Spatial and Temporal Patterns of Deep Dissipation Near Palau

Much of the mixing in the deep ocean is energized by a combination of internal tides and near-inertial waves. Here we investigate the spatial and temporal patterns of mixing near a steep ridge north of Palau in the tropical west Pacific to understand the contributions from tides, winds and topographic eddies. Using a combination of traditional temperature sensors and dedicated mixing instruments (chipods), we characterize the spatial patterns of energy flux and thermal dissipation rates, and relate these to the internal tide energetics, eddy activity, and spring-neap tidal forcing. Using these, combined with numerical models, we trace energy pathways that link high dissipation events to eddy-modulated internal tides and near-inertial waves, both of which produce layers of high shear and mixing. A particularly interesting signal is associated with a high wavenumber semi-diurnal internal tide that creates elevated shear far from the bottom (at 1000 m depth); a fraction of this signal is predictable with astronomical spring-neap forcing during the 10 month record, but much is not. The temporal variability implies that the interactions of internal tides and low-frequency flow modulates the dissipation at this depth on seasonal time scales providing one mechanism for low-frequency flow to affect small scale dissipation near Palau.