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Lespinas F.,CNRS Training and Research Center on Mediterranean Environments | Lespinas F.,Center Meteorologique Canadien | Ludwig W.,CNRS Training and Research Center on Mediterranean Environments | Heussner S.,CNRS Training and Research Center on Mediterranean Environments
Journal of Hydrology | Year: 2014

This paper investigates the uncertainties associated with using regional climate models and one hydrological model calibrated from non-stationary hydroclimatic time series to simulate future water resources of six Mediterranean French coastal river basins. First, a conceptual hydrological model (the GR2M model) was implemented in order to reproduce the observed river discharge regimes. Climatic scenarios were then constructed from a set of Regional Climate Models (RCMs) outputs and fed into the hydrological model in order to produce water discharge scenarios for the 2071-2100 period. At last, an assessment of uncertainties associated with the hydrological scenarios is given.With respect to the 1961-1990 period, RCMs project a mean annual temperature increase of 4.3-4.5. °C (3.1-3.2. °C) under the IPCC A2 (B2) scenario. Precipitation changes, although more variable, indicate a decrease between -10% and -15.6% for A2 and between -6.1% and -11.6% for B2. As a result, the GR2M model simulates a general water discharge decrease between -26% (-14%) and -54% (-41%) for the A2 (B2) scenario, depending on the basin of interest.Sensitivity tests on the hydrological modelling revealed that the hydrological scenarios are sensitive to the choice of the PE formulation, although this climatic input is negligible in the model calibration. Also, a slight but significant drift between the modelled and observed time series was detected for most basins, indicating that the hydrological model fails to adapt to non-stationary discharge conditions. A simple correction method based on a dynamical parametrization of one model parameter with temperature data considerably reduces the model drift in half of the investigated basins. When extrapolated this new parametrization to the future climate scenarios, decrease of water discharge is found to be twice as great as estimated from the standard parametrization. Our results suggest that the uncertainties stemming from hydrological models with fixed parametrizations should be further addressed in any climate change impact study. © 2014.

Elguindi N.,CNRS Laboratory for Aerology | Somot S.,Meteo - France | Deque M.,Meteo - France | Ludwig W.,CNRS Training and Research Center on Mediterranean Environments
Climate Dynamics | Year: 2011

In this study we have evaluated the ability of the CNRM-ARPEGE CLIMATE V4 general circulation model (GCM) to estimate the present-day hydrological budget components [precipitation minus evaporation over the sea (P - E) and fresh water runoff (R)] over the Mediterranean, Black and Caspian sea basins. Three simulations were performed which were exactly identical except for horizontal resolution, allowing for a unique opportunity to isolate and study the effects of resolution on simulating the hydrological components. Model calculated values of runoff and P - E were compared to a variety of data sources and show that the model's performance improves significantly with increased resolution, especially in regions with mountainous terrain. Corresponding future climate simulations (following the IPCC A2 scenario) were also performed and indicate that while resolution does not seem to have a significant effect on the qualitative impacts of future climate change on the hydrologic balance, quantitatively the results vary significantly among the models. These results suggests that high resolution global models, or downscaling models such as RCMs, are necessary in order to assess the magnitude of future changes in the hydrological components of these basins. © 2009 Springer-Verlag.

Sanchez-Vidal A.,University of Barcelona | Higueras M.,CNRS Training and Research Center on Mediterranean Environments | Marti E.,CSIC - Center for Advanced Studies of Blanes | Liquete C.,European Commission - Joint Research Center Ispra | And 3 more authors.
Progress in Oceanography | Year: 2013

