Physical Oceanography
VII. Internal Tide

The internal tide in Monterey Submarine Canyon is one of the remarkable oceanographic effects caused by the presence of the Canyon cutting across the middle of Monterey Bay. The presence of large internal tides near the head of Monterey Submarine Canyon were observed in 1971 by Broenkow and McKain (1972) and were later investigated in more detail (Shea and Broenkow 1982). Baroclinic tidal heights of up to 120 m were found within 5 km of the Canyon head near Moss Landing. Energy lost upon breaking at the head of the Canyon leads to tidal rectification and promotes a net up-canyon flow, whose effects are similar to wind-driven upwelling. Shea and Broenkow (1982) estimated that tidal rectification of the internal waves may contribute up to 30% of the nutrients assimilated by phytoplankton during periods when upwelling is absent, and perhaps 10% of the required nutrients during periods of upwelling. As inferred from continuity, the internal tide would produce cross-shelf oscillating currents of 13 cm/s. Anecdotal information (V. Morejohn, pers. comm.) suggests that seabird feeding along the rim of the canyon may be associated with prey organisms advected above the canyon rim.

Heard (1992) measured baroclinic tidal currents using an Acoustical Doppler Current Profiler (ADCP) during a 12-hour anchor station near the head of the canyon where the depth was 185 m. At that time, the internal tide height was 60 m, the M2 and K1 up-canyon current amplitudes were 20 and 5 cm/s respectively, and the mean up-canyon velocity increased from 2 cm/s near the surface to 7 cm/s at 120 m (Figure 14).