Éditeur(s) : HAL CCSD SAGE Publications
Résumé : International audience
The distribution of redox-sensitive elements (V, U, Mo, Mn) was studied in a sedimentary archive of the Pierre-Blanche lagoon encompassing 3500 years of sedimentation. Between 240 and 255 cm (i.e. between 0 and 350 cal. ad) in the core, there was a dark layer with no mollusc shells. Enrichments of V, U and Mo and depletion of Mn were observed in this layer compared with overlying and underlying sediments. This was attributed to the occurrence of anoxia in bottom water or at the sediment/water interface during the Roman period. This episode was concomitant with the formation of a sandy barrier, which now isolates the lagoon from the sea. Our results suggest that the isolation of the lagoon, which was deeper in the period concerned than at present, favoured stagnation of the water. Combined with the excess nutrient inputs because of human activities in Lattara harbour, stagnation may have caused anoxia in bottom water at least in some parts of the Palavasian lagoon system. Bottom conditions nevertheless remained sufficiently reducing for the accumulation of U and Mo to persist until around 800 cal. ad. Although the lagoon has been hyper-eutrophic since at least the middle of the 20th century and although anoxia occurs frequently in summer, redox proxies show no evidence for their occurrence. The shallow water and associated resuspension and reoxidation events explain the lack of V, Mo and U enrichment in recent sediments.
ISSN: 0959-6836

hal-01062151
https://hal.archives-ouvertes.fr/hal-01062151

Éditeur(s) : HAL CCSD European Geosciences Union (EGU) European Geosciences Union
Résumé : The Moroccan Mediterranean coast is located in one of the area's most vulnerable to extreme weather events or tsunami hazards. The objective of this research is to reconstruct the historical extreme submersion-event record using sea-induced deposits preserved in coastal lagoon. The Nador lagoon is the largest Moroccan lagoon (115 km2). It is located along the western Mediterranean, which has a high cyclogenetic character and is exposed to tsunamis from the Alboran Sea. The sandy barrier which separates the lagoon from the Mediterranean Sea is marked by much overwash, which indicate how intensely it has been exposed to the adverse sea events through history. Using the UWITEC© gravity coring platform, an undisturbed MC4.5 core (1.15 m long) was successfully sampled in the studied lagoon. To identify extreme sea events, a multi-proxy approach was applied combining sedimentological and geochemical data. Three paleoevents were identified; all of them are concentrated over the last 500 years, and the most recent event corresponds to the 1889 storm. For the others deposits, it is difficult to determine exactly their origin; however, the high frequency of storm events over the relevant period and the absence of historical tsunamis evidence is more in favor of the meteorological origin.
ISSN: 1561-8633

hal-01146451
https://hal.archives-ouvertes.fr/hal-01146451
DOI : 10.5194/nhess-15-203-2015

Éditeur(s) : HAL CCSD Inter-Research
Résumé : Precise knowledge of lifetime migrations is vital in exploited fish species, since all essential habitats must be protected to maintain sustainable stock levels. The present study used multi-element otolith fingerprints of the gilthead sea bream Sparus aurata (L.) to discriminate its main juvenile and adult habitats in the Languedoc-Roussillon region (Gulf of Lions, northwest Mediterranean) and infer the lifetime migrations of 12 individuals from the area (11 from the present day and 1 from the Roman era). This allowed for the first time the identification of key habitats for the successful completion of the species' life cycle in the Gulf of Lions, and the connectivity between them. Our results revealed that lagoon use by S. aurata is probably ancient (>2500 yr) and confirmed its current commonness. Yet, although most observed migration patterns were in accordance with the migratory behavior previously described for the species, strong inter-individual variations and new patterns in habitat use were detected. At the juvenile stage, a preference for shallow lagoons with low salinities was evidenced. Nevertheless, the first year of life can also be successfully completed in marine conditions. At the adult stage, lagoon use was shown to occur until at least age 4 yr, with periods of lagoon residency of up to 11 mo in a year, often including winter months. Because overwintering in the lagoons was previously thought to be impossible for S. aurata due to low temperatures, this finding has important implications for future stock management, especially since the species breeds in winter.
Marine Ecology Progress Series

hal-00682003
https://hal.archives-ouvertes.fr/hal-00682003
DOI : 10.3354/meps09444

