Coastal Upwelling Ecosystems Analysis. Technical Report 59. Physical Dynamics of the Coastal Upwelling Frontal Zone off Oregon

摘要

The transient (wind-driven), coastal upwelling frontal zone off Oregon is described in terms of the main kinematic and hydrographic scales, geostrophy, potential vorticity, cross-shelf circulation and mixing. Along-shelf flow is in geostrophic balance in the interior one third of the water column over the shelf, with a tendency for the geostrophic shear to exceed the observed shear inshore of the frontal zone above 40 m. During spin-down, the surface density front moves shoreward and intensifies; the interior density front remains stationary at mid-shelf and weakens. Transport is shore-ward in the upper 2/3 of the water column, and seaward in the layer near the bottom. The structures of the water mass front, chlorophyll distributions, and horizontal velocity fields suggest a re-circulation cell occurs in-shore of the interior density front. The frontal zone is most two-dimensional during intervals of sustained upwelling or downwelling favorable winds exceeding a minimum magnitude. During times of slack winds or wind reversals, the frontal zone is inherently three-dimensional.