The Irish coastal current: a seasonal jet-like circulation

During 25 July-3 August 2001 a comprehensive cruise was undertaken along the western coast of the Republic of Ireland to resolve the three-dimensional density field and circulation. Towed undulating CTD revealed the strong thermocline beyond the 60 m contour with more diffuse stratification inshore. Argos drifters deployed in the late summer of 1999, 2000 and 2001 demonstrated strongly northward flow, their motion was uncorrelated with wind forcing but was consistent with the predicted geostrophic currents generated by the bottom fronts intersecting the seabed. These flows were evident in the data from the vessel mounted 153.6 kHz acoustic Doppler current profiler (ADCP) although the jets are relatively narrow (15-20 km). This region is heavily influenced by storm events and Atlantic influence with high salinity contributing to strong vertical and horizontal density gradients particularly in the south of the region. However, the seasonal heating cycle coupled with tidal mixing is the dominant force of buoyancy production that ensures that the frontal features occur every year. In combination with similar features found in the Celtic Sea [Brown, J., et al., 2003. Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea. Continental Shelf Research 23, 533-561] these observations demonstrate the existence of a continuous pathway in summer from the north Cornish coast to Malin Head with average residual velocities >7.5 cm s. The data set described here provides the necessary basis for environmental management and knowledge of the pathway for contaminants, the dynamics of nutrients and an understanding of the movement of larvae and juvenile fish, in a geographic location that had previously been little studied. Crown