Éditeur(s) : Gauthier-Villars
Résumé : This review addresses the problem of recently introduced plants in the Mediterranean in order to analyse their vectors, the dispersal processes and the possible ecological and economic consequences. Ninety-five cases (94 macroscopic algae and one seagrass) are listed and discussed. Three major routes of access into the Mediterranean are indicated: shipping, the Suez canal and aqua-culture. The recent introduction of Caulerpa taxifolia along our coasts has called attention to a new potential source: aquaria. Among the successful acclimatizations, cold-temperate Pacific and Atlantic species remain confined to the north of the Mediterranean (Gulf of Lions, Adriatic), whereas some tropical or sub-tropical plants colonize large areas. Some introduced algae proliferate to the detriment of the indigenous Mediterranean vegetation. In contrast with some terrestrial introductions, no population crash has been observed in the Mediterranean, although some notable fluctuations seem to occur in coastal lagoons. From an economic point of view, the two activities most affected by this phenomenon are aquaculture and fishing. With the gradual disappearance of European frontiers, the worldwide development of marine cultures and the multiplication of giant Seaworlds, the transfer of live marine organisms will become routine and the risk of new introductions will considerably increase in the Mediterranean. Only international legislation, established by the countries of the littoral, will be able to control these problems.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 1 , P. 1-23

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20879/18493.pdf
http://archimer.ifremer.fr/doc/00098/20879/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Big storm events represent a major risk for populations and infrastructures settled on coastal lowlands. In the Western Mediterranean, where human societies colonized and occupied the coastal areas since the Ancient times, the variability of storm activity for the past three millennia was investigated with a multi-proxy sedimentological and geochemical study from a lagoonal sequence. Mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal/marine origin of sediments deposited into the lagoon. The multi-proxy analysis shows that coarser material, low magnetic susceptibility, and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence. A comparison with North Atlantic and Western Mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods, suggesting a climatically-controlled mechanism for the occurrence of these storm periods. Besides, an in-phase storm activity pattern is found between the Western Mediterranean and Northern Europe. Spectral analyses performed on the Sr content revealed a new 270-year solar-driven pattern of storm cyclicity. For the last 3000 years, this 270-year cycle defines a succession of ten major storm periods (SP) with a mean duration of 96 ± 54 yr. Periods of higher storm activity are recorded from >680 to 560 cal yr BC (SP10, end of the Iron Age Cold Period), from 140 to 820 cal yr AD (SP7 to SP5) with a climax of storminess between 400 and 800 cal yr AD (Dark Ages Cold Period), and from 1230 to >1800 cal yr AD (SP3 to SP1, Little Ice Age). Periods of low storm activity occurred from 560 cal yr BC to 140 cal yr AD (SP9 and SP8, Roman Warm Period) and from 820 to 1230 cal yr AD (SP4, Medieval Warm Period).
ISSN: 0277-3791

hal-01277796
https://hal.archives-ouvertes.fr/hal-01277796
DOI : 10.1016/j.quascirev.2015.10.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
With only a narrow opening through the Gibraltar and Suez Canals, the Mediterranean Sea is one of thelargest semi-enclosed seas. The marine flora and fauna are some of the richest in the world, relative to itssize, particularly in the coastal habitats, which are also characterized by numerous endemic speciesalthough the introduction of non-indigenous species threatens its rich and unique biodiversity. Followingthe opening of the Suez Canal, and in combination with shipping and aquaculture activities, nonindigenousspecies (NIS) introduction has had measurable impacts on the Mediterranean. Lagoon ecosystemsalong the French coastline, with approx. 100 NIS identified, are considered hot-spot areas forthese species. Rapid assessment sampling for sessile benthic species together with DNA barcoding is arapid, easy and cheap method to detect non-indigenous species. Two nearby and different ecosystemswere sampled for invertebrate species: Saint-Nazaire lagoon, a Special Protection Area within the Natura2000 Network and Canet port, a marina in a small village. The DNA barcoding tool for species identificationwas used for confirming the taxonomy. This showed that, despite the Saint-Nazaire Lagoonclassification within the Natura 2000 network, it is already contaminated with a single NIS that wasfound in high densities and is clearly beginning to dominate the system. It is proposed that a rapidassessment of the sampled environment and the DNA barcode approach are efficient and can providesufficient information on the new target species to be used in conservation planning and ongoingmanagement efforts.
ISSN: 0272-7714

