Sources and exchanges of mercury in the waters of the Northwestern Mediterranean margin
Ocean margins are focal regions in terms of mercury (Hg) exchanges between the continent and the open sea. The aim of this paper is to describe the distribution and partition of Hg between the gaseous, dissolved and particulate phases in the waters of the Northwestern Mediterranean (NWM) margin, in order to assess the Hg sources and exchanges within the continuum between the continental shelf (Gulf of Lions) and the open sea (Northern Gyre). Mean (± standard deviation) of total Hg species (HgT) concentrations in unfiltered water samples were 1.52 ± 1.00 pmol L-1 (n=36) in the inner shelf, 1.09 ± 0.15 pmol L-1 (n=30) along the slope, and 1.10 ± 0.13 pmol L-1 (n=99) in the Northern Gyre. The dissolved phase (<0.45µm) average concentrations were 0.80 ± 0.47 pmol L-1 (n=37) in the inner shelf, 0.93 ± 0.20 pmol L-1 (n=4) along the slope and 0.84 ± 0.10 (n=20) pmol L-1 in the Northern Gyre. The particulate fraction of Hg decreased very strongly seaward from around 60% on the shelf to 10-25% above the Northern Gyre. Very low dissolved HgT concentrations occurred in the inner shelf water, consistent with the results of incubation experiments, which demonstrated that shelf water is very efficient in both production and release of dissolved gaseous Hg into the atmosphere. In the North Gyre waters column HgT presents a distribution pattern inverse to that of dissolved oxygen, and a slight Hg enrichment in the deep layer (Western Mediterranean Deep Water). The Hg from the open sea water is the largest Hg input to the Gulf of Lions (∼5.7 kmol yr-1), whereas inputs from the riverine source account for ∼3.4 kmol yr-1 and atmospheric deposition for less than 0.5 kmol yr-1. The Hg accumulated in the sediments of the shelf is ∼4.5 kmol yr-1, including 0.6-1.7 kmol yr-1 in the Rhône prodelta sediments. The evasion to the atmosphere represents a Hg flux of ∼2.6 kmol yr-1.
(Progress in Oceanography. vol. 163, n° 0079-6611, pp. 172-183, 01/04/2018)
BE, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Ozonolysis of unsaturated BVOCs in the presence of SO2: formation of Stabilised Criegee Intermediates, their reactivity and role in the particle formation
Biogenic volatile organic compounds (BVOCs), including monoterpenes, are one of the most abundant chemical group in the troposphere having major influences on air quality, climate and human health through chemical oxidation processes and secondary organic aerosol (SOA) formation. It is now established that gas-phase ozonolysis of monoterpenes leads to the formation of Stabilized Criegee Intermediates (SCIs) which can act as atmospheric oxidant for trace gases and lead to the formation of sulfate aerosols. However, the fate of these biradical species remains uncertain and need further investigation. Here we present the results of the first set of experiments which are a part of the COGNAC project (Chemistry of Organic biradicals: GeNesis of AtmospheriC aerosols). We have investigated the gas-phase ozonolysis of several BVOCs, including isoprene, a-pinene and limonene, in the presence or absence of SO2, in order to explore the fate of different SCIs. Experiments were performed in HELIOS simulation chamber, a large 90m3 Teflon chamber (S/V = 1.2 m-1), using different analytical instruments for the chemical and physical characterization of the gaseous and particulate species: an in-situ FTIR for monitoring organic and inorganic infra-red absorbing species (optical length = 302.6 m) including SF6 for the calculation of the dilution rate, a PTR-ToF-MS 8000 (Ionicon Analytik Gmbh) for the gas-phase detection of the reacting monoterpenes and products, a Figaero-ToF-CIMS (Aerodyne Research) in H3O+ and acetate mode, allowing the detection of both gas and particulate phases, a chemical ionisation mass spectrometer (CIMS) for the detection of hydroxyl and peroxy radical species and sulfuric acid, and a ATD-GC-MS (Thermo Fisher Scientific). Measurements of ancillary data (particle size distribution and mass concentration, O3, CO, SO2 and HCHO concentrations) were also conducted using a set of online monitors. Kinetic rate constants of a-pinene, limonene and isoprene ozonolysis have been determined using an absolute method ((1.28±0.04) × 10^16, 2.02× 10^17, 2.25 × 10^-16 cm3.molecule-1.s-1, respectively). Since H2SO4 can be formed by the reaction between SCIs and SO2 (and by the reaction between SO2 and OH, if present), its concentration given by CIMS can therefore be used as a proxy for SCIs detection in this study. The Figaero-ToF-CIMS shows a significant response up to m/z 417 in the particulate phase. Analysis of the observed high-resolution mass spectra have been used for mass assignment. This set of experiments is a preliminary study for a better understanding of SCIs formation, reactivity and fate, and the reaction mechanism of monoterpene ozonolysis in the presence of SO2.