Rivers are the primary pathway for organic matter transport from the terrestrial to the marine environment and, thus, river fluxes are critical in regulating the quantity of terrestrial organic matter that reaches the coastal ecosystems. Hydrodynamic processes typical of the coastal zone can lead to the transport of terrestrial organic matter across the continental shelf and beyond. Such organic matter can eventually reach the deep margin and basin ecosystems. Riverine inputs of organic matter to the sea can be a significant food source to marine ecosystems contributing to carbon cycling in these ecosystems. In order to assess the marine carbon cycle it is essential to know the biogeochemical characteristics and temporal dynamics of the fluvial organic matter input discharged by rivers to the coastal zone. In this study we present a one and a half year long (November 2008 to May 2010) assessment on organic carbon (OC) and nitrogen (N) inputs from the three main rivers discharging into the North Catalan margin (Tordera, Ter and Fluvià, from south to north). Furthermore, we investigate the characteristics of the particulate organic matter discharged by these rivers by means of stable isotopic (δ13C and δ15N) and grain size analyses.We found that the hydrological regime of the rivers is a relevant factor in regulating the quantity and mediating the quality of organic matter inputs to the North Catalan margin. Overall, the three main rivers discharging into the study area deliver 1266 and 159 tonnes of terrestrial OC and N per year, respectively, to the coastal zone. Most of the OC and N load is transported during floods, which indicates that the Mediterranean climate of the area, with a strong seasonal contrast in precipitation, determines the timing of the main inputs of OC and N to the sea. Therefore, the annual OC and N load experiences a high temporal variability associated to the number and magnitude of floods with in each hydrological year. In addition, we found that water reservoirs along the rivers act as traps for terrestrial organic matter, reducing its delivery and ultimate burial into marine sediments. River hydrology also affects the quality of organic matter that reaches the coastal zone (both in terms of C and N) by shifting the relative weight of the various sources of terrestrial organic matter. During low river discharge (i.e., in summer and early autumn) the main contributor to the organic matter pool is mostly associated with freshwater primary producers, whereas with relatively high water flows (i.e., in winter and spring) the main contributor is associated with erosion and release of soil organic matter. Furthermore, the impact of waste water treatment plants into the studied rivers results in the alteration of the isotopic signal of suspended N. The three studied rivers play a major role in transporting terrestrial organic matter to the North Catalan margin, but the fraction that is exported to the deep margin by high-energy episodic hydrodynamic events, such as large coastal storms, has a minor importance. © 2013 Elsevier Ltd.

Lavigne H.,University Pierre and Marie Curie | D'Ortenzio F.,University Pierre and Marie Curie | Migon C.,University Pierre and Marie Curie | Claustre H.,University Pierre and Marie Curie | And 5 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

Phytoplankton phenology is primarily affected by physical forcing. However, its quantification is far from being completely understood. Among the physical forcing factors, the mixed layer depth (MLD) is considered to have the strongest impact on phytoplankton dynamics, and consequently, on their phenology. The role of MLD variations in shaping the phytoplankton phenology was explored in the Mediterranean Sea, a basin displaying contrasting phenological regimes. A database of MLD estimations was merged with ocean color chlorophyll concentrations ([Chl]SAT) to generate concomitant annual MLD and [Chl]SAT cycles. Several indices were calculated to quantitatively analyze these cycles. The relevance of indices summarizing the temporal difference between main characteristics of MLD and [Chl]SAT cycles was emphasized. As previously observed, two dominant phenological regimes coexist in the Mediterranean Sea. The first is marked by a typical spring bloom, as in temperate regions. The second displays a low seasonality and an absence of an intense [Chl]SAT peak as in subtropical areas. The MLD is shown to play a key role in determining the dominant phenological regime in a given area. Results also show that regions having low seasonality display concomitant MLD and [Chl]SAT maxima, whereas [Chl]SAT peaks are generally observed 30 days after MLD peaks in regions with strongest seasonality. Over the whole basin, [Chl]SAT increase starts 1 month after the initiation of MLD deepening. Finally, after examining the impact of MLD on light and nutrient availability for phytoplankton, mechanisms were proposed to explain the time lags between MLD and [Chl]SAT increase and MLD and [Chl]SAT maxima. ©2013. American Geophysical Union. All Rights Reserved.

Rigual-Hernandez A.S.,University of Salamanca | Sierro F.J.,University of Salamanca | Barcena M.A.,University of Salamanca | Flores J.A.,University of Salamanca | Heussner S.,CNRS Training and Research Center on Mediterranean Environments
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2012

In order to investigate the seasonal and interannual variability of planktic foraminiferal fluxes in the NW Mediterranean, 266 samples from two 12-year-long sediment traps were analyzed. Two mooring lines were deployed at the east (Station Planier) and the west (Station Lacaze Duthiers) of the Gulf of Lions. The moorings were deployed at a water depth of around 1000m and were equipped with sediment traps at 500m above bottom (mab). In addition, an array of 13 core-tops recovered from different key areas of the Gulf of Lions is described. At Lacaze Duthiers, average foraminiferal fluxes were about double (411.8shellsm -2d -1) those found at the Planier sampling site (225.4shellsm -2d -1), probably due to the fertilizing effect of the Rhone river plume and the general oceanographic circulation. The annual total foraminiferal fluxes exhibited a unimodal trend, with maxima recorded during the winter-spring transition, i.e. the spring bloom, and minima during summer. Therefore, planktic foraminifers found in the sedimentary record in the Gulf of Lions may reflect the flux during the winter-spring period, rather than throughout the annual cycle. A total of eleven planktic foraminiferal species were identified in the sediment trap and core-top samples but only four species were dominant in the assemblages: Globigerina bulloides Neogloboquadrina pachyderma (dex.), Globorotalia inflata and Globorotalia truncatulinoides. The foraminiferal assemblages in the Gulf of Lions reflected the relatively cold conditions of the Northern Basin. No clear relationship between the NAO (North Atlantic Oscillation) and planktic foraminiferal fluxes was found in the sediment trap records. The low planktic foraminiferal fluxes recorded during the spring of 1998 were probably related to the anomalous environmental conditions triggered by the 1997-98 El Niño event. Furthermore, sediment trap samples were compared with surficial sediments recovered from different environmental and sedimentary settings of the Gulf of Lions and the application of these results in paleoceanographic reconstructions is discussed. © 2012 Elsevier Ltd.

