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International audience; Abrupt and large-scale climate changes have occurred repeatedly and within decades during the last glaciation. These events, where dramatic warming occurs over decades, are well represented in both Greenland ice core mineral dust and temperature records, suggesting a causal link. However, the feedbacks between atmospheric dust and climate change during these Dansgaard-Oeschger events are poorly known and the processes driving changes in atmospheric dust emission and transport remain elusive. Constraining dust provenance is key to resolving these gaps. Here, we present a multi-technique analysis of Greenland dust provenance using novel and established, source diagnostic isotopic tracers as well as results from a regional climate model including dust cycle simulations. We show that the existing dominant model for the provenance of Greenland dust as sourced from combined East Asian dust and Pacific volcanics is not supported. Rather, our clay mineralogical and Hf-Sr-Nd and D/H isotopic analyses from last glacial Greenland dust and an extensive range of Northern Hemisphere potential dust sources reveal three most likely scenarios (in order of probability): direct dust sourcing from the Taklimakan Desert in western China, direct sourcing from European glacial sources, or a mix of dust originating from Europe and North Africa. Furthermore, our regional climate modeling demonstrates the plausibility of European or mixed European/North African sources for the first time. We suggest that the origin of dust to Greenland is potentially more complex than previously recognized, demonstrating more uncertainty in our understanding dust climate feedbacks during abrupt events than previously understood.

Extracting information about past tectonic or climatic environmental changes from sedimentary records is a key objective of provenance research. Interpreting the imprint of such changes remains challenging as signals might be altered in the sediment-routing system. We investigate the sedimentary provenance of the Oligocene/Miocene Upper Austrian Northern Alpine Foreland Basin and its response to the tectonically driven exhumation of the Tauern Window metamorphic dome (28 ± 1 Ma) in the Eastern European Alps by using the unprecedented combination of Nd isotopic composition of bulk-rock clay-sized samples and partly previously published multi-proxy (Nd isotopic composition, trace-element geochemistry, U-Pb dating) sand-sized apatite single-grain analysis. The basin offers an excellent opportunity to investigate environmental signal propagation into the sedimentary record because comprehensive stratigraphic and seismic datasets can be combined with present research results. The bulk-rock clay-sized fraction εNd values of well-cutting samples from one well on the northern basin slope remained stable at ∼−9.7 from 27 to 19 Ma but increased after 19 Ma to ∼−9.1. In contrast, apatite single-grain distributions, which were extracted from 22 drill-core samples, changed significantly around 23.3 Ma from apatites dominantly from low-grade (

International audience; The Mid-Pleistocene transition (MPT; 1200 to 800 thousand years, kyr) is marked by the shift from 41-kyr to 100-kyr interglacial-glacial cyclicity without substantial change in the astronomical forcing. This change in climate response relied on internal feedback processes including interaction between ice sheet/sea ice, ocean circulation and the carbon cycle. It was suggested that a major perturbation of global oceanic carbon chemistry occurred at around 900 ka (Marine Isotope Stage, MIS, 24-22) although the mechanism responsible for the change is still to be elucidated. To investigate the link between the Atlantic Meridional Overturning Circulation (AMOC) and oceanic carbon storage for the past 1100 kyr, we combined neodymium isotopic composition (Nd-143/Nd-144 or epsilon(Nd)) recorded in foraminiferal authigenic fractions with epibenthic foraminiferal delta C-13 and delta O-13 from two cores in the North- and South-east Atlantic Ocean. Glacial/interglacial eNd amplitude is smaller before the 900-ka event than after the event. The 900-ka event is marked by increase in seawater epsilon(Nd) at both sites. These observations are consistent with previous studies, suggesting basin-wide epsilon(Nd) changes. Combined with existing data, these new results reveal a persistent meridional gradient of seawater epsilon(Nd) in the Atlantic Ocean over the past 1100 kyr. By comparing the reconstructions with numerical modelling results, we propose that weaker AMOC and changes in Nd sources to the North Atlantic were the main reasons for the observed eNd shift at the 900-ka event in relation to the evolution of the Northern hemisphere cryosphere. The influence of enhanced Southern Ocean overturning circulation on eNd values was estimated to be minor. Seawater epsilon(Nd) and benthic delta C-13 relationship for the whole study period indicates the presence of carbon-rich glacial deep water (>3000 m) in the North and the South Atlantic, in particular at MIS 22 and 24. This suggests that, in addition to weaker AMOC, reduction of deep-water ventilation and/or air-sea exchange in the Southern Ocean could have been responsible for the observed low benthic delta C-13 values. Together with increased biological productivity due to iron fertilization in the Southern Ocean, the physical process significantly contributed to the deep Atlantic carbon storage during the 900-ka event and the subsequent glacial periods. (C) 2020 Elsevier Ltd. All rights reserved.