(01/04/2018)
ICARE, UO, CNRS, INSIS - CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRCELYON, UCBL, INC-CNRS, CNRS, LPC2E, INSU - CNRS, UO, CNRS, CNES
Recent morphology and sedimentary processes along the western slope of Great Bahama Bank (Bahamas)
Carbonate slopes and associated resedimented deposits have recently gained renewed interest because they represent volumetrically significant parts of carbonate platforms. Carbonate slopes are highly variable compositionally, architecturally and spatially due to a spectrum of sediment sources, resedimentation processes and controlling factors. Here, new high resolution acoustic data (including EM302 multi-beam echo-sounder and very high resolution seismic) and piston cores document highly diverse and complex morphological features along the north-western slope of Great Bahama Bank. The recent morphology of the slope is the result of the interplay between depositional and erosive processes that vary through time and along strike. The different sedimentary processes are recorded as a Pleistocene lowstand surface, characterized by many erosional features and a Holocene sedimentary wedge along the upper to middle slope that partially covers the underlying Pleistocene surface. Sedimentary processes during the Holocene are dominated by density cascading flows, which export muddy aragonitic sediment from the platform top towards the slope. Sedimentation rates, however, vary along strike due to platform top morphology combined with the variable strength of the basinal current. Reefs and islands in the Bimini area block off-bank sediment export, and shoals and tidal deltas from Cat Cay to the south reduce the density cascading processes. Numerous small and large slope failure scars show the instability of the steep slopes of Great Bahama Bank. Bottom currents dominate the lower slope and the basin. Striations and moats are the morphological expressions of current directions, while areas of non-deposition document strong current and concomitant removal of off-bank transported sediment along parts of the slope, while the Santaren Drift and the drift on the north-western edge of Great Bahama Bank act as the depositional locus for the fine-grained sediments transported in the current.
(Sedimentology. vol. 65, n° 0037-0746, pp. 2088-2116, 31/03/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Transient biogeochemistry in intertidal sediments: New insights from tidal pools in Zostera noltei meadows of Arcachon Bay (France)
Several studies highlighted the occurrence of circular pools in intertidal flats of different coastal systems and their transient water chemistry over both tidal and diurnal cycles. However, little is known about (1) the response of benthic biogeochemical reactions and fluxes at the sediment-water interface over such short time scales, and (2) the role of these tidal pools in the biogeochemical functioning of coastal systems. Based on in situ microprofiles and water sampling, we investigated the dynamics of dissolved oxygen (O2), nutrients, sulfides and metals, and the associated fluxes at the sediment-water interface in tidal pools from the Arcachon Bay (Atlantic coast of France). Our integrative approach included several tidal and diurnal cycles over two different seasons in the presence and absence of Zostera noltei. The results show that water temperature and light irradiance were the main factors driving the biogeochemical functioning of the tidal pools, as they controlled the physiological activity of the microphytobenthos. Changes in light radiations induced diurnal fluctuations of O2 concentrations within surficial sediment, thus resulting in fluctuations of the O2 diffusive fluxes at the sediment-water interface and of the O2 penetration depth in sediment. At high tide, the increase in turbulence above the sediment induced the advection of oxygenated water within the first millimeters of sediment, resulting in a significant increase in porewater O2 concentrations and sediment O2 penetration depth. Porewater sulfide concentrations and apparition depth were concomitant with the O2 dynamic over both diurnal and tidal cycles, indicating that intermediate redox diagenetic processes were impacted by O2 dynamic over such short time-scale. The rapid changes in redox processes in the sediment column are confirmed by a significant flux of dissolved manganese toward the water column during nighttime. The consumption of nitrate and the release of ammonium and phosphate, associated to the mineralization of the organic matter in the surface sediment did not appeared related however to such short time cycles. The efflux of dissolved silica from the sediment was most likely associated with the enhanced dissolution of Si-bearing particles in surface sediment at higher temperatures, although silica uptake by Z. noltei was also noted. This study clearly shows that tidal pools function as natural incubators of transient biogeochemical processes. A rough assessment of the nutrient budget at the scale of the bay indicates the tidal pools may contribute significantly to the biogeochemical functioning of Arcachon Bay.
