Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO •. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO. levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed

Very high annual rates of precipitation in the coastal mountains that border the northeast PacificOcean produce large fresh water discharges (23000 m 3 s-i). This discharge has been ignored previously since it does not enter the ocean in the form of large rivers, but, instead, the water enters by way of numerous small rivers and streams. Thus, it acts as a line source instead of a point source. This coastal discharge contributes at least 40% of the fresh water that enters the northeast Pacific from the atmosphere. The discharge is comparable to the mean annual discharge of the Mississippi River system. The fresh water creates a cross-shelf density gradient that drives an alongshore baroclinic jet.The width of this jet is less than 25 km with speeds in excess of 100 cm s -•. It extends along the coast from southeast Alaska to at least Kodiak Island. Apparently, the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year.

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Declines of Steller sea lion (Eumetopias jubatus) populations in the Aleutian Islands and Gulf of Alaska could be a consequence of physical oceanographic changes associated with the 1976-77 climate regime shift. Changes in ocean climate are hypothesized to have affected the quantity, quality, and accessibility of prey, which in turn may have affected the rates of birth and death of sea lions. Recent studies of the spatial and temporal variations in the ocean climate system of the North Pacific support this hypothesis. Ocean climate changes appear to have created adaptive opportunities for various species that are preyed upon by Steller sea lions at mid-trophic levels. The east-west asymmetry of the oceanic response to climate forcing after 1976-77 is consistent with both the temporal aspect (populations decreased after the late 1970s) and the spatial aspect of the decline (western, but not eastern, sea lion populations decreased). These broad-scale climate variations appear to be modulated by regionally sensitive biogeographic structures along the Aleutian Islands and Gulf of Alaska, which include a transition point from coastal to open-ocean conditions at Samalga Pass westward along the Aleutian Islands. These transition points delineate distinct clusterings of different combinations of prey species, which are in turn correlated with differential population sizes and trajectories of Steller sea lions. Archaeological records spanning 4000 yr further indicate that sea lion populations have experienced major shifts in abundance in the past. Shifts in ocean climate are the most parsimonious underlying explanation for the broad suite of ecosystem changes that have been observed in the North Pacific Ocean in recent decades.

The circulation of Prince William Sound, Alaska, is described using hydrographic (1974–1989), current meter (1977–1979), and acoustic Doppler current profiler (1986–1990) observations from both the sound and the adjacent Gulf of Alaska. Ancillary data include data for winds, freshwater runoff, and satellite‐tracked drifters. Prince William Sound is a small inland sea in that it is wide enough to have appreciable horizontal cyclonic circulation. It is also a fjord in that it has basin depths to 700 m but is stilled at 180 m to the open ocean. The general circulation pattern is defined by a portion of the westward flowing Alaska Coastal Current on the Gulf of Alaska shelf that enters Prince William Sound through Hinchinbrook Entrance and transits the sound from east to west before exiting through Montague Strait and rejoining the coastal current. However, there is much variability in this circulation, especially in the transport through Hinchinbrook Entrance. In addition, some of the water entering the sound becomes involved in the cyclonic circulation in the northern sound and so has a longer residence time. The circulation is strongly mediated by seasonal and interannual variations in winds and freshwater runoff as well as by local topography both inside and outside the sound. In winter, the strong cyclonic winds over the Gulf of Alaska cause coastal downwelling and strong flow in the upper layers into Prince William Sound through Hinchinbrook Entrance and out through Montague Strait. In summer, the downwelling ceases, allowing subsurface denser water to rise above the sill and flow into the sound through the bottom layers of Hinchinbrook Entrance. We conclude that the best transport data came from Montague Strait, from which we estimate that ∼40% of the volume of Prince William Sound is flushed in summer (May–September). This estimated volume rises to about 200% in winter (October–April).