Observations of Strong Mid-Pacific Internal Tides above Horizon Guyot

Abstract

Large semidiurnal current and isotherm oscillations were observed by one current meter continuously for 9 months in the waters above Horizon Guyot, a seamount located in the central Pacific. The M2 tides dominated the current-meter record. The M2 current ellipse was oriented along 142°; the semi-major amplitude was 7.6 cm s−1 and the currents rotated in a clockwise direction. The M2 isotherm deflection amplitude was 20 m. The M2 currents observed above the guyot were two to three times larger than M2 currents either observed in or predicted for this region of the mid-Pacific. Evidence suggests that the semidiurnal tide was predominantly an internal tide that was generated at the guyot. The observed internal tide had a narrow bandwidth and a constant amplitude and phase for 9 months, and had characteristics similar to a vertically propagating, rather than a vertically standing, internal wave.