Hydrography and circulation west of Sardinia in June 2014

Abstract

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 vesselmounted 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<σ /(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.

High-resolution observations in the western Mediterranean Sea: the REP14-MED experiment

“…The objectives of the experiment as defined in the introduction have been addressed by nine scientific articles (including this one) which are assembled in a special issue of Ocean Science: using the data collected by the shipborne CTD probes, gliders, towed instruments, and vessel-mounted ADCPs, Knoll et al (2017) investigated the hydrography and circulation patterns in the experimental area and compared them with previous knowledge. It turned out that the distribution of the water masses and the circulation resembled the classical picture as described by Millot (1999), but there were also significant differences: the temperature and salinity of MAW, LIW, and bottom water had increased compared to the observations during the last decade.…”

Quality assurance and control on hydrological data off western Sardinia (2000–2004), western Mediterranean

“…microfiber filters for Chl a and 0.22 µm membrane filter (Sartorius, Minisart, SM 16534 K) for DOC and CDOM; this was to remove the particulate fraction immediately after collection. Then filters were frozen at +4 • C to be analyzed at labs following standard procedures described by Lazzara et al (1990) for Chl a and by Vignudelli et al (2004) and Santinelli et al (2008) for CDOM and DOC. For nutrients, during the first three MedGOOS cruises, water samples were partially analyzed on board by a Systea µCHEM autoanalyzer, while remaining samples were frozen at −20 • C following Strickland and Parsons (1972).…”

“…In 2014, the NATO Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE), based in La Spezia, organized a 2-week experiment with extensive use of ocean instruments and two research vessels in a limited area (110 km × 110 km). Its aims were to improve local ocean numerical simulations and forecasts and study the local ocean variability and structures (Onken, 2017a, b;Knoll et al, 2017;Hemming et al, 2017;Onken et al, 2018;Hernandez-Lasheras and Mourre, 2018).…”

PROTEVS-MED field experiments: Very High-Resolution Hydrographic Surveys in the Western Mediterranean Sea

“…Testor et al (2018) summarized the observations of convection during the dedicated experiment HYMEX. Multi-platform strategies including gliders, mooring, combined cruises ( Onken et al, 2018;Pascual et al, 2017;Petrenko et al, 2017;Knoll et al, 2017;Ruiz et al, 2009;Troupin et al, 2019), or colocation with altimetric tracks (Borrione et al, 2016;Heslop et al, 2017;Aulicino et al, 2018, Carret et al 2019 can provide part of the missing synoptic view.…”