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

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, <I>K_T</I>, range from 10^&minus;5 to 10⁰ m² s⁻¹ in the weakly-stratified stations, and range from 3 &times; 10^&minus;4 to 2 &times; 10⁰ m² s⁻¹ in the well-mixed stations. The turbulent kinetic energy dissipation rates, ε, range from 3 &times; 10^&minus;8 to 2 &times; 10^&minus;6 m² s⁻³ south of the transition zone, and from 10^&minus;7 to 10^&minus;5 m² s⁻³ north of the transition zone. The station-averaged <I>K_T</I> 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 (&epsilon; &approx; 1.8 <I>u</I>_&star;³/(&minus;&kappa;<I>z</I>)). The values of <I>K_T</I> 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.