Flow of the Alaskan Stream and its variations

Abstract

Data from cruises in winter 1980 and summer 1981, which traversed the region from the head of the Gulf of Alaska to the western Aleutian Islands, are used to examine the flow of the Alaskan Stream and its changes. The physical property distributions reveal seasonal changes, interactions with shelf and offshore waters, and the effects of large-scale variations in circulation. Peak geostrophic speeds, referred to 1500 db, were typically 100 cm s −1; consideration of the baroclinic structure below 1500 db would increase the speeds slightly, but the usual volume transports (about 12 × 10 6 m 3 s −1, referred to 1500 db) would increase by about 3 × 10 6 m 3 s −1 near 150°W and by about 8 × 10 6 m 3 s −1 near 180°. In winter 1980 the Alaskan Stream had essentially constant transport (referred to 1500 db) from the head of the gulf to the western Aleutians, with some southward recirculation of upper waters near 175°W and a southward flow through Amchitka Pass. In summer 1981 the circulation pattern was markedly different; only about half the normal flow entered the upper gulf, and the rest was deflected northward across the southern stream boundary. The two flows converged near 165°W to produce typical transports along the Aleutians. It appears that the rare flow structure of summer 1981 was related to an anomalous distribution of wind-stress curl, which may have altered isopycnal slopes and the geostrophic flow.