This thesis aims to advance our knowledge of the hydrology of the intermediate and deep water masses of the Mediterranean during the last climatic cycle (last 145 ka), and to constrain the ocean circulation models that allowed the deposition of organic matter-rich sediments (ENT and sapropels). The Nd isotopic composition (εNd) of foraminifera samples in cores located at intermediate and deep bathymetries of the Tyrrhenian Sea, the Adriatic Sea, the Ionian Sea and the Levantine Basin were analyzed. This work allowed to highlight that the intermediate and deep waters of the Eastern Mediterranean are systematically more radiogenic during the glacial stadiums than during the interglacials. We have shown that these changes cannot be entirely attributed to variations in dust and river inputs from northern Africa but to significant changes in the amount of Atlantic (AW) water entering the Mediterranean. Periods of low sea ice levels are associated with a reduction in Atlantic water flows through the straits of Gibraltar and Siculo-Tunisia by inducing more radiogenic deep-water masses in the eastern Mediterranean. Superimposed on these glacial-interglacial fluctuations, African humid periods and sapropel deposits are systematically characterized by more radiogenic εNd values. This has been attributed to the cessation of deep convection of less radiogenic surface water associated with an increase in the contact time of deep-water bodies with radiogenic sediments from the continental margins of the Levantine basin. Our results highlight during terminations I and II an increase in the contribution of less salty water of North Atlantic origin (MAW) of around 55% which may have pre-conditioned the eastern Mediterranean several thousand years before the deposit S1 and S5 sapropels. A comparison of the εNd recordings obtained in the Eastern and Western basins over the last climate cycle shows a stronger gradient of εNd between the two basins at intermediate and deep depths during the glacial stadiums. This is consistent with a weaker water exchange across the Siculo-Tunisian Strait during periods of low sea ice. On the contrary, during the high sea levels of the interglacial periods, water exchanges are stronger between the two basins, inducing a transfer to the Tyrrhenian Sea of variations in the isotopic composition of Nd observed in the eastern Mediterranean. Thus, the African wet periods inducing a stratification of the water masses and the deposits of sapropels in the east, are associated with signatures of more radiogenic waters which are then transported by the LIW in the Tyrrhenian Sea. Superimposed on these orbital variations, rapid variations in εNd could be highlighted in the Corsica channel. Each cold event in the high latitudes of the Northern Hemisphere (Younger Dryas and Heinrich events) is characterized by a more radiogenic LIW in the Tyrrhenian Sea involving a reduction in the formation of intermediate water in the Gulf of Lion (linked to more strong freshwater inflows from the Atlantic during the Heinrich events) and / or a greater production of LIW in the eastern Mediterranean (linked to a cooling of the northern Mediterranean surface during the Heinrich events).; Cette thèse vise à faire progresser notre connaissance de l’hydrologie des masses d’eaux intermédiaires et profondes de la Méditerranée au cours du dernier cycle climatique (derniers 145 ka), et de contraindre les modèles de circulation océanique ayant permis les dépôts de niveaux riches en matière organique (ORL et sapropèles). La composition isotopique en Nd (εNd) d’échantillons de foraminifères de carottes localisées à des bathymétries intermédiaires et profondes de la mer Tyrrhénienne, de l’Adriatique, de la mer Ionienne et du bassin Levantin ont été analysées. Ce travail a permis de mettre en évidence que les eaux intermédiaires et profondes de la Méditerranée Orientale sont systématiquement plus radiogéniques durant les périodes glaciaires que durant les interglaciaires. Nous avons démontré que ces changements ne peuvent pas être attribuée entièrement aux variations des apports éoliens et fluviatiles du Nord de l’Afrique mais à d’importantes modifications dans la quantité d’eau Atlantique (AW) pénétrant en Méditerranéen. Les périodes de bas niveaux marins glaciaire sont associées à une réduction des flux d’eau Atlantique à travers les détroits de Gibraltar et Siculo-tunisien en induisant des masses d’eau profonde plus radiogéniques en Méditerranée orientale. Surimposées à ces fluctuations glaciaires-interglaciaires, les périodes humides Africaines et de dépôts de sapropèles sont systématiquement caractérisées par des valeurs εNd plus radiogéniques. Cela a été attribué à l’arrêt de la convection profonde des eaux moins radiogéniques de surface associée à une augmentation du temps de contact des masses d’eaux profondes avec les sédiments radiogéniques des marges continentales du bassin Levantin. Nos résultats mettent en évidence durant les terminaisons I et II une augmentation de la contribution d’eau moins salées d’origine Nord Atlantique (MAW) d’environ 55 % pouvant avoir pré-conditionné la Méditerranée orientale plusieurs milliers d’année avant le dépôt des sapropels S1 et S5.La comparaison des enregistrements d’εNd obtenus dans les bassins Orientale et Occidentale sur le dernier cycle climatique montre un gradient d’εNd plus fort entre les deux bassins aux profondeurs intermédiaires et profondes durant les stades glaciaires. Cela est cohérent avec un échange d’eau plus faible de part et d’autre du détroit Siculo-tunisien durant les périodes de bas niveau marin glaciaire. Durant les hauts niveaux marins des périodes les interglaciaires les échanges d’eau sont au contraires plus forts entre les deux bassins induisant un transfert à la mer Tyrrhénienne des variations de la composition isotopique en Nd observée en Méditerranée orientale. Ainsi, les périodes humides africaines induisant une stratification des masses d’eaux et les dépôts de sapropèles à l’est, sont associées à des signatures d’eaux plus radiogéniques qui sont alors transportées par la LIW en Mer Tyrrhénienne. Surimposé à ces variations orbitales, des variations rapides de l’εNd ont pu être mises en évidence dans le chenal de Corse. Chaque événements froids des hautes latitudes de l’hémisphère Nord (Younger Dryas et événements de Heinrich) se caractérisent par une LIW plus radiogénique dans la mer Tyrrhénienne impliquant une réduction de la formation d’eau intermédiaire dans le Golfe du Lion (lié à de plus forts apports d’eaux douces depuis l’Atlantique lors des événements de Heinrich) et/ou une production plus importante de LIW en Méditerranée orientale (lié à un refroidissement de la surface du Nord de la Méditerranée lors des événements de Heinrich).

