description

Las Cruces (33° 30’ S; 71° 40’ W),lies between two important upwelling centers: Punta Curaumilla to the North, and Punta Toro to the South (Strub et al. 1998, Wieters et al. 2003). It has been shown that slightly warmer waters tend to be retained in front of Las Cruces, within the Cartagena Bay, entrained by the cold waters upwelled upstream at Punta Toro (Wieters et al. 2003, Narváez et al. 2004). These cold waters are typically driven into Las Cruces area toward the end of an upwelling event, 1-2 days after the onset of upwelling favorable winds (Narváez et al. 2004). Therefore, it has been suggested that the area off Las Cruces is located in an upwelling shadow (sensu Graham & Largier 1997).

About 4-5 Km to the southwest of Las Cruces there is a break in the continental shelf produced by the Submarine Canyon of San Antonio (Hagen et al. 1996), which is associated to Maipo River (located about 12 km to the south of Las Cruces). Studies have shown that the plume of this river is transported to Las Cruces by the sea breeze on a daily basis during spring and summer months (Piñones at al. in preparation). Moreover, large daily fluctuations of surface temperature are also observed in coastal waters, produced by a combination of solar heating of the ocean surface, transport/mixing of this warm surface layer by the sea breeze (Kaplan et al. 2003) and internal tidal bores in the inner shelf region (Vargas et al. 2004).

The coastal zone off central Chile is characterized by a marked seasonal thermocline from mid October to early April and southerly winds that intensify in spring and summer, producing upwelling of colder waters at some sites along the coast (Narváez et al. 2004, Poulin et al. 2002). General aspects of the dynamics of wind driven upwelling and relaxation and its spatial variability have been documented in some detail for this region (Strub et al. 1998, Narváez et al., in preparation).

Currents measurements on the inner shelf (30m) show mainly barotrophic currents in periods of weak stratification. However in period of strong stratification the currents are mainly baroclinic. Synoptical variability ( 3-10 day) of the currents shows good relationship with atmospheric coastal trapped waves. In hourly time-scales the currents presents semidiurnal variability associated not only with tides but also with the see-breeze.