XBT monitoring of a meridian section across the western Mediterranean Sea

During the Thetis-2/MAST-2 tomography experiment, T7-XBT calibrated (accura cy similar to 0.05 degrees C) probes were launched similar to 28 km apart b etween France and Algeria, twice a month from Feb. to Sep. 1993. Combined w ith infrared images, altimetric data and ship drifts, they provide definite information on the structure, drift and role of the eddy-like mesoscale ph enomena generated by the Algerian Current instability. When embedded in thi s alongslope current, these phenomena generally propagate downstream at a f ew km/day and are markedly asymmetrical. Because of the topography in the e astern part of the Algerian Basin, they separate from the current, become m ore symmetrical and follow an anticlockwise circuit in the open basin. Thes e phenomena are deeper than similar to 750 m and entrain seaward pieces of the Levantine Intermediate Water (LIW) vein flowing along the Sardinian slo pe, thus being responsible of the large spatial and temporal variability of the LIW distribution in the open basin. The non-existence of a LIW vein fl owing westward across the Algerian Basin is definitely demonstrated. In the Gulf of Lions, new insights are provided into the formation and spreading of the Winter Intermediate Water (WIW), which is the Western Mediterranean counterpart of LIW. Considering the large amount of WIW formed during this mild winter, it is clear that this water has not received enough attention yet, and is certainly a major component of the Mediterranean outflow at Gib raltar. Finally, the XBT data account for the eastward flow of the Western Mediterranean Deep Water (WMDW) off Algeria. (C) 2000 Elsevier Science Ltd. All rights reserved.