hal-01488926
https://hal-univ-perp.archives-ouvertes.fr/hal-01488926
DOI : 10.1016/j.ecss.2017.02.004

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : A study combining very high resolution seismic and sediment core data has been carried out on the Thau lagoon (Mediterranean coast, microtidal setting, SE France) in order to understand more clearly the dynamics and Holocene chronology of its closure through the different stages of its filling. One main seismic unit (U2) has been defined into the infill, above the rocky basement (U0) and a composite unit U1, which is interpreted as remnants of Pleistocene fluvial terraces or/and to early marine Holocene deposits. Unit U2, that reaches locally 9 m in thickness, rests conformably on U1 in the central part of the lagoon and onlaps U0 or U1 close to the edge of the lagoon. It is divided in two sub-units, U2-1 and U2-2. U2-2 rests paraconformably on U2-1 in the central part of the lagoon where the infill is the thickest, while a marked erosional unconformity is observed between U2-1 and U2-2 on topographic highs of the basement and on the seaward edge of the lagoon. A total of seven elementary sequences have been observed in U2-1 and U2-2.;According to core data, U2 consists in a series of mud-dominated sequences, with shell fragments dispersed at the base. The vertical distribution of the fauna into U2-1 and U2-2 reveals a lagoonal environment. However in U2-1, marine species are more abundant in the south of the lagoon. C-14 AMS dating provides three ages: similar to 6000 cal yr B.P. in the lower part of U2-1 on CAL1, 5400 cal yr B.P. just above the boundary between U2-1 and U2-2 on CAL4, similar to 3000 cal yr B.P. in the middle of U2-2 on CAL4.;A scenario to explain the lagoon infill stratigraphy and geometry is proposed. The beginning of the lagoon infill occurred with the initiation of the barrier construction, as soon as the sea-level rise slowed down significantly, i.e. between 7000-6000 yr B.P. The sediment-fill began into the back-barrier system, with a high rate of sedimentation for U2-1, according to the radiocarbon data. At 5400 yr B.P., the barrier is assumed to be totally closed leading to the deposition of the fully lagoonal U2-2 succession. The unconformity between U2-1 and U2-2 is interpreted as the result of a rapid landward retreat of the barrier. This severe retreat could be related to climate forcing and/or brutal change in sediment discharge driven by the Rhone River, which is the main sediment source of the longshore drift. In this scenario, the last sub-unit, U2-2, represents most of the late Holocene infill. In this framework, the elementary sequences observed in U2-2 could be related to high frequency climate changes of about 1000-1500 years periodicity according to C-14 dates.
EISSN: 1777-5817

hal-00486386
https://hal.archives-ouvertes.fr/hal-00486386
DOI : 10.2113/gssgfbull.181.2.197

