Ferron, B., F. Kokoszka, H. Mercier, P. Lherminier, T. Huck, A. Rios, V. Thierry, 2015: Variability of the diapycnal mixing along the A25 Greenland-Portugal transect repeated from 2002 to 2012. Journal of Physical Oceanography, submitted 22juin2015.

Abstract

The variability of the diapycnal mixing due to internal waves is quantified using a finescale parameterisation applied to the A25 Greenland-Portugal transect repeated every two years from 2002 to 2012. The internal wave velocity shear and strain are estimated from full depth vertical profiles of density and velocity repeated at 91 stations. The 2002–2012 averaged dissipation rate, <$\epsilon_{2002–2012}$>, in the upper ocean lies in the range 1–10.10$^{-10}$ W kg$^{-1}$ . At depth, <$\epsilon_{2002–2012}$> is smaller than 1.10$^{-10}$ W kg$^{-1}$ except over rough topography. The latter region concern the continental slopes, the Reykjanes Ridge and a region delimited by the Azores-Biscay Rise and Eriador Seamount.  There, the vertical energy flux of internal waves is preferentially oriented toward the surface and <$\epsilon_{2002–2012}$> is in the range 1–20.10$^{-10}$ W kg$^{-1}$ . The interannual variability in the dissipation rates is remarkably small over the whole transect. A few strong dissipation rate events exceeding the noise of the finescale parameterisation occur at depth between the Azores-Biscay Rise and Eriador Seamount. This region is also marked by an enhanced surface mesoscale energy level and enhanced bottom velocities. Estimates of the vertical energy fluxes into the internal tide and into topographic internal waves suggest that the latter are responsible for the strong dissipation events. At Eriador Seamount, both topographic internal waves and internal tide contribute with the same order of magnitude to the dissipation rate while around the Reykjanes Ridge the internal tide provide the bulk of the dissipation rate.