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Active fault geometry, available Quaternary rates on major faults, and the far‐field plate motion are used to determine crustal kinematics in the collision zone between India and Asia. Using a finite element formalism to construct a spherical shell model of the Asian continent with embedded faults, we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault‐bounded blocks. By doing so, we test the assumption that long‐term deformation within continents is mostly localized into major faults. In the solution, fault motion accounts for more than 80% of the deformation, allowing us to describe our velocity model in terms of quasi‐rigid block rotations on the sphere. South China is rotating clockwise about a pole located southwest of Borneo, implying an E‐ESE velocity vector of ∼11 mm/yr for a point at Shanghai, in agreement with the velocity vector determined by very long baseline interferometry [Heki et al., 1995]. The eastward movement of south China is accommodated by oblique extension along the Red River fault at a rate of 10 ± 5 mm/yr in the south and by the combination of left‐lateral strike‐slip motion on the Qinling‐Dabie Shan fault and the counterclockwise rotation of the Ordos and adjacent blocks in the north. The Tarim rotates clockwise with respect to Dzungaria about a pole located at 44°N, 92°E, consistent with increasing crustal shortening toward the west throughout the Tien Shan. Assuming incompressibility, a crustal volume budget over a domain encompassing the Tertiary mountain ranges in Asia shows that, over the last 10,000 years, 73 ± 4% of the north‐south shortening between India and Asia has been absorbed by thickening of the lithosphere, and 27% has been accommodated by lateral extrusion of continental blocks. The present‐day predominance of thickening in Asia results from the relatively slow eastward motion of south China, controlled by strike‐slip faulting in the Qinling Shan and oblique extension in northeastern China.

[1] The seasonal cycle of water masses and sea ice in the Gulf of St. Lawrence is examined using a three-dimensional coastal ice-ocean model with realistic tidal, atmospheric, hydrologic, and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation. A model simulation over 1997-1998 is verified against available data on sea ice, temperature, and salinity. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The accuracy of radiative, momentum, and sensible heat exchanges at the sea surface, and the production of turbulent kinetic energy from winds and tides, are critical to the accuracy of the modeled circulation. The analysis of the mean error on near-surface temperature and salinity in the late summer and fall using standard bulk exchange coefficients and radiation (about 1°C too cold and 1 salinity unit too fresh) shows the tradeoff between tidal mixing at the head of the Laurentian Channel, and winddriven circulation and mixing in the surface waters. The results suggest year-long stratification in the estuary and northwestern Gulf, with little mixing except near the head region, where relatively deep warmer waters are mixed to the surface during winter, and cold intermediate waters are efficiently withdrawn during summer. The results suggest that the summer cold waters found at intermediate depths in the estuary and northwestern Gulf are not formed in situ. A significant fraction of these waters enters through the Strait of Belle Isle in wintertime, eventually reaching the estuary within about 6 months.

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The action of tides on density-driven circulation, internal gravity waves, and mixing was investigated in the St. Lawrence Estuary between Rimouski and Québec City. Timevarying fields of water level, currents and density were computed under typical summer conditions using a three-dimensional hydrostatic coastal ocean model that incorporates a second order turbulence closure submodel. These results are compared with current meter records and other observations. The model and the observations reveal buoyancy effects produced by tidal forcing. The semi-diurnal tide raises the isopycnals over the sills at the head of the Laurentian Trough and English Bank, producing internal tides radiating seaward. Relatively dense intermediate waters rise from below 75-m depth to the near surface over the sills, setting up gravity currents on the inner slopes. Internal hydraulic controls develop over the outer sills; during flood, surface flow separation occurs at the entrances of the Saguenay Fjord and the upper estuary west of Ilet Rouge Bank. Early during ebb flow (restratification), the surface layer deepens to encompass the tops of the sills. As the ebb current intensifies, the model predicts the formation of seaward internal jumps over the outer sills, which were confirmed from acoustic reflection observations. As the internal Froude number increases further, flow separation migrates up to sill height. As a result of these transitions, internal bores emanate from the head region one to two hours before low water. We find that the mixing of oceanic and surface waters near the sills is driven by the vertical shear produced during ebb in the channel south of Ilet Rouge, the shear produced in the bottom gravity flood currents, and, to a lesser extent, the processes over the sills. résumé L'action des marées sur l'écoulement associé à la flottabilité, les ondes de gravité internes et le mélange a été étudiée pour l'estuaire du Saint-Laurent entre Rimouski et la ville de Québec. Les variations du niveau d'eau, des courants et de la densité ont été calculées dans des conditions estivales typiques en utilisant un modèle hydrostatique tridimensionnel pour les eaux côtières incorporant un sous-modèle de fermeture turbulente au second ordre. *Corresponding author: saucierf@dfo-mpo.gc.ca 506 / François J. Saucier and Joël Chassé Ces résultats ont été comparés avec des enregistrements de courantomètres et d'autres observations. Le modèle et les observations nous révèlent des effets de flottabilité produits par la marée. La marée semi-diurne élève les isopycnes au-dessus des seuils à la tête du chenal Laurentien et du banc des Anglais, produisant des marées internes qui se propagent vers l'océan. Des eaux intermédiaires relativement denses, se trouvant sous 75 m de profondeur, remontent prés de la surface au-dessus des seuils, produisant des courants de gravité sur les pentes internes. Des contrôles hydrauliques internes se développent au-dessus des seuils extérieurs; durant le flot, une séparation de l'écoulement de surface a lieu à l'ent...