Currents in the deep ocean off Chile (30°S)

Results are reported from the first recording current meter observations in the eastern boundary current system off Chile. Currents at 100 m and 3400 m were observed for a 4-6 month period during the austral spring-summer-fall period of 1991-1992 at a deep ocean site 150 km off the Chilean coast and 70 km seaward of the axis of the Peru-Chile Trench. Results indicate energetic inertial oscillations, low eddy kinetic energy at 3400 m, southward flow, decreasing from austral spring to summer, at 100 m and 3400 m, and quite strong eastward flow, increasing from spring to summer, at 100 m. The latter result may help to explain satellite images, showing the zone of high biological production near the coast in the study region to be very narrow during the austral summer despite strong coastal upwelling in that season. The authors current observations, local geostrophic current profiles and abyssal potential temperature distributions indicate a five-layer structure for the alongshore flow in the eastern boundary current system off Chile: northward flow above 100 m, between about 400 m and 1700 m (maximum around 600-700 m, northward transport of Antarctic Intermediate Water) and below 3400 m; southward flow from above 100 m to about 400 m (maximum at 180 m, Peru-Chile Undercurrent) and from about 1700 m to below 3400. This proposed vertical structure is consistent with temperature, salinity, dissolved oxygen and nutrient distributions of the study area and bears resemblance to eastern boundary current simulations (McCreary et al., 1987).