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Coral reef records related to past higher and/or rising sea levels provide an important baseline for developing projections regarding the response of modern coastal systems to future sea-level rise. Sea-level rise at the end of the current century is expected to range between 5.5 and 10 mm. yr-1 on average, depending on the various scenarios of global warming [IPCC, 2019]. The Last Deglaciation (23 to 6 kyr B.P.) is seen as a potential recent analogue of the environmental changes that the Earth may face in the near future as a consequence of ocean thermal expansion and the melting of polar ice sheets. The last deglacial record from Barbados suggests a non-monotonous sea-level rise averaging 10 mm.yr-1 and punctuated by two ‘meltwater pulses’ (MWP) characterized by several centuries of extremely rapid sea-level rise related to catastrophic ice-sheet collapse [Fairbanks, 1989, Nature, 342, 637; Bard et al., 1990, Nature, 346, 456; Peltier & Fairbanks, 2006, Quat. Sci. Rev., 25, 3322].IODP Expedition 310 ‘Tahiti Sea Level’ and land drilling on the modern barrier reef of Papeete have provided unparalleled coral reef records encompassing the period covered by the two MWP identified previously in Barbados. Reefs accreted continuously between 16 and 10 kyr B.P. in Tahiti, mostly through aggradational processes, at growth rates averaging 10 mm yr–1. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to non-monotonous sea-level rise and coeval environmental changes [Camoin et al., 2012; Geology, 40, 643; Camoin & Webster, 2015; Sedimentology, 62, 401].While the MWP-1B at approximately 11.3 kyr B.P. in Barbados is absent or very small in Tahiti [Bard et al. 1996; Nature, 382, 241; Bard et al., 2010; Science, 327, 1235; Bard et al., 2016; Paleoceanography, 31], the Tahiti offshore record has provided the opportunity to document the MWP-1A at several drill sites. A sea-level rise of 16±2 m in amplitude has been evidenced between 14.65 and 14.3 kyr B.P., coeval with the Bølling warming [Deschamps et al., 2012, Nature, 483, 559]. The rate of eustatic sea-level rise ranged from 40 to 50 mm.yr-1 during MWP-1A, implying that this episode corresponds to one of the fastest rises in sea level ever documented in Earth history.This paper documents in unprecedented detail the reef response to extreme sea-level rise during MWP-1A in Tahiti. It is based on new accurate U-series and 14C AMS ages of corals and algae and the reappraisal of the environmental significance and paleowater depth interpretation of various coralgal assemblages. The succession in time and space of successive reef assemblages involved in reef accretion during the MWP-1A leads, for the first time, to reconstruct reef accretion patterns during this dramatic period, which is of prime importance to help forecasting coral reef response to future sea-level change.

International audience; New insights into the geodynamic evolution, the paleogeographic framework and the paleoclimatic setting of the Upper Eocene-Oligocene lacustrine basins from SouthEast France have been provided by an integrative approach combining geochronology, micropaleontology and stable isotope analyses. U-Pb dating on calcite, pollen-based climatostratigraphy and strontium and sulfur isotope signatures of sulfates provided a robust chronostratigraphic framework for the Upper Eocene and Oligocene succession from the Vistrenque, Alès and Roussillon basins. The thick Priabonian-lower Rupelian lacustrine succession from the Vistrenque Basin is interpreted to be deposited in a strike-slip basin associated with the latest stages of pyrenean shortening. Floral assemblages are used to reconstruct the vegetation cover in the lacustrine systems and their neighbouring lowlands and highlands. Composition of saltwater inferred from strontium and sulfur isotope signatures of sulfates, the occurrence of calcareous nannofossils, dinoflagellate cysts and pollen grains of mangrove-related plants provided strong evidence for marine intrusions into the Alès Basin during the Priabonian and the Vistrenque Basin during the Rupelian and Chattian. Paleogeographic reconstructions of Southeast France during the Priabonian and late Rupelian strongly suggest marine incursions from the Alpine Sea via two potential pathways: upper Rhône Valley via the Crest Sill and lower Rhône Valley via the Haut-Var Pyrenean synclines. On the other hand, Upper Oligocene evaporite basins in the Camargue area have been subjected to marine intrusions from the Western Mediterranean Sea following the collapse of the eastern pyrenean relief during the Liguro-Provençal rifting stage. Finally, pollen analysis and Climate Amplitude Method revealed a brief but significant stage of cooling and aridification at the very base of the Rupelian which could represent the regional and terrestrial expression of the global climate cooling following the Eocene-Oligocene Transition.

International audience

International audience; The age of brittle deformation in the superficial part of orogens is generally constrained by relative, cross-cutting structural relationships. However, it becomes possible to decipher the timing of fault activity by a combination of methods based on U-Pb dating and stable isotope composition of calcite-filled fault and veins. This methodology is applied to constrain the timing of deformation of the frontal part of an orogenic system, through the example of the Tertiary development of subalpine massifs fold and thrust belt (composed by Bauges, Chartreuse, Vercors massifs). The architecture of the massifs is well constrained, but the chronology and the nature of involved fluids is unknown. Clumped isotope Δ47 analysis shows a significant variation of fluid temperature from 54 °C to the west up to 149 °C for the internal Vercors thrust to the east. These temperature estimates highlight a deep underthrusting with a significant exhumation of the eastern Vercors (4-6 km), while a shallow underthrusting at a depth of around 2 km is estimated for the central Vercors. Carbon and oxygen stable isotope analyses, reveal three fluid signatures corresponding to heated fluids from meteoric or basin-derived origin, which interacted at various extents with the host-rock. These data are in agreement with a low altitude frontal belt, and with a progressive reequilibration of downwards infiltrating fluids with the composition of the host-rocks. The successfully dated calcites are those exhibiting the highest fluid-rock ratios, which allowed U enrichment in a mainly uranium-poor rock environment. In-situ U-Pb calcite dating was performed on fault mirrors of main thrusts and on fractured pebbles of the underthrusted molasses of eight major thrusts. Preserved Oligocene ages of extensional veins related to pre-Alpine rifting demonstrate that U-Pb calcite is a robust method to characterize multiple superimposed events of a whole mountain building history. Furthermore, the presence of multiple deformation events in the same location point out the importance of inherited structures on the strain localization processes. Thrust related U-Pb on calcite ages on an E-W section between the Vercors and Chartreuse massifs record a major Miocene shortening phase, and the timing of strain propagation towards the foreland. The oldest thrust dated at 15 Ma, corresponds to the activation of the most internal preserved thrust mobilizing 149 °C fluids. In the central subalpine massifs, ages range from 14 Ma (Chartreuse) to 12 Ma (Vercors) mobilizing 54 °C fluids. On the western part, the initiation of the most external thrust has been dated between 10 Ma and 7 Ma. These geochronological constraints are consistent with an 'in-sequence' westward propagation of the deformation between 15 Ma and 7 Ma and contemporaneous with the exhumation of the Belledonne External Crystalline Massif and the development of flexural basin sedimentation. Paleostress calculations indicate a three-stage evolution of the subalpine nappe stack. Reverse and strike-slip deformations are interpreted as a diffuse tectonic reactivation in an 'hors-sequence' mode from 10 Ma to present in a broadly similar stress field.

