Antonioli, Fabrizio

The interpretation of sea level variations along the coasts of the Mediterranean region must be accompanied by the evaluation of vertical land movements associated with seismic and volcanic sources. This can be tentatively carried out through seismic strain analysis based on data pertaining the last 2 millennia as well as from the study of maritime archaeological structures.

Since the Mediterranean region is affected by the dynamics of the African and Eurasian plates, and includes active volcanic areas, the contribution of the recent vertical crustal movements to the observed relative sea level changes, require an estimation from i) available modern geodetic data, ii) geomorphological and biological indicators and iii) the height distribution of the Tyrrhenian level MIS 5.5. The latter provides the long term rate of deformations (125 kyr BP) and defines the overall stability of a region, while the middle term rates (10 kyr BP) can be obtained from geomorphological and biological indicators. Recent results indicate for the stable areas of Italy an average sea level change at -135 centimetres in 2000 years, while in Israel sea level was ± its present elevation at around 2000 years ago.

This paper provides new relative sea level data inferred from coastal archaeological sites located along the Turkish coasts of the Gulf of Fethye (8 sites), and Israel, between Akziv and Caesarea (5 sites). The structures selected are those that, for effective functioning, can be accurately related to sea level at the time of their construction. Thus their positions with respect to present sea level provide a measure of the relative sea level change since their time of construction. Useful information was obtained from the investigated sites spanning an age range of ˜2.3–˜1.6 ka BP. The inferred changes in relative sea level for the two areas are distinctly different, from a rise of 2.41 to 4.50 m in Turkey and from 0 to 0.18 m in Israel. Sea level change is the combination of several processes, including vertical tectonics, glacio–hydro-isostatic signals associated with the last glacial cycle, and changes in ocean volume. For the Israel section, the present elevations of the MIS-5.5 Tyrrhenian terraces occur at a few meters above present sea level and vertical tectonic displacements are small. Data from GPS and tide gauge measurements also indicate that any recent vertical movements are small. The MIS-5.5 shorelines are absent from the investigated section of the Turkish coast, consistent with crustal subsidence associated with the Hellenic Arc. The isostatic signals for the Israel section of the coast are also small (ranging from −0.11 mm/yr to 0.14 mm/yr, depending on site and earth model) and the observed (eustatic) average sea level change, corrected for this contribution, is a rise of 13.5 ± 2.6 cm during the past ˜2 ka. This is attributed to the time-integrated contribution to sea level from a combination of thermal expansion and other increases in ocean volume. The observed sea levels from the Turkish sites, in contrast, indicate a much greater rise of up to 2.2 mm/yr since 2.3 ka BP occurring in a wide area between Knidos and Kekova. The isostatic signal here is also one of a rising sea level (of up to ˜1 mm/yr and site and earth-model dependent) and the corrected tectonic rate of land subsidence is ˜1.48 mm/yr. This is the primary cause of dramatic relative sea level rise for this part of the coast.

Le variazioni del livello del mare lungo le coste italiane e più in generale del mare Mediterraneo, dipendono dalla somma di movimenti eustatici, glacio-idro-isostatici e tettonici. I primi sono dovuti all’alternanza di fasi climatiche fredde (glaciazioni) con fasi più calde (periodi interglaciali) che provocano rispettivamente l’accrescimento e la riduzione delle calotte polari con conseguenti variazioni del livello degli oceani. La presenza di indicatori archeologici tra la foce del fiume Trainiti e Briatico, area attualmente in sollevamento, permette di stimare le variazioni relative tra terra e mare avvenute negli ultimi 2000 anni lungo questo tratto di costa della Calabria tirrenica. Le informazioni desunte dai dati archeologici sono state anche confrontate con osservazioni geomorfologiche. La quota dei marker archeologici è stata misurata e corretta per il livello del mare al momento delle misure. La interpretazione degli impianti ha fornito dati originali sui movimenti relativi tra terra e mare per tettonica e glacio-idro-isostasia.

