Ontogenetic Habitat Shifts of the Atlantic Tomcod (<Emphasis Type="Italic">Microgadus tomcod</Emphasis>) Across an Estuarine Transition Zone     

Marc Antoine Couillard  Gilbert Cabana  Jean François Dery  Gaétan Daigle  Julian John Dodson 《Estuaries and Coasts》2011,34(6):1234-1245

Tomcod (Microgadus tomcod) in the St. Lawrence estuarine transition zone (ETZ) undergo an ontogenetic habitat shift. Older age classes, characterised by a male-dominated sex ratio, disperse downstream over the summer months to occupy the colder more saline waters of the estuary. Significant differences in length and mass along the salinity gradient were observed in September with upstream fish of any given age class generally exhibiting greater growth. These differences were not seen in early summer. Benthic amphipod δ ³⁴S signatures were strongly correlated with salinity and served to demonstrate that tomcod δ ³⁴S signatures were not in isotopic equilibrium in the more saline waters of the ETZ. Seasonal distributional patterns, growth dynamics and isotopic disequilibrium all indicate that the observed habitat shift may occur on an annual basis, following winter aggregation in warmer, less saline waters. Tomcod located in the downstream parts of the ETZ, predominantly males, were significantly more sexually developed than upstream tomcod for a given age. On the other hand, greater growth early in life is insured by occupying warmer, upstream waters during the summer months.  相似文献   

A brief review of Agenian rhinocerotids in Western Europe     

Pierre-Olivier Antoine  Damien Becker 《Swiss Journal of Geoscience》2013,106(2):135-146

The Agenian is the earliest Neogene European Land Mammal Age. It encompasses the mammalian zones MN1 (23.03–22.7 Ma) and MN2 (22.7–20.0 Ma) and roughly coincides with the Aquitanian standard age. Agenian mammalian assemblages from Western Europe encompass a mixture of rhinocerotid taxa of Oligocene affinities and of Miocene newcomers, mostly recorded in France, Germany, Switzerland, and to a lesser extent, Spain. Rhinocerotidae are documented by seven species referred to five genera (Pleuroceros pleuroceros, Protaceratherium minutum, Plesiaceratherium aquitanicum, Mesaceratherium paulhiacense, Diaceratherium lemanense, D. asphaltense, and D. aginense), further attesting to a low suprageneric diversity. Their systematics, morphology, ecology, stratigraphical and geographical ranges are detailed in the present article. Occurrences and geographical ranges of all seven rhinocerotid species are illustrated on palaeogeographical maps of the circum-Mediterranean region at 23 Ma (MN1) and 21 Ma (MN2). The richest Agenian localities (Paulhiac, MN1; Laugnac, MN2) record a specific diversity similar to that of Orleanian rhinocerotid assemblages, with up to five/six associated species. All Agenian rhinocerotid species from Western Europe are endemic to the concerned region, which is consistent with the complete geographic isolation of Western Europe by earliest Miocene times. However, all five genera are documented by twin species in coeval localities of South and Central Asia, which implies (1) vicariant speciation events by latest Oligocene times and (2) the existence of intermittent pathways for terrestrial megamammals such as rhinocerotids during the concerned interval.  相似文献   

Analysis and interpretation of the October 21, 1766 earthquake in the Southeastern Caribbean     

Antoine Mocquet 《Journal of Seismology》2007,11(4):381-403

The October 21, 1766 earthquake is the most widely felt event in the seismic history of Trinidad and Venezuela. Previous works diverged on the interpretation of the historical data available for this event. They associated the earthquake either with the Lesser Antilles subduction zone, with strike-slip motion along El Pilar fault, or with intraplate deformation at the edge of Guyana shield. Isoseismal areas are proposed after a new search and analysis of primary and secondary sources of historical information. Two of the largest earthquakes of the twentieth century which occurred in the region, the 1968 (M _S 6.4, h = 103 km), and the 1997 (M _W 6.9, h = 25 km) events, for which both intensity data and instrumentally determined source parameters are available, are used to calibrate the isoseismal areas and to interpret them in terms of source depth and magnitude. It is concluded that the large extent of intensity values higher than V is diagnostic of the depth (85 ± 20 km) of the 1766 source, and of local amplifications of ground motion due to soft soil conditions and to strong contrasts of impedance at the edge of Guyana shield. It is proposed that the event occurred either in slab, or close to the bottom lithospheric interface between the Caribbean and South American plates (∼11°N; ∼62.5°W). The value of the magnitude is estimated at 6.5 < M _S < 7.5 depending on the source depth and on the decay of ground motion as a function of distance. Deep and intermediate depth earthquakes can induce important casualties in Trinidad, Venezuela, and Guyana, possibly more damaging than those induced by shallower earthquakes along the strike of El Pilar Fault.  相似文献   