Ludwig W.,CNRS Training and Research Center on Mediterranean Environments | Bouwman A.F.,Netherlands Environmental Assessment Agency | Bouwman A.F.,Wageningen University | Dumont E.,CNRS Training and Research Center on Mediterranean Environments | And 3 more authors.
Global Biogeochemical Cycles | Year: 2010

The aim of this study is to produce future scenarios on the river inputs of water and nutrients (nitrate and phosphate) into the Mediterranean and Black Sea. They are based on the four contrasting scenarios that were developed by the Millenium Ecosystem Assessment (MEA) for the years 2030 and 2050 and implemented in a spatially explicit manner into the IMAGE model. We first identified the major drivers of the river fluxes by regression analyses, then tested the retained models against the past evolutions between 1970 and 2000, and finally applied the models to the MEA scenarios. For nutrients, the considered river data mainly refer to the large rivers for which long-term time series exist (Rhone, Po, Ebro, and Danube). Here, recent trends were principally driven by fertilizer spreads (NO3, PO4), together with urban wastewater releases (PO4). Future trends remain in the envelope of the observed variability during the last 40 years, both for the large rivers and, when extrapolated to the basin scales, also for the entire Mediterranean and Black Sea. At regional scales, however, the budgets considerably change. In the northern parts of the Mediterranean drainage basin, they uniformly tend to decrease, but they may strongly increase in the south and east. Water discharge is examined on a basis of 37 rivers, showing that this parameter is clearly linked to the evolution of climate. Because of the ongoing evolution toward dryer and warmer conditions, we predict a significant trend of decreasing freshwater fluxes for the future, which already started in the past. Regional hot spots for this decrease are the drainage basin of the Alboran Sea and, when also considering the inhabitant specific water fluxes, the basins of the Aegean and north Levantine seas. © 2010 by the American Geophysical Union.

Palanques A.,CSIC - Institute of Marine Sciences | Puig P.,CSIC - Institute of Marine Sciences | Durrieu de Madron X.,CNRS Training and Research Center on Mediterranean Environments | Sanchez-Vidal A.,University of Barcelona | And 5 more authors.
Progress in Oceanography | Year: 2012

An array of mooring lines deployed between 300 and 1900. m depth along the Lacaze-Duthiers and Cap de Creus canyons and in the adjacent southern open slope was used to study the water and sediment transport on the western Gulf of Lions margin during the 2006 intense cascading period. Deep-reaching cascading pulses occurred in early January, in late January and from early March to mid-April. Dense water and sediment transport to the deep environments occurred not only through submarine canyons, but also along the southern open slope. During the deep cascading pulses, temporary upper and mid-canyon and open slope deposits were an important source of sediment to the deep margin. Significant sediment transport events at the canyon head only occurred in early January because of higher sediment availability on the shelf after the stratified and calm season, and in late February because of the interaction of dense shelf water cascading with a strong E-SE storm. During the January deep cascading pulses, increases in suspended sediment concentration within the canyon were greater and earlier at 1000. m depth than at 300. m depth, whereas during the March-April deep cascading pulses sediment concentration only increased below 300. m depth, indicating resuspension and redistribution of sediments previously deposited at upper and mid-canyon depths. Deeper than 1000. m depth, net fluxes show that most of the suspended sediment left the canyon and flowed along the southern open slope towards the Catalan margin, whereas a small part flowed down-canyon and was exported basinward. Additionally, on the mid- and lower-continental slope there was an increase in the near-bottom currents induced by deep open-sea convection processes and the propagation of eddies. This, combined with the arrival of deep cascading pulses, also generated moderate suspended sediment transport events in the deeper slope regions. © 2012 Elsevier Ltd.

