Analysis of current and temperature data collected in the channel of Sardinia during the SALTO and MFSPP experiments
Abstract
The SALTO experiment was conducted from July 1999 to April 2000 to study the intermediate and deep circulation in the channel of Sardinia. Five moorings were aligned from southeast (M1) to northwest (M5) along one of the XBT lines monitored twice monthly during the MFSPP experiment. They were set about 10 miles apart over isobaths of 1000-2000 m, and they were equipped with 12 current meters at 500 and 900 m (M1, M5), 1000 and 1400 m (M2, M4), 500, 1000, 1400 and 1900 m (M3). The time series were first qualified according to the analysis of the tidal components, which have amplitudes ranging from a few mm/s to about 1 cm/s there (Albérola et al., 1995). Consistently with the current time series collected in 1993-1994 during the PRIMO-1 experiment (Bouzinac et al., 1999), the mean circulation on the Sardinian side (M4, M5) was a few cm/s alongslope from the Tyrrhenian subbasin. The mean circulation in the middle of the channel (M3), which was low and erratic close to the bottom in 1993-1994, was now significant (a few cm/s) and directed eastwards, roughly along the channel axis there. The mean circulation on the Tunisian side (M1, M2), which was never measured before, was low at M1 and significant (a few cm/s) at M2, but strangely south-southeastwards, i.e. perpendicular to the slope. The overall temperature distribution was consistent with that previously described by Bouzinac et al. (1999) and by Sammari et al. (1999). Since the sole significant circulation of water of Atlantic origin is eastwards along Tunisia, isotherms in a 200-300 m surface layer are sloping down southwards there. Since waters at intermediate and greater depths are relatively warm (resp. cool) on the Sardinian side (resp. Tunisian side), all isotherms below about 500 m are sloping up southwards. Mean differences of about 0.4 °C between one side of the channel and the other are permanently encountered at depths ranging from about 500 to 1500 m. However, the variability is much larger on the Tunisian side. None of the EOF analyses performed with either the original time series or the low-passed filtered ones allows defining an energetic mode significantly involving all time series; hence, there was no overall circulation at intermediate and greater depths. Mode 1 (about 30% of the total variance) involves M4 and M5 with similar phases at both moorings and rectilinear variations in the same direction; it corresponds to fluctuations of the flow from the Tyrrhenian subbasin along the Sardinian slope. Mode 2 (about 25%) involves M3 and M4 with specific phases at each mooring (different by less than about 40°) and marked changes in direction; it corresponds to fluctuations of the flow from the Algerian subbasin that sometimes concern the lower part of the Sardinian slope. Mode 4 (about 20%), which involves M2 alone, corresponds to fluctuations that are specific to the lower part of the Tunisian slope. Thanks are due to the crew of the R.V. Hannibal managed by INSTM. REFERENCES Albérola C., S. Rousseau, C. Millot, M. Astraldi, J. Font, J. Garcia-Lafuente, G.P. Gasparini, U. Send and A. Vangriesheim, 1995. Tidal currents in the interior of the Western Mediterranean Sea. Oceanol. Acta, 18, 2, 273-284. Bouzinac C., J. Font and C. Millot, 1999. Hydrology and currents observed in the channel of Sardinia during the PRIMO-1 experiment from November 1993 to October 1994. J. Mar. Systems, 20, 1-4, 333-355. Sammari C., C. Millot, I. Taupier-Letage, A. Stefani and M. Brahim, 1999. Hydrological characteristics in the Tunisia-Sicily-Sardinia area during spring 1995. Deep-Sea Res., I-46, 1671-1703.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....1405R