Abstract

The subinertial flow on the continental shelf off Concepción (central Chile) and its relation with the local wind-forcing and the topography are studied. Emphasis is placed on the three-dimensional aspects and the effect of the topography on the classical two-dimensional approach to the coastal upwelling. Time series coming from 18 current meters installed on six moorings during March-April 1994 were analyzed. Hydrographic data were collected during two hydrographic cruises (6-7 March and 30-31 March). Complementary information includes wind data and sea level. Empirical orthogonal functions using all series showed two principal subinertial flow patterns. The first mode corresponds to an alongshore flow responding to the intensification of southwesterly wind on a 3- to 10-day scale. The second mode is dominated by the cross-shore fluctuations at the shelf break. The importance of the local wind-forcing appears clearly when comparing the theoretical and observed Ekman transport in the north and central shelf (R = 0.8). Near the bottom a mean southward flow was found with a clear southward intensification induced by the bathymetry and probably by a meridional pressure gradient. This bottom flow modifies the typical coastal upwelling pattern through an offshore Ekman transport in the surface and bottom layers. This implies that the compensation flow for the coastal divergence comes from intermediate waters that arrive onto the shelf through ageostrophic process related with the submarine canyons located toward the north and south of the shelf. Copyright 2004 by the American Geophysical Union.