Spatial discordance in fish,coral, and sponge assemblages across a Caribbean atoll reef gradient          下载免费PDF全文

Charles Acosta  Robin Barnes  Rebecca McClatchey 《Marine Ecology》2015,36(2):167-177

Certain biodiversity patterns on coral reefs are generally consistent but we still lack fundamental insight into how assemblages vary across spatially heterogeneous reef systems. We compared fish, coral, and sponge assemblages across a symmetrical physiographical gradient (windward forereef, lagoon patch reef, leeward forereef) of the Glover's Reef atoll, Belize. Species richness of fishes and corals was highest in the deep habitat (15 m) on the windward forereef. Sponges were diverse and abundant on both deep windward and leeward forereefs but not on the exposed shallow (5 m) windward forereef. Fish and benthic assemblages were relatively distinct in each reef zone, with the lagoon patch reef communities consisting of a combination of leeward and windward species. Nevertheless, there were no clear patterns in community similarity matrices of fish and benthic assemblages, suggesting that overall coral and sponge assemblages had weak or no direct association with patterns in fish assemblages. A closer examination of fish trophic groups indicated that planktivores and predators were predictably associated with depth, whereas herbivores were associated with shallow protected reefs. None was specifically associated with spatial location along the atoll gradient. These patterns of diversity distribution are important for identifying spatial conservation priorities. A Marine Protected Area (MPA) at Glover's Reef encompasses substantial windward forereef and patch reef habitats. A much lesser extent of protection is afforded the leeward forereef that supports faunal assemblages that are unique and productive, if not as diverse as the windward forereef. Isolated coral atolls can serve as ideal systems to study spatial heterogeneity and biodiversity patterns, but more experimental studies are needed to reveal the mechanistic processes underlying these patterns.  相似文献   

Preface to the Special Issue on Summer 2020: Record Rainfall in Asia — Mechanisms,Predictability and Impacts     

Robin T.CLARK  Xiquan DONG  Chang-Hoi HO  Jianhua SUN  Huiling YUAN  Tetsuya TAKEMI 《大气科学进展》2021,38(12):1977-1979

Throughout vast areas of Asia, the summer of 2020 was extraordinarily wet. After an exceptionally wet May in North-east India and Bangladesh, excessive rainfall hit at least 10 provinces in central and southern China in June and July, caus-ing extensive flooding in many rural and urban locations. Long standing rainfall, lake and river level records were con-sequently broken in several parts of the region with the Yangtze-Huaihe river valleys, particularly badly impacted, with con-sequential economic losses. Floods and landslides also affected parts of Japan with at least one location in Kumamoto province even experiencing a record-breaking 1000 mm of rainfall in just 3 days in early July. The 2020 wet season in South Korea was also exceptionally long, lasting 54 days, compared to their more usual 32.  相似文献   

Seismic‐stratigraphic record of a deglaciation sequence: from the marine Laflamme Gulf to Lake Saint‐Jean (late Quaternary,Québec,Canada)     

Alexis Nutz  Jean‐François Ghienne  Mathieu Schuster  Raphaël Certain  Nicolas Robin  Claude Roquin  Olivier Raynal  Frédéric Bouchette  Philippe Duringer  Pierre A. Cousineau 《Boreas: An International Journal of Quaternary Research》2014,43(2):309-329

The stratigraphy of the last deglaciation sequence is investigated in Lake Saint‐Jean (Québec Province, Canada) based on 300 km of echo‐sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice‐front recession to the present‐day situation. Ten seismic units have been identified that reflect spatio‐temporal variations in depositional processes characterizing different periods of the Saint‐Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio‐isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river‐related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind‐driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf‐type body. The fingerprints of a forced regression are well expressed by mouth‐bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth‐bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf‐type body, respectively. The Lake Saint‐Jean record is an example of a regressive succession driven by a glacio‐isostatic rebound and showing the transition from late‐glacial to post‐glacial depositional systems.  相似文献   

Lower and Middle Pleistocene human settlements recorded in fluvial deposits of the middle Loire River Basin,Centre Region,France     

Jackie Despriée  Pierre Voinchet  Hélène Tissoux  Jean-Jacques Bahain  Christophe Falguères  Gilles Courcimault  Jean Dépont  Marie-Hélène Moncel  Sophie Robin  Marta Arzarello  Robert Sala  Laurent Marquer  Erwan Messager  Simon Puaud  Salah Abdessadok 《Quaternary Science Reviews》2011,30(11-12):1474-1485

This paper records the findings from c. 80 prehistoric sites that have been discovered in the alluvial deposits of the rivers Creuse, Cher, and Loir, tributaries of the middle Loire River, over the period since 1981. These deposits comprise river terrace aggradations formed during successive glacial–interglacial cycles which have recorded climate and environment during Quaternary time. The systematic dating of these river deposits by Electron Spin Resonance (ESR) applied to optically bleached sedimentary quartz has resulted in the establishment of a chronological framework for the evolution of these rivers during Lower and Middle Pleistocene (between 1.7 Ma and 130 ka). Evidence for Early Palaeolithic (Mode 1) industries with an in situ context (workshops, soils) in the highest aggradations indicates that Hominins were present in the study area, near the geographical centre of France (47°N), around 1.1 Ma. Examination of the sites indicates that Human occupations were located along valley bottom sites during temperate episodes. Subsequently, after a gap of several hundred thousand years industries with handaxes appear in the Middle Loire Basin in the interval between 700 and 600 ka, and then continuously from 400 ka. These two phases of settlement produced industrial assemblages with clear differences in their responses to the supplies of raw materials and in the modes of making flakes.  相似文献   

