Turbulence Observations below Drifting Sea Ice: TKE Production and Dissipation in the Meltwater-Influenced Boundary Layer

Abstract During Arctic summer, meltwater inputs and a fragmented ice cover impede quantifying the role of boundary stress for turbulent mixing in the ice–ocean boundary layer. Here, we show that less than two-thirds of the turbulent kinetic energy (TKE) generated from mean flow shear under drifting sea ice is dissipated, and the remainder can be attributed to balancing stabilizing buoyancy fluxes. We deployed a high-resolution acoustic Doppler current profiler under an ice floe to estimate Reynolds stress, shear production, and dissipation rate of TKE. At 0.75 m below the interface, dissipation rates from 1.5 × 10 −9 to 4.2 × 10 −7 m 2 s −3 and shear production from 6.9 × 10 −10 to 7.7 × 10 −7 m 2 s −3 were measured (5%–95% percentiles), with shear production exceeding dissipation on average. The turbulent stress was largest during an event with ∼9.2-h-period oscillations in the upper ocean, consistent with tidally forced lee waves generated near steep topography. An overall estimate of the quadratic skin drag coefficient representative of the ice floe is . We further identified three qualitative regimes of atmosphere–ice–ocean coupling in our observations: a high-frequency range [>4 cycles per day (cpd)] in which the ice acts like a rigid lid atop the ocean, an intermediate range, and a low-frequency range (<0.8 cpd), where wind-driven ice drift determines the under-ice current. As the latter only contained half of the variance of the ice-relative flow, we emphasize that resolving subdaily time scales is crucial in observing and modeling atmosphere–ice–ocean coupling.