Éditeur(s) : HAL CCSD Station Biologique
Résumé : International audience
This study deals with temporal variations in eel diet Anguilla anguilla sampled at each of the four seasons in the Languedocian Prévost lagoon (Gulf of Lion) from Autumn 1998 to Summer 1999. The following feeding indices were calculated based on observations of 12 categories of prey found in the contents of full stomachs: coefficient of vacuity CV, degree of fullness DR, occurrence frequency PP, relative abundance N (in %) and relative weight P (in %). The interpretation of results is also based on the Costello's method (1990) which combines PP and N. Anguilla anguilla mainly feeds on benthic organisms, primarily Gammarus gr. locusta, Polychaeta, insect larvae, small fish. Based on variations in eel diet, seasonal influence is illustrated by a decrease in feeding activity in summer which gradually increases during the following seasons. The good trophic quality available to eels in the Prévost lagoon depends on its hydrodynamics which is directly related to the movement of water entering and leaving lagoon by a short communication with the sea. This water movement accelerates the enrichment and production processes of this ecosystem. Changes observed during the four seasons illustrate an opportunistic type of feeding behaviour. Eels consume the most available benthic prey. They favour the importance of the prey at a given moment without using a particular feeding strategy like specialisation or generalisation. Thus, eel adapts its diet in adjusting available energy resources in the ecosystem. Because of this, the lagoon-resident species Anguilla anguilla is an obvious indirect bioindicator of the trophic capacity and present level of confinement in the brackish water lagoon ecosystem of Prévost.
ISSN: 0007-9723

hal-00753021
https://hal.univ-antilles.fr/hal-00753021

Éditeur(s) : Wiley-blackwell
Résumé : 1. Abiotic and biotic variables of coastal lagoons are highly heterogeneous in both space and time, and this heterogeneity complicates the assessment of their ecological status. These variables are essential to the monitoring and preservation of these fragile ecotones and the resources and services they sustain. 2. An integrative approach for evaluating the ecological status of coastal lagoons, based on field investigations of the key parameters driving their functioning and a set of selected ecological indicators matching lagoon management information needs for societal benefits, is investigated. Consistency in lagoon status evaluation from multiple and different variables was estimated, through a case study comparing three adjacent yet contrasting French Mediterranean shallow water lagoons. 3. French Mediterranean shallow water lagoons are used to demonstrate the potential of such an approach and to underline the need for a multi-faceted framework, for correctly evaluating lagoon status, and underlining the need for high-frequency lagoon monitoring to avoid errors in status assessment and resulting management plans. 4. Based on the results, a continuous monitoring system is proposed that would record high frequency biotic and abiotic data in the lagoons. The use of such an ad hoc observatory system, based on appropriate diagnostic indicators and risk estimators would simplify interactions between scientists and managers and would improve the efficiency of their analyses. 5. A lagoon management plan based on a holistic approach is proposed to help scientists and local managers to reach a consensus about the set of ecological indicators to monitor in the lagoons needed to assess their global health status in accordance with both conservation and/or societal needs. Copyright (c) 2011 John Wiley & Sons, Ltd.
Aquatic Conservation-marine And Freshwater Ecosystems (1052-7613) (Wiley-blackwell), 2011-11 , Vol. 21 , N. 7 , P. 728-742

Droits : 2011 John Wiley & Sons, Ltd.
http://archimer.ifremer.fr/doc/00056/16702/14202.pdf
DOI:10.1002/aqc.1231
http://archimer.ifremer.fr/doc/00056/16702/

Éditeur(s) : HAL CCSD Elsevier
Résumé : Finding records of past catastrophic storm events is essential to evaluate the long term climatic evolution in a given coastal area. This question has been addressed by the study of sediment cores sampled in a small coastal lagoon of the French Mediterranean coast (Pierre Blanche lagoon). Two cores were studied in detail and revealed the presence of three main storm events. The sedimentation rates calculated using the CFCS Pb-210 model, in agreement with Cs-137 data, are 3 +/- 0.4 and 4.2 +/- 0.7 mm y(-1) near the border and in the center of the lagoon respectively. This suggests that the 0.6 m deep lagoon could be filled with sediments over the next 150 yr. Our study shows that storm events can be characterized in sedimentary sequences identified by facies, grain size and faunal assemblages (lagoonal and marine species). Comparison of Pb-210, C-14 chronology and historical accounts suggest that the three identified storm events took place in 1742, 1839 and 1893 A.D. (i.e. about one catastrophic event per century).
ISSN: 0025-3227

