The first estimation of Fleuve Manche palaeoriver discharge during the last deglaciation: Evidence for Fennoscandian ice sheet meltwater flow in the English Channel ca 20–18 ka ago
The Fleuve Manche (English Channel) palaeoriver represents the largest river system that drained the European continent during Pleistocene lowstands, particularly during the Elsterian (Marine Isotope Stage 12) and Saalian Drenthe (MIS 6) glaciations when extensive ice advances into the North Sea area forced the central European rivers to flow southwards to the Bay of Biscay (NE Atlantic). Numerous long piston cores and high-resolution acoustic data from the northern Bay of Biscay have been correlated using a well-constrained chronostratigraphical framework, and for the first time allow the estimation of the discharge of the Fleuve Manche palaeoriver at the end of the last glacial period (i.e. Weichselian). Our results, discussed in the light of relationships between river loads and drainage area characteristics, strongly suggest that the Bay of Biscay collected sediment-laden meltwater from the Northern European lowlands and the southern part of the Fennoscandian ice sheet at the end of the last glacial period and particularly during the paroxysmal phase of the European deglaciation ca 20–18 ka ago. This demonstrates that the Fleuve Manche drainage area at that time was equivalent to those dating from the major Elsterian and Saalian Drenthe glaciations. Based on our data, we propose a revision of the palaeogeographical and palaeoglaciological evolution of the North Sea area while showing that the British and Fennoscandian ice sheets entered the North Sea basin until ca 18 ka initiating isostatic adjustment of the basin. This allowed the North Sea fluvial system to flow southwards through the Dover Strait. Finally, we discuss the Fleuve Manche freshwater discharge during the maximum European ice sheet retreat ca 18 ka. The estimated discharge at this time appears important and sufficiently sustained to possibly contribute to the profound destabilisation of the thermohaline circulation recognised in the North Atlantic from ca 18 to 16 ka.
(Earth and Planetary Science Letters. vol. 290, n° 0012-821X, pp. 459-473, 20/02/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GM, IFREMER, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LDO, INSU - CNRS, UBO EPE, CNRS, UEB, CAM
Assessing coastal benthic macrofauna community condition using best professional judgement - Developing consensus across North America and Europe
Benthic indices are typically developed independently by habitat, making their incorporation into large geographic scale assessments potentially problematic because of scaling inequities. A potential solution is to establish common scaling using expert best professional judgment (BPJ). To test if experts from dif- ferent geographies agree on condition assessment, sixteen experts from four regions in USA and Europe were provided species-abundance data for twelve sites per region. They ranked samples from best to worst condition and classified samples into four condition (quality) categories. Site rankings were highly correlated among experts, regardless of whether they were assessing samples from their home region. There was also good agreement on condition category, though agreement was better for samples at extremes of the disturbance gradient. The absence of regional bias suggests that expert judgment is a via- ble means for establishing a uniform scale to calibrate indices consistently across geographic regions.
(Marine Pollution Bulletin. vol. 60, n° 0025-326X, pp. 589-600, 18/02/2010)
SCCWRP, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, IRSNB / RBINS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UOC, GU, CEAB, CSIC
Comments on ``The Depth-Dependent Current and Wave Interaction Equations: A Revision
Equations for the wave-averaged three-dimensional momentum equations have been published in this journal. It appears that these equations are not consistent with the known depth-integrated momentum balance, especially over a sloping bottom. These equations should thus be considered with caution as they can produce erroneous flows, in particular outside of the surf zone. It is suggested that the inconsistency in the equations may arise from the different averaging operators applied to the different terms of the momentum equation. It is concluded that other forms of the momentum equations, expressed in terms of the quasi-Eulerian velocity, are better suited for three dimensional modelling of wave-current interactions.
