A new method of stating recent sea level rises and a comparison with tide gauge records

A series of dynamic penetration tests were performed up to a maximum depth of 2 m along sandy coastlines of Sardinia and Latium, Italy, in order to examine the change in resistance showed by sands. A maximum of resistance appears at the depth where the current sea level varies with tide fluctuations; this maximum resistance is due to capillary forces, which occur and disappear two times a day. A second maximum of sand resistance was found about half a meter under the first. In two cases where it was possible to attribute an age to the sands showing this more ancient level, the ages were before 37 AD and about 1700 AD. The features of this compact sand level suggest that between these two ages the sea level must have been practically constant, and unchanged until 300 years ago. These results were compared with tide gauge data recorded in the Netherlands, northern Italy and France. The data from the Amsterdam region, the oldest ones in the world, were reinterpreted as follows: the site of the Amsterdam tide gauge station is recognised as having undergone local settlements, while the entire region is denied to have been, as previously claimed, subject to a regional subsidence in the period of interest. As a consequence, also in the Amsterdam region the sea level maintained nearly the same position at least from 1700 up to about 1800. Then this level, which as from now can be labelled as “pre-industrial”, rose more and more rapidly, in agreement with the accelerated character of the increase of CO2 in the atmosphere. In the Netherlands, northern Italy and France the amount of sea level rise in the last 200 years seems to be slightly smaller (20–23 cm) than the mean sea rise in the world (about 27 cm), while in the study area (central Mediterranean) the sea rise is shown to be about twice as much. Another result of this study regards the tendency of sea level change. The study showed that, of the two peaks of sand resistance found, the most recent peak is not coincident with the present sea level at the moment of the tests: it is about 10 cm higher. This difference is possibly due to an actual lowering of the sea, a countertendence likely to have begun in the year 2000. If this interpretation is true, it would mean that the pattern of the sea level rise, which up to now had been found to follow an upward accelerated movement, has presently ceased, to possibly invert its movement.