FY 1987

Observations of currents, surface winds, and bottom pressure in Shelikof Strait, Autumn 1984

Roach, A.T., J.D. Schumacher, and P. Stabeno

NOAA Tech. Memo. ERL PMEL-74, NTIS: PB88-121736, 116 pp (1987)

An extensive array of current meters and bottom pressure gauges was deployed in Shelikof Strait, Alaska, during 1984/85 as part of the Fisheries Oceanography Coordinated Investigations (FOCI). FOCI is aimed at understanding the physical and biological environment surrounding the early life stages of the Pacific pollock (theragra chalcogramma). These data, as well as calculated surface wind time series, were analyzed to investigate the influence of the Alaska Coastal Current (ACC) in this region. The ACC induced a strong mean flow (15 to 25 cm/s) during this season concentrated along the Alaska Peninsula on the northern side of the Strait. Outside the influence of the ACC, mean currents were weak (5-8 cm/s). This highly variable flow bifurcated in the vicinity of the Semidi Islands, with 75% of the ACC volume flux flowing seaward out of a deep (200+m) sea valley which meets the shelf break at a sill southwest of Kodiak Island. This strong outflow can induce an estuarine type circulation through entrainment of bottom water causing a mean inflow at depth. The remainder of the flow continues along the Alaska Peninsula. The currents were generally well correlated in the vertical at each mooring, while the horizontal correlations were weak, indicating the horizontal spatial scales of coherence were less than the 8 to 15 km mooring separation. Surface winds from a location near the Barren Islands (200 km north of the Strait) showed the strongest relation to currents and transport. There was an indication that the winds drove the pressure differences and thereby the currents, as there was a significant correlation between bottom pressure differences and currents.