnke, L. Bosse, Ed C Hathorne, Philipp Böning, Martin FrankAbstract:Abstract The distribution of dissolved rare earth elements (REEs) and Neodymium Isotopes (eNd) in the open ocean traces water mass mixing and provides information on lithogenic inputs to the source regions of the water masses. However, the processes influencing the REE budget at the ocean margins, in particular source and sink mechanisms, are not yet well quantified. In this study the first dissolved REE concentrations and Nd isotope compositions of seawater from the Panama Basin (RV Meteor cruise M90) in the Eastern Equatorial Pacific (EEP) are presented. The EEP is characterized by one of the world's largest oxygen minimum zones (OMZs). It is dominated by high particle fluxes that are expected to enhance the removal of REEs from the water column by scavenging. The measured REE concentrations peak at the surface indicating high lithogenic input, which is supported by shale-normalized REE patterns in surface waters and highly radiogenic eNd signatures ranging between +1.4 and +4.3, the latter value constituting the most radiogenic value measured for seawater to date. In contrast, intermediate and deep water REE concentrations are low compared to other Pacific Basins and suggest enhanced removal via scavenging associated with high particle fluxes. The eNd signatures of intermediate and deep waters are less radiogenic than surface waters ranging between −1.4 and +1.3 but significantly more radiogenic than source water masses in the EEP. The eNd signatures consequently do not reflect mixing of intermediate and deep water masses entering the Panama Basin but can only be explained by lithogenic inputs originating from source rocks with highly radiogenic Nd isotope signatures such as the Central American Volcanic Arc ( e Nd = + 3 to +10). Our data demonstrate significant surface input via continental particles, which are partially dissolved in the water column and thereby release REEs and particularly radiogenic Nd isotope signatures to the subsurface ocean. Data obtained from a re-occupied station in the southern Panama Basin for the first time shows that these processes can partially reset water mass Nd isotope and REE signatures of the entire water column proximal to continental sources on time scales of a few years.
Nicolas Freslon - One of the best experts on this subject based on the ideXlab platform.
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rare earth elements and Neodymium Isotopes in world river sediments revisited
Geochimica et Cosmochimica Acta, 2015Co-Authors: Germain Bayon, Samuel Toucanne, Sylvain Bermell, Sandrine Chéron, Joël Etoubleau, Charlotte Skonieczny, Luc Andre, Bernard Dennielou, Nicolas FreslonAbstract:Over the past decades, rare earth elements (REE) and their radioactive Isotopes have received tremendous attention in sedimentary geochemistry, as tracers for the geological history of the continental crust and provenance studies. In this study, we report on elemental concentrations and Neodymium (Nd) isotopic compositions for a large number of sediments collected near the mouth of rivers worldwide, including some of the world's major rivers. Sediments were leached for removal of non-detrital components, and both clay and silt fractions were retained for separate geochemical analyses. Our aim was to re-examine, at the scale of a large systematic survey, whether or not REE and Nd Isotopes could be fractionated during Earth surface processes. Our results confirmed earlier assumptions that river sediments do not generally exhibit any significant grain-size dependent Nd isotopic variability. Most sediments from rivers draining old cratonic areas, sedimentary systems and volcanic provinces displayed similar Nd isotopic signatures in both clay and silt fractions, with Delta epsilon Nd(clay-silt) < vertical bar 1 vertical bar. A subtle decoupling of Nd Isotopes between clays and silts was identified however in a few major river systems (e.g. Nile, Mississippi, Fraser), with clays being systematically shifted towards more radiogenic values. This observation suggests that preferential weathering of volcanic and/or sedimentary rocks relative to more resistant lithologies may occur in river basins, possibly leading locally to Nd isotopic decoupling between different size fractions. Except for volcanogenic sediments, silt fractions generally displayed homogeneous REE concentrations, exhibiting relatively flat shale-normalized patterns. However, clay fractions were almost systematically characterized by a progressive enrichment from the heavy to the light REE and a positive europium (Eu) anomaly. In agreement with results from previous soil investigations, the observed REE fractionation between clays and silts is probably best explained by preferential alteration of feldspars and/or accessory mineral phases. Importantly, this finding clearly indicates that silicate weathering can lead to decoupling of REE between different grain-size fractions, with implications for sediment provenance studies. Finally, we propose a set of values for a World River Average Clay (WRAC) and Average Silt (WRAS), which provide new estimates for the average composition of the weathered and eroded upper continental crust, respectively, and could be used for future comparison purposes. (C) 2015 Elsevier Ltd. All rights reserved.
