Coastal sea level trends in Southern Europe

Abstract

Low frequency sea level variability in the Mediterranean Sea and in the Atlantic Iberian coast is investigated by use of tide gauge records. The five tide gauge records that span most of the 20th century show positive trends between 1.2 and 1.5 ± 0.1 mm yr−1 and negative accelerations between −0.3 ± 0.3 and −1.5 ± 0.4 mm yr−1 century−1. Sea level trends obtained from the 21 longest records (>35 yr) are smaller in the Mediterranean (0.3 ± 0.4 to −0.7 ± 0.3 mm yr−1) than in the neighbouring Atlantic sites (1.6 ± 0.5 to –1.9 ± 0.5 mm yr−1) for the period 1960–2000. Decadal sea level trends in the Mediterranean are not always consistent with global values, in particular for the 1990s, during which the Mediterranean has shown enhanced sea level rise of up to 5 mm yr−1 compared to the global average (mostly attributed to higher warming). The atmospheric and steric contributions to the observed sea level trends for 1960–2000 are also examined. The atmospherically induced sea level is obtained from a barotropic model forced by wind and atmospheric pressure. The atmospheric contribution accounts for 20–50 per cent of the observed yearly sea level variability and introduces negative trends of –0.2 to –0.9 mm yr−1. The steric sea level, obtained from T and S climatologies, has negative trends ranging from −2.1 ± 0.6 to −0.1 ± 0.3 mm yr−1. Other shorter tide gauge records (>7 yr) are used to quality check longer series and to explore their consistency with the long-term records and identify short but apparently consistent tide gauge records.