The event-scale variability of across-shelf transport was investigated using observations made in 15 m of
water on the central Oregon inner shelf. In a study area with intermittently upwelling-favorable winds and
significant density stratification, hydrographic and velocity observations show rapid across-shelf movement of
water masses over event time scales of 2–7 days. To understand the time variability of across-shelf exchange,
an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum
from velocity profiles and wind forcing. Depth-averaged eddy viscosity varied over a large dynamic range,
but averaged 1.3 X 10⁻³ m² s⁻¹ during upwelling winds and 2.1 X 10⁻³ m² s⁻¹ during downwelling winds. The
fraction of full Ekman transport present in the surface layer, a measure of the efficiency of across-shelf
exchange at this water depth, was a strong function of eddy viscosity and wind forcing, but not stratification.
Transport fractions ranged from 60%, during times of weak or variable wind forcing and low eddy viscosity,
to 10%–20%, during times of strong downwelling and high eddy viscosity. The difference in eddy viscosities
between upwelling and downwelling led to varying across-shelf exchange efficiencies and, potentially,
increased net upwelling over time. These results quantify the variability of across-shelf transport efficiency
and have significant implications for ecological processes (e.g., larval transport) in the inner shelf