This thesis aims to advance our knowledge of the hydrology of the intermediate and deep water masses of the Mediterranean during the last climatic cycle (last 145 ka), and to constrain the ocean circulation models that allowed the deposition of organic matter-rich sediments (ENT and sapropels). The Nd isotopic composition (εNd) of foraminifera samples in cores located at intermediate and deep bathymetries of the Tyrrhenian Sea, the Adriatic Sea, the Ionian Sea and the Levantine Basin were analyzed. This work allowed to highlight that the intermediate and deep waters of the Eastern Mediterranean are systematically more radiogenic during the glacial stadiums than during the interglacials. We have shown that these changes cannot be entirely attributed to variations in dust and river inputs from northern Africa but to significant changes in the amount of Atlantic (AW) water entering the Mediterranean. Periods of low sea ice levels are associated with a reduction in Atlantic water flows through the straits of Gibraltar and Siculo-Tunisia by inducing more radiogenic deep-water masses in the eastern Mediterranean. Superimposed on these glacial-interglacial fluctuations, African humid periods and sapropel deposits are systematically characterized by more radiogenic εNd values. This has been attributed to the cessation of deep convection of less radiogenic surface water associated with an increase in the contact time of deep-water bodies with radiogenic sediments from the continental margins of the Levantine basin. Our results highlight during terminations I and II an increase in the contribution of less salty water of North Atlantic origin (MAW) of around 55% which may have pre-conditioned the eastern Mediterranean several thousand years before the deposit S1 and S5 sapropels. A comparison of the εNd recordings obtained in the Eastern and Western basins over the last climate cycle shows a stronger gradient of εNd between the two basins at intermediate and deep depths during the glacial stadiums. This is consistent with a weaker water exchange across the Siculo-Tunisian Strait during periods of low sea ice. On the contrary, during the high sea levels of the interglacial periods, water exchanges are stronger between the two basins, inducing a transfer to the Tyrrhenian Sea of variations in the isotopic composition of Nd observed in the eastern Mediterranean. Thus, the African wet periods inducing a stratification of the water masses and the deposits of sapropels in the east, are associated with signatures of more radiogenic waters which are then transported by the LIW in the Tyrrhenian Sea. Superimposed on these orbital variations, rapid variations in εNd could be highlighted in the Corsica channel. Each cold event in the high latitudes of the Northern Hemisphere (Younger Dryas and Heinrich events) is characterized by a more radiogenic LIW in the Tyrrhenian Sea involving a reduction in the formation of intermediate water in the Gulf of Lion (linked to more strong freshwater inflows from the Atlantic during the Heinrich events) and / or a greater production of LIW in the eastern Mediterranean (linked to a cooling of the northern Mediterranean surface during the Heinrich events)., Cette thèse vise à faire progresser notre connaissance de l’hydrologie des masses d’eaux intermédiaires et profondes de la Méditerranée au cours du dernier cycle climatique (derniers 145 ka), et de contraindre les modèles de circulation océanique ayant permis les dépôts de niveaux riches en matière organique (ORL et sapropèles). La composition isotopique en Nd (εNd) d’échantillons de foraminifères de carottes localisées à des bathymétries intermédiaires et profondes de la mer Tyrrhénienne, de l’Adriatique, de la mer Ionienne et du bassin Levantin ont été analysées. Ce travail a permis de mettre en évidence que les eaux intermédiaires et profondes de la Méditerranée Orientale sont systématiquement plus radiogéniques durant les périodes glaciaires que durant les interglaciaires. Nous avons démontré que ces changements ne peuvent pas être attribuée entièrement aux variations des apports éoliens et fluviatiles du Nord de l’Afrique mais à d’importantes modifications dans la quantité d’eau Atlantique (AW) pénétrant en Méditerranéen. Les périodes de bas niveaux marins glaciaire sont associées à une réduction des flux d’eau Atlantique à travers les détroits de Gibraltar et Siculo-tunisien en induisant des masses d’eau profonde plus radiogéniques en Méditerranée orientale. Surimposées à ces fluctuations glaciaires-interglaciaires, les périodes humides Africaines et de dépôts de sapropèles sont systématiquement caractérisées par des valeurs εNd plus radiogéniques. Cela a été attribué à l’arrêt de la convection profonde des eaux moins radiogéniques de surface associée à une augmentation du temps de contact des masses d’eaux profondes avec les sédiments radiogéniques des marges continentales du bassin Levantin. Nos résultats mettent en évidence durant les terminaisons I et II une augmentation de la contribution d’eau moins salées d’origine Nord Atlantique (MAW) d’environ 55 % pouvant avoir pré-conditionné la Méditerranée orientale plusieurs milliers d’année avant le dépôt des sapropels S1 et S5.La comparaison des enregistrements d’εNd obtenus dans les bassins Orientale et Occidentale sur le dernier cycle climatique montre un gradient d’εNd plus fort entre les deux bassins aux profondeurs intermédiaires et profondes durant les stades glaciaires. Cela est cohérent avec un échange d’eau plus faible de part et d’autre du détroit Siculo-tunisien durant les périodes de bas niveau marin glaciaire. Durant les hauts niveaux marins des périodes les interglaciaires les échanges d’eau sont au contraires plus forts entre les deux bassins induisant un transfert à la mer Tyrrhénienne des variations de la composition isotopique en Nd observée en Méditerranée orientale. Ainsi, les périodes humides africaines induisant une stratification des masses d’eaux et les dépôts de sapropèles à l’est, sont associées à des signatures d’eaux plus radiogéniques qui sont alors transportées par la LIW en Mer Tyrrhénienne. Surimposé à ces variations orbitales, des variations rapides de l’εNd ont pu être mises en évidence dans le chenal de Corse. Chaque événements froids des hautes latitudes de l’hémisphère Nord (Younger Dryas et événements de Heinrich) se caractérisent par une LIW plus radiogénique dans la mer Tyrrhénienne impliquant une réduction de la formation d’eau intermédiaire dans le Golfe du Lion (lié à de plus forts apports d’eaux douces depuis l’Atlantique lors des événements de Heinrich) et/ou une production plus importante de LIW en Méditerranée orientale (lié à un refroidissement de la surface du Nord de la Méditerranée lors des événements de Heinrich).

