Tide gauge data archaeology provides natural subsidence rates along the coasts of the Po Plain and of the Veneto-Friuli Plain, Italy

In Northern Italy, natural subsidence affects the Po and Veneto-Friuli Plains. Anthropogenic activities which started during the 1930s enhanced the natural rates considerably. Information on land lowering can be obtained not only by geodetic or geological data, but also analysing and comparing sea-level time-series of neighbouring tide gauges. In the Northern Adriatic, several tide gauge stations were operational before the onset of the anthropogenic activities. We analysed data spanning the period 1873-1922 from Marina di Ravenna, Venice and Trieste, in Italy. The 1897-1922 data of Pula, Croatia, were also considered for the analysis, but this time-series was finally discarded because it was too short. Trieste, located in a relatively stable area, is characterized by a sea-level rate of 1.21 ± 0.35 mm yr-1 (1875-1922) that can be assumed to be a reliable estimate of the local sea-level rise during the period of interest. We compared the rate observed at Trieste with those obtained at Marina di Ravenna, 3.09 ± 0.31 mm yr-1 (1873-1922), and Venice, 2.05 ± 0.22 mm yr-1 (1873-1922). This comparison shows that the natural subsidence rate decreases from Marina di Ravenna to Venice and Trieste, turning out to be 1.88 ± 0.47 and 0.84 ± 0.41 mm yr-1 at Marina di Ravenna and Venice, respectively.