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51.
Origin and mechanism of Subantarctic Mode Water formation and transformation in the Southern Indian Ocean 总被引:1,自引:0,他引:1
The sources and pathways of mode waters and lower thermocline waters entering the subtropical gyre of the Indian Ocean are
examined. A Lagrangian analysis is performed on an eddy-admitting simulation of the Global Ocean performed by the DRAKKAR
Group (NEMO/OPA), which captures the main observed features. We trace the subducted mode water’s pathways, identify their
formation regions and trace whether their source waters come from the Atlantic, Pacific or Indian sectors of the Southern
Ocean. Three main sites for mode waters ventilation in the Indian sector are identified with different circulation pathways
and source water masses: (a) just north of Kerguelen, where 4.2 Sv of lighter Subantarctic Mode Waters (SAMW); σ
0 ∼ 26.5) are exported—originating in the Atlantic and Agulhas Retroflection regions; (b) SW of Australia, where 6.5 Sv of
medium SAMW (σ
0 ∼ 26.6) are ventilated—originating in the southern and denser Agulhas Retroflection region; (c) SW of Tasmania and along
the South Australian coast, where 3 Sv of denser SAMW (σ
0 ∼ 26.75) are ventilated—originating from three sources: Leeuwin Current waters, Tasman Sea (Pacific) waters and Antarctic
Surface Waters. In all cases, modelled mode waters were last ventilated in the Indian Ocean just north of the deepest winter-mixed
layers. For the waters subducted SW of Australia, the last ventilation site extends even further north. Waters ventilated
in the deepest mixed layers north of the Subantarctic Front are then re-ventilated 5 years later southwest of Australia. The
model results raise new hypotheses that revisit the classical picture of the SAMW formation and transformation, where a large
homogeneous mixed layer is subducted and ‘slides’ equatorward, essentially maintaining the T/S characteristics acquired at
the surface. Firstly, the last ventilation of the modelled mode waters is not in the region of the deepest mixed layers, as
previously thought, but further north in regions of moderate meso-scale eddy activity. Secondly, the model shows for the first
time a significant source region for Indian Ocean mode waters coming from deep winter-mixed layers along the south Australian
coast. Finally, this analysis shows how the mode water characteristics are modified after subduction, due to internal eddy
mixing. The simulation shows that resolved eddies have a strong impact on the mixed layer properties and that isopycnal eddy
mixing also contributes to the generation of more homogeneous mode water characteristics in the interior. 相似文献
52.
53.
We present a theoretical weakly nonlinear analysis of the dynamics of an inviscid flow submitted to both rotation and precession of an unbounded cylindrical container, by considering the coupling of two Kelvin (inertial) waves. The parametric centrifugal instability known for this system is shown to saturate when one expands the Navier–Stokes equation to higher order in the assumed small precession parameter (ratio of precession to rotation frequencies) with the derivation of two coupled Landau equations suitable to describe the dynamics of the modes. It is shown that an azimuthal mean flow with differential rotation is generated by this modes coupling. The time evolution of the associated dynamical system is studied. These theoretical results can be compared with water experiments and also to some numerical simulations where viscosity and finite length effects cannot be neglected. 相似文献
54.
Rémy Thibaud Géraldine Del Mondo Thierry Garlan Ariane Mascret Christophe Carpentier 《Transactions in GIS》2013,17(5):742-762
Defining a model for the representation and the analysis of spatio‐temporal dynamics remains an open domain in geographical information sciences. In this article we investigate a spatio‐temporal graph‐based model dedicated to managing and extracting sets of geographical entities related in space and time. The approach is based on spatial and temporal local relations between neighboring entities during consecutive times. The model allows us to extract sets of connected entities distant in time and space over long periods and large spaces. From GIS concepts and qualitative reasoning on space and time, we combine the graph model with a dedicated spatial database. It includes information on geometry and geomorphometric parameters, and on spatial and temporal relations. This allows us to extend classical measurements of spatial parameters, with comparisons of entities linked by complex relations in space and time. As a case study, we show how the model suggests an efficient representation of dunes dynamics on a nautical chart for safe navigation. 相似文献
55.
Use of LIDAR in landslide investigations: a review 总被引:13,自引:0,他引:13
Michel Jaboyedoff Thierry Oppikofer Antonio Abellán Marc-Henri Derron Alex Loye Richard Metzger Andrea Pedrazzini 《Natural Hazards》2012,61(1):5-28
This paper presents a short history of the appraisal of laser scanner technologies in geosciences used for imaging relief
by high-resolution digital elevation models (HRDEMs) or 3D models. A general overview of light detection and ranging (LIDAR)
techniques applied to landslides is given, followed by a review of different applications of LIDAR for landslide, rockfall
and debris-flow. These applications are classified as: (1) Detection and characterization of mass movements; (2) Hazard assessment
and susceptibility mapping; (3) Modelling; (4) Monitoring. This review emphasizes how LIDAR-derived HRDEMs can be used to
investigate any type of landslides. It is clear that such HRDEMs are not yet a common tool for landslides investigations,
but this technique has opened new domains of applications that still have to be developed. 相似文献
56.
Santos RG Martins AS Farias Jda N Horta PA Pinheiro HT Torezani E Baptistotte C Seminoff JA Balazs GH Work TM 《Marine pollution bulletin》2011,62(6):1297-1302
To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear. 相似文献
57.
Nadia Senechal Stéphane Abadie Edith Gallagher Jamie MacMahan Gerd Masselink Hervé Michallet Ad Reniers Gerben Ruessink Paul Russell Damien Sous Ian Turner Fabrice Ardhuin Philippe Bonneton Stéphane Bujan Sylvain Capo Raphael Certain Rodrigo Pedreros Thierry Garlan 《Ocean Dynamics》2011,61(12):2073-2098
A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results. 相似文献
58.
59.
Ahmed El-Sabbagh Abdel Aziz Tantawy Gerta Keller Hassan Khozyem Jorge Spangenberg Thierry Adatte Brian Gertsch 《Cretaceous Research》2011,32(6):705-722
Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ13C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ13C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ13C peak and end at or near the Cenomanian–Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco. 相似文献
60.
Anne Nédélec Jean‐Louis Paquette Elder Yokoyama Ricardo I. F. Trindade Thierry Aigouy David Baratoux 《Meteoritics & planetary science》2013,48(3):420-431
The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures. 相似文献