Plio-Pleistocene sequence stratigraphic architecture of the eastern Niger Delta: A record of eustasy and aridification of Africa     

P. Jermannaud  D. Rouby  C. Robin  T. Nalpas  F. Guillocheau  S. Raillard 《Marine and Petroleum Geology》2010,27(4):810-821

This study synthesizes the stratigraphic behavior of the whole eastern Niger Delta during the Plio-Pleistocene and discusses controls on deposition by eustasy, subsidence and sediment supply at various scales. The sequence stratigraphic architecture is determined by integrating the whole sedimentary system from the coastal plain down to the abyssal plain. We combined structural geology, sedimentology biostratigraphy, and seismic stratigraphy. Data included 2D regional sections connected by 3D seismic surveys and 45 well-logs for lithologic calibration and well-cuttings for biostratigraphic calibration.We identified three sequence orders in the stratigraphic architecture of the eastern Niger Delta and calibrated their biostratigraphic ages into absolute ages using two end-member models to estimate uncertainties. We discuss their causes and propose that the major influence was climate-driven eustasy for both the (i) short-duration (around 0.1–0.4 Myr in duration) and (ii) long-duration progradation/retrogradation sequences (around x1 Myr in duration). Two different modes of climatic control are suggested for the (iii) long-term stratigraphic trend over the Plio-Pleistocene: global climate-driven eustatic variations for the initial progradation until 2.5 Myr ago and a regional climate change (e.g. the warming of the East Atlantic and the aridification of western Africa) for the following aggradation/retrogradation period, controlled by a decrease in the sedimentary supply to the eastern delta counteracting the ongoing eustatic fall.  相似文献   

Research on the precambrian in the United States     

Robin Brett 《Precambrian Research》1982,19(2):P1-P2

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The role of fluids in the metamorphism of komatiites,Agnew nickel deposit,western Australia     

Martin J. Gole  Stephen J. Barnes  Robin E. T. Hill 《Contributions to Mineralogy and Petrology》1987,96(2):151-162

The Agnew nickel sulfide deposit is spatially associated with a lenticular body of ultramafic rocks which shows a concentric zonation in metamorphic mineralogy. Olivine + tremolite + chlorite + cummingtonite ±enstatite assemblages occur at the margin of the ultramafic lens, giving way to olivine + anthophyllite, olivine + talc and olivine + antigorite assemblages successively inwards. These rocks are interpreted as having crystallized from komatiitic lavas, and exhibit a spectrum of compositions from those of original flow tops to pure olivine adcumulates. The relative modal abundances of metamorphic olivine, tremolite and chlorite reflect original proportions of cumulus olivine and komatiite liquid in the protolith. Peak metamorphic conditions are estimated at 550° C, based on garnet-biotite thermometry, at a maximum pressure of 3 kb. This temperature falls within the narrow range over which metamorphic olivine may co-exist with enstatite, anthophyllite, talc or antigorite depending upon the fugacity of water in the metamorphic fluid. The observed mineralogical zonation is therefore attributed to infiltration by CO₂-rich fluids, generated by decarbonation of talc-carbonate rocks formed during pre-metamorphic marginal alteration of the ultramafic lens. Metamorphic fluids were essentially binary mixtures of water and CO₂, with minor H₂S having a maximum partial pressure less than 1 percent of total pressure. Enstatite-bearing assemblages formed in the presence of CO₂-rich fluids at fluid: rock volume ratios close to one, while anthophyllite, talc and antigorite bearing assemblages formed in the presence of progressively more water-rich fluids at progressively lower fluid-rock ratios.  相似文献   

Hunt the salmon up the Thames     

Robin Moody 《Marine pollution bulletin》1973,4(5):69

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Repetitive mixing events and holocene pyroclastic activity at Pico de Orizaba and Popocatepetl (Mexico)     

J. M. Cantagrel  A. Gourgaud  C. Robin 《Bulletin of Volcanology》1984,47(4):735-748

The Holocene volcanic activity which built up the present terminal cones of Pico de Orizaba and Popocatepetl in eastern Mexico, was characterized by repeated pyroclastic Saint-Vincent type eruptions. Radiocarbon data show that these paroxysmal events occurred at more or less regular intervals, and were followed by moderate activity producing ash and pumice falls and andesitic lava flows from the summit craters.Typical ash and scoria pyroclastic flows exhibit a heterogeneous composition given by the interaction of a dacitic component with a more basic andesitic one. Scoria bombs are characterized by banded to emulsified textures, mineralogical desequilibrium assemblages and linear chemical variations on element-element plots as exemplified by the Loma Grande flow at Pico.Periodic replenishments of the magmatic reservoir could be the major phenomenon that started mixing and consequently triggered the pyroclastic eruptions.  相似文献   

Hydrodynamic dispersion during absorption of water by soil: 2. Immobile water model     

M.J.L. Robin  K.B. Laryea  D.E. Elrick 《Journal of Hydrology》1983,65(4):333-348

The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m³ m^?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient.  相似文献