Des etudes paleoenvironnementales anterieures ont montre que des changements majeurs de la vegetation et de l’environnement se sont produits en Afrique centrale a partir de l’Holocene moyen (ex. Maley & Brenac 1998). Plusieurs d’entre elles mettent en evidence une origine humaine et supposent que les grandes migrations de population, les innovations techniques (par exemple, la technologie de la fonte du fer) et/ou de nouveaux choix dans les pratiques agricoles, conduisant a la deforestation et au defrichement, sont les moteurs de ces changements. Cependant, a ce stade, l’absence de reconstitution demographique ne permet pas de soutenir pleinement ces hypotheses. Notre etude utilise une base de donnees archeologiques georeferencees pour deduire la dynamique des populations et l’evolution des pratiques culturelles en Afrique centrale occidentale au cours des 5000 dernieres annees. Cette base de donnees comprend 1139 dates calibrees au 14C provenant de 425 sites – localises dans le sud du Cameroun, au Gabon, en Republique du Congo, en Guinee equatoriale et dans la partie occidentale de la Republique democratique du Congo –, remontant a un maximum de 5000 ans cal. BP. La modelisation des donnees indique une possible croissance de la population entre ~2500 et ~1500 ans cal. BP, coincidant avec l’apparition a l’echelle regionale de techniques et de pratiques specifiques. L’augmentation concomitante des fosses depotoirs, des vestiges d’utilisation de palmier a huile Elaeis guineesis, l’apparition de rares restes de millet Pennisetum glaucum et la montee en puissance des vestiges de metallurgie du fer ont eu lieu pendant la seconde moitie du Neolithique, a partir d’environ 2800 ans cal. BP. Dans les regions cotieres, la croissance de la population concerne le Neolithique et le debut de l’âge du fer (2500-2000 ans cal. BP et 2000-1500 ans cal. BP), tandis que dans l’Hinterland cette croissance semble legerement plus tardive (2400 et 1300 ans cal. BP). Il n’est pas possible d’identifier un phenomene commun de diffusion a partir d’un seul centre. Les innovations techniques et les nouvelles pratiques semblent plutot s’etre repandues a travers un large reseau d’interactions culturelles qui a favorise la formation des societes d’Afrique centrale occidentale au cours du troisieme millenaire avant notre ere.

This study assesses the detailed water budget of the Saq–Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions were tested for their local compatibility to compute groundwater storage (GWS) variations in combination with the three soil moisture datasets available from the land surface models (LSMs) of the Global Land Data Assimilation System (GLDAS). Accounting for groundwater pumping, artificial recharge, and natural discharge uniformly distributed over the Saq–Ram domain, the GRACE-derived mass balance calculation for water yields a long-term estimate of the domain-averaged natural recharge of (2.4±1.4) mm yr−1, corresponding to (4.4±2.6) % of the annual average rainfall (AAR). Beyond the regional-scale approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin: chiefly induced by irrigation excess over irrigated surfaces (about 1 % of the domain), artificial recharge corresponds to half of the total recharge of the aquifer. The second source of recharge heterogeneity identified here is natural: volcanic lava deposits (called harrats on the Arabian Peninsula) which cover 8 % of the Saq–Ram aquifer domain but contribute to more than 50 % of the natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge, which has been poorly discussed hitherto. Due to large lag times of the diffuse recharge mechanism, the annual analysis using this GRACE–GLDAS approach in arid domains should be limited to areas where focused recharge is the main mechanism, while long-term analysis is valid regardless of the recharge mechanism. Moreover, it appears that about 15 years of GRACE records are required to obtain a relevant long-term recharge estimate.

Chemical and isotopic tracers are powerful tools to study the water cycle and may constitute complementary methods in areas where instrumental records are insufficient. Tritium has been used routinely up to the 2000’s, but because of its short half-life, the bomb-3H spike of the 1960’s is today hardly distinguishable from the natural background level. Bomb-produced 36Cl offers an alternative tool, due to the conservative behavior of chloride and the large amounts of 36Cl released during the marine nuclear tests of the 1950’s.In this study, we use the bomb-36Cl pulse to assess the residence time of water in five volcanic lakes (Mbalang, Tabere, Tizon, Gegouba and Baledjam) of the Adamawa plateau in the northern region of the Cameroon Volcanic Line. Sediment cores from Mbalang and Tizon have been studied previously for paleo-environments, but otherwise, the Adamawa lakes received little attention so far.The lakes chloride content is low (0.009-0.035 meq/L) but higher than that of the rainwater samples (0.0019-0.0095 meq/L). In all the lakes, the 36Cl/Cl ratio (1*10-12 to 3*10-12 at/at) is higher by at least one order of magnitude than the natural atmospheric ratio (0.2*10-12 at/at) as determined previously from groundwater measurements in the lake Chad basin and in the Northern Saharan CT aquifer (Bouchez et al.2019, Hadj Ammar (2016)). These high ratios are a definite signature of the nuclear imprint, and thus of the lakes memory of atmospheric deposition, as already observed by our group in lake Chad, Iro and Fitri (Bouchez et al. 2019, Poulin (2019)). These data can then be used to determine the hydrological budget of the lake, independently of any water flux measurement, based on a simple one-box model assuming steady state for water and chloride. Indeed, simulating the transient response of the lake’s 36Cl to the bomb pulse allows us to estimate simultaneously the water residence time and the evaporation/precipitation ratio. Results from this model, as well as discussion of their comparison with classical hydrologic data will be shown at the meeting.References:Bouchez C. et al. 2019, (Paper in Scientific Report)Hadj Ammar F. 2016 (Thesis)Poulin C. 2019 (Thesis)

