IN MARCH 1989, North America's largest marine oil spill occurred in one of its largest estuaries: Alaska's Prince William Sound. Observations of the spill trajectory serve to delineate the circulation within the sound and along the southern coast of Alaska. This region has very high rates of freshwater discharge and intense wind stresses: the average annual amount of fresh water entering the Northeast Pacific drainage system is at least 20% larger than the Mississippi River system, and the seasonal signals of wind stress and wind stress curl here are the largest in the North Pacific. Even as the oil was being released in the sound, it came under the influence of this coastal circulation. The spilled oil and subsequently released surface drifters have served as tracers that can be used to examine our knowledge of the processes affecting regional coastal flow. This knowledge might be applied to coastal processes elsewhere. Oceanographic and meteorological processes played an important role in distributing the spilled oil within the sound and along the coast after the accident. Were these processes unusual or typical of the region and time of year'? How, if at all, did they contribute to the spill? Are they helping to remove or concentrate the oil spill debris? How have the spill observations and other recently acquired data improved our knowledge of the regional oceanography? The Setting The coastal orography which defines Prince William Sound (Fig. 1, p. 4) affects the coastal circulation in several ways. The water motion is restricted by topography, and coastal mountains alter the meteorology. This vast coastal mountain range extends from British Columbia throughout southeast and southcoast Alaska to Kodiak Island. The heights of the coastal mountains exceed 4 km. Since the height of the tropopause is beneath that elevation at this latitude, atmospheric disturbances are usually blocked from moving inland. This regional tendency for orographic blockage of storm systems occurs along the northeast Pacific from British Columbia to the northern Gulf of Alaska. The adiabatic elevation of the moisture-laden
Five bottom pressure gages were deployed.in the Middle-Atlantic Bight during the late winter of 1974. Analysis of the resulting pressure ser. ies and neighboring i:oastal tide gage series shows that tides are the dominant pressure signal in this section of the continental shelf. Most of the remaining pressure fluctuations appear to be forced by meteorological transients. During March 21, 1974, a developing cyclone moving up.the coast excited a coherent group of sea level oscillations with characteristic periods of 5-7 hours, which are interpreted here as coastal-trapped edge waves. Spectra of the nontidal pressure series are red, however; most of the nontidal variability is caused by lower-frequency (subtidal) components. The subsurface pressure (SSP) fluctuations do appear coherent over the spatial extent of the array in the most energetic subtidal frequency bands, and estimates made of the relative horizontal SSP gradients indicate that cross-shelf gradient variations are significan y larger than alongshore gradient ..t• variations. Som e consequences of these large weatherqnduced grad•efit fluctuations on the shelf circulation are discussed.
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