hal-00411189
https://hal.archives-ouvertes.fr/hal-00411189
DOI : 10.1016/j.margeo.2008.03.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A high-resolution record of paleostorm events along the French Mediterranean coast over the past 7000 years was established from a lagoonal sediment core in the Gulf of Lions. Integrating grain size, faunal analysis, clay mineralogy and geochemistry data with a chronology derived from radiocarbon dating, we recorded seven periods of increased storm activity at 6300-6100, 5650-5400, 4400-4050, 3650-3200, 2800-2600, 1950-1400 and 400-50 cal yr BP (in the Little Ice Age). In contrast, our results show that the Medieval Climate Anomaly (1150-650 cal yr BP) was characterised by low storm activity.;The evidence for high storm activity in the NW Mediterranean Sea is in agreement with the changes in coastal hydrodynamics observed over the Eastern North Atlantic and seems to correspond to Holocene cooling-in the North Atlantic. Periods of low SSTs there may have led to a stronger meridional temperature gradient and a southward migration of the westerlies. We hypothesise that the increase in storm activity during Holocene cold events over the North Atlantic and Mediterranean regions was probably due to an increase in the thermal gradient that led to an enhanced lower tropospheric baroclinicity over a large Central Atlantic-European domain. (C) 2011 University of Washington. Published by Elsevier Inc. All rights reserved.
ISSN: 0033-5894

hal-00760909
https://hal.archives-ouvertes.fr/hal-00760909
DOI : 10.1016/j.yqres.2011.09.002

Éditeur(s) : Gauthier-Villars
Résumé : The biogeological organization of Thau lagoon was investigated through the granulometric analysis of surficial sediments and study of the qualitative and the quantitative distribution of benthic macrofauna and meiofauna. These show clearly that the lagoonal system is organized according to confinement as conceived by Guelorget and Perthuisot (1983 a; 1992), which depends upon the rate of exchanges with the open sea and the hydrodynamic pattern of the basin. The latter appears to be composed of a pair of lagoonal subsystems separated by a hydrodynamically unstable barrier. The northern subsystem displays the classical concentric organization of Mediterranean lagoons with a clearly defined hydraulic umbilicus. The southern subsystem displays a transverse original organization due to a large zone of exchanges with the sea through the sand bar. The basin is globally subject to only slight confinement, but displays signs of organic matter accumulation due to the intensification of shellfish culture.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 1 , P. 105-114

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20880/18494.pdf
http://archimer.ifremer.fr/doc/00098/20880/

Éditeur(s) : HAL CCSD European Geosciences Union (EGU)
Résumé : International audience
Holocene climate fluctuations and human activity since the Neolithic have shaped present-day Mediter-ranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean pale-oenvironmental changes over the last millennia remains a challenging issue. High-resolution pollen analyses were un-dertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamics over the last 4500 years. Results are compared with climatic, historical and archeological archives. A long-term aridification trend is highlighted during the late Holocene, and three superimposed arid events are recorded at 4600–4300, 2800–2400 and 1300–1100 cal BP. These periods of high-frequency climate variability coincide in time with the rapid climatic events observed in the Atlantic Ocean (Bond et al., 2001). From the Bronze Age (4000 cal BP) to the end of the Iron Age (around 2000 cal BP), the spread of sclerophyllous taxa and loss of forest cover result from anthropogenic impact. Classical Antiquity is characterized by a major reforestation event related to the concentration of rural activity and populations in coastal plains leading to forest recovery in the mountains. A major regional deforestation occurred at the beginning of the High Middle Ages. Around 1000 cal BP, forest cover is minimal while the cover of olive, chestnut and walnut expands in relation to increasing human influence. The present-day vegetation dominated by Mediterranean shrubland and pines has been in existence since the beginning of the 20th century.
ISSN: 1814-9324

hal-01447627
https://hal-univ-tlse2.archives-ouvertes.fr/hal-01447627
https://hal-univ-tlse2.archives-ouvertes.fr/hal-01447627/document
https://hal-univ-tlse2.archives-ouvertes.fr/hal-01447627/file/Azuara%20et%20al%202015_cor.pdf
DOI : 10.5194/cp-11-1769-2015

