During the Joint Air-Sea Interaction Experiment (JASIN), mean flow and turbulent fluctuations were measured throughout the depth of the atmospheric boundary layer by shipborne surface instrumentation, multiple-instrument packages suspended from tethered balloons and research aircraft flying in low level formation. These enabled both individual localized events and representative area-average (70 km $\times $ 70 km) measurements to be investigated. The results are summarized and show that continuous small-scale turbulent mixing was generally confined to an Ekman layer a few hundred metres deep. The structure of this layer is examined in detail, particularly the momentum balance. Spectral analysis reveals two energy-containing regions, one of which, at higher wavenumbers, scales with the Ekman layer depth and carries most of the vertical fluxes. Direct coupling between the Ekman layer and the overlying atmosphere is weak and appears to be strongly dependent on cloud processes, which are intermittent and irregularly distributed on the scale of these measurements.