Assessment of the ecological quality status of soft-bottoms in Reunion Island (tropical Southwest Indian Ocean) using AZTI marine biotic indices   总被引：2，自引：1，他引：1  

Bigot L  Grémare A  Amouroux JM  Frouin P  Maire O  Gaertner JC 《Marine pollution bulletin》2008,56(4):704-722

The ability of the two synthetic marine biotic indices, AMBI and M-AMBI, to account for changes in the ecological quality of coastal soft bottoms of Reunion Island according to disturbances was assessed from macrobenthic samples collected in five sectors between 1994 and 2004. Samples were collected under non-perturbed conditions and at two sites subjected to heavy organic enrichment. Both indices are based on a classification of macrofauna into ecological groups (EG), and their transfer to tropical waters required some adaptations. These indices proved efficient in detecting a degradation of habitat quality. Their use resulted in the classification of all sites sampled between 1996 and 1998 as "good" or "high". M-AMBI nevertheless tended to result in the attribution of a slightly worse ecological quality status than AMBI. Together with an update of the EG species list for the Indian Ocean area, our results support the extension of both indices for the assessment of tropical soft bottoms.  相似文献   

Times of sand: Sedimentary history and archaeology at the Sigatoka Dunes,Fiji     

Atholl Anderson  Richard Roberts  William Dickinson  Geoffrey Clark  David Burley  Antoine de Biran  Geoffrey Hope  Patrick Nunn 《Geoarchaeology》2006,21(2):131-154

The orthodox archaeological sequence at the Sigatoka Dunes site (VL 16/1) in Fiji proposes three phases of occupation spanning Fijian prehistory, each associated with a period of dune stability. It has been taken as the standard model of Fijian prehistory for more than 30 years. Recently, however, it has been argued that there is no stratigraphic support for three discrete levels and that the occupation history was fragmented, complex, and continuous within a volatile dune system. We present new data, from optical and radiocarbon dating, to argue that a three‐phase model, although somewhat more complex in detail, remains the most robust interpretation of site history. The longest stable phase (Level 2) began 2500–2300 cal yr B.P. and is possibly associated with relatively low ENSO frequency. Substantial sand dune accumulation began after ˜1300 cal yr B.P. © 2006 Wiley Periodicals, Inc.  相似文献   

A luminescence‐based chronology for the Harletz loess sequence,Bulgaria     

Johanna Lomax  Markus Fuchs  Pierre Antoine  Denis‐Didier Rousseau  France Lagroix  Christine Hatt  Samuel N. Taylor  Jessica L. Till  Maxime Debret  Olivier Moine  Diana Jordanova 《Boreas: An International Journal of Quaternary Research》2019,48(1):179-194

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.  相似文献   

Calculation of dynamic motions and tensions in towed underwatercables     

Hover  F.S. Grosenbaugh  M.A. Triantafyllou  M.S. 《Oceanic Engineering, IEEE Journal of》1994,19(3):449-457

A matrix method for mooring system analysis is extended to address the dynamic response of towed underwater systems. Key tools are equivalent linearization and small perturbation theory, and a pitching towfish model. Two examples of application of the technique are provided. The first studies a fundamental limitation to constrained passive heave compensation, while the second concerns the use of floated tethers as a means for dynamic decoupling  相似文献   

Mean flux estimation and cospectra of airborne carbon dioxide and water vapour eddy flux measurements in the planetary surface layer     

Antoine Saucier  Mike R. Duncan  G. L. Austin 《Boundary-Layer Meteorology》1991,55(3):227-254

CO₂ and H₂O eddy-flux measurements derived from airborne vertical wind and concentration data are examined to determine the accuracy of the eddy-flux estimate in moderately unstable conditions within the surface layer. Integral scale estimation is used to determine the minimum length of a sample required to achieve a given accuracy. Cospectral analysis is used to examine the scales responsible for the transport of water vapour and carbon dioxide in the surface layer. Cospectra are found to broaden as the sampling altitude increases, a well known result. At low altitudes, the cospectrum is found to become negative for large scales. A significant fraction of the flux is carried by this range of scales, which suggests that scales larger than the boundary-layer height may play an important role in the transport at low altitudes.  相似文献   

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)          下载免费PDF全文

Alexandre Normandeau  Patrick Lajeunesse  Antoine G. Poiré  Pierre Francus 《Sedimentology》2016,63(7):2106-2129

High‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front.  相似文献   

The Perte-du-Rhône Formation,a new Cretaceous (Aptian-Cenomanian) lithostratigraphic unit in the Jura mountains (France and Switzerland)     

Antoine Pictet  Michel Delamette  Bertrand Matrion 《Swiss Journal of Geoscience》2016,109(2):221-240

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