(18/02/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SHOM, LOS, IFREMER
New insights into the size distribution of fluorescent dissolved organic matter in estuarine waters
The study of the fate and composition of organic matter in aquatic systems is of interest since organic matter is believed to play a key role in biogeochemical cycles. Fluorescent dissolved organic material (FDOM) represents a major fraction of dissolved organic matter (DOM) but is under explored, particularly in estuarine environments. In this study, 3D fluorescence excitation-emission matrix (EEM) spectroscopy was combined with tangential ultrafiltration (UF) to investigate the changes in FDOM properties during the mixing of fluvial and marine waters in two estuaries on the French Atlantic coast. Water samples were sequentially filtered through three membranes of decreasing molecular weight (MW) cut off points (3 kDa, 1 kDa and 500 Da). Four ultrafiltration fractions were obtained and were analysed using EEM spectroscopy, as well as for their DOC content. Satisfactory fluorescence and DOC mass balances were obtained after the sequential UF fractionation despite the variable DOC concentration and ionic strength of the estuarine samples, showing the reliability of the UF systems. DOC distribution in the different size classes was observed to vary between the upstream and downstream parts of the estuaries and to be different in the two estuaries. The value of combining UF and EEM spectroscopy was shown, since the coupling allowed observation and isolation of some fluorophores which could not be distinguished in the spectra of bulk samples. Thus, the β fluorophore, observed mainly in marine samples until now, and which is associated with material of autochthonous biological origin, was present in the lowest size fraction (MW < 500 Da) from all water samples, including freshwater ones. The γ fluorophore, characteristic of protein-like compounds, was observed in the small size fractions of some fresh and brackish water samples, but it was not visible in the spectra of the corresponding bulk water samples. The differences in fluorescence properties of the size fractions of DOM were further evaluated by determining three fluorescence indices: the fluorescence index (f450/f500), the humification index (HIX) and the index of recent autochthonous contribution (BIX). The origin and degree of transformation of DOM can be assessed through the calculation of these indices. We showed that the most humified OM was associated with different size fractions, depending on water sample origin, and was characterised by intermediate MW (higher for fresh than marine water). We also showed that DOM distribution and characteristics differ between the Gironde and Seine estuaries.
(Organic Geochemistry. vol. 41, n° 0146-6380, pp. 595-610, 08/02/2010)
ISM, UB, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Does disturbance drive the collapse of biotic interactions at the severe end of a diversity–biomass gradient?
It has been recently proposed that the decrease in diversity towards the severe end of the humped-back diversity–biomass model of Grime was driven by a collapse of facilitation due to extreme conditions of either stress or physical disturbance. In order to test the hypothesis that disturbance is the primary direct factor driving the collapse of interactions occurring along environmental severity gradients, we conducted a removal experiment in the highly stressed French coastal dunes along a gradient of disturbance due to sand burial. Four dune species were used as targets and transplanted with and without neighbours in four communities along the gradient. The experiment was conducted twice, a dry and an average year. Results of the experiment showed that during the dry year the effect of the environment was prominent and only one species was facilitated for survival in the least disturbed community. During the average year, interactions for growth were important only in the same community, with positive or negative responses depending on the natural position of the target species within the coastal dune gradient. In accordance with our hypothesis, most interactions for both survival and growth were observed in the least disturbed community exhibiting the highest diversity. There were no interactions in the most disturbed community with the lowest diversity.
(Plant Ecology. vol. 206, n° 1385-0237, pp. 287-295, 01/02/2010)
ECODIV, UNIROUEN, NU, BioGeCo, INRA, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Mercury methylation rates of biofilm and plankton microorganisms from a hydroelectric reservoir in French Guiana
The Petit-Saut ecosystem is a hydroelectric reservoir covering 365 km2 of flooded tropical forest. This reservoir and the Sinnamary Estuary downstream of the dam are subject to significant mercury methylation. The mercury methylation potential of plankton and biofilm microorganisms/components from different depths in the anoxic reservoir water column and from two different sites along the estuary was assessed. For this, reservoir water and samples of epiphytic biofilms from the trunk of a submerged tree in the anoxic water column and from submerged branches in the estuary were batch-incubated from 1 h to 3 months with a nominal 1000 ng/L spike of Hg(II) chloride enriched in 199Hg. Methylation rates were determined for different reservoir and estuarine communities under natural nutrient (reservoir water, estuary freshwater) and artificial nutrient (culture medium) conditions. Methylation rates in reservoir water incubations were the highest with plankton microorganisms sampled at − 9.5 m depth (0.5%/d) without addition of biofilm components. Mercury methylation rates of incubated biofilm components were strongly enhanced by nutrient addition. The results suggested that plankton microorganisms strongly contribute to the total Hg methylation in the Petit-Saut reservoir and in the Sinnamary Estuary. Moreover, specific methylation efficiencies (%Me199Hgnet/cell) suggested that plankton microorganisms could be more efficient methylating actors than biofilm consortia and that their methylation efficiency may be reduced in the presence of biofilm components. Extrapolation to the reservoir scale of the experimentally determined preliminary methylation efficiencies suggested that plankton microorganisms in the anoxic water column could produce up to 27 mol MeHg/year. Taking into account that (i) demethylation probably occurs in the reservoir and (ii) that the presence of biofilm components may limit the methylation efficiency of plankton microorganisms, this result is highly consistent with the annual net MeHg production estimated from mass balances (8.1 mol MeHg/year, Muresan et al., 2008a).