Dissolved neodymium (Nd) isotopic composition (expressed as ?Nd) has been analysed for 82 seawater samples collected from 13 stations stretching from the Alboran Sea to the Iceland Basin. The distribution of the ?Nd values of water masses was thus investigated for the first time along the western European margin in order to explore whether the water masses flowing in the eastern subpolar and subtropical Atlantic reveal distinct isotopic patterns. The Modified Atlantic Water (MAW) in the Alboran Sea displays ?Nd values (between -9.2 ± 0.2 and -8.9 ± 0.2) that are significantly more radiogenic than those reported in previous studies (-10.8 ± 0.2 to -9.7 ± 0.2), suggesting temporal variations in the Nd isotopic composition of the water that enters the Mediterranean Sea from the Strait of Gibraltar. The ?Nd value of the underlying modified Winter Intermediate Water (WIW) has been established for the first time (-9.8 ± 0.3) and is compatible with a Nd signature acquired from the sinking of MAW in the northwestern Mediterranean Sea. Within the Gulf of Cádiz, southern Mediterranean Sea Water (MSW) (-10.6 ± 0.2) differs slightly from the northern MSW (-9.9 ± 0.4) owing to a significant contribution of modified East Antarctic Intermediate Water (EAAIW) (-10.9 ± 0.2). In the northeast Atlantic, the North Atlantic Current surface water located in the inter-gyre region (north of 46°N) displays ?Nd values of between -14.0 ± 0.3 and -15.1 ± 0.3, reflecting the subpolar gyre signature. Along the western European margin, ?Nd values of surface water decrease toward the north (from -10.4 ± 1.6 to -13.7 ± 1.0) in agreement with the gradual mixing between subtropical and subpolar water. At intermediate depth, ?Nd values decrease from -9.9 ± 0.4 within the Gulf of Cádiz to -12.1 ± 0.2 within the Porcupine Seabight, indicating a strong dilution of the MSW with subpolar water. Within the Rockall Trough and the Iceland Basin, the more negative ?Nd values at mid-depth (

International audience; Rare Earth Element (REE) concentrations and Nd isotopic compositions (εNd) of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated (1) to establish the distribution of the Nd isotopic composition of water masses along the tropical Western Pacific and the SCS until now underexplored, (2) to constrain hydrological exchanges between the SCS and the Philippine Sea through the Luzon Strait, and (3) to test, in the context of the semi-closed marginal sea (SCS), the possible impact of the process of exchange of Nd between SCS water masses and unradiogenic sediments from its north-western margin.εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from −2.3 to −4.4 and generally increase slightly as water depth increases. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach −2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterised by less radiogenic Nd (−4.1±0.5) indicating the intrusion of southern-sourced water. For most of the stations in the Northern SCS, water masses below 1500 m (PDW) display homogenous εNd values (~−4.1) identical to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500–1500 m) vary from −3.0 to −3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS display local modification (~−5.3 to −7.0) in areas where water passes above sediment drift deposit systems. This implies locally confined “boundary exchange’’ with unradiogenic sediments (around −11) insufficient to alter the Nd isotopic composition of the PDW in the Northern SCS. In addition, εNd values analysed for the first time in nepheloid layers collected along the north-western margin of the SCS do not exhibit any significant modification of the seawater εNd which remains into a narrow range between −3.7 and −4.3, similar to that of the PDW. A compilation of εNd from the sea surface water of the SCS indicates lower εNd values in the western and the central SCS (−3.3 to −9.5), induced by sediments riverine input which are characterised by unradiogenic εNd (around −11). Finally, as significant variations are observed in seawater εNd at mid-depth between the SCS and the Philippine Sea, εNd values could be used in the future to track intermediate water mass exchange in the Luzon Strait, a process which, at present, remains poorly understood.