The Mediterranean basin is a natural laboratory for the reconstruction of the sea level variations since paleo-historical times. Recent results indicate for the central Mediterranean significant variations of relative sea level in the last 2000 years, suggesting that the observed signal can be accounted for by eustatism and isostatic adjustment as well as by land movements in active zones. The average modern eustatic sea level rise recorder by tide-gauges, close to 1 mm/year, has not been constant since the Roman epoch, but it is likely to be representative of the last 100-150 years. Here we show new results on the reconstruction and modeling of sea level changes in the Mediterranean during the Holocene from a combined data set and competing models of glacial isostatic adjustment.

Following the pioneering work of Schmiedt et al. (1972) on establishing the level of the Tyrrhenian Sea in Antiquity, a number of studies have examined this evidence from Roman Period fish tanks but with significantly different outcomes due primarily to different interpretations of the functional level of these pools at the time of their construction. As part of a longer term project to understand the causes of sea-level change around the Italian coast, we have reexamined and resurveyed 12 well-documented fish tanks, all based on the same construction principles, from the Tyrrhenian coast (between Formia and Orbetello) for which it can be established that they were in open contact with the sea at the time of operation. The structural features that tidally control the exchange of water used to define the ancient local sea level are identified as the channel thresholds, the sluice gate and sliding post positions, and the lowest level crepido. These are consistent for all the tanks examined, permitting the local sea-level change over the past 2000 years to be established at each location with a precision of ± 20 cm and against which other coastal archaeological features can be calibrated. We conclude that published local sea levels that are based on the present-day elevations of the foundations of protective walls constructed around the tanks and lie ~ 50 cm above our inferred levels are inconsistent with the successful functioning of the water exchange and have to be rejected. In one case, for Santa Liberata, we have been able to calibrate our interpretation against sedimentary evidence from the nearby Orbetello Lagoon that confirm our interpretation of the functional control level of the tanks and we conclude that the accuracy of our local sea levels is also ± 20 cm. The causes of sea-level change along this section of the coast are several, including land motion driven by tectonic and glacio-isostatic processes and any change in ocean volume. The individual estimates for the observed local sea levels range from − 0.9 to − 1.5 m with a mean value of − 1.22 ± 0.20 m. These values show that the spatial variability of the local levels is small and consistent with model-inferences of the glacioisostatic process that indicate near-constant contributions for this section of coast and with tectonic inference from the elevations of the Last Interglacial shoreline.

New data of sea level changes for the Mediterranean region along the coasts of northern Africa are presented. Data are inferred from archaeological sites of Punic-Roman age located along the coast of Tunisia, between Tunis and Jerba island and along the western coast of Libya, between Sabratha and Leptis Magna. Data are based on precise measures of presently submerged archaeological markers that are good indicators of past sea-level elevation. Nineteen selected archaeological sites were studied in Tunisia and four in Libya, all aged between ∼2.0 and ∼1.5 ka BP. The functional elevations of significant archaeological markers were measured with respect to the sea level at the time of measurements, applying corrections for tide and atmospheric pressure values. The functional elevations of specific architectural parts of the sites were interpreted, related to sea level at the time of their construction providing data on the relative changes between land and sea. Observations were compared against sea level change predictions derived from the glacio-hydro-isostatic model associated with the Last Glacial cycle. The results indicate that local relative sea level change along the coast of Tunisia and Libya, has increased 0.2 ÷ 0.5 m since the last ∼2 ka. Besides minor vertical tectonic movements of the land, the observed changes are produced by eustatic and glacio-hydro-isostatic variations acting in the Mediterranean basin since the end of the last glacial maximum.

