59 research outputs found
Restaurer ou laisser faire la nature ?
International audienc
Resilience of the native flora on a Mediterranean island after eradication of ice plant (Carpobrotus spp.)
Les invasions dâespĂšces Ă©tant considĂ©rĂ©es comme une menace majeure vis-Ă -vis des espĂšces indigĂšnes, particuliĂšrement pour les systĂšmes insulaires, les programmes dâĂ©radication des espĂšces invasives constituent une des alternatives pour la prĂ©servation de la biodiversitĂ©. Dans ce contexte, les gestionnaires du Parc national de Port-Cros (PNPC) ont lancĂ© en 2010, un programme de contrĂŽle manuel sur 2 ha des Griffes de sorciĂšre (Carpobrotus sp. Aizoaceae), plantes invasives dans le bassin mĂ©diterranĂ©en et, particuliĂšrement, sur lâĂźle de Bagaud (Var, France). Les changements temporels des communautĂ©s vĂ©gĂ©tales (i.e., richesse spĂ©cifique et recouvrement vĂ©gĂ©tal) ont Ă©tĂ© analysĂ©s au sein de placettes permanentes (100 mÂČ et 16 mÂČ) avant (2010-2011) et aprĂšs Ă©radication (2013-2014) de Carpobrotus sp. Ces communautĂ©s en cours de restauration sont Ă©galement comparĂ©es Ă des communautĂ©s vĂ©gĂ©tales indigĂšnes de lâĂźle, qualifiĂ©es de rĂ©fĂ©rence. La richesse spĂ©cifique et le recouvrement vĂ©gĂ©tal de la flore indigĂšne augmentent considĂ©rablement Ă partir de 2013 du fait de la germination de la banque de graines des plantes indigĂšnes. En zone littorale, la reprise de la flore indigĂšne, comprenant des communautĂ©s halo-rĂ©sistantes, semble plus rapide que dans lâintĂ©rieur de lâĂźle, comprenant Ă la fois des espĂšces de matorral bas et halonitrophiles. Les opĂ©rations de contrĂŽle doivent inclure un suivi temporel des rĂ©ponses des plantes indigĂšnes pour savoir si la reprise est transitoire ou durable dans le cadre de la restauration dâĂ©cosystĂšmes dĂ©gradĂ©s ou de la conservation dâespĂšces menacĂ©es.Species invasions are considered as a major threat relative to native species, especially for island systems. Eradication programs of invasive species are an alternative for the preservation of island's native biodiversity. In this context, the managers of the Port-Cros national Park have implemented in 2010 a 2 ha manual control program of ice plant (Carpobrotus sp., Aizoaceae), invasive in the Mediterranean basin and, particularly, on the island of Bagaud (Var, France). Temporal changes of plant communities (i.e. species richness and plant cover) were analysed in permanent plots (100 mÂČ and 16 mÂČ) before (2010-2011) and after (2013-2014) Carpobrotus sp. eradication. These plant communities were also compared with native reference plant communities of this island. Species richness and plant cover of native flora significantly increased in 2013 due to the germination of native plants seed bank. On coastal sites, the recovery of native flora is faster and matches with the halo-resistant reference plant community. On inland sites, the recovery of native flora includes low matorral and halonitrophilous species. Invasive species control must include monitoring through time of native plant species to find out whether recovery is transient or long lasting in the context of degraded ecosystems restoration or threatened species conservation
Continental weathering as a driver of Late Cretaceous cooling : new insights from clay mineralogy of Campanian sediments from the southern Tethyan margin to the Boreal realm
21 pagesInternational audienceNew clay mineralogical analyses have been performed on Campanian sediments from the Tethyan and Boreal realms along a palaeolatitudinal transect from 45° to 20°N (Danish Basin, North Sea, Paris Basin, Mons Basin, Aquitaine Basin, Umbria-Marche Basin and Tunisian Atlas). Significant terrigenous inputs are evidenced by increasing proportions of detrital clay minerals such as illite, kaolinite and chlorite at various levels in the mid- to upper Campanian, while smectitic minerals predominate and represented the background of the Late Cretaceous clay sedimentation. Our new results highlight a distinct latitudinal distribution of clay minerals, with the occurrence of kaolinite in southern sections and an almost total absence of this mineral in northern areas. This latitudinal trend points to an at least partial climatic control on clay mineral sedimentation, with a humid zone developed between 20° and 35°N. The association and co-evolution of illite, chlorite and kaolinite in most sections suggest a reworking of these minerals from basement rocks weathered by hydrolysis, which we link to the formation of relief around the Tethys due to compression associated with incipient Tethyan closure. Diachronism in the occurrence of detrital minerals between sections, with detrital input starting earlier during the Santonian in the south than in the north, highlights the northward progression of the deformation related to the anticlockwise rotation of Africa. Increasing continental weathering and erosion, evidenced by our clay mineralogical data through the Campanian, may have resulted in enhanced CO2 consumption by silicate weathering, thereby contributing to Late Cretaceous climatic cooling
Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364
Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900â3700 m/s, 2.06â2.37 g/cm3, and 20â35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements of 3650â4350 m/s, density measurements of 2.26â2.37 g/cm3, and porosity measurements of 19â22%. We associate the low velocity, low density, and high porosity of suevite and impact melt rock with rapid emplacement, hydrothermal alteration products, and observations of pore space, vugs, and vesicles. The uplifted granitic peak ring materials have values of 4000â4200 m/s, 2.39â2.44 g/cm3, and 8â13% for velocity, density, and porosity, respectively; these values differ significantly from typical unaltered granite which has higher velocity and density, and lower porosity. The majority of Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable rock damage, and are consistent with numerical model predictions for peak-ring formation where the lithologies present within the peak ring represent some of the most shocked and damaged rocks in an impact basin. We integrate our results with previous seismic datasets to map the suevite near the borehole. We map suevite below the Paleogene sedimentary rock in the annular trough, on the peak ring, and in the central basin, implying that, post impact, suevite covered the entire floor of the impact basin. Suevite thickness is 100â165 m on the top of the peak ring but 200 m in the central basin, suggesting that suevite flowed downslope from the collapsing central uplift during and after peak-ring formation, accumulating preferentially within the central basin
Ocean Drilling Perspectives on Meteorite Impacts
Extraterrestrial impacts that reshape the surfaces of rocky bodies are ubiquitous in the solar system. On early Earth, impact structures may have nurtured the evolution of life. More recently, a large meteorite impact off the YucatĂĄn Peninsula in Mexico at the end of the Cretaceous caused the disappearance of 75% of species known from the fossil record, including non-avian dinosaurs, and cleared the way for the dominance of mammals and the eventual evolution of humans. Understanding the fundamental processes associated with impact events is critical to understanding the history of life on Earth, and the potential for life in our solar system and beyond.
Scientific ocean drilling has generated a large amount of unique data on impact pro- cesses. In particular, the YucatĂĄn Chicxulub impact is the single largest and most sig- nificant impact event that can be studied by sampling in modern ocean basins, and marine sediment cores have been instrumental in quantifying its environmental, cli- matological, and biological effects. Drilling in the Chicxulub crater has significantly advanced our understanding of fundamental impact processes, notably the formation of peak rings in large impact craters, but these data have also raised new questions to be addressed with future drilling. Within the Chicxulub crater, the nature and thickness of the melt sheet in the central basin is unknown, and an expanded Paleocene hemipelagic section would provide insights to both the recovery of life and the climatic changes that followed the impact. Globally, new cores collected from todayâs central Pacific could directly sample the downrange ejecta of this northeast-southwest trending impact.
Extraterrestrial impacts have been controversially suggested as primary drivers for many important paleoclimatic and environmental events throughout Earth history. However, marine sediment archives collected via scientific ocean drilling and geo- chemical proxies (e.g., osmium isotopes) provide a long-term archive of major impact events in recent Earth history and show that, other than the end-Cretaceous, impacts do not appear to drive significant environmental changes
Probing the hydrothermal system of the Chicxulub impact crater
The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earthâs crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 Ă 105 km3 of Earthâs crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years
