FY 1983

The physical environment of the Peruvian upwelling system

Brink, K.H., D. Halpern, A. Huyer, and R.L. Smith

Prog. Oceanogr., 12, 285–305, doi: 10.1016/0079-6611(83)90011-3 (1983)

Knowledge of the characteristics of the physical environment of the Peru coastal upwelling zone increased greatly during the past decade. Observations made during 1976 and 1977, many made as part of the Coastal Upwelling Ecosystem Analysis JOINT-II expedition, provide the basis for an interpretative description of the physical processes and phenomena occurring in Peru coastal waters. Four important phenomena are discussed: wind-driven upwelling, the poleward undercurrent, surface mixed layer deepening, and low-frequency coastal-trapped waves. The coastal winds were invariably favorable for coastal upwelling, even during the 1976 El Niño. The agreement between the offshore transport in the relatively shallow (30 m) surface layer and the Ekman transport, deduced from the local wind, was good for both the mean and variable state. The agreement with the deeper onshore transport was less good, consistent with the marked three-dimensionality and spatial variability of the upwelling. The poleward undercurrent was apparently continuous from 5°S to at least 15°S, flowing just below the surface layer over the continental she1f and slope, and supplying the upwelling water. The variability in the alongshore velocity field was dominated by baroclinic free coastal-trapped waves with periods of 5-20 days. Although there is appreciable temporal and spatial variability in the Peru coastal upwelling system, the upwelling, the undercurrent, and the low-frequency coastal-trapped waves were ubiquitous.