FY 1987

Physical oceanography

Reed, R.K., and J.D. Schumacher

In The Gulf of Alaska: Physical Environment and Biological Resources, D.W. Hood and S.T. Zimmerman (eds.), DOC/NOAA, DOI, 57–75 (1986)

We review the state of both the circulation and the physical property knowledge for the Gulf of Alaska. The largest-scale feature we cover is the offshore boundary current. This current is relatively wide (~400 km) and slow (~30 cm/s) on the east side of the Gulf, but it narrows to less than 100 km from Kodiak Island westward, with peak speeds of ~100 cm/s. Although occasional large changes occur in the path, transport, and properties of the Alaskan Stream, high-frequency variability is not typical. The Stream may transfer heat and momentum into coastal waters, although the relative importance of this process has not been established. Other features covered by our review include a continental shelf circulation system which is generally separate from the Alaskan Stream. On the outer shelf, there is weak net flow, but circulation seems to be steered by the bathymetry in large troughs which transect the shelf. On the east side of the Gulf, the flow tends to be variable but is probably stronger in winter than in summer as a result of local wind forcing. Along the Kenai Peninsula there is a distinct narrow current flowing westward with typical speeds of 20 cm/s, but which can range as high as 100 cm/s in the fall. This rapid fall spin-up results from a maximum freshwater discharge in September-October, and is accompanied by surface salinities as low as 25 parts per thousand. Winds may constrain the relatively dilute flow along the coast. This geostrophic coastal flow first enters Shelikof Strait where the barotropic mode may be important, then continues west along the Alaska Peninsula. These features of coastal circulation are clearly seen in seasonal sea level cycles at various tide stations. Large interannual changes also occur in the Gulf of Alaska. In general, the wind regime along the coast produces downwelling at the coast rather than upwelling.