Barotropic and baroclinic tidal currents on the Mackenzie shelf break in the southeastern Beaufort Sea

Abstract

Tidal currents near the outer shelf break of the Mackenzie Shelf in the southern Beaufort Sea were examined using year‐long (1987–1988) current measurements from the upper (∼35 m) and lower (∼150 m) layers at four sites along the southeast (SS1), northeast (SS2), north central (SS3), and northwest (SS4) perimeter of the shelf. At all stations, semidiurnal currents were dominant, and upper layer currents were approximately double those observed in the lower layer. Maximum M2 currents were observed above the sharp northeastern corner of the Mackenzie Shelf (6.0–7.5 cm·s−1), while in the Mackenzie Canyon they were negligible. Diurnal currents were weaker and depth uniform; maximum K1 currents (1.5–3.0 cm·s−1) were found in the eastern part of the shelf. Diurnal and lower layer semidiurnal currents were in good agreement with those computed numerically by Kowalik and Proshutinsky [1994], indicating that these currents are essentially barotropic. In contrast, upper layer semidiurnal currents were mainly baroclinic. About 74% of the total energy of semidiurnal currents was associated with baroclinic coherent (phase‐locked) tidal currents, while barotropic (12%), baroclinic incoherent (7%), and inertial (7%) components are the remaining semidiurnal currents in this area. High baroclinic generation coefficients (the ratio of locally generated baroclinic waves to barotropic waves) for stations SS2 and SS3 (about 7.0–8.0 in comparison with 0.3 for SS1 and SS4) located near the northeastern Mackenzie Shelf identify this region as a probable generation source of intensive internal tidal waves, which become then locally resonantly trapped between the shelf and the critical latitudes.