TURBULENT MIXING NEAR THE YERMAK PLATEAU DURING THE COORDINATED EASTERN ARCTIC EXPERIMENT

During the ice camp component of the Coordinated Eastern Arctic Experiment (CEAREX) in March-April 1989, 1500 profiles of temperature, conductivity, and velocity shear microstructure were obtained near the Yermak plateau. The dominant signal in isopycnal displacements was the diurnal variability near the plateau, consistent with the enhanced diurnal currents found in this region previously from the Fram III and Fram IV ice camps. The dissipation rate of turbulent kinetic energy epsilon reached maximum values of about 10(-6) W kg-1 in two distinct regions, the surface mixing layer and the pycnocline between 120 and 220 m. There was a significant component of diurnal variability in epsilon in each region. In the surface layer, epsilon was proportional to the cube of the ice-relative current speed at 30 m below the ice, and it decayed approximately exponentially with increasing depth. Major mixing events in the pycnocline were correlated with large-amplitude, short-duration, isopycnal displacements. The lowest dissipation rates were recorded over the deep Nansen basin, north of the plateau, and in the subsurface core of a submesoscale baroclinic eddy in northern Fram Strait. The time-averaged vertical eddy diffusivity near the slope of the plateau was about 2.5 x 10(-4) m2 s-1 in the pycnocline above the Atlantic layer, implying an upward heat flux of 25 W m-2, although only a small fraction of this heat reached the base of the mixed layer. The results confirm that current interactions with steep topography are critical to the modification of Atlantic Water in the eastern Arctic Ocean.