The Continental Intercalaire aquifer (CI) (North Africa) is one of the largest transboundary aquifer systems in the world. It contains around 20 000 × 109 m3 of groundwater. The recharge comes mainly from the occidental part of the aquifer (southern foothills of the Saharan Atlas, Algeria) going east to the outlet area in South Tunisia. Several studies have showed, using 14C, that the principal recharge has taken place in Late Pleistocene and Holocene. However, doubts exist about the results of some of these studies as it was demonstrated that samples containing less than 10pmc could have been contaminated by modern air during the sampling procedure.Based on a new field survey and the combination of new 14C and 36Cl data, the data of the previous studies are reviewed and new insights on the groundwater age are given. Close to recharge area, 14C age showed a significant amount of modern recharge (less than 2Ky B.P.). Any sample was found to have an age between 2 to 11Ky P.B. This means that during this period, Northern Sahara was dominated by a hyperarid climate. From 11 to 30Ky, it is observed that there is cyclicity of approximately 4Ky between given ages. This indicates that this period is dominated by an arid climate. Those 14C ages are calculated using F&G model.Beyond 30 Ky P.B., the use 14C is critical because of its limited half-time. 36Cl is more relevant in that case (half-time equal to 301Ky). Samples close to recharge area, where 14C activities are sufficiently high and halite dissolution is not significant, are explored in order to define initial values of 36Cl. There, the initial 36Cl/Cl ratio is around 145 × 10-15 at/at and the initial chlorine concentration is around 175mg/L. Based on these values, the age of CI groundwater in the Great Oriental Erg basin and South Tunisia has to be 300 to 700Ky old instead of 40 to 50Ky calculated by 14C. This is supported by the ages calculated by 81Kr performed in the South Tunisia. However, the applicability limit of each technic has to be investigated.

International audience; Organic compounds are widely used for paleoclimatic and paleoenvironmental reconstructions. Bulk organic proxies, however, are more complicated to interpret due to the multiple causes of variation in climatic and environmental conditions and the degree of diagenetic alteration. As labile compounds, rich in easily degradable function and generally richer in heteroatoms such as oxygen and nitrogen, decompose, the remaining organic matter becomes progressively richer in refractory carbon and its carbon content increases. Thus, in a peat deposit composed almost entirely of organic matter, total organic carbon (TOC) is expected to increase with time and depth, which could mask the paleoclimatic signal. We propose a simple model for peat sediments to remove the decomposition signal based on a logarithmic function fitted with a partial dataset where decomposition is the main parameter. The subtraction of the obtained logarithmic function to the raw data (i.e., measured data) leads to “residual” data. We discuss the influence of different parameters (water table depth, vegetation, microbial community) on the “residual” data and their possible link to paleoclimatic and paleoenvironmental variations. This method is tested on bulk elemental and isotopic data obtained from a new peat core from the Adamawa Plateau (North-East Cameroon) covering nearly 10 ka cal BP. Comparison with Rock-Eval® parameters highlights similar variations between the Hydrogen Index and residual TOC variations, supporting the interpretation based on residual TOC. Our approach allows to extract paleoenvironmental information from decomposition-prone bulk organic proxies and can be generalized to peat deposits where decomposition plays a major role in controlling bulk data.

International audience; The timing of porosity destruction in reservoir rock is key for hydrocarbon exploration. This study constrains the porosity destruction of the syn-rift Barremian (130-125 Ma) TOCA Fm. from one drill core located in the Lower Congo basin (West African passive margin). We apply an unprecedented multi-proxy approach to reconstruct the absolute timing of mechanical compaction, pressure-solution and cementation as well as their relative contribution to porosity destruction. LA-ICP-MS U–Pb geochronology combined with petrological observations suggest that the main interstitial diagenetic cement C1 filling the porosity of the packstones and dated 127.4 ± 2.2 to 119.4 ± 6.4 Ma predates pressure-solution. The quantification of the cement distribution by image analysis indicates that C1 clogged ∼30% of the initial porosity before the strata were buried at 400 m. We assume that the early cementation limited the effect of mechanical compaction on porosity reduction which is estimated to ∼2% in the first 100 m of burial. In contrast, a first order estimate of the chemical compaction-reprecipitation can account for up to ∼6% of the initial porosity destruction, as estimated by the inversion of sedimentary stylolite roughness. This technique also documents that the burial-related pressure-solution in the TOCA Fm. occurred in the 550–1750 m burial depth range corresponding to a time spanning from 117 to 95 Ma considering the burial-time model of the TOCA Fm. Our study reveals that the initial porosity of carbonates was reduced down to its current value of 4–8% within the first 35 Ma of its burial history, reaching ∼10% after only 10 Ma, i.e. in the first 400–500 m of burial. This case study indicates that the fate of reservoir properties in bioclastic carbonate formations such as the TOCA Fm. may be largely controlled by early, very shallow diagenetic processes rather than subsequent deep-burial mesogenetic reactions.

Normal fault zones can have a significant role on fluid flows as they can form barriers or drains (Agosta et al., 2010; Bense et al., 2013; Brogi and Novellino, 2015). In carbonates rocks, which are very sensitive to fluid-rock interactions, these fault-related fluid flows can strongly enhance or alter carbonate reservoir properties (Deville de Periere et al., 2017; Fournier and Borgomano, 2009).This work aims at determine fluid flow evolution in a carbonate reservoir affected by a normal fault. For this purpose, we studied structural and diagenetic properties of the Esperelles normal fault and the surrounding Barremian and Aptian formations located on the northern flank of Nerthe anticline (SE France). Esperelles fault developed during the Durancian uplift (Albian) and was weakly reactivated during the opening of Liguro-Provençal basin during Oligo-Miocene times.We defined seven different cements under cathodoluminescence (C0 to C6), their distributions along the outcrop, their geochemical properties (18O and 13C stable isotopes, Δ47 thermometry), and their ages (U-Pb). Diagenetic properties have been correlated with petrophysical measurements. We determined the paragenetic sequence, as well as the nature and temperature of the fluids that led to the formation of C1 and C6 cements. Four U-Pb ages have been obtained using an ELEMENT XR (Thermo-Fisher) SF-ICP-MS coupled to a 193 nm Excimer Laser (ESI) at CEREGE (Aix-en-Provence, France). These ages allowed to relate the C6 cementing phase with the opening of Liguro-Provençal basin. This study shows that fault zone development impacted reservoir fluid flows, leading to significant diagenetic events and development of heterogeneous reservoir properties. ReferencesAgosta, F., Alessandroni, M., Antonellini, M., Tondi, E. and Giorgioni, M.: From fractures to flow: A field-based quantitative analysis of an outcropping carbonate reservoir, Tectonophysics, 490(3–4), 197–213, doi:10.1016/j.tecto.2010.05.005, 2010.Bense, V. F., Gleeson, T., Loveless, S. E., Bour, O. and Scibek, J.: Fault zone hydrogeology, Earth-Science Rev., 127, 171–192, doi:10.1016/j.earscirev.2013.09.008, 2013.Brogi, A. and Novellino, R.: Low Angle Normal Fault (LANF)-zone architecture and permeability features in bedded carbonate from inner Northern Apennines (Rapolano Terme, Central Italy), Tectonophysics, 638(1), 126–146, doi:10.1016/j.tecto.2014.11.005, 2015.Deville de Periere, M., Durlet, C., Vennin, E., Caline, B., Boichard, R. and Meyer, A.: Influence of a major exposure surface on the development of microporous micritic limestones - Example of the Upper Mishrif Formation (Cenomanian) of the Middle East, Sediment. Geol., 353, 96–113, doi:10.1016/j.sedgeo.2017.03.005, 2017.Fournier, F. and Borgomano, J.: Critical porosity and elastic properties of microporous mixed carbonate-siliciclastic rocks, Geophysics, 74(2), E93–E109, doi:10.1190/1.3043727, 2009.