Life and death in the Chicxulub impact crater: a record of the PaleoceneâEocene Thermal Maximum
latitudes, with sea surface temperatures at some localities exceeding the 35ââC at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new record of the PETM from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEXH86-based sea surface temperatures (SSTs) averaging âŒ37.8ââC, an increase in terrestrial input and surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from Mexico, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest with a remarkably high abundance of fungal spores, indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived
The formation of peak rings in large impact craters
Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust
Palaeoclimatic and palaeoceanographic changes during the Campanian - mineralogical and geochemical approach
Les causes du refroidissement climatique global qui caractĂ©risent le CrĂ©tacĂ© supĂ©rieur (~100 â 65 Ma) ne sont pas encore bien Ă©tablies. LâĂ©volution de la courbe des tempĂ©ratures des eaux de fond et de surface des ocĂ©ans montre une accĂ©lĂ©ration de ce refroidissement au cours du Campanien (~84 Ma), aussi lâobjectif de ce travail Ă©tait-il dâexplorer les causes possibles de ce refroidissement en se focalisant sur lâĂ©tude des sĂ©diments dâĂąge Campanien de divers bassins sĂ©dimentaires tĂ©thysiens, borĂ©aux et atlantiques.Le premier objectif fut de dĂ©terminer lâextension spatiale des changements de cortĂšges argileux dans la TĂ©thys et le domaine borĂ©al. La minĂ©ralogie des argiles de plusieurs sites (hĂ©mi)pĂ©lagiques, sĂ©lectionnĂ©s selon un transect N-S de 5 Ă 45° N, a rĂ©vĂ©lĂ© une intensification de lâaltĂ©ration continentale au Campanien, marquĂ©e notamment par des apports accrus de kaolinite. Au cours du temps, ces apports liĂ©s au soulĂšvement de nouveaux domaines continentaux semblent se propager du Sud au Nord. Cette propagation est trĂšs certainement gouvernĂ©e par le mouvement antihoraire de la plaque africaine et de son rapprochement progressif de la plaque europĂ©enne. Lâintensification de lâaltĂ©ration continentale semble aussi sâaccompagner de la mise en place dâune ceinture climatique plus humide Ă lâorigine du dĂ©veloppement des bauxites.Le Campanien est Ă©galement marquĂ© par dâimportantes modifications palĂ©ogĂ©ographiques, telles que lâĂ©largissement de lâAtlantique Sud et Nord ainsi que la restriction du domaine tĂ©thysien. Le dĂ©placement des masses continentales est probablement Ă lâorigine dâune rĂ©organisation majeure des courants ocĂ©aniques. Dans le domaine tĂ©thysien, au CrĂ©tacĂ© supĂ©rieur la courantologie est dominĂ©e par le « Tethyan Circumglobal Current » (TCC), courant latitudinal traversant lâocĂ©an tĂ©thysien et le passage des CaraĂŻbes, dâest en ouest, qui semblerait sâintensifier au Campanien. Nous avons donc tentĂ© de reconstituer lâĂ©volution de la circulation profonde du TCC au cours du CrĂ©tacĂ© supĂ©rieur, grĂące une approche fondĂ©e sur les isotopes du nĂ©odyme (Nd). LâĂ©volution de lâÉNd des eaux de fond locales de trois sites (hĂ©mi)pĂ©lagiques situĂ©s sur le trajet potentiel de ce courant a Ă©tĂ© analysĂ© Ă partir de la fraction carbonatĂ©e des sĂ©diments : la coupe de Shahneshin Ă lâentrĂ©e du corridor tĂ©thysien (bassin du Zagros, Iran), la coupe de Gubbio â la Bottaccione dans la TĂ©thys centrale (bassin des Marches â Ombrie, Italie) et le forage DSDP Site 146 dans le passage des CaraĂŻbes (bassin du Venezuela, mer des CaraĂŻbes). LâÉNd de la fraction rĂ©siduelle des sĂ©diments a Ă©galement Ă©tĂ© dĂ©terminĂ©e, afin de discuter lâimpact potentiel des Ă©changes locaux eau-sĂ©diments. LâĂ©volution de lâÉNd des eaux de fond locales, couplĂ©e Ă la minĂ©ralogie des argiles et Ă celle de lâÉNd des rĂ©sidus a rĂ©vĂ©lĂ© que les signatures minĂ©ralogiques et gĂ©ochimiques des sites de Shahneshin et 146 semblent ĂȘtre affectĂ©es de façon significative par des processus locaux (tectonique, volcanisme). Une augmentation de lâĂ©cart entre lâÉNd de lâeau de fond locale et des rĂ©sidus est cependant compatible avec des apports accrus dâeaux du Pacifique dans lâest de la TĂ©thys au cours du Campanien. Le site de Gubbio semble quant Ă lui recevoir des apports dâeaux atlantiques en profondeur, suggĂ©rant que si le TCC est prĂ©sent dans cette rĂ©gion, il nâatteint pas la base de la colonne dâeau au niveau de ce site.The origin of the Late Cretaceous (~100 â 65 Ma) global cooling is not yet well understood. The evolution of sea surface and bottom temperatures