(Marine Chemistry. vol. 200, n° 0304-4203, pp. 1-13, 20/03/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CHROME, UNIMES
Response of the carbon cycle in an intermediate complexity model to the different climate configurations of the last nine interglacials
Atmospheric CO2 levels during interglacials prior to the Mid-Brunhes Event (MBE, ∼ 430 ka BP) were around 40 ppm lower than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to different external forcings before and after the MBE, might have increased the ocean carbon storage in pre-MBE interglacials, thus lowering atmospheric CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings, ice sheet configurations and atmospheric CO2 concentrations over the last nine interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few parts per million. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 levels are lower during these pre-MBE simulated interglacials including all these effects, but the magnitude is still far too small. These results suggest a possible misrepresentation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, to fully account for the lower atmospheric CO2 concentrations during pre-MBE interglacials.
(Climate of the Past. vol. 14, n° 1814-9324, pp. 239 - 253, 02/03/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Carbon dioxide degassing at the groundwater-stream-atmosphere interface: isotopic equilibration and hydrological mass balance in a sandy watershed
(Journal of Hydrology. vol. 558, n° 0022-1694, pp. 129-143, 01/03/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
High-Throughput DNA sequencing of ancient wood
Reconstructing the colonization and demographic dynamics that gave rise to extant forests is essential to forecasts of forest responses to environmental changes. Classical approaches to map how population of trees changed through space and time largely rely on pollen distribution patterns, with only a limited number of studies exploiting DNA molecules preserved in wooden tree archaeological and subfossil remains. Here, we advance such analyses by applying high-throughput (HTS) DNA sequencing to wood archaeological and subfossil material for the first time, using a comprehensive sample of 167 European white oak waterlogged remains spanning a large temporal (from 550 to 9,800 years) and geographical range across Europe. The successful characterization of the endogenous DNA and exogenous microbial DNA of 140 (~83%) samples helped the identification of environmental conditions favouring long-term DNA preservation in wood remains, and started to unveil the first trends in the DNA decay process in wood material. Additionally, the maternally inherited chloroplast haplotypes of 21 samples from three periods of forest human-induced use (Neolithic, Bronze Age and Middle Ages) were found to be consistent with those of modern populations growing in the same geographic areas. Our work paves the way for further studies aiming at using ancient DNA preserved in wood to reconstruct the micro-evolutionary response of trees to climate change and human forest management.
(Molecular Ecology. vol. 27, n° 0962-1083, pp. 1138-1154, 01/03/2018)
AMIS, UT3, Comue de Toulouse, CNRS, BioGeCo, INRA, UB, UCPH, CReAAH, UM, UR, UR2, CNRS, UFR HHAA, UN, MC, DRAC Normandie, MCC, MC, DRASSM, MC, EDYTEM, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, ARCHIMEDE, UNISTRA, Université de Haute-Alsace (UHA), MCC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DAI, UAB, CSIC, UBM, CNRS
Dynamics of particulate organic matter composition in coastal systems: Forcing of spatio-temporal variability at multi-systems scale
In costal systems, particulate organic matter (POM) results from a multiplicity of sources having their respective dynamics in terms of production, decomposition, transport and burial. The POM pool experiences thus considerable spatial and temporal variability. In order to better understand this variability, the present study employs statistical multivariate analyses to investigate links between POM composition and environmental forcings for a panel of twelve coastal systems distributed along the three maritime regions of France and monitored weekly to monthly for 1 to 8 years.At multi-system scale, two main gradients of POC composition have been identified: a 'Continent-Ocean' gradient associated with hydrodynamics, sedimentary dynamics and depth of the water column, and a gradient of trophic status related to nutrient availability. At local scale, seasonality of POC composition appears to be station-specific but still related to part of the above-mentioned forcings. A typology of systems was established by coupling spatial and temporal variability of POC composition. Four groups were highlighted: (1) the estuarine stations where POC composition is dominated by terrestrial POM and driven by hydrodynamics and sedimentary processes, (2) the oligotrophic systems, characterized by the contribution of diazotrophs due to low nutrient availability, and the marine meso/eutroph systems whose POC composition is (3) either deeply dominated by phytoplankton or (4) dominated by phytoplankton but where the contribution of continental and benthic POC is not negligible and is driven by hydrodynamics, sedimentary processes and the height of the water column.Finally, the present study provides several insights into the different forcings to POM composition and dynamics in temperate coastal systems at local and multi-system scales. This work also presents a methodological approach that establishes statistical links between forcings and POM composition, helping to gain more objectively insight of forcings.
