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

Abstract

Small-scale temperature and conductivity varia-tions have been measured in the upper 100 m of the northeastAtlantic during the STRATIPHYT-II cruise (Las Palmas–Reykjavik, 6 April–3 May 2011). The measurements weredone at midday and comprised 2 to 15 vertical profiles at eachstation. The derived turbulent quantities show a transitionbetween weakly-stratified (mixed layer depth, MLD,<100)and well-mixed waters (MLD>100), which was centered atabout 48◦N. The temperature eddy diffusivities,KT, rangefrom 10−5to 100m2s−1in the weakly-stratified stations, andrange from 3×10−4to 2×100m2s−1in the well-mixed sta-tions. The turbulent kinetic energy dissipation rates,ε, rangefrom 3×10−8to 2×10−6m2s−3south of the transition zone,and from 10−7to 10−5m2s−3north of the transition zone.The station-averagedKTvalues throughout the mixed layerincrease exponentially with the wind speed. The station-averagedεvalues throughout the mixed layer scale with thewind stress similarity variable with a scaling factor of about1.8 in the wind-dominated stations (ε≈1.8u3∗/(−κz)). Thevalues ofKTandεare on average 10 times higher comparedto the values measured at the same stations in July 2009.The results presented here constitute a unique data set giv-ing large spatial coverage of upper ocean spring turbulencequantities.