This study assesses the detailed water budget of the Saq-Ram Aquifer System (520 000 km²) over the 2002-2019 period using satellite-gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions (JPL, CSR, GSFC) were tested for their local compatibility to compute groundwater storage variations in combination with soil moisture datasets (VIC, CLSM, NOAH) available from the Global Land Data Assimilation System (GLDAS) land surface models. Accounting for groundwater pumping (15.7 ± 1.1 mm yr-1), artificial recharge (2.2 ± 0.8 mm yr-1) and natural discharge (0.3 ± 0.06 mm yr-1) uniformly distributed over the Saq-Ram domain, the GRACE-derived water mass balance calculation yields a long-term estimate of the domain-averaged natural recharge of 2.4 ± 1.4 mm yr-1, corresponding to 4.4 ± 2.6% of the annual average rainfall. Beyond the global approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin. Within agricultural plots, irrigation excess is great enough to artificially recharge the aquifer (i.e. 167 ± 83 mm yr-1 distributed over irrigated areas). However, on the outskirts of these crop areas subjected only to the natural recharge but still influenced by pumping drawdown, there is a risk of relative disconnection from the infiltration front with the declining water table (i.e. the unsaturated zone thickens faster than percolation flows through it), making effective recharge locally zero. The second source of recharge heterogeneity identified here is natural: Volcanic lava deposits (called Harrats on the Arabian Peninsula) which cover 8% of the Saq-Ram Aquifer domain but contribute to more than 50% of the total natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge which has been poorly discussed hitherto.

International audience; The climate history of the Sahara desert during recent millennia is obscured by the near absence of natural climate archives, hampering insight in the relative importance of southerly (tropical) and northerly (midlatitude) weather systems at submillennial time scales. A new lake sediment record from Ounianga Serir oasis in northern Chad, spanning the Late Holocene without interruption, confirms that immediately before ca 4200 years ago, the Sahara experienced an episode of hyperaridity even more extreme than today's desert climate. The hypersaline terminal lake which formed afterwards never desiccated during the late Holocene due to continuous inflow of fossil groundwater, yet its water balance was sensitive to temporal variation in local rainfall and lake surface evaporation. Our in-lake geochemical proxies show that, during the last 3000 years, century-scale hydroclimate variation in the central Sahara primarily tracked the intensity of the tropical West African monsoon, modulated at shorter time scales by weather patterns linked to shifts in midlatitude Atlantic Ocean circulation.

SF and the Si isotope measurements at STAiG were supported by NERC grant NE/R002134/1 to PS; PS would also like to cite the support of a Carnegie Trust Research Incentive Grant, which helped the setup of various isotope techniques in the St Andrews Isotope Geochemistry (STAiG) laboratories. C.D. Coath is thanked for laboratory support and the European Research Council is acknowledged for funding (ICY-LAB, grant agreement 678371). The use of silicon (Si) isotopes has led to major advances in our understanding of Si cycling in modern and past environments. This inter‐laboratory comparison exercise provides the community with the first set of soil and plant reference materials with an analytically challenging matrix containing organic material that is known to induce isotopic bias, for use as secondary reference materials in Si isotope measurement. Seven laboratories analysed four soil reference materials (GBW‐07401, GBW‐07404, GBW‐07407, TILL‐1) and one plant reference material (ERM‐CD281). Participating laboratories employed a range of chemical preparation methods and analytical setups but all analyses were performed by MC‐ICP‐MS. Irrespective of the chemical preparation method or analytical conditions, the results show excellent agreement among laboratories within 2s for at least three replicates. Data were combined together to calculate δ29Si and δ30Si mean values (relative to NBS 28) and their expanded uncertainties (U, coverage factor k = 2). The δ30Si values are as follow: GBW‐07401: ‐0.27 ± 0.06 ‰, GBW‐07404: ‐0.76 ± 0.12 ‰, GBW‐07407: ‐1.82 ± 0.17 ‰, TILL‐1: ‐0.16 ± 0.06 ‰ and ERM‐CD281: ‐0.28 ± 0.11 ‰. Also, a compilation of published data provides an up‐to‐date mean δ30Si for BHVO‐2 of ‐0.28 ± 0.08 ‰. Postprint

International audience; The Isotrace CNRS workgroup in collaboration with National Research Council of Canada has characterized a number of trace element mass fractions and isotope ratios currently not certified in AQUA-1 natural drinking water reference material (NRC Canada). This survey further expands the use of this material as a tool for environmental quality control, method validation, and method development tool for the international community. Simultaneously, the SLRS-6 river water was analyzed as quality control and also in order to compare both water characteristics, which were sampled in the same area but having undergone different treatment. Mass fractions for B, Cs, Li, Ga, Ge, Hf, Nb, P, Rb, Rh, Re, S, Sc, Se, Si, Sn, Th, Ti, Tl, W, Y, Zr, REEs, and six isotopic ratios are proposed for Sr and Pb. Measurements were mostly performed using ICP-MS with various calibration approaches. The results are reported as consensus or indicative values depending on the number of available datasets, with their associated uncertainties.

International audience; The environmental pollution by ecotoxic heavy metals is a problem of increasing significance for ecological and human health reasons. Among these elements, cadmium (Cd) is of special concern due to its high mobility in the soil/plant system and its acute toxicity. To limit Cd contamination in plants, and to enhance food safety, it is critical to understand Cd biogeochemical cycle, in particular what controls the bioavailability of this element. Previous studies have demonstrated that Cd bioavailability in soils depends ultimately on its chemical speciation. It has been proposed that non-protein thiols and organic acids play a major role in cadmium phytoavailability and distribution in plants. In the Cd-hyperaccumulator Solanum nigrum and non-accumulator Solanum melongena, the role of these organic ligands in the accumulation and detoxification mechanisms of Cd are debated. Here, we used X-ray absorption spectroscopy to investigate Cd speciation in these plants (roots, stem, leaves) and in the soils used for their culture to unravel the plants responses to Cd exposure. The results show that Cd in the 100 mg.kg-1 Cd-doped clayey loam soil is sorbed onto iron oxyhydroxides. In both S. nigrum and S. melongena, Cd in roots and fresh leaves is mainly bound to thiol ligands, with a small contribution of inorganic S ligands in S. nigrum leaves. We interpret the Cd binding to sulfur ligands as detoxification mechanisms, possibly involving the sequestration of Cd complexed with glutathione or phytochelatins in the plant vacuoles. In the stems, results show an increase binding of Cd to -O ligands (>50% for S. nigrum). We suggest that Cd is partly complexed by organic acids for transportation in the sap. To further constrain the fate of Cd in S. nigrum and S. melongena, we performed Cd stable isotope analysis of our samples. These new results will be presented at Goldschmidt 2021, and put in perspective with the XAS measurements.