Éditeur(s) : Elsevier
Résumé : The family Kareniaceae is mostly known in France for recurrent blooms of Karenia mikimotoi in the Atlantic, English Channel, and Mediterranean Sea and for the unusual green discoloration in the saltwater lagoon of Diana (Corsica) caused by Karlodinium corsicum in April 1994. In terms of diversity, this taxonomic group was long overlooked owing to the difficult identification of these small unarmored dinoflagellates. In this study, thanks to the molecular characterization performed on single cells from field samples and cultures, twelve taxonomic units were assigned to the known genera Karenia, Karlodinium and Takayama, whereas one could not be affiliated to any described genus. The molecular phylogeny inferred from the D1–D2 region of the LSU rDNA showed that five of them formed a sister taxon of a known species, and could not be identified at species-level, on the basis of molecular analysis only. Among these latter taxa, one Karlodinium which was successfully cultured was investigated by studying the external morphological features (using two procedures for cells fixation), ultrastructure, pigment composition, and haemolytic activity. The results of our analyses corroborate the genetic results in favour of the erection of Karlodinium gentienii sp. nov., which possesses an internal complex system of trichocysts connected to external micro-processes particularly abundant in the epicone, and a peculiar pigment composition. In addition, preliminary assays showed a haemolytic activity.
Harmful Algae (1568-9883) (Elsevier), 2014-12 , Vol. 40 , P. 75-91

Droits : 2014 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00225/33611/32310.pdf
DOI:10.1016/j.hal.2014.10.006
http://archimer.ifremer.fr/doc/00225/33611/

Éditeur(s) : HAL CCSD
Résumé : The effects of climate change on extreme events are difficult to assess because extremes present large variability and consequently, it is difficult to identify significant trends in relation to the lack of instrumental long time series. Here we present a record of these extreme storm events in the French Mediterrannean coast over the past 7000 years based on a long sediment core from lagoonal environment in Gulf of Lions. Using a high resolution multiproxies approach on core associating grain size, faunal to reconstruct Mid to Late Holocene history of backbarrier deposits in relation to landfalling activity. Even if change in lagoon geomorphological setting over the Holocene does not allow to compare storm events in terms of intensity trough time, we have recorded six periods of increase in storm activity at 6200, 5500, 4400, 3200, 1500 yr cal B.P. and over the LIA (450 and 100 yr cal B.P.). These evidences of changes in coastal hydrodynamic, inversely correlated to periods of aridification in Western Mediterranean region, are in phase with those observed over the North Atlantic and correspond to Holocene cooling events. This increase in storm activity during Holocene cold events over Mediterranean region was probably due to thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic-European domain. This study demonstrates that temperatures in North Atlantic region influence the severe storm activity and therefore the Mediterranean climate at Holocene timescale.
Les effets du changement climatique sur les événements extrêmes sont difficiles à estimer car ces phénomènes présentent une large variabilité, et par conséquent il est délicat d'identifier des tendances significatives compte tenu de l'absence de longues séries de données instrumentales. Dans cette étude, nous présentons un enregistrement de ces tempêtes extrêmes sur la côte Méditerranéenne française au cours des 7000 dernières années à partir de carottes sédimentaires prélevées dans un système lagunaire du Golfe du Lion. L'utilisation d'une approche multi-traceur à haute résolution avec des analyses granulométriques, faunistiques, géochimiques (XRF), en minéraux argileux associées à des données chronologiques de radiocarbone et de 210Pb, 137Cs ; nous a permis de reconstruire l'histoire, au cours de l'Holocène, des dépôts lagunaires en relation avec l'activité des tempêtes. Bien que les paramètres morphologiques de cet environnement lagunaire aient changé durant l'Holocène, ne permettant pas de comparer ces événements au cours du temps en terme d'intensité, nous enregistrons six périodes d'augmentation de l'activité des tempêtes datées à 6200, 5500, 4400, 3200, 1500 an cal B.P. et durant le Petit Age Glaciaire (de 450 à 100 an cal B.P.). Ces changements de l'activité hydrodynamique côtière, en antiphase avec les périodes d'aridifications en Méditerranée de l'Ouest, sont corrélées avec celles observées dans le bassin Nord Atlantique et correspondent aux événements de refroidissement Holocène. L'augmentation de l'activité des tempêtes dans la cette région de la Méditerranée durant les périodes froides, associée à une diminution des températures au pôle Nord, est probablement liée à l'augmentation du gradient thermique qui, par interaction barocline, favorise les cycles d'évolution des tempêtes dans toute l'Europe et la Méditerranée de l'Ouest. Cette étude démontre ainsi que la température dans la région Nord Atlantique influence l'activité des tempêtes extrêmes et donc du climat Méditerranéen à l'échelle de l'Holocène.
https://tel.archives-ouvertes.fr/tel-00437757

tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757/document
https://tel.archives-ouvertes.fr/tel-00437757/file/Sabatier_these.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The paleostorm history of coastal lagoon environments (Pierre Blanche Lagoon, central part of the Gulf of Lions) has been established by integrating clay mineralogy and geochemical analysis. Clay mineralogy combined with bulk major and trace elements concentrations allow for the definition of four different end members: the Mosson drainage basin, the sandy barrier, the biogenic and the anthropic components. The two main sedimentary sources of the lagoonal system are the Mosson drainage basin which has a high concentration of smectite and Al2O3, and the sandy barrier characterized by high contents of illite, chlorite, SiO2 and Zr. Smectite/(illite + chlorite), SiO2/Al2O3 and Zr/Al2O3 ratios can be used to reconstruct the past storm history of the Pierre Blanche Lagoon. Our results indicate that the sensitivities of the clay mineralogy and geochemistry proxies are different. These sensitivities could be related: 1) first, to the comparison between different grain size for geochemistry and for clay mineralogy: 2) second, to the complexity of the mix (four end-members for the geochemistry and two end-members for the clay minerals): and 3) third, by the storm's ability to transport sediment of different sizes. (C) 2010 Elsevier B.V. All rights reserved.
ISSN: 0037-0738

hal-00512614
https://hal.archives-ouvertes.fr/hal-00512614
DOI : 10.1016/j.sedgeo.2010.04.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Understanding long-term variability in the frequency of intense storm activity is important for assessing whether changes are controlled by climate evolution. Understanding this variability is also important for predicting present and future community vulnerability and economic loss. Our ability to make these assessments has been limited by the short (less than 50 years) instrument record of storm activity. Storm-induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on longer timescales. In this study, we present a record of these extreme climatic events that have occurred in the French Mediterrannean coast over the past 1500 years. The identification of these extreme events is based on the analysis of sediment cores from Gulf of Aigues-Mortes lagoons that contain a specific sedimentary and geochemical signature associated with intense storms.;Overwash deposits do not show any evidence of intense storm landfalls in the region for several hundred years prior to the late 17th century A.D. The apparent increase in intense storms around 250 years ago occurs during the latter half of the Little Ice Age, a time of lower continental surface temperatures. Comparison of the sediment record with palaeoclimate records indicates that this variability was probably modulated by atmospheric dynamics. The apparent increase of the superstorm activity during the latter half of the Little Ice Age was probably due to the thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic/European domain and leading to a modification of the occurrence of extreme wind events along the French Mediterranean coast. A complete understanding of the relationship between climate fluctuations, storm activity, and the coastal response will be crucial to predicting the impacts of future climate change.
ISSN: 0031-0182

