Microstructure observations during the spring 2011 STRATIPHYT-II cruise in the Northeast Atlantic

Small-scale temperature and conductivity variations have been measured in the upper 100 m of the Northeast Atlantic during the STRATIPHYT-II cruise (Las Palmas–Reykjavik, 6 April–3 May 2011). The measurements were done at midday and comprised 2 to 15 vertical profiles at each station. The derived turbulent quantities show a transition between weakly-stratified and well-mixed waters, which was centered at about 48° N. The temperature eddy diffusivities, KT, range from 10 5 to 100 m2s 1 in the weakly-stratified stations, and range from 3 × 10 4 to 2 × 100 m2s 1 in the well-mixed stations. The turbulent kinetic energy dissipation rates, ε, range from 3 × 10 8 to 2 × 10 6m2s 3 south of the transition zone, and from 10 7 to 10 5m2s 3 north of it. The station-averaged KT values throughout the mixed layer increase exponentially with the wind speed. The station-averaged ε values throughout the mixed layer scale with the wind stress similarity variable, u*3/( κ z), with a scaling factor of about 1.8 in the wind-dominated stations. The values of KT and ε are about 10 times higher compared to the values measured at the same stations in July 2009. The results presented here constitute a unique data set giving large spatial coverage of upper ocean spring turbulence quantities.