International audience; The water-mass exchange between Indian and Atlantic oceans, occurring through Agulhas current and its leakage, is one of the return flows of global thermohaline circulation. To investigate the Indian-Atlantic subsurface- and deep-water mass exchangeover the last 600 kyrs, we analyzed Nd isotopic composition (εNd) on planktic foraminiferal authigenic fraction, epibenthic foraminiferal stable carbon isotopes ( δ13C), and planktic foraminiferal warm species in the sediment core MD96-2077 (SW Indian Ocean, 3,781 m). At present, this sedimentary sequence is bathed by modified Circumpolar Deep Water and it is below the flow path of the Agulhas current. The obtained εNd and δ13C records show glacial/interglacial variability ranging between -8.0 and -10.3, and between -1.1 and 0.7 ‰, respectively, with higher εNd values coinciding with more depleted δ13C values and vice versa. Planktic warm species relative abundances vary from 1.2 to 37.6 % with a marked increase during terminations. The most striking feature of our record is systematic very low glacial δ13C values similar torecords from the deep SE Atlantic (ODP Site 1090). Relationship between εNd and δ13C of the studied core compared with existing records indicates similar trends with deep SE Atlantic water masses, suggesting that deep glacial carbon-rich water extendedfrom the SE Atlantic into the SW Indian Ocean. Contribution of Indian deep water cannot account for the low benthic δ13C values observed at the study site. The increases in warm planktic species relative abundances during the terminations are coincident withreconstructed Agulhas leakage peaks, suggesting a possible link between Agulhas current and Agulhas leakage during terminations. To better constrain the deep-water variability of the northern and southern source water masses arriving at the SWIndian Ocean, we are analyzing the foraminiferal εNd in core MD96-2052 (2,627 m water depth) from the Mozambique Channel. This core is currently occupied by North Atlantic Deep Water (NADW) as confirmed by an εNd value of -11.7 in the core-top sample, in the range expected from present-day NADW. Based on this new record, we will investigate the changes in northern and southern source waters together with subsurface water conditions

Study Region Chari-Logone River basin, Lake Chad basin. Study Focus The objective of this study was to better understand the hydrological functioning of the Chari-Logone basin under the effect of the high variability of rainfall which has affected the Sahel during the last sixty years. The study is based on hydro-climatic data for the period between 1960 and 2015 obtained from the national and international institutions. This work based on the following steps: 1) Average hydrological balances were estimated for different geographical areas, to identify the most productive parts of the basin. 2) The rainfall-runoff relation was compared for the wettest and driest decades of the study period, to identify the areas that contribute most to the amplification of the hydrological response to variations in rainfall. 3) The long-term period stability of the rainfall-runoff relation was evaluated for climatic conditions close to the average situation, in order to detect potential evidence of the anthropogenic impact. New Hydrologic Insights for the Region During the period 1960–2015, the average water flow in the Chari-Logone basin (42 mm/year) represented only 5% of precipitation. Between the two climatically most contrasted wet (1960−1971) and dry (1982−1997) periods, the average flow differed by 75 % against a decrease of 15 % of precipitation. Our hydroclimatic data show no clearly detectable evidence of an anthropogenic impact responsible for a decrease in flows or a modification of the hydrological regime in the Chari-Logone basin.

In this paper, we describe a sea-level database compiled using published last interglacial, Marine Isotopic Stage 5 (MIS 5), geological sea-level proxies within East Africa and the Western Indian Ocean (EAWIO). Encompassing vast tropical coastlines and coralline islands, this region has many occurrences of well-preserved last interglacial stratigraphies. Most notably, islands almost entirely composed of Pleistocene reefs (such as Aldabra, the Seychelles) have provided reliable paleo relative sea-level indicators and well-preserved samples for U-series chronology. Other sea-level proxies include uplifted marine terraces in the north of Somalia and Pleistocene eolian deposits notched by the MIS 5 sea level in Mozambique to tidal notches in luminescence-limited eolian deposits in Mozambique. Our database has been compiled using the World Atlas of Last Interglacial Shorelines (WALIS) interface and contains 58 sea-level indicators and 2 terrestrial-limiting data points. The open-access database is available at https://doi.org/10.5281/zenodo.4302244 (Version 1.03; Boyden et al., 2020).

One of the most puzzling properties of silicon (Si) is its differential absorption by plants. Depending on the plant species, water and soil Si availability, environmental factors such as grazing and temperature, plant Si contents can vary from 0.1 % to 10 %(on a dry weight basis). Advances in genomics improved our understanding of biochemical and molecular mechanisms underlying plant Si uptake providing a framework to explain the variability of Si in plants and its distribution. Yet complex Si roles in plant strategies, its dependence on environmental factors and in mediating interactions with their environments and other organisms remain misunderstood. How is plant Si uptake affected by soil Si availability and how is Si distribution between tissue types controlled? It is hard for us to answer those questions even if Si plant traits are an indicator of the soil Si status. For example, a few studies showed that Si content and phytolith distribution are mainly controlled by Si availability. In this study, a pot experiment was conducted in a greenhouse where wheat (Triticum turgidum L.) was grown on three different soils: an aric podzol, an andosol and a calcosol. These soils are contrasted in term of clay size distribution, SiO2 concentrations and organic matter content and are presumed to reflect French soils variability in term of Si dynamics. Here, we focus on how plant Si patterns, both Si content and Si isotopes, are linked to soil Si availability leading to new insights to the mechanisms underlying the different Si uptake and translocation strategies. This work is supported by the BIOSiSOL project (ANR-14-CE01-0002).

