Articles | Volume 13, issue 6
Ocean Sci., 13, 889–904, 2017

Special issue: REP14-MED: A Glider Fleet Experiment in a Limited Marine...

Ocean Sci., 13, 889–904, 2017

Research article 13 Nov 2017

Research article | 13 Nov 2017

Hydrography and circulation west of Sardinia in June 2014

Michaela Knoll1, Ines Borrione2, Heinz-Volker Fiekas1, Andreas Funk1, Michael P. Hemming3,4, Jan Kaiser3, Reiner Onken5, Bastien Queste3, and Aniello Russo2 Michaela Knoll et al.
  • 1Wehrtechnische Dienststelle für Schiffe und Marinewaffen, Maritime Technologie und Forschung (WTD71),Berliner Straße 115, 24340 Eckernförde, Germany
  • 2NATO Science and Technology Organization, Centre for Maritime Research and Experimentation (CMRE), Viale San Bartolomeo 400, 19126 La Spezia, Italy
  • 3Centre for Ocean and Atmospheric Sciences (COAS), School of Environmental Sciences, University of East Anglia (UEA), Norwich Research Park, Norwich, NR4 7TJ, UK
  • 4Laboratoire d'Océanographie et du Climat, 4 Place Jussieu, 75005 Paris, France
  • 5Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research (HZG), Max-Planck-Straße 1, 21502 Geesthacht, Germany

Abstract. In the frame of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD (conductivity, temperature, depth) instruments, towed devices, and vessel-mounted ADCPs (acoustic doppler current profilers), are presented and compared with previous knowledge. So far, the circulation is not well-known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72<σΘ/(kg m−3) < 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15′ E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s−1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transports of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition.

Short summary
The hydrography and circulation west of Sardinia, observed in June 2014 during REP14-MED by means of various measuring platforms, are presented and compared with previous knowledge. So far, the circulation of this area is not well-known and the hydrography is subject to long-term changes. The different water masses are characterized and temporal changes are emphasized. The observed eddies are specified and geostrophic transports in the upper ocean are presented.