(Progress in Oceanography. vol. 162, n° 0079-6611, pp. 271-289, 01/03/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DYNECO, IFREMER, CRESCO, MNHN, IFREMER, CRESCO, MNHN, IFREMER, LIENSs, INSU - CNRS, ULR, CNRS, CHIM, AD2M, SU, CNRS, SBR, SU, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO, LOMIC, OOB, UPMC, CNRS, UPMC, CNRS, SBR, SU, CNRS, FR2424, SBR, SU, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, LOV, INSU - CNRS, SU, CNRS, IMEV, INSU - CNRS, SU, CNRS, NutriNeuro, INRA, UB, IPREM, UPPA, INC-CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, OASU, UB, INSU - CNRS, ULR, CNRS, INRAE, LOB, INSU - CNRS, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, CREC, UNICAEN, NU, AD2M, SU, CNRS, SBR, SU, CNRS
UV and IR Photochemistries of Malonaldehyde Trapped in Cryogenic Matrices
(Journal of Physical Chemistry A. vol. 122, n° 1089-5639, pp. 2376-2393, 20/02/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PIIM, AMU, CNRS, ETH Zürich
Etat de la qualité des eaux de l’estuaire de la Gironde : cas du cadmium et des butylétains
L’estuaire de la Gironde est affecté par une pollution polymétallique historique, dont la contamination persistante en cadmium (Cd) empêche une reprise complète et le développement de la conchyliculture girondine, avec un risque potentiel pour le 1er site ostréicole français (Marennes-Oléron). D’autre part, le suivi de l’état de la qualité chimique des masses d’eau, mis en place par la Directive Cadre sur l’Eau (DCE) a déclassé en 2009 la masse d’eau « Gironde centrale » à cause de niveaux élevés en tributylétain (TBT), hautement toxique et interdit depuis plusieurs décennies, détecté dans l’estuaire de la Gironde.Ce travail se base sur 12 campagnes océanographiques comprenant un suivi temporel mensuel pendant l’année 2015 aux sites de surveillance DCE (PK52 et PK86), à PK 30 et 3 profils longitudinaux sur l’ensemble du gradient salin depuis Bordeaux jusqu’à l’embouchure. Les mesures in-situ et les échantillons visaient à caractériser l’état actuel de la qualité des eaux girondines pour Cd et butyl-étains dans le contexte historique de décontamination et de résilience du système fluvio-estuarien. Les résultats ont montré les plus faibles additions en Cd dissous (Cdd) dans le gradient salin depuis 2002, pour des conditions hydriques contrastées. Le développement de plusieurs méthodes de calcul a permis de montrer une diminution des flux nets de Cdd au cours des 30 dernières années d’un facteur ~10. Les concentrations en Cd particulaire (Cdp) présentent des valeurs de l’ordre de 0,45 ± 0,07 mg/kg ces 10 dernières années. Cette valeur est supérieure au bruit de fond géochimique de l’estuaire salin (0,2 mg/kg) suggérant la persistance d’un potentiel de contamination de la zone côtière par désorption. Des mesures ADCP à l’embouchure de l’estuaire couplées à des analyses géochimiques ont permis d’estimer quantitativement les flux nets en matières en suspension (MES) et Cdp pour des conditions hydrologiques extrêmes. La prise en compte de l’ensemble de résultats scientifiques (mesures et modélisation hydrosédimentaire) antérieures et l’analyse des évènements de crue et des coefficients de marée depuis 1990 ont permis de proposer un modèle conceptuel d’export de MES et Cdp en zone côtière. Le suivi mensuel sur l’année 2015 montre que l’estuaire de la Gironde reste déclassé en TBT avec deux valeurs ponctuelles supérieures à la NQE-CMA et avec des moyennes annuelles supérieures à la NQE-MA pour les PK30, PK52 et PK86. Les enregistrements longitudinaux des butylétains (TBT, dibutylétain (DBT) et monobutylétain (MBT)) dans les compartiments eaux, MES et sédiments de l’ensemble de l’estuaire de la Gironde ont permis de mettre en évidence plusieurs sources potentielles actuelles localisées au niveau de Bordeaux, du Bec d’Ambès, mais surtout au niveau de la masse d’eau aval.
(12/02/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS