An observational study of the summer circulation in the Celtic Sea is presented which focuses on the density-driven (baroclinic) near-surface currents associated with bottom fronts. A combination of instrumentation, such as ship-mounted ADCP, satellite-tracked drifters, bottom-mounted ADCP and towed undulating CTD vehicle (Scanfish), was used. The analysed data set constitutes the first direct current measurements and extensive hydrographic data collected during the summertime in the Celtic Sea to date. The extensive analysis of the resulting data set is presented. In particular, a comparison of two detiding techniques for ship-mounted ADCP data has been performed and an alternative approach to removing the tidal signal is proposed.
The collected high-resolution hydrographic information allows us to define a dense, cold-pool bottom structure bounded by sharp bottom fronts. Although the dense cold-pool is mainly a thermal structure, salinity contributes to reinforce the frontal areas. Moreover, the findings have revealed that strong near-surface currents (up to 0.30 - 0.40 m s^-1 ) can be observed at the margin of the sharp bottom fronts. The area with the strongest horizontal density gradients was the St. George's Channel, where a cyclonic circulation was observed. The exchange between the Celtic Sea and the Irish Sea, seems to be restricted, however, but intermittent intrusion of surface water may occur with considerable velocities
 (up to 0.30 m s^{- 1}). These results have shown the importance of baroclinic conditions for maintenance of near-surface flows and have shown flow variability away from frontal regions. In addition, other structures such as an eddy-like feature can co-exist with bottom fronts, which can influence the predicted density-driven flows.
The results of this thesis add to the hypothesis that baroclinic conditions during the summer, in particular bottom fronts, can drive, in a broad context, the residual circulation in shelf seas.