shows an acceleration of the cooling during the Campanian stage (~84 Ma). The main goal of this study was to explore the processes driving this cooling, focusing on Campanian sediments from the Tethyan, Boreal and Atlantic realms.The clay mineralogical assemblages of several (hemi)pelagic sites, selected along a S-N transect, from 5° to 45°N, reveal an increase in continental weathering during the Campanian, expressed by enhanced kaolinite inputs. The detrital input related to the uplift of new continental areas seems to evolve from south to north. This propagation is likely linked to the anticlockwise rotation of the African plate and the progressive closure to the Tethys Ocean. Enhanced continental weathering seems also linked to more hydrolysing conditions in the studied regions, resulting in bauxite development.The Campanian stage was characterised by major palaeogeographic changes, such as the widening of south and north Atlantic oceans and the closure of the Tethyan realm. The motion of continental plates is likely responsible for a major reorganization of the oceanic currents. During the Late Cretaceous, the so called âTethyan Circumglobal Currentâ (TCC) current flows latitudinally through the Tethyan Ocean to the Caribbean gateway, from east to west, and seems to intensify during the Campanian stage. Thus, we tried to reconstruct the evolution of the deep oceanic circulation within the TCC pathway during the Late Cretaceous, based on a geochemical approach using the neodymium (Nd) isotopes. The evolution of ÉNd of local bottom water of three (hemi)pelagic sites located on the possible pathway of this current has been analysed on the carbonate fraction of the sediments : the Shahneshin section located at the main entrance of the Tethyan passage (Zagros basin, Iran), the Gubbio â la Bottaccione section located at the centre of the Tethys (Umbria â Marche basin, Italy) ocean and the DSDP site 146 located in the Caribbean gateway (Venezuela basin, Caribbean sea). The ÉNd of the insoluble fraction of the sediments was analysed, in order to discuss of the role of local exchanges between water and sediments. The evolution of the deep water ÉNd along with that of residue ÉNd and clay mineralogical assemblages shows that geochemical and mineralogical signatures of Shahneshin and 146 sites are largely controlled by local processes (tectonic and volcanism), although an increased input of radiogenic Pacific waters may be detected at Shahneshin during the Campanian. The Gubbio site seems to be influenced by atlantic waters entering western Tethys, suggesting that the TCC did not reach the base of the water column at this site
Changements climatiques et ocĂ©anographiques au cours du Campanien â approche couplĂ©e minĂ©ralogie et gĂ©ochimie
The origin of the Late Cretaceous (~100 â 65 Ma) global cooling is not yet well understood. The evolution of sea surface and bottom temperatures shows an acceleration of the cooling during the Campanian stage (~84 Ma). The main goal of this study was to explore the processes driving this cooling, focusing on Campanian sediments from the Tethyan, Boreal and Atlantic realms.The clay mineralogical assemblages of several (hemi)pelagic sites, selected along a S-N transect, from 5° to 45°N, reveal an increase in continental weathering during the Campanian, expressed by enhanced kaolinite inputs. The detrital input related to the uplift of new continental areas seems to evolve from south to north. This propagation is likely linked to the anticlockwise rotation of the African plate and the progressive closure to the Tethys Ocean. Enhanced continental weathering seems also linked to more hydrolysing conditions in the studied regions, resulting in bauxite development.The Campanian stage was characterised by major palaeogeographic changes, such as the widening of south and north Atlantic oceans and the closure of the Tethyan realm. The motion of continental plates is likely responsible for a major reorganization of the oceanic currents. During the Late Cretaceous, the so called âTethyan Circumglobal Currentâ (TCC) current flows latitudinally through the Tethyan Ocean to the Caribbean gateway, from east to west, and seems to intensify during the Campanian stage. Thus, we tried to reconstruct the evolution of the deep oceanic circulation within the TCC pathway during the Late Cretaceous, based on a geochemical approach using the neodymium (Nd) isotopes. The evolution of ÉNd of local bottom water of three (hemi)pelagic sites located on the possible pathway of this current has been