Modeling study of seasonal and inter-annual variability of circulation in the coastal upwelling site of the El Loa River off northern Chile

Abstract

A three-dimensional numerical model using the Finite Element Method (FEM) was used to diagnose coastal currents off the El Loa River (21° S) in the northern upwelling region of Chile. This site has been recognized as an important spawning zone of the southern anchovy Engraulis ringens. Diagnostic current fields were obtained for summer and winter during the 1997–1998 El Nino conditions and during a “normal” upwelling year. The results show this site as an efficient retention area in the nearshore, because of a reduced cross-shelf flow, a strong alongshore flow and presence of several anticyclonic eddies. A simulated Lagrangian experiment indicated that retention within the nearshore (<10 km) may last for more than 4 days under a steady-state wind condition. Wind regimes and water density fields during 1997–1998 (El Nino) and 1995–1996 (“normal” upwelling) did not cause differences in the general pattern of coastal circulation. However, the magnitudes of both the alongshore and the cross-shelf flows are substantially reduced during El Nino in the nearshore spawning zone, possibly as a consequence of an anomalous water mass in the coastal area. This altered condition may limit the transport and dispersion of anchovy spawning products.