Multivariate analysis of the surface circulation in the Balearic Sea

This study gives a comprehensive view of the regional surface circulation of the Balearic Sea in early summer. Its spatial variability and dynamics are described from a multivariate analysis of AXBT, CTD and ADCP data collected during the mesoscale experiment FE-91 (May 22-June 2,1991). The results provide evidence of two energetic frontal jets that drive the circulation over the slopes: the southward Continental current (0.9Sv) and the northward Balearic current (0.5Sv). In the southern Balearic basin, to the north of the Ibiza sill, the analyses show that the slope circulation is drastically modified by a wide pool (approximate to 70km) of Winter Intermediate Waters (WIW). In this region, both the Continental and Balearie currents leave the slopes and merge offshore. As a result, the Continental current veers cyclonically to the north and flows along the insular slope. Numerous mesoscale structures (eddies, meanders and filaments) are found in the centre of the basin, directly related to instabilities of the frontal jets often induced by sharp topographic irregularities and subsurface eddies, and involving significant offshore transport of slope waters. Assuming stationarity of the velocity field, a Lagrangian integration is performed to establish the trajectories and time scales associated with the analysed velocity field. The calculations indicate that a drifter released in the core of the Continental current at 22m depth drifts cyclonically around the Balearic basin and reaches the north of Mallorca in less than 40 days. This is consistent with data from an in situ surface drifter deployed in June 1993, and suggests that the velocity field obtained from FE-91 data is representative of the summer circulation of the Balearic Sea. All these results are discussed in the perspective of the general circulation of the Western Mediterranean, Copyright (C) 1996 Published by Elsevier Science Ltd