In the last decade, important improvements in dating methods have been made and make it possible to go into the details of fault gouge formation and evolution. Common minerals like calcite and hematite can now bring detailed information on timing of fault development and fluid-rock interaction. We applied those novel techniques to a tectonically well constrains alpine context, though still lacking key chronological constrains. The targeted fault zone is the Penninic Frontal Thrust (PFT) of SW Alps, which is a major tectonic boundary that juxtaposed the metamorphic internal Alps over the unmetamorphosed external Alps, primarily as a thrust during the Oligocene (Simon-Labric et al., 2009). The PFT was later reactivated as an extensional detachment in the Mio-Pliocene, though the age of this reactivation remained unconstrained. Sue and Tricart (2003) showed that ongoing extensional seismic activity along the PFT, corresponding to the High-Durance Fault System (HDFS), is characterized at the surface, by an extensional fault network. In this context, the HDFS corresponds to extensional reactivation of the PFT as a consequence of Pelvoux external crystalline massif exhumation.In this study, we coupled field tectonic, in-situ calcite U-Pb and hematite (U-Th-Sm)/He dating to stable and clumped isotope analysis to infer the HDFS activation age and to investigate the related fluid circulations. Isotopic signature (δ13C and δ18O) of compressional veins, en-echelon extensional veins and cataclasite fault gouge have been determined (Bilau et al., 2020).This study allows pinpointing the evolution of deformation and fluid-rock interaction in the PFT footwall during its progressive extensional exhumation. The older U-Pb ages obtained on the cement of the gouge fault range between 5 to 3.5 Ma and taking into consideration uplift rate, comparison to currently seismicity depth and calcite brittle/ductile transition temperature, calcite crystallization may have occurred between 5 to 2 km. The hematite crystallization appears at shallower levels in the latest stages of the fault displacement at 3-1 km depth. A transition in the nature of fluids, controlling the redox state, can be highlighted here. This transition occurs between the calcite and hematite forming events at 2-3 km depth, which is probably related to a significant influx of meteoric fluids into the drainage of the fault system.

The Cameroon Volcanic Line (CVL) in Central Africa hosts numerous volcanic lakes. While Nyos and Monoun lakes in western Cameroon were well studied following the catastrophic release of CO2 that occurred in 1980s, other volcanic lakes such as those of the Adamaoua Plateau remain less documented. Although some of these (Mbalang and Tizon) have been investigated through their sedimentary archives in order to reconstruct past-environments, the functioning of these hydro-systems located in the northern part of the CVL is not well constrained. Here, we characterize the hydrological functioning of five volcanic lakes by coupling classical hydrology methods and isotope tracers. Specifically, we assess water residence time in these lakes using radioactive (36Cl) and stable isotopes of water.36Cl is a cosmogenic isotope of chlorine produced naturally in the stratosphere by spallation of 40Ar induced by cosmic-rays and has been massively injected into the atmosphere by nuclear tests during the 1950s. This pulse of bomb-36Cl can thus be used as a tracer to estimate recharge rates in the unsaturated zone and to constrain water transit times at a regional scale. While water stable isotopes have been widely used to establish lakes hydrological balance in Sahelian regions, only a few studies have been reported to date using 36Cl for the same purpose in tropical areas.In this study, together with major elements and stable isotopes, we analyzed 36Cl contents in water from lakes Mbalang, Tabere, Tizon, Gegouba and Baledjam around Ngaoundere, to assess residence time in these lacustrine systems. 36Cl/Cl ratios range from 1400.10-15 to 2800.10-15 at/at and are significantly higher than the natural baseline as assessed by data obtained in local groundwater or at a larger scale in the Lake Chad Basin (36Cl/Cl ~200.10-15 at/at, see Bouchez et al., Scientific Reports, 2019). These 36Cl/Cl ratios above the natural baseline are clearly tagged with the bomb-36Cl footprint. We will illustrate at the meeting how a simple transient-state one-box model can be used to explain why these lakes have different 36Cl/Cl ratios, and how these results can help to constrain the E/I ratios of the lakes, and be compared with their hydrological characteristics and stable isotopes signatures.

In this study, we developed two-dimensional hydrodynamic age expressions for the free-surface aquifer problem required for radiocarbon data interpretation in terms of recharge. Time-varying recharge is accounted for in fully transient or pseudo-steady state alternative analytical expressions applying to weakly or highly hydraulically reactive unconfined aquifers, respectively. These expressions extending a previous model based on a constant recharge represent a convenient alternative approach to the more complex numerical resolution of a particle tracking problem considering climate variability. An application of the developed expressions was carried out to assess past (40ky) and present recharge rates for the North Western Saharan Aquifers System (NWSAS) and the Djeffara plain (Tunisia-Libya). Using the available 14C data at different outcrops, we obtained local recharge values ranging from 1.27 to 6.86 mm yr-1. A linear relation between the present recharge and the average annual rainfall was obtained and used to identify the regional distribution of the recharge and domain-averaged values. Global values of 1.32 ± 1.47 mm yr-1 for the NWSAS and 3.97 ± 1.46 mm yr-1 for the Djeffara are in excellent agreement with the values obtained by hydrogeological models and derived using Satellite gravity data. The relation between recharge and rainfall obtained here can be used as a first-order estimate for hydrogeological modeling or water management analysis for aquifers in the Saharan area.

