Understanding upwelling circulation off Antofagasta (northern Chile): A three-dimensional numerical-modeling approach

A three-dimensional (313) numerical model using the finite element method was used to diagnose coastal currents off Antofagasta, in the upwelling region of northern Chile. The diagnosis was emphasized in the nearshore zone off Peninsula Mejillones (23degreesS), a well-known upwelling site off northern Chile. Water density fields, available from seasonal climatologies of the region, were used to predict currents for the austral winter, and summer conditions. Steady-state conditions were simulated under absence of wind, with a constant southwest wind of 10 knots (5.14 in s(-1)), which is the dominant upwelling-favorable wind in the zone, and with a constant north wind of 10 knots. Spatial variability of winds was examined by using historical wind fields for the region. A 3D particle tracking program was further used to diagnose expected particle trajectories over a 72 It steady-state period. Coastal circulation was dominated by alongshore currents, and presence of reversal currents and coastal eddies. Wind forcing accelerated the flow of the nearsurface layer in most cases, but did not considerably alter the circulation pattern of the average water column. Simulation of passive particle drift showed that the whole nearshore zone might act as an efficient retention area. It was concluded that, as a result of the interactions among distinct water masses, upwelling plumes, and alongshore currents, physical barriers may develop and give rise to semi-enclosed habitats. Physical structuring may have important ecological implications for the upwelling ecosystem. (C) 2003 Elsevier Ltd. All rights reserved.