Why biological time series require physical ones ? Isabelle

INTRODUCTION The first studies on the general circulation of water masses in the Mediterranean began in the early 1900s (Nielsen, 1912), depicting a circulation smooth and stable along the slopes. Major revisions arose only in the 1980s, after the satellite imagery revealed upwellings, meanders and eddies, that is the mesoscale dynamics (see for instance Millot, 1985, 1987a; Le Vourch et al., 1992). In the western basin, its role and consequences have been assessed with satellite observations that were later confirmed by in situ studies using a mesoscale-dedicated sampling strategy. Besides validating the use of satellite thermal images (SST: Sea Surface Temperature) to infer circulation features (Millot et al., 1994, 1997) such a strategy has shown that mesoscale must be taken into account since it can impact the general circulation (e.g. Millot, 1987b; Millot and Taupier-Letage, 2003). The revised schemes for the western basin display meandering and eddying alongslope currents in a counter clockwise circuit (Millot, 1999). In the eastern basin, a major fieldwork effort (POEM) was carried out in the 1990s (e.g. Robinson, 1991; POEM group, 1992). The resulting representations of the surface circulation showed jets crossing the central part of the basin, instead of alongslope. It is worth noting that the southern parts from the Ionian to the Levantine sub-basins were not investigated, and that the sampling strategy was not adapted to assess the mesoscale (especially with a sampling interval too large, generally half a degree), which was then most likely to be deceiving. Another revisit of the surface circulation in the eastern basin has just been completed, based on the analysis of a ~4-year time series of SST images, which provide a synoptic view with a fine spatio-temporal resolution (~1 km, ~1 day). They show that the circulation is alongslope, as one might expect from the simple application of the Coriolis effect, and is affected by mesoscale dynamics. The resulting new scheme (Hamad et al., 2003) strongly differs from that mentioned above, and shows a meandering and eddying alongslope circulation forming a counter clockwise circuit, which is confirmed by modelling work carried out in the LODYC (Alhammoud, 2003).