The turbulent boundary layer on the continental shelf

Abstract

IN the late summer of 1973 we made measurements of the current structure in the thermal boundary layer on the continental shelf. The measurements were taken under conditions of complete neutrality, well away from the influence of local coastlines. Figure 1 shows the positions of two moorings, 001 (48° 10.5′N, 07° 54′W), and 002 (48° 16.5′N, 07° 47′W) separated by 15 km. This compares with a tidal excursion of about 10 km for the surface water. Both moorings were in 180 m of water and more than 200 km from the nearest mainland. The current meters were supported by subsurface buoyancy. The thermal structure of the water column, and the depths at which current meter observations were made in relation to the thermal boundary layer is shown in Fig. 2. The temperature of the bottom 100 m of the water column increases with depth. This marginal increase of temperature at the adiabatic rate (1.3 × 10⁻⁶° C cm⁻¹) is expected of a turbulent boundary layer, because the production of turbulent energy is much greater than the stabilising effect of the buoyancy flux. The absolute accuracy is only 0.02° C, using a mercury-in-glass reversing thermometer as the calibration standard. The resolution is, however, considered quite genuine to ±0.0005° C(ref. 1).