Microstructure observations during the spring 2011 STRATIPHYT-II cruise in the northeast Atlantic
1Institute for Marine and Atmospheric Research Utrecht (IMAU), Dept. of Physics and Astronomy, Utrecht University, Utrecht, The Netherlands
2Institute for Environmental Studies (IVM), VU University Amsterdam, Amsterdam, The Netherlands
*now at: Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Jordi Girona 18–26, Barcelona 08034, Spain
Abstract. 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 (mixed layer depth, MLD, <100) and well-mixed waters (MLD > 100), which was centered at about 48° N. The temperature eddy diffusivities, KT, range from 10−5 to 100 m2 s−1 in the weakly-stratified stations, and range from 3 × 10−4 to 2 × 100 m2 s−1 in the well-mixed stations. The turbulent kinetic energy dissipation rates, ε, range from 3 × 10−8 to 2 × 10−6 m2 s−3 south of the transition zone, and from 10−7 to 10−5 m2 s−3 north of the transition zone. 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 with a scaling factor of about 1.8 in the wind-dominated stations (ε ≈ 1.8 u☆3/(−κz)). The values of KT and ε are on average 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.