Dissolved rare earth element (REE) concentration data from intermediate and deep seawater form an array characterized by higher middle REE enrichments (MREE/MREE*) in the North Atlantic and a progressive increase in heavy-to-light REE ratios (HREE/LREE) as water masses age. The REEs in foraminifera are fractionated towards higher MREE/MREE* and lower HREE/LREE relative to seawater. Calculations based on a scavenging model show that the REE patterns in uncleaned core-top foraminifera resemble those adsorbed onto calcite, particulate organic material, and hydrous ferric oxides but the full extent of the REE fractionation measured in foraminifera was not reproduced by the model. However, differences in the HREE/LREE, MREE/MREE* ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater REE distribution. Under oxic conditions, the HREE/LREE and MREE/MREE* compositions of uncleaned foraminifera at the sediment/seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth. In suboxic sedimentary environments, all uncleaned foraminiferal REE concentrations are elevated relative to core-top values indicating addition of REEs from pore waters. The HREE/LREE ratio is highest when sedimentation rates were greatest [Lippold et al., 2009] and when high Fe/Ca ratios in the uncleaned foraminifera indicate that Fe was mobile. In sediments that have not experienced suboxic conditions during burial, uncleaned foraminifera preserve the seawater signal taken up at the sediment/seawater interface and are therefore suggested to be a suitable archive of changes in the REE signal of past bottom waters. This article is protected by copyright. All rights reserved.

A metabasite lens with eclogite-facies relics discovered within high-grade gneisses, at Punta Orvili (Posada) in NE Sardinia, has proven to be the first example of within-plate basalt among the eclogite-derived, tholeiitic metabasites from the Variscan belt in Sardinia. The composition of the Punta Orvili metabasite is unusual: SiO(2) < 47.6 wt%, Al(2)O(3) < 9.6 wt%, MgO >= 13 wt%, Fe(2)O(3tot) > 13 wt%, Cr > 550 ppm, Ni > 270 ppm, Mg # 68-70. Detailed investigation of the major and trace element content rules out any significant geochemical modification of the protolith by alteration and/or metamorphic processes. Normative contents of mafic minerals up to 55-79 wt%, very small amounts of Al(2)O(3) and Na(2)O and very high concentrations of MgO, Cr and Ni suggest a protolith of picritic nature. The steeply sloping REE patterns, with La(N)/Yb(N) = 13.0-17.3, suggest low-degree partial melting and the presence of garnet, as retention phase of HREE in the mantle source. Enrichment factors are 60-180 times higher for LREE, 30-60 times for MREE, 10-20 times for HREE. The primitive manntle-normalized trace element abundance patterns of the Punta Orvili metabasite show enrichment in Ba, Th, Nb, La, Ce, compared to eclogite-derived metabasites. Values of La/Nb, La//Ta, Ce/Nb, Th/Nb, Sm/Yb, Ce/Sm, Th/Y, Nb/Y, Th/Yb and Ta/Yb differ significantly from those of average crust, upper, lower and mid-crust, indicating an OIB-like source. Two values of (87)Sr/(86)Sr((i)) were obtained around 0.709 with epsilon(Sri) =+69-71. The corresponding values of the (143)Nd/(144)Nd((i)) are about 0.51197 with epsilon(Ndi) similar to -1.50 assuming an age of 460 Ma, i.e. the mean age of Sardinian eclogite. Isotope and geochemical data suggest that the Punta Orvili protolith was generated by interaction of OIB-like melts with an enriched sub-continental lithospheric mantle, similar in composition to Group II kimberlites and/or to their garnet peridotite xenoliths.

