High-resolution observations of internal wave induced turbulence in the deep ocean

An overview is presented of high-resolution temperature (T) observations above underwater topography in the deep, stably stratified ocean. The Eulerian mooring technique is used to monitor T-variations with typically 100 sensors distributed over lines between 40 and 400 m long. The independent sensors sample at a rate of 1 Hz for up to one year with a precision better than 0.1 mK. Under conditions of a tight Tsalinity (T-density) relationship, the temperature data are used to quantify turbulent overturns. These observations show two distinctive turbulence processes that are associated with different phases of a largescale (mainly tidal) internal gravity wave: i) highly nonlinear turbulent bores during the upslope propagating phase, and ii) Kelvin-Helmholtz billows, at some distance above the bottom, during the downslope phase. Both convective turbulence following Rayleigh-Taylor instabilities and shear-induced instabilities are observed with internal waves breaking. With a newly developed five-lines (3D-)mooring, the transition from isotropy (full turbulence) to anisotropy (stratified turbulence/internal waves) is revealed.