An understanding of the processes that link the ice pack to the upper Arctic Ocean is required in order to predict Arctic climate change accurately. As an aspect of the SHEBA Program, measurements of the upper ocean velocity field were obtained while the SHEBA ice camp drifted in the Beaufort Sea. Two Doppler sonars documented flows in the upper thermocline and in the boundary layer immediately under the ice. The "Deep Sonar" profiled to depths of 300 m, with 3 m vertical resolution and 2 minute integration time. Its task is to document the relationship between the immediate under-ice environment and the deeper Arctic Ocean. The "Flux Sonar" achieved depths of 20-70 m under the ice, with 1 m depth resolution and 10s temporal sampling. The objective of this instrument is the measurement of momentum fluxes in the boundary layer.
The under-ice environment in SHEBA was unusual in that a layer of relatively fresh (28 ppt salinity) water was found in the 20 m immediately below the ice. Perhaps a relic of the previous summer's melting, it persisted througout the fall and well into the winter. In addition to the turbulent motions which usually prevail in the boundary layer, the stratification enabled the propagation of internal waves. Under-ice topography can extend nearly into this stratified region, and is presumably an efficient generator of wave motions.
As of July 1 1998, both instruments are in operation at the SHEBA site. We look forward to identifying the principal phenomena active under the ice and documenting the momentum fluxes in both stratified and unstratified regimes.