The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records obtained from foraminifera spanning the past 25kyr. Display a wide range of values, ranging from -4±0.2 to -6.7±0.3, suggesting important changes in the contribution of the NPDW (εNd=-4) and the UCDW (εNd -6 to -8) in the subtropical western Pacific. During the period of deglaciation, εNd records indicate a relative decrease in the negative excursions of the εNd implying a higher proportion of SSW during the time intervals 17-15 cal kyr BP and 10-8 cal kyr BP; these intervals are coeval with the HS1 and early Holocene. The negative shifts centered on the HS1coincide with an enhanced upwelling in the Southern Ocean, associated with a polewards shift of the southern westerlies, inducing an enhanced formation of the SSW that propagates to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10-8 cal kyr BP) indicates a higher relative proportion of SSW that could be associate with higher production of the SSW, as has been recently observed in the South Atlantic, and/or with a possible reduction of the NPIW. Our data suggest that the present modern circulation pattern in the western subtropical Pacific Ocean was fully established after 4.6 cal kyr BP.; Le but de cette étude est de retracer l’évolution de l’hydrologie dans la partie occidentale de l’Océan Pacifique subtropical en utilisant le proxy εNd analysé sur les foraminifères et sur les oxydes de ferromanganèse authigéniques dans les sédiments. Ceux-ci proviennent de carottes sédimentaires prélevées au nord de la Mer de Chine du Sud (MCS). Avant d’utiliser l’εNd dans les sédiments profonds de la MCS, 16 profils d’eau de mer, collectés au nord de la MCS et dans le Mer des Philippines, ont été analysés afin d’établir la distribution d’εNd des masses d’eau dans l’ouest du Pacifique tropical et dans la MCS, qui jusqu’à aujourd’hui n’était pas documentée. Les valeurs d’εNd des masses d’eau profondes et intermédiaires varient de -2,7 à -4,4 et augmentent légèrement avec la profondeur. Dans la mer des Philippines, les valeurs d’εNd de l’eau intermédiaire du Pacifique Nord (North Pacific Intermediate Water, NPIW) atteint -2.7±0.4 à moyenne profondeur (500 à 1400m). En-dessous de de 1800m, l’eau profonde Pacifique (Pacific Deep Water, PDW) est caractérisée par du Nd moins radiogénique (-4.1±0.5), indiquant l’intrusion de masses d’eau australes. Pour la plupart des stations du nord de la MCS, les masses d’eau en-dessous de 1500m (PDW) affichent des valeurs d’εNd homogènes (~ -4.1), similaires à celles de la PDW dans la Mer des Philippines. Les valeurs d'εNd pour l'eau intermédiaire de la mer de Chine du Sud (South China Sea Intermediate Water, SCSIW, 500-1500m) varient entre -3.0 et -3.9 dû au mélange vertical de la NPIW avec la PDW. Les valeurs d'εNd de l'eau de mer dans la MCS (-5.3 à -7.0) affichent des modifications locales dans des zones où l'eau s'écoule au-dessus de systèmes de dépôt sédimentaire. Ceci implique que "l'échange à la marge" avec des sédiments non radiogéniques (autour de -11) peut se produire dans le temps et dans l'espace sans modifier la composition isotopique du Nd de la PDW dans le Nord de la MCS. Dans un second temps, l’εNd extrait des foraminifères planctoniques G. ruber a été étudié sur la carotte MD05-2904, collectée à 2000m de profondeur sur la marge nord-ouest de la MCS. Cette étude a été conduite dans le but de retracer les variations hydrologiques depuis le Dernier Maximum Glaciaire (DMG) dans la partie occidentale du Pacifique Nord subtropical. Les enregistrements d'εNd ainsi obtenus couvrent les derniers 25 000 ans. Ils affichent une large gamme de valeurs de -4±0.2 à -6.7±0.3, suggérant d'importants changements dans la contribution de la NPDW (εNd=-4) et de la UCDW (Upper circumpolar Deep Water, εNd -6 to -8) dans la zone étudiée. Durant la déglaciation, les enregistrements d'εNd indiquent une diminution des excursions négatives de l'εNd impliquant une plus forte proportion de SSW (Southern-sourced Water) entre 17 et 15 ka BP ainsi qu'entre 10 et 8 ka BP. Ces intervalles de temps sont contemporains de l’évènement Heinrich 1 (HS1) et de l’Holocène inférieur. Les shifts négatifs centrés sur le HS1 coïncident avec un phénomène d'upwelling renforcé dans l'océan austral, associé à un déplacement vers le pôle des vents d'ouest. Ceci implique une augmentation de la formation de la SSW qui se propage dans l'Ouest du Pacifique subtropical. L'excursion négative de l'εNd durant l’Holocène inferieur (~10-8 cal ka BP) indique une plus grande proportion de SSW qui pourrait être associée avec une plus forte production de SSW, comme observé récemment dans l'atlantique Sud, et/ou avec une possible réduction de la NPIW. Nos données suggèrent que le schéma de circulation actuel dans la partie occidental du Pacifique subtropical s'est mis en place il y a 4600 ans.