hal-00617525
https://hal.archives-ouvertes.fr/hal-00617525
DOI : 10.1016/j.palaeo.2010.11.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The marine Messinian deposits of Tunisia cover a narrow littoral strip some 300 km long between the northern Bizerte and Cap Bon areas and the central-eastern Sahel region. Litho- and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits.;The lower Messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic/bioclastic limestones organized in an eastward facing ramp. Westward (landward), this ramp changes into coastal lagoons, sometimes containing evaporites. Eastward, the ramp passes to the reefal Pelagian Platform extending as far as Lampedusa.;Two main sedimentary cycles are distinguished: 1) an early Messinian siliciclastic retrogradational then oolitic/bioclastic progradational cycle (Beni Khiar Formation and lower Oued bel Khedim Formation): 2) a late Messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons (Cued el Bir Formation and upper Oued bel Khedim Formation). The Tunisian early Messinian cycle is partly eustatically controlled, but the late Messinian cycle cannot be confidently correlated to other well-known Messinian series because of tectonic movements.;The lower Messinian deposits of Tunisia are also characterized by abundant suspension-feeding organisms (molluscs and bryozoans) and rare corals, calcareous algae, echinoids, and larger benthic foraminifers. The proposed palaeoenvironmental model shows that the lower Messinian ramp of Tunisia was located on a current-protected margin and subjected to continent-derived sediment and nutrient supply. Eastward, nutrient influx diminished and a shallow-water isolated carbonate platform with coralgal facies developed between the western and the eastern Mediterranean basins. The main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the Pelagian Platform, south of Sicily and Malta.
ISSN: 0031-0182

hal-00475583
https://hal.archives-ouvertes.fr/hal-00475583
DOI : 10.1016/j.palaeo.2009.10.028

Éditeur(s) : HAL CCSD Station Biologique
Résumé : International audience
This study focuses on the diet of the eel Anguilla anguilla, sampled during one month of each of the four seasons from autumn 1998 to summer 1999 in the Languedocian Ingril Lagoon (Gulf ot Lion). The following feeding indices were calculated based on observations of 11 categories of prey found in the contents of full stomachs: coefficient of vacuity (CV), degree of fullness (DR), occurrence frequency (PP, in %), relative abundance (N, in %) and relative weight (P, in %). A parallel monitoring of the benthic macrofauna was conducted in autumn and spring. The interpretation of the results is based on the degree III of the scale of confinement established by Guélorget & Perthuisot (1983) and on the Costello et al. (1990) method, which combines PP and N. A. anguilla mainly feeds on benthic organisms, primarily amphipods crustaceans, polychaetes, insect larvae and small fish. The eel's feeding activity is very low in November and February and usually increases during May. The trophic quality available to the eel population in the Ingril Lagoon depends on its hydrodynamic variables, which are directly related to its close communication with the sea. Changes observed in the eel's diet over this year long study illustrate an opportunist type of feeding behaviour that reflects the typical composition of the macroinvertebrate species assemblage at a given point in time. Eels consume the type of benthic prey that is most available at a given moment without using a particular feeding strategy (e.g., specialisation or generalisation). The eels adapt by shifting their diet according to the energetic resources available in the ecosystem, which vary depending on hydrological regime. Thus, the facultative catadromous migrant species Anguilla anguilla could be used as a bioindicator of changes in the biological zonation and in the available food resources in the brackish ecosystem of Ingril Lagoon during its lagoon-resident ecophase.
ISSN: 0007-9723

hal-00753020
https://hal.univ-antilles.fr/hal-00753020

Éditeur(s) : Gauthier-Villars
Résumé : The biology and ecology of the green tropical algae Caulerpa taxifolia (Vahl) C. Agardh have been studied in the lagoons of New Caledonia (South Pacific) with a view to understanding the invasion which began in 1984 in the northwest Mediterranean Sea. A total of 1772 stations were used to establish the spatial and depth distribution of this species, which can be considered as common in New Caledonia, since it has been found in 9 % of the stations. C. taxifolia occurred mainly at depths between 10 and 30 m. Monthly sampling has shown that its growth is maximum during the southern hemisphere spring. From 180 stations randomly sampled in the southwest lagoon we obtained a mean biomass of 0.046 g afdw/m(2), which accounts for only 0.18 % of the macrophytobenthic biomass in this lagoon. Nevertheless the species constitutes a food source which is specific to the small herbivorous mollusc sacoglosses.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 5 , P. 563-569

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00099/21013/18639.pdf
http://archimer.ifremer.fr/doc/00099/21013/