On the variability of Mean Sea Level

The long-term sea level change during 1985-2001 is investigated in the Mediterranean Sea from satellite altimetry data of the Geosat, Topex-Poseidon (T/P), ERS-1 and ERS-2 missions and from tide gauge data. Discrepancies in the linear change observed between T/P and ERS-1/2 and between T/P and Geosat are reduced by fitting the ERS and Geosat data to T/P, as T/P time-series show the higher agreement with tide gauge data. A model of sea level variability constructed using sea surface temperature data is used in case of the non-contemporaneous Geosat and T-P missions. The regional mean sea level (RMSL) linear change is spatially not uniform. During the first eight years of the T/P mission the average linear sea level change over the entire Mediterranean Sea is 2.2 mm/yr, in agreement with the global mean sea level (GMSL) change, in the western Mediterranean Sea the change is small (0.4 mm/yr), while it is higher in the eastern Mediterranean and in the Ionian Sea, 9.3 mm/yr and –11.9 mm/yr respectively. The tide gauge data analysis shows agreement with altimetry data during 1985-2001. During 1990-2000 an increase in sea level rise with respect to the previous decade occurs. Sea level rise of almost similar strength was observed in the past from the longer tide gauge records indicating that the rise observed today by altimetry may have interannual or decadal frequencies.