Vertical tectonic displacements in Italy since 125 to 1 Kyr BP are drawn from relative sea-level (RSL) history studies at coastal sites, and, together with instrumental observations, allow to bridge the gap with events recorded in the geologic (1 Ma) archive. Our analysis aims at establishing the appropriate spatial extent, rate and duration of vertical tectonic motion within individual crustal segments, and at placing constraints on the contribution to displacements coming from regional (deep) and local (shallow-crustal) sources. The central and northern Tyrrhenian Sea and the Ligurian Sea margins show stability at all scales, except for subsidence in coastal basins and uplift, at places high, at volcanic centers. On the contrary, sustained, large magnitude uplift of Calabria embeds a deep-seated contribution, highlighted by the spatial coincidence of the uplifting province with a lithospheric slab, and a contribution from local faults and folds. Holocene uplift was up larger than since Middle-Late Pleistocene, with rate changes tuned among all sites. The recent increase in uplift rate, detected also in the instrumental record, is related to clustering of strain release, possibly triggered by isostatic response to deglaciation. A weak deformation signal is recorded on the central Adriatic coastline, and records slow Apennines thrust belt migration. In the northern Adriatic Sea, vertical tectonic motions result from opposite displacements in the southern Alps, internal Dinarids and northern Apennines, but flexure of the Adriatic (micro-) plate beneath the Northern Apennines is the dominating contributor. Here, rate and spatial extent of displacements are steady over different time-scales, suggesting prevailing control exercised by plate dynamics.

The northern Adriatic plate underwent Permian-Mesozoic rifting and was later shortened by three orogenic belts (i.e., Apennines, Alps and Dinarides) developed along three independent subduction zones. The inherited Mesozoic horst and graben grain determined structural undulations of the three thrust belts. Salients developed in grabens or more shaly basins, whereas recesses formed regularly around horsts. A new interpretation of seismic reflection profiles, subsidence rates from stratigraphic analysis, and GPS data prove that the three orogens surrounding the northern Adriatic plate are still active. The NE-ward migration of the Apennines subduction hinge determines the present-day faster subsidence rate in the western side of the northern Adriatic (>1 mm/year). This is recorded also by the SW-ward dip of the foreland regional monocline, and the SW-ward increase of the depth of the Tyrrhenian sedimentary layer, as well as the increase in thickness of the Pliocene and Pleistocene sediments. These data indicate the dominant influence of the Apennines subduction, which controls the asymmetric subsidence in the northern Adriatic realm. The Dinarides front has been tilted by the Apennines subduction hinge, as shown by the eroded Dalmatian anticlines subsiding in the eastern Adriatic Sea. GPS data suggest that southward tilting of the western and central Southern Alps, whereas the eastern Southern Alps are uplifting. The obtained strain rates are on average within 20 nstrain/year. The horizontal shortening obtained from GPS velocities at the front of the three belts surrounding the northern Adriatic plate are about 2–3 mm/year (Northern Apennines), 1–2 mm/year (Southern Alps), and <1 mm/year (Dinarides). The shortening directions tend to be perpendicular to the thrust belt fronts. The areas where the strain rate sharply decreases along a tectonic feature (e.g., the Ferrara salient, the Venetian foothills front) are proposed to be occupied by locked structures where stress is accumulating in the brittle layer and thus seismically prone. Finally, we speculate that, since the effects of three independent subduction zones coexist and overlap in the same area, plate boundaries are passive features.

The investigation of submerged speleothems for sea level studies has made significant contributions to the understanding of the global and regional sea level variations during the Middle and Late Quaternary. This has especially been the case for the Mediterranean Sea, where more than 300 submerged speleothems sampled in 32 caves have been analysed so far. Here, we present a comprehensive review of the results obtained from the study of submerged speleothems since 1978. The studied speleothems cover the last 1.4 Myr and are mainly focused on Marine Isotope Stages (MIS) 1, 2, 3, 5.1, 5.3, 5.5, 7.1, 7.2, 7.3, and 7.5. The results reveal that submerged speleothems represent extraordinary archives providing accurate information on former sea level changes. New results from a stalagmite collected at Palinuro (Campania, Italy) and characterized by marine overgrowth are also reported. The measured elevations of speleothems are affected by the local response to glacial and hydro-isostatic adjustment (GIA), and thus might significantly deviate from the global eustatic signal. A comparison of the ages and altitude values of the Mediterranean speleothems and flowstone from the Bahamas with local GIA provides a new scenario for MIS 5 and 7 sea level reconstructions