Along with density and mass variations of the oceans driven by global warming, Glacial Isostatic Adjustment (GIA) in response to the last deglaciation still contributes significantly to present-day sea-level change. Indeed, in order to reveal the impacts of climate change, long term observations at tide gauges and recent absolute altimetry data need to be decontaminated from the effects of GIA. This is now realized by means of global models constrained by the observed evolution of the paleo-shorelines since the Last Glacial Maximum, which account for the complex interactions between the solid Earth, the cryosphere and the oceans. In the recent literature, past and present-day effects of GIA are often expressed in terms of fingerprints describing the spatial variations of several geodetic quantities like crustal deformation, the harmonic components of the Earth's gravity field, relative and absolute sea level. However, since it is driven by the sluggish readjustment occurring within the viscous mantle, GIA shall taint the pattern of sea-level variability also during the forthcoming centuries. The shapes of the GIA fingerprints reflect inextricable deformational, gravitational, and rotational interactions occurring within the Earth system. Using up-to-date numerical modeling tools, our purpose is to revisit and to explore some of the physical and geometrical features of the fingerprints, their symmetries and intercorrelations, also illustrating how they stem from the fundamental equation that governs GIA, i.e., the Sea Level Equation.

The Lambousa fishtank, an archaeological structure entirely carved in bedrock, can be easily recognized and measured in plan on Google Earth (GE). We surveyed in situ this excellent archaeological marker in 2016 through direct measurements using traditional field measurements, such as metric tapes and invar rods, and terrestrial photogrammetry, using Structure from Motion (SfM) methods. The bedrock on which the fishtank is founded is an Upper Pleistocene calcarenite also containing Persistrombus Latus. The age of the studied fishtank has not been previously published, but on the basis of the construction technique and the interpretation provided by [1] and references therein . We assume that it was built in the period between 2.1 and 1.8 ka BP, like similar fishtanks in the Mediterarranen area. Architectural structures consist of an evident crepido ora a stone base, and a tunnel which allows for sea water exchange during high tides. The aforementioned hole is well correlated with the crepido which lies around the fishtank. These architectural components allow to evaluate the palaeosea level with significant precision during the time when the fishtank was active. MIS 5.5 coastal deposits that outcrop in the study area are located at a maximum altitude of a few meters, while the inner margin of the MIS 5.5 terrace allows us to hypothesize a “quasi-tectonic stability” also in the long-term. We have also tested several GIA predictions of relative sea level at Lambousa for the past 3.5 kyr according to GIA models ICE-6G (VM5a), ICE-7G (VM7) and to the GIA model by Lambeck and Purcell (2015), obtained with the SELEN4 sea level equation solver.