Critical levels for forced Rossby and continental shelf waves

The generation of waves on a geostrophic shear flow by a travelling forcing pattern is considered. The model describes both atmospheric Rossby waves on a zonal shear flow and continental shelf waves on a boundary current. By means of the Laplace transform technique, the development of the solution in time is studied, starting from some initial instant when the forcing starts. The asymptotic form of the forced solution is shown to depend crucially upon whether the speed of the travelling forcing lies inside the range of the current or not. The possible application of the results to the Florida current is discussed.     

Internal tides and waves near the continental shelf edge

Abstract

The subject is reviewed from the viewpoints of theory, internal tide and wave structure and their implications.

A wider theoretical context suggests scope for further investigation of natural or nearly-trapped forms above the inertial frequency.

Although internal tides in many locations are observed to have first-mode vertical structure, higher modes are seen offshore from shallow shelf-break forcing and for particular Froude numbers, and may be expected locally near generation. Bottom intensification is often observed where the sea floor matches the characteristic slope. Solitons form from internal tides of large amplitude or at large changes of depth.

Internal tides and solitons are observed also at many sills and in straits, and to intensify in canyons.

Non-linear effects of the waves, especially solitons, include the conveyance of water, nutrients, ‘‘mixing potential'’ etc. away from their source to other locations, and the generation of mean currents. The waves transfer energy and possibly heat between the ocean and shelf, may be a source of medium frequency waves on the shelf (periods of minutes) and can contribute to interior mixing and overturning, bottom stirring and sediment movement.     

Unstructured,anisotropic mesh generation for the Northwestern European continental shelf,the continental slope and the neighbouring ocean

A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective is to demonstrate the ability of anisotropic unstructured meshes to adequately address the challenge of simulating the hydrodynamics occurring in these three regions within a unique mesh. The refinement criteria blend several hydrodynamic considerations as the tidal wave propagation on the continental shelf and the hydrostatic consistency condition in steep areas. Several meshes illustrate both the validity and the efficiency of the refinement strategy. The selection of the refinement parameters is discussed. Finally, an attempt is made to take into account tidal ellipses, providing another cause for anisotropy in the mesh.     

A vessel-towed camera platform for surveying seafloor habitats of the continental shelf

A vessel-towed camera platform with unique design features, developed to photograph seafloor habitat types on the continental shelf off southeastern Australia, is described. Photographic images contributed to the evaluation of the importance of habitat types to demersal fishery productivity. The significant features of the towed automatically compensating observation system (TACOS) are: it is a towed system that enables collection of photographic data along transects of several kilometres in length; it provides real-time video to the ship which permits fine operational control and real-time capture of images and data; it maintains a constant height above the bottom, and can traverse a range of bottom types including high-relief reefs. It is a low-cost system, relative to remotely operated vehicles (ROVs) or submersible camera platforms, based on an easily fabricated framework and commercially available components. The system has been successfully field tested to depths of 190 m in exposed open-ocean conditions.     

Long-term development and current status of the Barcelona continental shelf: A source-to-sink approach

The Barcelona continental shelf, off the city of Barcelona (NE Spain), is a relatively narrow canyon-bounded shelf in the northwestern Mediterranean Sea. Three medium-size rivers (Tordera, Besós and Llobregat) and several ephemeral rivulets flow into this margin. Two main domains have been recognized in the Barcelona shelf: (i) a modern, river-influenced area, and (ii) a relict, sediment depleted area, both affected by a variety of human impacts. A detailed geomorphologic study based on multibeam bathymetry and backscatter data, high resolution seismic profiles, and surface sediment samples allowed mapping and interpreting the main distinctive seafloor features on the Barcelona shelf. Modern sedimentary features reveal that the Llobregat River is the main sediment source of the Barcelona prodeltaic shelf. High-discharge fluvial events result in the formation of suspended sediment plumes and sediment waves on the shelf floor. Relict (late Pleistocene–Holocene) sedimentary features reflect that an important shift occurred in the seashore direction between MIS 4 and MIS 2, and that recent neotectonic reactivation has created a set of seafloor faults. The Barcelona inner and middle shelf is severely impacted by anthropogenic activities such as the enlargement works of the Port of Barcelona, sewage pipes, dredging, anchoring and trawling.     

200海里以外大陆架划界技术及其应用

本文讨论了法律意义的大陆架与科学意义的大陆边缘的异同,介绍了扩展200海里以外大陆架的两条公式线、两条限制线和海脊规则等主要的外大陆架划界技术方法,论述了运用这些划界规则的条件和标准,并指出了我国东海部分海域外大陆架划界案的基本原则、科学基础、法律依据和外部界限.     

Observations of near-inertial oscillations along the Brazilian continental shelf break

Ocean Dynamics - Near-inertial oscillations (NIO) are intermittent motions with a frequency close to the inertial frequency and represent an important fraction of the energy to the currents in the...     

Geochemistry of I-type granitoids in the Karaburun Peninsula, West Turkey: Evidence for Triassic continental arc magmatism following closure of the Palaeotethys

Abstract Triassic granitoids related to Palaeo- and Neo-Tethyan events occur widely in the metamorphic terranes largely affected by the Alpine orogeny. A first recorded unmetamorphosed plutonic body intruded into the Palaeotethyan mélange in western Turkey, called the Karaburun granodiorite, is composed of two small intrusive stocks that were emplaced between 240 and 220 Ma. It is compositionally diverse, ranging from granodiorite and tonalite to diorite. These rocks show heterogeneous compositions with 54 to 65 wt % SiO₂ and are calc-alkaline in character. They are also subalkaline with molar ratios of Al₂O₃/(Na₂O + K₂O) from 0.74 to 1.00 and are metaluminous. Most samples are diopside-normative (0.36–8.64), with Na₂O > K₂O. Chondrite normalized rare earth element (REE) patterns show various degrees of light REE (LREE) enrichment, with La _N = 57.79 to 99.59 and (La/Yb) _N = 5.98–7.85 and Eu negative anomalies (Eu/Eu* = 0.62–0.86). These rocks have coherent patterns in ocean ridge granite (ORG) normalized trace-element plots, marked by variable enrichment in K, Rb, Ba, Th, Ce and depletion in Ta and Nb, similar to I-type granites from subduction zones. In primitive mantle-normalized multi element variation diagrams, the granodiorites show pronounced depletions in the high-field-strength elements (HFSE; Nb, Ta, Zr), Sr, P, and Ti. Trace-element modeling of the Karaburun granodiorite suggests an origin through partial melting of the subduction-modified mantle wedge with minor contribution of crustal components through a process of strong fractional crystallization (FC) combined with slight assimilation-fractional crystallization (AFC). Exposures of typical continental-arc granodiorites in the Karaburun Mélange support the validity of the subduction-accretion model that implies the presence of an active continental margin following closure of the Palaeotethyan Ocean during the Triassic.