International audience; The Chari-Logone watershed is the only hydrologically active part of the Lake Chad Basin (Central Africa). The Chari-Logone River and Lake Chad exchange water with the surrounding unconfined aquifers of sedimentary and crystalline rock types. In this study, the groundwater contribution to stream flow was quantified by taking advantage of a comprehensive hydrological and chemical database from the 1970s for the upper catchment, which has no equivalent to date. The study area was limited to the larger Chari catchment where the exchanges are mainly oriented from the aquifers to the stream. Upon identification of the mixing poles using end-member mixing analysis (EMMA), and a Monte Carlo inversion of a monthly mixing mass-balance model, an annual averaged base flow of 59 ± 10% of the total stream flow was estimated for 1969–1973. Then, a hydrological model accounting for baseflow and surface flow was calibrated using a 47-year-long monthly discharge time series, and the 4-years’ monthly averaged chemical data available. The simulations yielded an average baseflow of 64% of the annual discharge. The time-constant of the reservoir model (τ = 0.2 years) used to simulate the baseflow was interpreted in terms of hydraulic diffusivity, yielding a value in the order of 101 m2 s−1. This large value corresponds to a highly productive bedrock and thick sedimentary aquifers. The main contribution to the Chari stream flows is restricted to a 140,000-km2 subcatchment located in the southern tropical zone, where the recharge rate reaches 72 ± 6 mm year−1.; La cuenca hidrográfica de Chari-Logone es la única parte hidrológicamente activa de la cuenca del lago Chad (África central). El río Chari-Logone y el lago Chad intercambian agua con los acuíferos no confinados circundantes de rocas sedimentarias y cristalinas. En este estudio, la influencia de las aguas subterráneas en el caudal de los cursos de agua se cuantificó aprovechando una extensa base de datos hidrológicos y químicos de la década de 1970 para la cuenca superior, que no tiene equivalente hasta la fecha. El área de estudio se limitó a la cuenca superior del Chari, donde los cambios se orientan principalmente desde los acuíferos hacia el arroyo. Tras la identificación de los puntos de intercambio utilizando el análisis de mezcla de los miembros finales (EMMA), y una inversión de Monte Carlo de un modelo de balance de masa de mezcla mensual, se estimó un flujo base anual promediado de 59 ± 10% del flujo total del arroyo para 1969–1973. Luego, se calibró un modelo hidrológico que tenía en cuenta el flujo base y el flujo de superficial, utilizando una serie temporal de descargas mensuales de 47 años de duración, y los promedios mensuales de los cuatro años de datos químicos disponibles. Las simulaciones arrojaron un flujo de base promedio del 64% de la descarga anual. La constante temporal del modelo del reservorio (τ = 0.2 años) utilizado para simular el flujo base se interpretó en términos de difusividad hidráulica, dando un valor del orden de 101 m2 s−1. Este elevado valor corresponde a un lecho de roca altamente productivo y a acuíferos sedimentarios de alto espesor. La principal contribución a los flujos de la corriente de Chari se restringe a una subcuenca de 140,000-km2 situada en la zona tropical meridional, en la que la tasa de recarga alcanza los 72 ± 6 mm año−1.; Le bassin Chari-Logone est la seule partie hydrogéologiquement active du bassin du Lac Tchad (Centrafrique). La Rivière Chari-Logone et le Lac Tchad échangent leur eau avec les aquifères libres environnants de types sédimentaire et cristallin. Dans cette étude, la contribution des eaux souterraines au débit du cours d’eau a été quantifiée en mettant à profit une base de données hydrologiques et chimiques complète des années 1970 concernant le bassin supérieur, qui n’a pas d’équivalent à ce jour. L’aire d’étude a été limitée au bassin versant le plus grand du Chari, dans lequel les échanges sont principalement orientés des aquifères vers le cours d’eau. Lors de l’identification des pôles du mélange à l’aide de l’analyse de ses membres extrêmes et d’une inversion de Monte Carlo du modèle de son bilan massique mensuel, un débit de base annuel moyen de 59 ± 10% de l’écoulement total du cours d’eau a été estimé pour la période 1969–1973. Ensuite, un modèle hydrologique rendant compte du débit de base et de l’écoulement de surface a été calé en recourant à une série temporelle du débit mensuel sur une période de 47 ans et aux données chimiques moyennes mensuelles disponibles sur 4 ans. Les simulations ont donné un débit de base moyen correspondant à 64% du débit annuel. La constante de temps du modèle de réservoir (τ = 0.2 ans) utilisée pour simuler le débit de base a été interprétée en terme de diffusivité hydraulique, donnant une valeur de l’ordre de 101 m2 s−1. Cette valeur importante correspond à un substratum fortement productif et à des aquifères sédimentaires puissants. L’apport principal au débit du Chari est réduit à un sous-bassin versant de 140,000 km2 situé dans la zone tropicale méridionale, où le taux de la recharge atteint 72 ± 6 mm an−1.; A bacia hidrográfica Chari-Logone é a única parte hidrologicamente ativa da Bacia do Lago Chade (África Central). O Rio Chari-Logone e o Lago Chade trocam água com os aquíferos não confinados circundantes de tipos de rochas sedimentares e cristalinas. Neste estudo, a contribuição da água subterrânea para o fluxo do rio foi quantificada tirando proveito de um banco de dados hidrológico e químico abrangente da década de 1970 para a bacia hidrográfica superior, que não tem equivalente até o momento. A área de estudo foi limitada à bacia hidrográfica de Chari maior, onde as trocas são principalmente orientadas dos aquíferos para o riacho. Após a identificação dos pólos de mistura usando análise de mistura de membro final (AMMF) e uma inversão de Monte Carlo de um modelo de equilíbrio de massa de mistura mensal, um fluxo de base médio anual de 59 ± 10% do fluxo total da corrente foi estimado para 1969–1973. Em seguida, um modelo hidrológico que considera o fluxo de base e o fluxo de superfície foi calibrado usando uma série de tempo de descarga mensal de 47 anos e os dados químicos médios mensais de quatro anos disponíveis. As simulações produziram um fluxo de base médio de 64% da vazão anual. A constante de tempo do modelo do reservatório (τ = 0.2 anos) usada para simular o escoamento de base foi interpretada em termos de difusividade hidráulica, resultando em um valor da ordem de 101 m2 s−1. Este grande valor corresponde a uma base rochosa altamente produtiva e a aquíferos sedimentares espessos. A principal contribuição para os fluxos do córrego Chari é restrita a uma sub-bacia hidrográfica de 140,000 km2 localizada na zona tropical do sul, onde a taxa de recarga atinge 72 ± 6 mm ano−1.