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, A. Kripounoff, Marie-laure RougetAbstract:We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2-0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases.The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with σREE=109±86ppm (mean±s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285±150ppm; mean±s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water).The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition.Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, Alexis Khripounoff, Emmanuel PonzeveraAbstract:Abstract We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n = 25), estuaries (n = 18), open-ocean settings (n = 15), and cold seeps (n = 12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2–0.02 M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25 M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n = 58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n = 12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display eNd values that typically range between the eNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit eNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.
Sylvain Bermell - One of the best experts on this subject based on the ideXlab platform.
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extensive wet episodes in late glacial australia resulting from high latitude forcings
Scientific Reports, 2017Co-Authors: Germain Bayon, Sylvain Bermell, Y. Germain, Kazuyo Tachikawa, Patrick De Deckker, John W Magee, Marc D NormanAbstract:Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use Neodymium Isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.
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rare earth elements and Neodymium Isotopes in world river sediments revisited
Geochimica et Cosmochimica Acta, 2015Co-Authors: Germain Bayon, Samuel Toucanne, Sylvain Bermell, Sandrine Chéron, Joël Etoubleau, Charlotte Skonieczny, Luc Andre, Bernard Dennielou, Nicolas FreslonAbstract:Over the past decades, rare earth elements (REE) and their radioactive Isotopes have received tremendous attention in sedimentary geochemistry, as tracers for the geological history of the continental crust and provenance studies. In this study, we report on elemental concentrations and Neodymium (Nd) isotopic compositions for a large number of sediments collected near the mouth of rivers worldwide, including some of the world's major rivers. Sediments were leached for removal of non-detrital components, and both clay and silt fractions were retained for separate geochemical analyses. Our aim was to re-examine, at the scale of a large systematic survey, whether or not REE and Nd Isotopes could be fractionated during Earth surface processes. Our results confirmed earlier assumptions that river sediments do not generally exhibit any significant grain-size dependent Nd isotopic variability. Most sediments from rivers draining old cratonic areas, sedimentary systems and volcanic provinces displayed similar Nd isotopic signatures in both clay and silt fractions, with Delta epsilon Nd(clay-silt) < vertical bar 1 vertical bar. A subtle decoupling of Nd Isotopes between clays and silts was identified however in a few major river systems (e.g. Nile, Mississippi, Fraser), with clays being systematically shifted towards more radiogenic values. This observation suggests that preferential weathering of volcanic and/or sedimentary rocks relative to more resistant lithologies may occur in river basins, possibly leading locally to Nd isotopic decoupling between different size fractions. Except for volcanogenic sediments, silt fractions generally displayed homogeneous REE concentrations, exhibiting relatively flat shale-normalized patterns. However, clay fractions were almost systematically characterized by a progressive enrichment from the heavy to the light REE and a positive europium (Eu) anomaly. In agreement with results from previous soil investigations, the observed REE fractionation between clays and silts is probably best explained by preferential alteration of feldspars and/or accessory mineral phases. Importantly, this finding clearly indicates that silicate weathering can lead to decoupling of REE between different grain-size fractions, with implications for sediment provenance studies. Finally, we propose a set of values for a World River Average Clay (WRAC) and Average Silt (WRAS), which provide new estimates for the average composition of the weathered and eroded upper continental crust, respectively, and could be used for future comparison purposes. (C) 2015 Elsevier Ltd. All rights reserved.
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, A. Kripounoff, Marie-laure RougetAbstract:We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2-0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases.The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with σREE=109±86ppm (mean±s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285±150ppm; mean±s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water).The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition.Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation
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Rare earth elements and Neodymium Isotopes in sedimentary organic matter
Geochimica et Cosmochimica Acta, 2014Co-Authors: Nicolas Freslon, Germain Bayon, Samuel Toucanne, Sylvain Bermell, Claire Bollinger, Sandrine Chéron, Joël Etoubleau, Y. Germain, Alexis Khripounoff, Emmanuel PonzeveraAbstract:Abstract We report rare earth element (REE) and Neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n = 25), estuaries (n = 18), open-ocean settings (n = 15), and cold seeps (n = 12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2–0.02 M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25 M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n = 58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n = 12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display eNd values that typically range between the eNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit eNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium Isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd Isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.
