Fossil turbulence in the Denmark Strait

Abstract

Temperature microstructure measurements by Oakey and Elliott [1980] in the Denmark Strait are interpreted using the fossil turbulence theory of Gibson [1980]. All of the microstructure appears to be fossil temperature turbulence at large scales; that is, remnant temperature fluctuations produced by overturning turbulence which persist after the fluid ceases to be turbulent at the scale of the fluctuations. Most of the microstructure appears to be fossil at all scales. Because completely active turbulence patches were not detected, the turbulent mixing process in the Denmark Strait has been undersampled. Consequently, actual average values of vertical diffusivity and turbulent dissipation of temperature and velocity may be much larger than those estimated from the Oakey and Elliott [1980] dropsonde measurements. This may resolve the discrepancy between the vertical heat flux estimated from bulk flow properties of the boundary overflow region, and a heat flux value 2 orders of magnitude less estimated from the measured dropsonde dissipation rates assuming the microstructure in the region is turbulent rather than fossil turbulence. To reliably infer space‐time average turbulence dissipation rates and diffusivities in the ocean from microstructure measurements apparently requires larger data samples and better models of stratified turbulence than are presently available.