analysed on the carbonate fraction of the sediments : the Shahneshin section located at the main entrance of the Tethyan passage (Zagros basin, Iran), the Gubbio â la Bottaccione section located at the centre of the Tethys (Umbria â Marche basin, Italy) ocean and the DSDP site 146 located in the Caribbean gateway (Venezuela basin, Caribbean sea). The ÉNd of the insoluble fraction of the sediments was analysed, in order to discuss of the role of local exchanges between water and sediments. The evolution of the deep water ÉNd along with that of residue ÉNd and clay mineralogical assemblages shows that geochemical and mineralogical signatures of Shahneshin and 146 sites are largely controlled by local processes (tectonic and volcanism), although an increased input of radiogenic Pacific waters may be detected at Shahneshin during the Campanian. The Gubbio site seems to be influenced by atlantic waters entering western Tethys, suggesting that the TCC did not reach the base of the water column at this site.Les causes du refroidissement climatique global qui caractĂ©risent le CrĂ©tacĂ© supĂ©rieur (~100 â 65 Ma) ne sont pas encore bien Ă©tablies. LâĂ©volution de la courbe des tempĂ©ratures des eaux de fond et de surface des ocĂ©ans montre une accĂ©lĂ©ration de ce refroidissement au cours du Campanien (~84 Ma), aussi lâobjectif de ce travail Ă©tait-il dâexplorer les causes possibles de ce refroidissement en se focalisant sur lâĂ©tude des sĂ©diments dâĂąge Campanien de divers bassins sĂ©dimentaires tĂ©thysiens, borĂ©aux et atlantiques.Le premier objectif fut de dĂ©terminer lâextension spatiale des changements de cortĂšges argileux dans la TĂ©thys et le domaine borĂ©al. La minĂ©ralogie des argiles de plusieurs sites (hĂ©mi)pĂ©lagiques, sĂ©lectionnĂ©s selon un transect N-S de 5 Ă 45° N, a rĂ©vĂ©lĂ© une intensification de lâaltĂ©ration continentale au Campanien, marquĂ©e notamment par des apports accrus de kaolinite. Au cours du temps, ces apports liĂ©s au soulĂšvement de nouveaux domaines continentaux semblent se propager du Sud au Nord. Cette propagation est trĂšs certainement gouvernĂ©e par le mouvement antihoraire de la plaque africaine et de son rapprochement progressif de la plaque europĂ©enne. Lâintensification de lâaltĂ©ration continentale semble aussi sâaccompagner de la mise en place dâune ceinture climatique plus humide Ă lâorigine du dĂ©veloppement des bauxites.Le Campanien est Ă©galement marquĂ© par dâimportantes modifications palĂ©ogĂ©ographiques, telles que lâĂ©largissement de lâAtlantique Sud et Nord ainsi que la restriction du domaine tĂ©thysien. Le dĂ©placement des masses continentales est probablement Ă lâorigine dâune rĂ©organisation majeure des courants ocĂ©aniques. Dans le domaine tĂ©thysien, au CrĂ©tacĂ© supĂ©rieur la courantologie est dominĂ©e par le « Tethyan Circumglobal Current » (TCC), courant latitudinal traversant lâocĂ©an tĂ©thysien et le passage des CaraĂŻbes, dâest en ouest, qui semblerait sâintensifier au Campanien. Nous avons donc tentĂ© de reconstituer lâĂ©volution de la circulation profonde du TCC au cours du CrĂ©tacĂ© supĂ©rieur, grĂące une approche fondĂ©e sur les isotopes du nĂ©odyme (Nd). LâĂ©volution de lâÉNd des eaux de fond locales de trois sites (hĂ©mi)pĂ©lagiques situĂ©s sur le trajet potentiel de ce courant a Ă©tĂ© analysĂ© Ă partir de la fraction carbonatĂ©e des sĂ©diments : la coupe de Shahneshin Ă lâentrĂ©e du corridor tĂ©thysien (bassin du Zagros, Iran), la coupe de Gubbio â la Bottaccione dans la TĂ©thys centrale (bassin des Marches â Ombrie, Italie) et le forage DSDP Site 146 dans le passage des CaraĂŻbes (bassin du Venezuela, mer des CaraĂŻbes). LâÉNd de la fraction rĂ©siduelle des sĂ©diments a Ă©galement Ă©tĂ© dĂ©terminĂ©e, afin de discuter lâimpact potentiel des Ă©changes locaux eau-sĂ©diments. LâĂ©volution de lâÉNd des eaux de fond locales, couplĂ©e Ă la minĂ©ralogie des argiles et Ă celle de lâÉNd des rĂ©sidus a rĂ©vĂ©lĂ© que les signatures minĂ©ralogiques et gĂ©ochimiques des sites de Shahneshin et 146 semblent ĂȘtre affectĂ©es de façon significative par des processus locaux (tectonique, volcanisme). Une augmentation de lâĂ©cart entre lâÉNd de lâeau de fond locale et des rĂ©sidus est cependant compatible avec des apports accrus dâeaux du Pacifique dans lâest de la TĂ©thys au cours du Campanien. Le site de Gubbio semble quant Ă lui recevoir des apports dâeaux atlantiques en profondeur, suggĂ©rant que si le TCC est prĂ©sent dans cette rĂ©gion, il nâatteint pas la base de la colonne dâeau au niveau de ce site
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