Levoy F.,University of Caen Lower Normandy | Anthony E.J.,Aix - Marseille University | Monfort O.,University of Caen Lower Normandy | Robin N.,CNRS Training and Research Center on Mediterranean Environments | Bretel P.,University of Caen Lower Normandy
Marine Geology | Year: 2013

A field of long-crested transverse bars was monitored from a 2.5-year series of topographic Lidar surveys in the vicinity of a tidal inlet on the macrotidal (mean spring tidal range. = 7 to 12. m) west coast of Cotentin (Normandy, France). The bar field, the alongshore extent of which is about 1.8. km, is composed of a total of 8 bars with lengths varying from 320. m to 1300. m and mean heights comprised between 0.5. m and 2.5. m. Bar cross-sections are variable between bars and for a single bar, and also over time. The surveys show a consistent northward migration of the bars at a mean rate of about 2. m/month, but the rate is larger in winter than in summer. The Lidar observations show that the tidal inlet, located at the southern limit of the bar field where the bars start forming, comprises a large sediment platform that acts as a source of sand for the bars. The ebb jet debouching from the inlet is deflected northward by the ambient strong shore-parallel tidal currents in this large tide-range setting, and this may be the primary mechanism leading to the emplacement of the bars. Smaller wave-formed swash bars that further feed the development of these large transverse bars have also been observed. Monitoring of bar migration in the course of six consecutive spring tides with fair-weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves. Storm wave resuspension of sand is thus expected to enhance bar mobility rates, as shown by the higher rates of winter bar migration compared to the summer rates. The ebb jet explains the slower bar migration rates at the vicinity of the inlet, these rates increasing with distance northward of the inlet as the tidal currents become unimpeded. The main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration, unlike the wave-driven migration of microtidal bars. The large tidal range, in conjunction with storm wave activity, also induces longshore and seasonal variability in bar morphology. The transverse bars of Normandy appear to be inscribed in a sand circulation system involving the west Cotentin coast, the large ebb tidal delta from which they are formed, and the central Cotentin embayment where they are ultimately incorporated into the nearshore sand pool. Longer-term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars. © 2013 Elsevier B.V.

Poisot T.,CNRS Integrative Biology of Marine Organisms | Verneau O.,CNRS Training and Research Center on Mediterranean Environments | Desdevises Y.,CNRS Integrative Biology of Marine Organisms
PLoS ONE | Year: 2011

Lamellodiscus Johnston & Tiegs 1922 (Monogenea, Diplectanidae) is a genus of common parasites on the gills of sparid fishes. Here we show that this genus is probably undergoing a fast molecular diversification, as reflected by the important genetic variability observed within three molecular markers (partial nuclear 18S rDNA, Internal Transcribed Spacer 1, and mitonchondrial Cytochrome Oxidase I). Using an updated phylogeny of this genus, we show that molecular and morphological evolution are weakly correlated, and that most of the morphologically defined taxonomical units are not consistent with the molecular data. We suggest that Lamellodiscus morphology is probably constrained by strong environmental (host-induced) pressure, and discuss why this result can apply to other taxa. Genetic variability within nuclear 18S and mitochondrial COI genes are compared for several monogenean genera, as this measure may reflect the level of diversification within a genus. Overall our results suggest that cryptic speciation events may occur within Lamellodiscus, and discuss the links between morphological and molecular evolution. © 2011 Poisot et al.

Roussiez V.,CNRS Training and Research Center on Mediterranean Environments | Aubert D.,CNRS Training and Research Center on Mediterranean Environments | Heussner S.,CNRS Training and Research Center on Mediterranean Environments
Marine Chemistry | Year: 2013

We tested the ability of rare earth elements (REE) to trace the lithogenic origin of particles escaping the Gulf of Lion (NW Mediterranean) during the exceptional oceanic flood of December 2003. Suspended particulate matters were simultaneously collected at the entrance (river mouths) and the exit (canyon heads) of the hydrosystem for analysis. River-specific signatures could be roughly discriminated while shelf-exported particles depicted a rather similar signal resembling that for the RhÔne particles. When normalizing data of shelf sediments and suspended particles in canyons to the RhÔne signature, a river-to-sea continuity in REE patterns was shown. This suggests that (i) middle- and outer-shelf areas are mainly fed by the solid discharges of the RhÔne River and (ii) particles leaving the shelf during the event mostly originate from this continental source (directly and/or indirectly via resuspension of shelf sediments). Upon closer examination, the influence of hydro-dynamical conditions on the composition of particles channeled to the open sea could be shown. During the flood event studied here, even though the influence of the RhÔne River is dominant, most of the shelf-exported particles are also composed of materials originating from small rivers. Conversely, during "normal" conditions, particles escaping the shelf clearly exhibit the Rhône particle imprint, suggesting that inputs from small rivers are too low to contribute significantly to the export. © 2013 Elsevier B.V.

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