Volume 19, numéro 1, march 1992

EN :

Techniques are now available to prepare bathymétrie maps of the sea floor with detail similar to that of topographic maps on land. Gridded data sets can be displayed as shad-owgrams to enhance particular morphologic features. Glacial geomorphological features on the continental shelf off eastern Canadacan be interpreted in a manner analogous toglacial features on land. The last major dataset acquired by the CSS BAFFIN from the eastern Scotian Shelf shows a complex topography interpreted as a series of glacial tunnel valleys, which indicate several episodes of sub-glacial meltwater flow anderosion.

EN :

Three mechanisms are responsible for the distribution of inorganic suspended particulate matter in a glacially influenced fiord suchas Knight Inlet, British Columbia. The most important is the influx of sediment from rivers draining hinterland ice fields, with maximum input levels reached in the summer melt season and during the autumn period of flashfloods. Sediment can also enter a fiord from the sea: 1) within the return flow of estuarine circulation that is fully developed during the late spring through early autumn, and 2) aspart of deep shelf water that exchanges and flushes out the deep water of the fiord basin, particularly during the winter season. The third mechanism for sediment accumulating on the sea floor is through the action of episodic turbidity currents. These sediment gravity flows carry coarse delta-front sediments to the otherwise muddy basin floor. The relative abundance of particulate iron within the suspended sediment load directly relates to higher levels of iron in glacially derived particles issuing from river mouths atthe head of the fiord. Elevated levels of particulate manganese may be a result of turbidity currents. They are observed in the water column nearest the sea floor where circulation and geochemical conditions would normally preclude their existence.

EN :

Deep-sea methane hydrate "ice" layers are found a few hundred metres beneath the continental slopes of a number of areas around the world, notably in subductionzones where large accretionary sedimentary prisms are formed. The ice-like clathratestructure is stable up to temperatures of 10°-30°C beneath the sea floor at the pressures generated by water depths greater than about 800 m. The primary indicator of deep-sea hydrate is a "bottom simulating reflector'' (BSR) that parallels the sea floor. These naturally occurring hydrate layers are estimated to contain a very large amount of methane, a potential clean fuel resource, butit is unlikely that recovery will be possible in the near future. Of more immediate concern is the role of such hydrate in global climate control. Because methane is a very strong greenhouse gas, release to the atmosphere of methane in hydrate resulting from a small amount of climatic warming could strongly enhance the warming trend, i.e., provide positive feedback. Recent results, especially from the Vancouver Island margin, are summarized, dealing with a) the distribution and amount of such hydrate, b) the nature of the hydrate layers revealed by detailed seismic reflection analysis, and c) the hydrate formation process. A hydrate BSR is found to be widespread in a 30 km wide band beneath much of the continental slope off Vancouver Island. The hydrate layer in this area is on the order of 20 m thick, concentrated at the baseof the stability field about 300 m below the sea floor. Because such deep-sea hydratere presents a very large global methane reservoir, its distribution, nature and formation warrant detailed study.

EN :

A digital grid of ocean floor ages was constructed from a combination of magnetic anomaly identifications and recent platekinematic models of the North Atlantic and Labrador Sea. Comparing large gridded geophysical data sets with these gridded agevalues is a powerful means of studying the variation of geophysical parameters with lithospheric age, and the dynamic processesin the Earth. The data set from the western North Atlantic and Labrador Sea shows the dependence on age of bathymetry, depth-to-basement and gravity.