SEA-LEVEL IN THE MEDITERRANEAN - A FIRST STEP TOWARDS SEPARATING CRUSTAL MOVEMENTS AND ABSOLUTE SEA-LEVEL VARIATIONS

The SELF (SEa Level Fluctuations: geophysical interpretation and envir onmental impact) project has been developed and realized in the framew ork of the Environment Programme designed by the Commission of the Eur opean Communities. The SELF project was aimed at providing a reliable base for the determination, in the Mediterranean area, of sea-level va riations which could then be used as a possible indicator of climate c hanges and to study the interactions taking place among the ocean, the atmosphere and the solid Earth. The project has made it possible to d efine a consistent network of well-established tide gauges encompassin g the Mediterranean Basin as far as the Black Sea and to determine to centimeter accuracy the tide gauge benchmark heights in a global well- defined reference system such as the one provided by the SLR/VLBI spac e techniques. The SELF network constitutes, for the Mediterranean, the necessary prerequisite towards achieving the actual capability to sep arate vertical crustal movements from true sea-level variations, This has been accomplished through the use of space techniques namely SLR, VLBI and GPS in conjunction with Water Vapor Radiometer observations a nd absolute gravity measurements. The analysis of the available tide g auge records has shown a high spatial coherence of the annual to multi decadal sea-level variability. Sea-level fluctuations at periods longe r than two months were found to be strongly correlated with air pressu re, The seasonal cycle was found to be variable in time. Relative sea- level trends determined from records longer than 30 years are less tha n 1.5 mm/yr. Crustal movement rates as determined from the tide gauge records are in general of the order +/- 1.0 mm/yr. The geological obse rvations have shed light on the fact that a marked variability of crus tal movements occurs on both the temporal and spatial scale, and it re presents a major contribution to relative sea-level fluctuations. This fact has been verified for the selected sector which belongs to one o f the more geodynamically active areas of the Central Mediterranean (A eolian Archipelago). However, this work has shown that, at least at th e tide gauges included in the present study, crustal movements are sma ll compared to the decadal to multidecadal sea-level variability but o f the same order as the long-term trend in sea level, thus necessitati ng a careful monitoring if crustal movement is to be separated from th e oceanographic contribution to relative sea-level changes.