Flow dynamics of a wide Arctic canyon

Abstract

We extend and interpret acoustic Doppler current profiler and conductivity‐temperature‐depth data collected in the summer of 1993 over Barrow Canyon in order to implement a high resolution (1.5 to 5 km) model of the Beaufort and Chukchi Seas. This paper addresses physical processes relevant to the Barrow Canyon region using common dynamical analyses of both field data and numerical results. The field data reveal the dominant physical processes that guide the design of our numerical experiments. The observed velocity field shows an intense and variable down canyon flow with transports ranging from 0.5 to 1.4 Sv. A momentum analysis reveals that the cross‐canyon dynamic balance for the barotropic component is primarily geostrophic. Conversely, the baroclinic cross‐canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying Coriolis acceleration and the cross‐canyon pressure gradient. In addition to the moderate influence of stratification (Froude number of 0.4 and Burger number of 0.06), the barotropic pressure gradient component across the canyon (inferred from the large magnitude and little vertical variability of the residuals) is dynamically important for both upcanyon and downcanyon flows that occur at different locations concurrently. The along‐canyon dynamic balance is ageostrophic since the time derivative and the Coriolis term are of the same order of magnitude (temporal Rossby number is approximately 1). An analysis of the longitudinal density and velocity fields from the model reveals that the main driving mechanism for generating the observed upcanyon flow is the nonlinear interaction of the variable barotropic flow with the steep topography. Stratification is maintained by the downcanyon advection of fresh and warm water from the Bering and Chukchi Seas and the upcanyon advection of saltier and colder water from the Arctic.