The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records obtained from foraminifera spanning the past 25kyr. Display a wide range of values, ranging from -4±0.2 to -6.7±0.3, suggesting important changes in the contribution of the NPDW (εNd=-4) and the UCDW (εNd -6 to -8) in the subtropical western Pacific. During the period of deglaciation, εNd records indicate a relative decrease in the negative excursions of the εNd implying a higher proportion of SSW during the time intervals 17-15 cal kyr BP and 10-8 cal kyr BP; these intervals are coeval with the HS1 and early Holocene. The negative shifts centered on the HS1coincide with an enhanced upwelling in the Southern Ocean, associated with a polewards shift of the southern westerlies, inducing an enhanced formation of the SSW that propagates to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10-8 cal kyr BP) indicates a higher relative proportion of SSW that could be associate with higher production of the SSW, as has been recently observed in the South Atlantic, and/or with a possible reduction of the NPIW. Our data suggest that the present modern circulation pattern in the western subtropical Pacific Ocean was fully established after 4.6 cal kyr BP., Le but de cette étude est de retracer l’évolution de l’hydrologie dans la partie occidentale de l’Océan Pacifique subtropical en utilisant le proxy εNd analysé sur les foraminifères et sur les oxydes de ferromanganèse authigéniques dans les sédiments. Ceux-ci proviennent de carottes sédimentaires prélevées au nord de la Mer de Chine du Sud (MCS). Avant d’utiliser l’εNd dans les sédiments profonds de la MCS, 16 profils d’eau de mer, collectés au nord de la MCS et dans le Mer des Philippines, ont été analysés afin d’établir la distribution d’εNd des masses d’eau dans l’ouest du Pacifique tropical et dans la MCS, qui jusqu’à aujourd’hui n’était pas documentée. Les valeurs d’εNd des masses d’eau profondes et intermédiaires varient de -2,7 à -4,4 et augmentent légèrement avec la profondeur. Dans la mer des Philippines, les valeurs d’εNd de l’eau intermédiaire du Pacifique Nord (North Pacific Intermediate Water, NPIW) atteint -2.7±0.4 à moyenne profondeur (500 à 1400m). En-dessous de de 1800m, l’eau profonde Pacifique (Pacific Deep Water, PDW) est caractérisée par du Nd moins radiogénique (-4.1±0.5), indiquant l’intrusion de masses d’eau australes. Pour la plupart des stations du nord de la MCS, les masses d’eau en-dessous de 1500m (PDW) affichent des valeurs d’εNd homogènes (~ -4.1), similaires à celles de la PDW dans la Mer des Philippines. Les valeurs d'εNd pour l'eau intermédiaire de la mer de Chine du Sud (South China Sea Intermediate Water, SCSIW, 500-1500m) varient entre -3.0 et -3.9 dû au mélange vertical de la NPIW avec la PDW. Les valeurs d'εNd de l'eau de mer dans la MCS (-5.3 à -7.0) affichent des modifications locales dans des zones où l'eau s'écoule au-dessus de systèmes de dépôt sédimentaire. Ceci implique que "l'échange à la marge" avec des sédiments non radiogéniques (autour de -11) peut se produire dans le temps et dans l'espace sans modifier la composition isotopique du Nd de la PDW dans le Nord de la MCS. Dans un second temps, l’εNd extrait des foraminifères planctoniques G. ruber a été étudié sur la carotte MD05-2904, collectée à 2000m de profondeur sur la marge nord-ouest de la MCS. Cette étude a été conduite dans le but de retracer les variations hydrologiques depuis le Dernier Maximum Glaciaire (DMG) dans la partie occidentale du Pacifique Nord subtropical. Les enregistrements d'εNd ainsi obtenus couvrent les derniers 25 000 ans. Ils affichent une large gamme de valeurs de -4±0.2 à -6.7±0.3, suggérant d'importants changements dans la contribution de la NPDW (εNd=-4) et de la UCDW (Upper circumpolar Deep Water, εNd -6 to -8) dans la zone étudiée. Durant la déglaciation, les enregistrements d'εNd indiquent une diminution des excursions négatives de l'εNd impliquant une plus forte proportion de SSW (Southern-sourced Water) entre 17 et 15 ka BP ainsi qu'entre 10 et 8 ka BP. Ces intervalles de temps sont contemporains de l’évènement Heinrich 1 (HS1) et de l’Holocène inférieur. Les shifts négatifs centrés sur le HS1 coïncident avec un phénomène d'upwelling renforcé dans l'océan austral, associé à un déplacement vers le pôle des vents d'ouest. Ceci implique une augmentation de la formation de la SSW qui se propage dans l'Ouest du Pacifique subtropical. L'excursion négative de l'εNd durant l’Holocène inferieur (~10-8 cal ka BP) indique une plus grande proportion de SSW qui pourrait être associée avec une plus forte production de SSW, comme observé récemment dans l'atlantique Sud, et/ou avec une possible réduction de la NPIW. Nos données suggèrent que le schéma de circulation actuel dans la partie occidental du Pacifique subtropical s'est mis en place il y a 4600 ans.

Nd isotopic compositions (epsilon Nd) of seawater profiles and deep-sea corals collected off the coast of Iberia and from the Bay of Biscay were measured (1) to constrain the Nd isotopic composition of water masses along the southwest European margin, (2) to track the Mediterranean Outflow Water (MOW) during its northward propagation, and (3) to establish hydrological changes during the last 1500 years. The Eastern North Atlantic Central Water (ENACW) is characterized by Nd isotopic composition of around -12.0. Mediterranean Sea Water (MSW) is collected from 800 and 1200 m depth and is characterized by epsilon Nd values ranging from -10.9, off the coast of Iberia, to -11.6 in the Bay of Biscay. These epsilon Nd results suggest a strong dilution of the pure MOW at the Strait of Gibraltar (epsilon Nd -9.4) of approximately 40% and 30% along its northward circulation pathway essentially with a contribution from ENACW. At around 2000 m depth, epsilon Nd water profiles display the occurrence of a nonradiogenic water mass (epsilon Nd -13), originating from the Labrador Sea (Labrador Sea Water). Fossil deep-sea corals, dated between 84 and 1500 years, display Nd isotopic compositions that vary moderately from present-day seawater values, suggesting a weaker influence of MOW in the formation of MSW during the Dark Ages and the Little Ice Age. These recent cold events seem to be associated with a reduction in the northward penetration of MSW, which may result from a greater eastward extension of the middepth subpolar gyre and/or a reduction of MSW formation, likely tied to a variation in deep Mediterranean water production.