Cet article veut exposer et soutenir une recherche-action conduite depuis deux ans par une equipe pedopsychiatrique d’orientation analytique au « Quartier des mineurs » de la Maison d’arret d’Aix-en-Provence (effectif theorique de 33 adolescents). Cette equipe estime avoir reuni des elements significatifs permettant d’enoncer qu’il est possible de nouer une relation a potentiel therapeutique avec la quasi-totalite des adolescents incarceres. Elle pense qu’une telle demarche requiert une methodologie deontologique-technique determinee articulee sur l’independance du Sanitaire par rapport au Complexe judiciaire-penitentiaire.Si l’on se refere aux histoires le plus souvent fracturees de ces adolescents, a leurs troubles de la subjectivation, aux dangers qu’ils courent et font courir a autrui, a leur reticence a rencontrer des psychistes en dehors du contexte carceral, on peut egalement lire cet article dans une dimension de Sante publique.L’auteur decrit le cadre materiel d’exercice de l’equipe. Les entretiens se font sur les lieux meme de la detention, au plus pres des adolescents et des autres adultes intervenants (surveillants et enseignants en particulier). Ce cadre contribue a installer un transfert de base groupal des adolescents sur les psychistes, et un contre-transfert de base des psychistes sur les adolescents delinquants. Contradictoirement, cette proximite facilitant les rencontres, les rend egalement difficiles au plan de leur faisabilite, en excitant les differents niveaux de conflictualite entre l’equipe pedopsychiatrique et l’administration Penitentiaire qui peuvent etre reperes et progressivement traites.Ce cadre materiel est le support d’une approche extensive (quasi-totalite) des adolescents incarceres. Cette possibilite d’une approche extensive, et son potentiel therapeutique, a ete verifiee par l’equipe a une certaine etape de la recherche. Il en est rendu compte par deux vignettes cliniques emblematiques en ce qu’elles concernent des adolescents de contacts et de fonctionnements psychiques particulierement difficiles d’acces. Deux limites de l’approche extensive sont etudiees. La principale est mise en rapport avec la theorie winnicottienne de « la tendance antisociale » : les hausses de la demographie du « Quartier des mineurs » (au-dela d’un seuil de 20-25 adolescents) conduisent a un certain abandon d’adolescents qui beneficiaient d’une offre de soins suffisamment continue, et cet abandon peut entrainer un rebond antisocial. Ainsi l’equipe doit-elle s’efforcer a fonctionner en dessous de ce qu’elle sait etre possible et souhaitable, dans l’attente que des moyens supplementaires lui soient donnes par des autorites de Tutelle qui ne sont pas a l’ecoute.L’etonnante ouverture a l’autre des adolescents incarceres qui ont la plupart du temps refuse farouchement de rencontrer des psychistes en milieu ouvert, est eclairee par ce que l’auteur appelle « le versant soignant de la prison ». Ce versant soignant est decline selon un modele metapsychologique ou les items s’enchainent en un idealtype : reintroduction de la dimension du Reel par l’arrestation-incarceration ; confrontation a une force etatique inebranlable pare-excitante externe ; diminution de la culpabilite inconsciente par l’experience vecue de la sanction ; triangulation de fait par la Justice et l’administration Penitentiaire de la relation mere-fils ; restauration des carences et des maltraitances par la face positive de la surveillance et de l’autorite. Une serie de vignettes cliniques vient appuyer chacun des items. Une vignette montre la limite absolue du modele, celle ou la prison n’est pas toleree, essentiellement du fait d’un sentiment de perte insoutenable. Les limites relatives (pouvant faire l’objet de reformes) du modele sont evoquees. Le tableau catastrophiste des abolitionnistes (opposants a la prison pour les mineurs) est recuse au nom de l’experience globale qu’a l’equipe des vecus et des evolutions des adolescents incarceres.L’expose de la methodologie deontologique-technique de l’equipe est precede d’une analyse serree des textes sanitaires, penitentiaires et de la Protection judiciaire de la jeunesse, concernant ce qui est communement appele la pluridisciplinarite dans les « Quartiers des mineurs ». L’auteur etablit que ces textes et les pratiques, en realite monodisciplinaires, qui en decoulent sont anti-deontologiques et anti-subjectifs. Il expose l’interet subjectalisant d’une methode qui offre a l’adolescent un haut niveau de garantie de la confidentialite des entretiens, et son implication veritable dans d’eventuels contacts de l’equipe pedopsychiatrique avec ceux qui interviennent egalement aupres de lui.L’idee courante de la necessite de mediateurs indispensables aux psychistes pour aborder ces adolescents, est relativisee. L’equipe croit beaucoup au couple (ou au moins au binome) therapeutique qui assure une meilleure assiette transfero-contre-transferentielle que la relation duelle. L’hypothese centrale est que ce couple fonctionne comme attracteur-reorganisateur des elements de la « Scene primitive » trop chaotiques ou violents que le patient a du cliver, voire forclore. Une vignette clinique montre cette technique a l’œuvre sous la focale grossissante de son utilisation selon des modalites particulierement actives avec un adolescent difficile pour lequel on dispose d’un recul d’un an sur son evolution apres son incarceration.Des perspectives de la recherche-action sont developpees. La position de l’equipe est precisee par rapport a la nouvelle donne que constituera la presence d’educateurs de la « Protection judiciaire de la jeunesse » en continu au « Quartier des mineurs ». La question cruciale des moyens est a nouveau evoquee, en termes de suivi post-penal indispensable, de formation d’Internes en Psychiatrie, et d’un travail d’etude comparative des approches pedopsychiatriques dans les « Quartiers des mineurs ».Un appareil de notes important donne les principales references theoriques de la demarche, et permet des developpements cliniques et metapsychologiques. L’auteur et son equipe sont conscients que les delinquances juveniles et leurs traitements, sont l’objet de constructions socio-politiques, avec leurs relais mediatiques, qui pesent d’un poids considerable sur les pratiques. Cet appareil de notes permet egalement au lecteur de prendre connaissance du contexte, de la tendance actuelle a un « tout carceral » parfaitement contraire a une approche mesuree qui doit traiter sur le meme plan les carences en moyens insupportables de l’activite du milieu ouvert, et l’amelioration des fonctionnements des « Quartiers des mineurs » existants. L’histoire du traitement des delinquances juveniles a montre que toute embardee dans un sens etait regulierement suivie de dementis.

Summary In this study, we investigate a 6-meter peat core from the NGaoundaba peatland (Northeastern Cameroon) covering almost 10 ka using bulk geochemical data and a large panel of biomarkers [Isoprenoid and branched glycerol-dialkyl-glycerol-tetraethers (isoGDGT and brGDGT respectively), n-alkanes, hopanoids and degradation products of plants]. Recent peat-specific temperature and pH calibrations based on brGDGTs ( Naafs et al., 2017 ) were applied to the NGaoundaba peatland stratigraphic record. GDGT-based temperature and pH are coherent with insolation variation ( Berger, 1981 ) and with pollen-based records from Lake MBalang ( Vincens et al., 2010 ), situated 20 km to the north of NGaoundaba. The recent peat-specific hopane-based pH calibration ( Inglis et al., 2018 ) was applied to the NGaoundaba record. Hopane and GDGT-based pH estimates present strikingly similar variations, raising new perspectives about potential brGDGT origins.

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.

International audience; The Djeffara plain, extending over Tunisia and Libya (48,000 km(2)), experiences unsustainable exploitation of groundwater, the severity of which needs to be determined. Here, we used data from Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) to assess the groundwater storage variation (Delta GWS) for the period 2002-2016. Delta GWS values, downscaled over a 0.5 degrees x 0.5 degrees grid using pumping wells spatial distribution and rates, were introduced in a discrete set of groundwater and salt budget equations to ascertain the recharge and the coastal fluxes. An average recharge of 4.3 +/- 2.7 mm.yr(-1) representing 2.2 +/- 1.4% of the domain-averaged annual rainfall was obtained. A saline intrusion of 147.3 x 10(6) and 46.9 x 10(6) m(3).yr(-1) was calculated for the Tripoli (Libya) and Djerba (Tunisia) areas, respectively. The overall Submarine Groundwater Discharge (SGD) of freshwater along the 450 km long Djeffara coast represents about 339.6 x 10(6) m(3).yr(-1) for the 2002-2016 period.