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Geophysical data from Gerlache Strait, Croker Passage, Bismarck Strait and the adjacent continental shelf reveal streamlined subglacial bedforms that were produced at the bed of the Antarctic Peninsula Ice Sheet (APIS) during the last glaciation. The spatial arrangement and orientation of these bedforms record the former drainage pattern and flow dynamics of an APIS outlet up‐flow, and feeding into, a palaeo‐ice stream in the Western Bransfield Basin. Evidence suggests that together, they represent a single ice‐flow system that drained the APIS during the last glaciation. The ice‐sheet outlet flowed north/northeastwards through Gerlache Strait and Croker Passage and converged with a second, more easterly ice‐flow tributary on the middle shelf to form the main palaeo‐ice stream. The dominance of drumlins with low elongation ratios suggests that ice‐sheet outlet draining through Gerlache Strait was comparatively slower than the main palaeo‐ice stream in the Western Bransfield Basin, although the low elongation ratios may also partly reflect the lack of sediment. Progressive elongation of drumlins further down‐flow indicates that the ice sheet accelerated through Croker Passage and the western tributary trough, and fed into the main zone of streaming flow in the Western Bransfield Basin. Topography would have exerted a strong control on the development of the palaeo‐ice stream system but subglacial geology may also have been significant given the transition from crystalline bedrock to sedimentary strata on the inner–mid‐shelf. In the broader context, the APIS was drained by a number of major fast‐flowing outlets through cross‐shelf troughs to the outer continental shelf during the last glaciation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Analyses of sea level and current-meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non-local coastal forcing and local tidal forcing in the northern reach of San Francisco Bay, a partially mixed estuary. Low-frequency variations in sea level are dominated by non-local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations. Low-frequency currents demonstrate a gravitational circulation which is modified by changes in tidal-current speed over the spring-neap tidal cycle. Transients in gravitational circulation induce internal oscillations with periods of two to four days. 相似文献
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Linearized water wave theory is used to show that a submerged long circular cylinder suitably constrained by springs and dampers to make small harmonic oscillations, can be extremely efficient in absorbing the energy in an incident regular wave whose crests are parallel to the axis of the cylinder. Experimental results are described which confirm the theory for small amplitude waves and which suggest that the device can still be fairly efficient in waves of moderate amplitude. 相似文献
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ANGUS photographs and ALVIN observational data from Fracture Zones A and B on the Mid-Atlantic Ridge near 37°N were examined for structural and sedimentological indications of the area's tectonics. Both transform fault zones are characterized by volcanic rubble, breccias, chalks, and undisturbed sediments typical of slow-slipping transforms.The photographic data consist of 16 camera-sled traverses from the FAMOUS Expedition using the ANGUS deep-towed camera system. These data cover several different morphotectonic provinces along the strike of both slow-slipping (2 cm yr-1) fracture zones. ALVIN data come from two dives in the central part of Fracture Zone B. The two fracture zones differ in their distribution of fractured and sheared chalks which indicate regions of strike-slip deformation along the transform. Evidence of shearing is confined to a very narrow region in the center of FZ A, whereas the zone of shear deformation is as much as 6 km wide across FZ B. Other differences include the morphology and depth of the transform valleys and their contiguous nodal basins and the extent of exposures of fresh-looking volcanic ridges in the nodal basin. 相似文献
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