Near-inertial motions over the continental shelf off Concepciَn, central Chile

The inertial response to wind forcing is studied on a continental shelf limited by two submarine canyons and near one of the biologically most important coastal areas in the Chile–Peru upwelling system (35°57′S–37°15′S). After a brief description of the tides (M2 and K1), the paper focuses on the temporal and spatial variability of the near-inertial band (0.045–0.055 cph), which accounts for 2.6–61.5% of the total observed current variance. Common features of near-inertial motion, especially the 180° phase difference between the upper and the lowers layers and the intermittency of this motion, are described for the first time for the Chilean shelf. Outstanding aspects appear when comparing the near-inertial currents in the inner shelf with those near the shelf break, where the subinertial background flow changes the effective Coriolis frequency, generating resonance between the near-inertial currents and the daily wind cycle. Also, the amplitudes of the near-inertial currents were stronger near the shelf break (about 20 cm s−1) and weaker near the coast (about 5 cm s−1). Intermittency in the enhanced near-inertial motions varied around 3.5–10 days and appears to be related to the beat period between diurnal and near-inertial frequencies.