Tidal and lower frequency currents above Fieberling Guyot

Abstract

An intensive, yearlong deployment of current meter moorings was made over and around Fieberling Guyot (32.5°N, 127.75°W) in the North Pacific. The measurements are used to investigate tidal currents, the mean flow, and subinertial current fluctuations. The K 1 and O 1 diurnal tides were greatly amplified over the seamount, apparently through dynamics resembling nonlinear seamount‐trapped waves. The diurnal tides interacted nonlinearly to induce constituents at the sum frequency (M 2 ) and difference frequency (fortnightly) above the summit. Diurnal amplification was strongest at about 450 m, and it extended from the seamount center out over the flanks. The S 2 semidiurnal tide was not substantially amplified over the seamount. The mean flow was primarily along isobaths and was strongest about 50 m above the seamount rim. It was driven by tidal rectification, so that mean along‐isobath velocity at a given location correlated well with the amplitude of the local fortnightly tide at that location. Accompanying the mean flow was a “cold dome” over the seamount that was presumably maintained by a balance of mean downward advection and eddy (tidal) radial heat transport. Lower frequency current fluctuations were enhanced near the seamount and were apparently driven by fluctuations in the ambient flow.