K. Horsburgh, A. E. Hill, James Brown
May 1, 2000
Progress in Oceanography
An extensive cruise program during 1994, 1995 and 1996 provided observations that describe the seasonal evolution of the three-dimensional density field in the western Irish Sea. A cold, dense pool flanked by strong nearbed density gradients was present from May until October. In spring, salinity had a dominant influence on the density structure but from June until October temperature controlled the density stratification. The trajectories of 55 satellite-tracked Argos drifters demonstrated the existence of the cyclonic circulation pattern that constitutes the western Irish Sea gyre and defined the gyre's spatial extent. Several distinct recirculation paths were observed and the implications for planktonic organisms of the seasonal variability in the recirculation are discussed. Drifter speeds were in good agreement with geostrophic calculations based on the observed density field and with de-tided acoustic Doppler current profiler (ADCP) measurements. The dynamical significance of strong nearbed gradients (bottom fronts) is highlighted. The location of the dynamically significant baroclinicity below the level of wind mixing explains the persistence of the cold pool and cyclonic circulation until late October. The dataset described here is valuable for environmental management purposes and it facilitates testing of the prognostic capabilities of the present generation of density-advecting numerical models.