Mediterranean biodiversity gradient initiated by basin restriction

Physical connectivity between marine basins facilitates population exchange and hence controls biodiversity. The Mediterranean Sea is a semi-restricted basin with only a small two-way connection to the global ocean, and it is a region heavily impacted by climate change and biological invasions today. The massive migration of non-indigenous species into the basin through the Suez Canal, driven and enabled by climate warming, is drastically changing Mediterranean biodiversity. Understanding therefore the origin and cause(s) of pre-existing biodiversity patterns is crucial for predicting future impacts of climate change. Mediterranean biodiversity exhibits a west-to-east decreasing gradient in terms of species richness, but the processes that resulted in this gradient have only been hypothesized. By examining the fossil record, we provide evidence that this gradient developed 5.33 million years ago at the end of the Messinian Salinity Crisis, and it was therefore caused by the re-population of the basin by marine species with a dominating western source at the Mediterranean¿Atlantic gateway

Photoinduced energy- and electron-transfer from a photoactive coordination cage to bound guests.

In a coordination cage which contains an array of twelve naphthyl chromophores surrounding a central cavity, photoinduced energy or electron-transfer can occur from the chromophore array to the bound guest in supramolecular host/guest complexes

Pliocene and pleistocene shallow-water chitons (Mollusca) from rhodes Island, Greece

The polyplacophoran faunas from the Pliocene and Pleistocene deposits of Rhodes Island (Aegean Sea, Greece) are described for the first time. Thirteen species are reported from five sections in three localities (Kritika, Faliraki and Ladiko) and their biostratigraphical position, faunal relationships and habitat specificity are investigated. The studied fauna developed in fully marine conditions and well-oxygenated waters from the shore to the detritic bottoms of the shelf edge. All these species are still living in the Mediterranean Sea and most of them also occur in the Atlantic Ocean. The following species have been identified: Lepidopleurus cajetanus, Leptochiton cimicoides, Ischnochiton rissoi, Callochiton septemvalvis, Rhyssoplax corallina, R. olivacea, Lepidochitona cf. canadensis, L. caprearum, L. cinerea, L. furtiva, L. monterosatoi, Acanthochitona crinita, and A. fascicularis. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung

Fossil assemblages associated with submerged beachrock beds as indicators of environmental changes in terrigenous sediments: Examples from the Gelasian (Early Pleistocene) of Rhodes, Greece

The lower Pleistocene Kritika Member of the Rhodes Formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds. A wide variety of sclerobionts occur in this environment, very different from the poorest soft-bottom populations occurring in other levels of the Kritika Member. The most characteristic, abundant and frequently diverse are the encrusting forms: coralline algae, bivalves, serpulid worms, and bryozoans. Numerous other groups of sessile and vagile organisms are associated with these crust-forming communities. A number of skeletal organisms (sometimes including zooxanthellate coral colonies) formed small carbonate buildups on top of several beachrock beds. Boring organisms also occur. Evidence for a two-step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data. The rapidly cemented sandy-conglomeratic beds were first colonised by a relatively shallow-water (around 20. m) biocoenosis of mostly encrusting organisms. Another association, with encrusting and erect organisms, was later established in a deeper environment (20-40. m). A comparison with Holocene beachrock occurring on the coast of Rhodes was also undertaken. Their submerged part provided habitat for poorer but similar biotas to those occurring in the Kritika Member. The lower Pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the Kritika Member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits. Notably, they can be used as indicators of relative sea-level changes. © 2012 Elsevier B.V

Coastal fish otoliths from the early Pleistocene of Rhodes (eastern Mediterranean)

Coastal fish assemblages are especially vulnerable to environmental changes, but little is known about their evolution through time, mainly due to the scarcity of fossil material from such settings. The aim of this study is to characterize the early Pleistocene coastal fish assemblages of the eastern Mediterranean and to reconstruct the related paleobathymetric and paleoecologic conditions. Based on otolith findings, we identified thirty-seven teleost fish species from three sedimentary outcrops on the northeastern part of Rhodes Island (southeastern Aegean, Greece, Eastern Mediterranean), which have been placed within the Gelasian (early Pleistocene). The stratigraphic distribution of fifteen taxa is expanded for this interval, while five species are reported for the first time as fossils. The otolith assemblages provided paleodepth estimates indicative of shallow coastal environments. The ecosystem consisted mostly of substrates of sand and mud, with significant rocky micro-habitats and underwater vegetation; the climate was subtropical. These data complement existing knowledge on the study area, while providing new information on the composition of the ichthyofauna of the eastern Mediterranean during the Gelasian. © 2019 Elsevier Masson SA

Facies associations in warm-temperate siliciclastic deposits: Insights from early Pleistocene eastern Mediterranean (Rhodes, Greece)

