Internal tide dissipation, mixing, and vertical nitrate flux at the shelf edge of NE New Zealand

An internal tide on the NE shelf of New Zealand was observed with a combination of moored temperature loggers and current meters and vertical profiling with a microstructure probe. Internal tide energy flux across the shelf edge was calculated to be ∼400 W m−1, with considerable variability driven by the passage of a storm through the region. Energy associated with the internal tide was significantly greater than the energy of the barotropic tide or of inertial shear. Dissipation of the internal tide calculated from the energy loss between two of the moorings was estimated to be 15±10 mW m−2. The associated vertical eddy diffusivity was (4 ± 3) × 10−4 m2 s−1. The microstructure observations indicated internal tide‐driven vertical diffusivities at the nitracline of ∼7×10−4 m2 s−1. The observations of vertical eddy diffusivities are combined with measurements of the vertical nitrate gradient to suggest that mixing driven by the internal tide is the dominant mechanism for driving diapycnal nutrient supply during summer. The calculated flux of about 12 mmol N m−2 d−1 into the photic zone is suggested to drive significant new subsurface production throughout the summer, amounting to a possible contribution to annual new production on the shelf of 100 g C m−2.