Tidal currents in the southwestern Pacific Basin and Campbell Plateau, southeast of New Zealand

Abstract

Tidal analyses of 7 months of hourly current meter records from nine current meters (five moorings) and 18 months of similar records at three depths, in the southwestern Pacific Basin (mean depth 5000 m) near 49°30′S, 170°W, 650 km east of the Subantarctic Slope are reported. The M 2 barotropic tide has a small positive (0.06) ellipticity and is consistent with a Kelvin wave progressing anticlockwise around New Zealand. There is a distinct vertical structure in the M 2 ellipticity that decreases with depth and becomes negative below about 2200 m. The distinct vertical structure results from superposition on the barotropic ellipse of a baroclinic ellipse (mainly the first baroclinic mode), which must be approximately perpendicular to the barotropic ellipse, that is, approximately perpendicular to the Subantarctic Slope. The S 2 tidal ellipse has minimal vertical structure and is consistent wave; the distinction between the S 2 and M 2 tides agrees with previous analyses based on tidal observations. Analysis of 7 months of hourly current meter records from the Campbell Plateau west of the top of the Subantarctic Slope indicates strong diurnal tidal currents with the relative K 1/M 2 admittance of the currents increasing by a factor of 10 from the southwestern Pacific Basin to the Subantarctic Slope. The strong diurnal currents are taken as evidence for the presence of an internal continental shelf wave on the Subantarctic Slope.