(Science of the Total Environment. vol. 408, n° 0048-9697, pp. 1338 - 1348, 01/02/2010)
LCPME, INC-CNRS, UL, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Serial analysis of gene expression in the skeletal muscles of zebrafish fed with a methylmercury-contaminated diet
Mercury (Hg) is a widespread environmental contaminant and its organic form, methylmercury (MeHg), has been known as a potent neurotoxic since the Minamata tragedy. In the Amazonian basin, gold mining leads to MeHg biomagnification all along the food web, culminating in piscivorous fish, ultimately responsible for contamination of human beings through fish consumption. In order to assess the biological impact of dietary MeHg on fish at the genome scale, we contaminated zebrafish with MeHg-contaminated food for 25 days (13.5 microg of Hg/g of food). A serial analysis of gene expression (SAGE) was conducted on the skeletal muscle because this tissue does not perform MeHg demethylation, and 19171 SAGE tags were sequenced from the control library versus 22 261 from the MeHg-contaminated library, corresponding to 5280 different transcripts. Among those identified, 60 genes appeared up-regulated and 15 down-regulated by more than 2 times. A net impact of MeHg was noticed on 14 ribosomal protein genes, indicating a perturbation of protein synthesis. Several genes involved in mitochondrial metabolism, the electron transport chain, endoplasmic reticulum (ER) function, detoxification, and general stress responses were differentially regulated, suggesting an onset of oxidative stress and ER stress. Several other genes for which expression varied with MeHg contamination could be clustered in various compartments of the cell's life, such as lipid metabolism, calcium homeostasis, iron metabolism, muscle contraction, and cell cycle regulation. This study reveals the effectiveness of the SAGE approach to acquire a better understanding of the MeHg global effects. Furthermore, this is the first time that the SAGE was used to characterize the effect of a toxicant at the genome scale in an aquatic organism.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 469-475, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sublethal effects of waterborne uranium exposures on the zebrafish brain: transcriptional responses and alterations of the olfactory bulb ultrastructure
The toxic action modes of uranium (U) in fish are still scarcely known. U is known to modify the acetylcholinesterase activity in the fish brain. To gain further insight into U neurotoxicity in fish, we examined transcriptional responses in the brain of the zebrafish, Danio rerio, exposed to 15 μg L−1 and 100 μg L−1 of waterborne U for 3 and 10 days. In parallel, an ultrastructure analysis of the neuropil of the olfactory bulb, an area in the brain of fish sensitive to metal contamination, was performed after 10 days of U exposure. This combined transcriptomic and histological study is the first report performed in the brain and specifically the olfactory bulb of fish exposed to U. We found that 56 transcripts responded to the metal exposure, and the anatomical structure of the olfactory bulb was damaged. The greatest gene response occurred at the lower U concentration and the numbers of responding genes common to any two U exposures were much smaller than those unique to each exposure. These data showed that the intensity of gene response may not correlate positively with toxicant concentrations according to our experimental design. Instead, different patterns of gene expression are expected for each exposure. Gene responses were categorized into eight functional classes, and the transcriptional responses of genes involved in the olfactory system were significantly affected. Collectively, the data suggest that genes in the olfactory region may be ecologically relevant and sensitive transcriptional biomarkers of U waterborne exposure.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 1438-1443, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Serial analysis of gene expression in the skeletal muscles of zebrafish fed with a methylmercury-contaminated diet
Mercury (Hg) is a widespread environmental contaminant and its organic form, methylmercury (MeHg), has been known as a potent neurotoxic since the Minamata tragedy. In the Amazonian basin, gold mining leads to MeHg biomagnification all along the food web, culminating in piscivorous fish, ultimately responsible for contamination of human beings through fish consumption. In order to assess the biological impact of dietary MeHg on fish at the genome scale, we contaminated zebrafish with MeHg-contaminated food for 25 days (13.5 microg of Hg/g of food). A serial analysis of gene expression (SAGE) was conducted on the skeletal muscle because this tissue does not perform MeHg demethylation, and 19171 SAGE tags were sequenced from the control library versus 22 261 from the MeHg-contaminated library, corresponding to 5280 different transcripts. Among those identified, 60 genes appeared up-regulated and 15 down-regulated by more than 2 times. A net impact of MeHg was noticed on 14 ribosomal protein genes, indicating a perturbation of protein synthesis. Several genes involved in mitochondrial metabolism, the electron transport chain, endoplasmic reticulum (ER) function, detoxification, and general stress responses were differentially regulated, suggesting an onset of oxidative stress and ER stress. Several other genes for which expression varied with MeHg contamination could be clustered in various compartments of the cell's life, such as lipid metabolism, calcium homeostasis, iron metabolism, muscle contraction, and cell cycle regulation. This study reveals the effectiveness of the SAGE approach to acquire a better understanding of the MeHg global effects. Furthermore, this is the first time that the SAGE was used to characterize the effect of a toxicant at the genome scale in an aquatic organism.
(Environmental Science and Technology. vol. 44, n° 0013-936X, pp. 469-475, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMBA, UBS, UBO EPE, CNRS