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

Abstract

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.

Keywords:

• vertical land motion
• sea level change
• altimetry
• tide gauge

Acknowledgments

The authors acknowledge NASA for the Pathfinder TOPEX-Poseidon data and the local organizations providing the hourly tide gauge data (Puerto del Estados, Universitat Politecnica de Catalunya in Barcelona, Système de l'Observation du Niveau des Eaux Littorales, Agenzia per la Protezione dell'Ambiente e dei Servizi tecnici, the Israel National Institute of Oceanography, and the Turkish Mapping Authority). Comments and suggestions of the two reviewers improved the quality of the article. Financial support to the first author was provided by the Deutsche Forschungsgemeinschaft and by the European Commision in the frame of the European Sea Level Service Research Infrastructure (ESEAS-RI) Project under contract EVR1-CT-2002-40025.