International audience; Nd isotopic compositions (ɛNd) of seawater profiles and deep‐sea corals collected off the coast of Iberia and from the Bay of Biscay were measured (1) to constrain the Nd isotopic composition of water masses along the southwest European margin, (2) to track the Mediterranean Outflow Water (MOW) during its northward propagation, and (3) to establish hydrological changes during the last 1500 years. The Eastern North Atlantic Central Water (ENACW) is characterized by Nd isotopic composition of around −12.0. Mediterranean Sea Water (MSW) is collected from 800 and 1200 m depth and is characterized by ɛNd values ranging from −10.9, off the coast of Iberia, to −11.6 in the Bay of Biscay. These ɛNd results suggest a strong dilution of the pure MOW at the Strait of Gibraltar (ɛNd −9.4) of approximately 40% and 30% along its northward circulation pathway essentially with a contribution from ENACW. At around 2000 m depth, ɛNd water profiles display the occurrence of a nonradiogenic water mass (ɛNd −13), originating from the Labrador Sea (Labrador Sea Water). Fossil deep‐sea corals, dated between 84 and 1500 years, display Nd isotopic compositions that vary moderately from present‐day seawater values, suggesting a weaker influence of MOW in the formation of MSW during the Dark Ages and the Little Ice Age. These recent cold events seem to be associated with a reduction in the northward penetration of MSW, which may result from a greater eastward extension of the middepth subpolar gyre and/or a reduction of MSW formation, likely tied to a variation in deep Mediterranean water production.

The Caucete Group is a low-grade metasedimentary sequence of probable late Neoproterozoic-Cambrian age. It is exposed on the western flank of the Sierra de Pie de Palo, a basement block of the Cuyania terrane from western Argentina. The geochemical composition (major, trace and rare-earth elements, and Sm-Nd isotopes) of the El Quemado, La Paz, El Desecho, and Angacos formations (Caucete Group) was used to characterize the sedimentary provenance. We recognized two types of sources: A felsic source (crustal signature) and another mafic source with juvenile signature. Provenance is interpreted to be the mixing between Paleoproterozoic felsic rocks and Mesoproterozoic-Neoproterozoic juvenile rocks sources. This is supported by previous geochronological studies. The Cuyania basement is interpreted to be the Mesoproterozoic and Neoproterozoic juvenile component defined in the Caucete Group (e.g.: ophiolite assemblage of Sierra de Pie de Palo). The Cuyania basement is also considered to be the felsic source (paragneisses and meta-greywackes of the Pie de Palo Complex). We do not consider Gondwana as a provenance source based on the discrepancies in the Sm-Nd isotopic signatures and the detrital zircon provenance ages between the Caucete Group and the surrounding units that are considered to be autochthonous to the southern margin of Gondwana. The Caucete Group Laurentian Sm-Nd isotopic signature suggests that this sector could have been part of the source area. Hence an allochthonous origin for the Caucete Group (Cuyania terrane), derived from southern Laurentia, is supported for the geochemical results presented in this contribution. Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Cingolani, C.A.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; Argentina Fil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Chemale Jr., F.. Universidade Federal do Sergipe; Brasil

International audience; Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia.;The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8 ka cal BP and the Saharan period from 98 to 72 ka BR For the first time, the last glacial period (Marine Isotope Stage (MIS) 2,3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes.;The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5 ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka. During the last glacial period, two wet periods are present around 60-50 ka BP and 38-30 ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concentrations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales.

International audience; We performed geochemical analyses (major- and trace-elements, Nd isotopes) of Late Variscan igneous rocks from the western Alps in order to better constrain the lithospheric evolution at the end of the Variscan orogeny. In the western Alps, the shoshonitic suite from the Croix de Fer pass and the alkaline Combeynot granite were emplaced during the Late Carboniferous. They were followed during the Early Permian by the calc-alkaline diorite porphyries from the “Zone Houillère Briançonnaise”, dated by 40Ar–39Ar, and by the calc-alkaline rhyodacites from the Guil valley. These suites postdate the Variscan orogeny and originated in a regime of lithospheric extension and thinning affecting the entire domain of the European Variscan belt. They display subduction-related geochemical features with the exception of the Combeynot granite. The Croix de Fer suite, the diorite porphyries from the Zone Houillère Briançonnaise and the felsic lavas from the Guil valley show the lowest (–7 >