Methods
We use a compilation of data on RSL changes drawn from previously published papers, and specifically from Ferranti et al. (2006), Antonioli et al. (2009) and Lambeck et al. (in press) for Late Pleistocene and Holocene data. The nature, accuracy and precision of observational data have been discussed at length in the quoted papers, to which the reader is referred for a thorough discussion. These information are briefly summarized in the following.
Markers attributed to the LIg are represented by notches, marine terraces, beach deposits, speleothem concretions, boreholes of molluscs living in the spray zone of rocky cliffs and, for subsiding regions, wells to depths of 100 m or deeper. These same kind of markers are used for the Holocene, with the addition of barnacle rims and lagoonal layers in shallower wells.
The uncertainty of sea-level positioning is constrained by the precision of the measurement, the accuracy with which the position of the indicator with respect to the paleo-sea-level is determined (which depends on the type of marker, see Ferranti et al., 2006; 2007), and the precision of the age of the indicator (the latter determined by radiometric, ecostratigraphic and geomorphologic techniques). Ecostratigraphy for the LIg terraced deposits relies on the index fossil Strombus bubonius and is less reliable when only barren ‘‘senegalaise fauna’’, which includes species still living today, occur. The accuracy of the paleo-sea level position is the most difficult to model and suffers of variable uncertainty. Scrutiny of the present occurrence of markers as well as the sea-floor topography helps in circumventing this problem. Also, errors in marker recognition can exist, as, for instance, inferred markers can be displaced above their coeval sea-level by processes other than tectonics. Fortunately, large tides and extreme storms are very infrequent in the central Mediterranean and were probably so in the Holocene.
For the Latest Holocene, a wealth of coastal archaeological indicators are available in Italy (fish-tanks, harbours, piers, and, with a greater uncertainty, quarries and tombs). The use of archaeological data for sea-level studies is afforded by definition of the "functional height" as the elevation of specific architectural parts of an archaeological structure with respect to an estimated mean sea level at the time of their construction. Antonioli et al. (2007; 2009) and Scicchitano et al. (2008), applied these observational constraints to estimate relative sea level changes and tectonics in Sardinia and eastern Sicily.
The vertical tectonic motion is stipulated as the residual between the observational data and the eustatic position predicted from global sea-level curves (e.g. Waelbroeck et al. 2002) and, for Holocene markers, from glacio-hydro-isostatic predicted sea-level curves specifically built for this region (Lambeck et al., in press). At the Mediterranean coasts, the average level attained by the sea during the LIg is inferred to be 6±3 m relative to the present sea position (Lambeck et al., 2004; Ferranti et al., 2006). During the Holocene, the position of the sea at any time changed along the coast as a result of the Glacial Isostatic Adjustment (GIA) that accompanied and followed the melting of the Late Pleistocene ice sheets, which is a dominating component on global scale, and the response to the ocean floor loading by the melt water – the glacio-hydro-isostatic and eustatic contributions (Lambeck et al., 2004; in press). Crustal loading during 120 m of eustatic sea-level variation is on the order of a few metres (e.g. Lambeck et al., 2004). In this paper, the GIA contribution to Holocene observational data is subtracted using the Lambeck et al. (in press) model prediction. On the other hand, this correction is not applied to Lig data, because for the complete glacial-interglacial cycle, given the range of observed elevations of Lig markers up to over 100 m, the GIA contributes little to the total uncertainty.
In a later chapter, data from GPS and tide-gauges are used to snapshot some contemporary trends in vertical crustal motion that can be compared to geological and archaeological rates.