Diverse, abundant and usually well-preserved communities of skeletal organisms occur in the lower Pleistocene (Gelasian) siliciclastic deposits of the Greek island of Rhodes. Benthic foraminifers, molluscs and bryozoans have been studied in four measured and sampled sections located in the northern part of the island. Among these bottom-dwelling organisms, numerous extant taxa are good environmental indicators and, combined with field observations and sedimentological data, they provide information on the probable conditions in which they developed. The siliciclastic deposits of the Kritika Formation have been divided into 14 different bio- and lithofacies, which have been further grouped into four facies associations corresponding to four different environmental settings: (1) continental to fluviatile; (2) brackish-water (lagoonal/deltaic); (3) infralittoral (0-20 m); and (4) upper circalittoral (depths of 20-40 m, but also down to c. 50-60 m). Among the marine facies associations, several characteristic biocoenoses have been recognized: soft-bottoms (fine to coarse sands and gravels); seagrass meadows; biogenic calcareous crusts on drowned beachrock slabs; red algal rhodoliths; and bivalve shell beds. In the studied sections, 13 superimposed genetic sequences have been documented. The repetition of similar facies associations within each sequence suggests: (1) a possibly eustasy-controlled, cyclic sedimentation; (2) a general subsidence of Rhodes during the deposition of the studied facies associations; and (3) a mostly constant range of environmental conditions (i.e. sedimentation rates and temperature) throughout the Gelasian. Copyright © Cambridge University Press 2015

Modelling of Boiling Heat Transfer in a Turbulent Channel Flow

International audienceA numerical study of boiling heat transfer in a turbulent liquid-vapor flow inside a heated channel is carried out for various flow conditions. The model used for the flow simulation is the Volume Of Fluid model (VOF) for liquid-vapor interface tracking coupled with a k−ε low Reynolds model to predict the effect of turbulence. Boiling and condensation phenomena are included in the model based on the general laws of phase change. The obtained results are compared with available experimental measurements in the literature, where the effect of subcooling, channel inclination and flow velocity on the vapor distribution were investigated. The computational predictions of the vapor bubble development along the heated wall are in satisfactory agreement with experimental results

Mosaic of environments recorded by bryozoan faunas from the Middle Miocene of Hungary

The marine sediments of the Badenian (Middle Miocene) of Hungary (Pannonian Basin, Central Paratethys) are composed of abundant bryozoan skeletal grains. Seventy-one bulk samples collected at 18 localities (outcrops and boreholes) yielded a total number of 238 bryozoan species. In order to reconstruct the Badenian palaeoenvironments, the present study investigates the composition of this very diverse fauna using a combination of statistical and palaeoecological methods. The statistical analyses make use of Cluster Analysis and Non-metric Multi-Dimensional Scaling. The palaeoecological approaches are based on the known ecological requirements of the bryozoan colonial growth forms and of the numerous extant species. Five facies have first been differentiated on the basis of sedimentological and palaeontological features: coral buildups, coralline algal limestones, biocalcarenites, sands, and marls. Each of them is characterized by the abundance, the diversity and the types of growth forms of the bryozoans. The palaeoecological, statistical and facies analyses further permitted to identify four depositional settings: carbonate platform (distal and proximal), terrigenous platform, slope, and basin. These environments developed at depths between 0 to about 300 m in a mixed carbonate–siliciclastic depositional system. Skeletal production and spatial distribution of carbonate factories were predominantly controlled by terrigenous input. This resulted in a complex mosaic of facies/habitats where rich bryozoan faunas could thrive. Many warm-water organisms, among them foraminifers, zooxanthellate corals, molluscs, bryozoans, and echinoids, were recorded from the study sites. The coexistence of coralgal and bryomol carbonate skeletal assemblages in this subtropical setting is explained mostly by variations in the productivity of surface waters. Periods of nutrient enrichment and increased benthiceutrophication affected coral diversity and abundance in favour of bryozoans

Spectacular preservation of seagrasses and seagrass-associated communities from the Pliocene of Rhodes, Greece

An exceptionally well-preserved fossil seagrass community occurs in the late Pliocene of the Greek Island of Rhodes. The siliciclastic deposits of the Kritika section (Kritika Member, Rhodes Formation) contain several beds of clay and fine-grained sand with abundant remains of the leaves of Posidonia oceanica. A coarser sand bed with in situ rhizomes of the same endemic Mediterranean phanerogam also was found. Samples yield a diverse skeletal assemblage of 121 species of crustose coralline algae, foraminifers, annelids, gastropods, bivalves, encrusting bryozoans, and ostracodes, some of which also live exclusively on the leaves of present-day P. oceanica. The community of organisms associated with the rhizomes is slightly poorer (57 species), with bivalves appearing as distinctively abundant components of this assemblage (21 species). An analysis of the relationships between skeletal organisms and fossil leaves and rhizomes shows that the majority of them lived together in the same seagrass-vegetated environment, were transported a short distance from their natural habitat, and buried very rapidly in fine-grained sediments, thus preserving this remarkable assemblage almost intact. The rhizomes were preserved in growth position within a coarse-grained sand trapped by their horizontal and vertical network. The fossil assemblage compares well in terms of major skeletal components with modern shallow-water P. oceanica meadows. This study also provides evidence for the presence during the Pliocene of an already well-established and widespread seagrass community with biotopes comparable to those of the present-day Mediterranean. Copyright © 2007, SEPM (Society for Sedimentary Geology)