Vertical Land Motion in the Mediterranean Sea from Altimetry and Tide Gauge Stations

We have computed estimates of the rate of vertical land motion in the Mediterranean Sea from differences of sea level heights measured by the TOPEX/Poseidon radar altimeter and by a set of tide gauge stations. The comparison of data at 16 tide gauges, using both hourly data from local datasets and monthly data from the PSMSL dataset, shows a general agreement, significant differences are found at only one location. Differences of near-simultaneous, monthly and deseasoned monthly sea level height time-series have been considered in order to reduce the error in the estimated linear-term. In a subset of 23 tide gauge stations the mean accuracy of the estimated vertical rates is 2.3 +/- 0.8 mm/yr. Results for various stations are in agreement with estimates of vertical land motion from geodetic methods. A comparison with vertical motion estimated by GPS at four locations shows a mean difference of -0.04 +/- 1.8 mm/yr, however the length of the GPS time-series and the number of locations are too small to draw general conclusions.